Digestion and Absorption

Overview of Digestion and Absorption

• Digestion and absorption are complex processes that begin in the mouth but occur primarily in the stomach Stomach The stomach is a muscular sac in the upper left portion of the abdomen that plays a critical role in digestion. The stomach develops from the foregut and connects the esophagus with the duodenum. Structurally, the stomach is C-shaped and forms a greater and lesser curvature and is divided grossly into regions: the cardia, fundus, body, and pylorus. Stomach: Anatomy and small intestine Small intestine The small intestine is the longest part of the GI tract, extending from the pyloric orifice of the stomach to the ileocecal junction. The small intestine is the major organ responsible for chemical digestion and absorption of nutrients. It is divided into 3 segments: the duodenum, the jejunum, and the ileum. Small Intestine: Anatomy.
• Carbohydrates Carbohydrates A class of organic compounds composed of carbon, hydrogen, and oxygen in a ratio of cn(H2O)n. The largest class of organic compounds, including starch; glycogen; cellulose; polysaccharides; and simple monosaccharides. Basics of Carbohydrates:
  • Must be broken down into monosaccharides Monosaccharides Single chain carbohydrates that are the most basic units of carbohydrates. They are typically colorless crystalline substances with a sweet taste and have the same general formula CNH2NON. Basics of Carbohydrates to be absorbed
  • Primary digestive enzymes Enzymes Enzymes are complex protein biocatalysts that accelerate chemical reactions without being consumed by them. Due to the body’s constant metabolic needs, the absence of enzymes would make life unsustainable, as reactions would occur too slowly without these molecules. Basics of Enzymes:
    • Amylase
    • Brush border Brush border Tubular System enzymes Enzymes Enzymes are complex protein biocatalysts that accelerate chemical reactions without being consumed by them. Due to the body’s constant metabolic needs, the absence of enzymes would make life unsustainable, as reactions would occur too slowly without these molecules. Basics of Enzymes
  • Absorbed via:
    • Apical side: sodium Sodium A member of the alkali group of metals. It has the atomic symbol na, atomic number 11, and atomic weight 23. Hyponatremia–glucose-linked transporter (SGLT) 1, glucose transporter Glucose transporter Tubular System ( GLUT GLUT Tubular System) 5
    • Basolateral side: GLUT2
• Proteins Proteins Linear polypeptides that are synthesized on ribosomes and may be further modified, crosslinked, cleaved, or assembled into complex proteins with several subunits. The specific sequence of amino acids determines the shape the polypeptide will take, during protein folding, and the function of the protein. Energy Homeostasis:
  • Broken down into peptides and individual amino acids Amino acids Organic compounds that generally contain an amino (-NH2) and a carboxyl (-COOH) group. Twenty alpha-amino acids are the subunits which are polymerized to form proteins. Basics of Amino Acids (AAs)
  • Primary digestive enzymes Enzymes Enzymes are complex protein biocatalysts that accelerate chemical reactions without being consumed by them. Due to the body’s constant metabolic needs, the absence of enzymes would make life unsustainable, as reactions would occur too slowly without these molecules. Basics of Enzymes:
    • Pepsin Pepsin Pepsin breaks down proteins into proteoses, peptones, and large polypeptides. Proteins and Peptides
    • Trypsin Trypsin A serine endopeptidase that is formed from trypsinogen in the pancreas. It is converted into its active form by enteropeptidase in the small intestine. It catalyzes hydrolysis of the carboxyl group of either arginine or lysine. Proteins and Peptides
    • Chymotrypsin Chymotrypsin A serine endopeptidase secreted by the pancreas as its zymogen, chymotrypsinogen and carried in the pancreatic juice to the duodenum where it is activated by trypsin. It selectively cleaves aromatic amino acids on the carboxyl side. Pancreatic Parameters
    • Carboxypeptidase Carboxypeptidase Enzymes that act at a free c-terminus of a polypeptide to liberate a single amino acid residue. Pancreatic Parameters
    • Elastase Elastase A protease of broad specificity, obtained from dried pancreas. Molecular weight is approximately 25, 000. The enzyme breaks down elastin, the specific protein of elastic fibers, and digests other proteins such as fibrin, hemoglobin, and albumin. Proteins and Peptides
  • Absorbed by specialized cotransporters
• Lipids Lipids Lipids are a diverse group of hydrophobic organic molecules, which include fats, oils, sterols, and waxes. Fatty Acids and Lipids:
  • Broken down into its constituents (e.g., triacylglycerides (TAGs) → glycerol + free fatty acids Acids Chemical compounds which yield hydrogen ions or protons when dissolved in water, whose hydrogen can be replaced by metals or basic radicals, or which react with bases to form salts and water (neutralization). An extension of the term includes substances dissolved in media other than water. Acid-Base Balance)
  • Primary digestive enzymes Enzymes Enzymes are complex protein biocatalysts that accelerate chemical reactions without being consumed by them. Due to the body’s constant metabolic needs, the absence of enzymes would make life unsustainable, as reactions would occur too slowly without these molecules. Basics of Enzymes:
    • Lipases Lipases An enzyme of the hydrolase class that catalyzes the reaction of triacylglycerol and water to yield diacylglycerol and a fatty acid anion. It is produced by glands on the tongue and by the pancreas and initiates the digestion of dietary fats. Lipid Metabolism
    • Cholesterol Cholesterol The principal sterol of all higher animals, distributed in body tissues, especially the brain and spinal cord, and in animal fats and oils. Cholesterol Metabolism esterase
    • Phospholipase A2 Phospholipase A2 Phospholipases that hydrolyze the Acyl group attached to the 2-position of phosphoglycerides. Nephrotic Syndrome
  • Lipids Lipids Lipids are a diverse group of hydrophobic organic molecules, which include fats, oils, sterols, and waxes. Fatty Acids and Lipids are reassembled in enterocytes before being released into the interstitial space.
  • Absorbed into the lymphatic circulation Circulation The movement of the blood as it is pumped through the cardiovascular system. ABCDE Assessment
• Vitamin and mineral absorption varies and depends on the nutrient.

Digestion and Absorption of Carbohydrates

Digestion

• Digested primarily by amylases Amylases A group of amylolytic enzymes that cleave starch, glycogen, and related alpha-1, 4-glucans. Digestion and Absorption of Carbohydrates and brush border Brush border Tubular System enzymes Enzymes Enzymes are complex protein biocatalysts that accelerate chemical reactions without being consumed by them. Due to the body’s constant metabolic needs, the absence of enzymes would make life unsustainable, as reactions would occur too slowly without these molecules. Basics of Enzymes
• Enzymes Enzymes Enzymes are complex protein biocatalysts that accelerate chemical reactions without being consumed by them. Due to the body’s constant metabolic needs, the absence of enzymes would make life unsustainable, as reactions would occur too slowly without these molecules. Basics of Enzymes hydrolyze large starch molecules to monosaccharides Monosaccharides Single chain carbohydrates that are the most basic units of carbohydrates. They are typically colorless crystalline substances with a sweet taste and have the same general formula CNH2NON. Basics of Carbohydrates

Amylases Amylases A group of amylolytic enzymes that cleave starch, glycogen, and related alpha-1, 4-glucans. Digestion and Absorption of Carbohydrates:

• Cleavage of α-1,4-glycosidic bonds in sugar molecules
• Creation of increasingly smaller polysaccharide chains until most α-1,4-glycosidic bonds are broken, leaving behind:
  • Monosaccharides Monosaccharides Single chain carbohydrates that are the most basic units of carbohydrates. They are typically colorless crystalline substances with a sweet taste and have the same general formula CNH2NON. Basics of Carbohydrates: individual sugar molecules
  • Disaccharides Disaccharides Oligosaccharides containing two monosaccharide units linked by a glycosidic bond. Basics of Carbohydrates: starches with 2 sugar molecules
  • Oligosaccharides Oligosaccharides Carbohydrates consisting of between two (disaccharides) and ten monosaccharides connected by either an alpha- or beta-glycosidic link. They are found throughout nature in both the free and bound form. Basics of Carbohydrates: starches with 3‒10 sugar molecules
  • Indigestible starches: sugars joined by other types of bonds
• Active at higher pH pH The quantitative measurement of the acidity or basicity of a solution. Acid-Base Balance:
  • Active in the mouth and small intestines
  • Inactivated in the stomach Stomach The stomach is a muscular sac in the upper left portion of the abdomen that plays a critical role in digestion. The stomach develops from the foregut and connects the esophagus with the duodenum. Structurally, the stomach is C-shaped and forms a greater and lesser curvature and is divided grossly into regions: the cardia, fundus, body, and pylorus. Stomach: Anatomy
• Types and location of amylase:
  • Salivary amylase Salivary amylase A subclass of alpha-amylase isoenzymes that are secreted into saliva. Digestion and Absorption of Carbohydrates: secreted in the mouth by the salivary glands Salivary glands The salivary glands are exocrine glands positioned in and around the oral cavity. These glands are responsible for secreting saliva into the mouth, which aids in digestion. There are 3 major paired salivary glands: the sublingual, submandibular, and parotid glands. Salivary Glands: Anatomy
  • Pancreatic amylase Pancreatic Amylase A group of amylolytic enzymes that cleave starch, glycogen, and related alpha-1, 4-glucans. Pancreatic Parameters: secreted into the duodenum Duodenum The shortest and widest portion of the small intestine adjacent to the pylorus of the stomach. It is named for having the length equal to about the width of 12 fingers. Small Intestine: Anatomy by the exocrine pancreas Pancreas The pancreas lies mostly posterior to the stomach and extends across the posterior abdominal wall from the duodenum on the right to the spleen on the left. This organ has both exocrine and endocrine tissue. Pancreas: Anatomy

Brush border Brush border Tubular System enzymes Enzymes Enzymes are complex protein biocatalysts that accelerate chemical reactions without being consumed by them. Due to the body’s constant metabolic needs, the absence of enzymes would make life unsustainable, as reactions would occur too slowly without these molecules. Basics of Enzymes:

Brush border Brush border Tubular System enzymes Enzymes Enzymes are complex protein biocatalysts that accelerate chemical reactions without being consumed by them. Due to the body’s constant metabolic needs, the absence of enzymes would make life unsustainable, as reactions would occur too slowly without these molecules. Basics of Enzymes are membrane-bound proteins Proteins Linear polypeptides that are synthesized on ribosomes and may be further modified, crosslinked, cleaved, or assembled into complex proteins with several subunits. The specific sequence of amino acids determines the shape the polypeptide will take, during protein folding, and the function of the protein. Energy Homeostasis on the luminal surface of enterocytes in the small intestine Small intestine The small intestine is the longest part of the GI tract, extending from the pyloric orifice of the stomach to the ileocecal junction. The small intestine is the major organ responsible for chemical digestion and absorption of nutrients. It is divided into 3 segments: the duodenum, the jejunum, and the ileum. Small Intestine: Anatomy. There are 4 major brush border Brush border Tubular System enzymes Enzymes Enzymes are complex protein biocatalysts that accelerate chemical reactions without being consumed by them. Due to the body’s constant metabolic needs, the absence of enzymes would make life unsustainable, as reactions would occur too slowly without these molecules. Basics of Enzymes involved in carbohydrate digestion.

• Isomaltase Isomaltase An enzyme that catalyzes the endohydrolysis of 1, 6-alpha-glycosidic linkages in isomaltose and dextrins produced from starch and glycogen by alpha-amylases. Digestion and Absorption of Carbohydrates: cleaves the α-1,6-glycosidic bonds
• Maltase Maltase Digestion and Absorption of Carbohydrates:
  • Hydrolyzes maltose → glucose Glucose A primary source of energy for living organisms. It is naturally occurring and is found in fruits and other parts of plants in its free state. It is used therapeutically in fluid and nutrient replacement. Lactose Intolerance + glucose Glucose A primary source of energy for living organisms. It is naturally occurring and is found in fruits and other parts of plants in its free state. It is used therapeutically in fluid and nutrient replacement. Lactose Intolerance
  • Hydrolyzes maltotriose → glucose Glucose A primary source of energy for living organisms. It is naturally occurring and is found in fruits and other parts of plants in its free state. It is used therapeutically in fluid and nutrient replacement. Lactose Intolerance + glucose Glucose A primary source of energy for living organisms. It is naturally occurring and is found in fruits and other parts of plants in its free state. It is used therapeutically in fluid and nutrient replacement. Lactose Intolerance + glucose Glucose A primary source of energy for living organisms. It is naturally occurring and is found in fruits and other parts of plants in its free state. It is used therapeutically in fluid and nutrient replacement. Lactose Intolerance
• Lactase Lactase An enzyme which catalyzes the hydrolysis of lactose to d-galactose and d-glucose. Defects in the enzyme cause lactose intolerance. Digestion and Absorption of Carbohydrates: hydrolyzes lactose → glucose Glucose A primary source of energy for living organisms. It is naturally occurring and is found in fruits and other parts of plants in its free state. It is used therapeutically in fluid and nutrient replacement. Lactose Intolerance + galactose Galactose An aldohexose that occurs naturally in the d-form in lactose, cerebrosides, gangliosides, and mucoproteins. Deficiency of galactosyl-1-phosphate uridyltransferase causes an error in galactose metabolism called galactosemia, resulting in elevations of galactose in the blood. Lactose Intolerance
• Sucrase Sucrase Digestive enzyme secreted in the intestines. It catalyzes hydrolysis of sucrose to fructose and glucose. Digestion and Absorption of Carbohydrates: 
  • Hydrolyzes sucrose → glucose Glucose A primary source of energy for living organisms. It is naturally occurring and is found in fruits and other parts of plants in its free state. It is used therapeutically in fluid and nutrient replacement. Lactose Intolerance + fructose
  • Hydrolyzes other small oligosaccharides Oligosaccharides Carbohydrates consisting of between two (disaccharides) and ten monosaccharides connected by either an alpha- or beta-glycosidic link. They are found throughout nature in both the free and bound form. Basics of Carbohydrates

Absorption

Carbohydrates Carbohydrates A class of organic compounds composed of carbon, hydrogen, and oxygen in a ratio of cn(H2O)n. The largest class of organic compounds, including starch; glycogen; cellulose; polysaccharides; and simple monosaccharides. Basics of Carbohydrates are absorbed as monosaccharides Monosaccharides Single chain carbohydrates that are the most basic units of carbohydrates. They are typically colorless crystalline substances with a sweet taste and have the same general formula CNH2NON. Basics of Carbohydrates by the enterocytes in the small intestines and transported via blood to the portal circulation Portal circulation A system of vessels in which blood, after passing through one capillary bed, is conveyed through a second set of capillaries before it returns to the systemic circulation. It pertains especially to the hepatic portal system. Systemic and Special Circulations. Carbohydrates Carbohydrates A class of organic compounds composed of carbon, hydrogen, and oxygen in a ratio of cn(H2O)n. The largest class of organic compounds, including starch; glycogen; cellulose; polysaccharides; and simple monosaccharides. Basics of Carbohydrates that cannot be broken down into monosaccharides Monosaccharides Single chain carbohydrates that are the most basic units of carbohydrates. They are typically colorless crystalline substances with a sweet taste and have the same general formula CNH2NON. Basics of Carbohydrates are not absorbed (e.g., fibers).

Monosaccharides Monosaccharides Single chain carbohydrates that are the most basic units of carbohydrates. They are typically colorless crystalline substances with a sweet taste and have the same general formula CNH2NON. Basics of Carbohydrates are:

• Moved into the enterocytes by 1 set of transport proteins Transport proteins Proteins and Peptides in the apical membrane:
  • SGLT1:
    • Found in the small intestine Small intestine The small intestine is the longest part of the GI tract, extending from the pyloric orifice of the stomach to the ileocecal junction. The small intestine is the major organ responsible for chemical digestion and absorption of nutrients. It is divided into 3 segments: the duodenum, the jejunum, and the ileum. Small Intestine: Anatomy
    • Transports 2 Na⁺, 1 glucose Glucose A primary source of energy for living organisms. It is naturally occurring and is found in fruits and other parts of plants in its free state. It is used therapeutically in fluid and nutrient replacement. Lactose Intolerance or galactose Galactose An aldohexose that occurs naturally in the d-form in lactose, cerebrosides, gangliosides, and mucoproteins. Deficiency of galactosyl-1-phosphate uridyltransferase causes an error in galactose metabolism called galactosemia, resulting in elevations of galactose in the blood. Lactose Intolerance, and water
    • Uses the chemical Na⁺ gradient generated by the Na⁺/K⁺ ATPase pump Pump ACES and RUSH: Resuscitation Ultrasound Protocols on the basolateral membrane (keeps intracellular Na⁺ concentration low)
    • Leads to secondary active transport Active transport The movement of materials across cell membranes and epithelial layers against an electrochemical gradient, requiring the expenditure of metabolic energy. The Cell: Cell Membrane
  • GLUT5: transports fructose into the cell down its concentration gradient via facilitated diffusion Diffusion The tendency of a gas or solute to pass from a point of higher pressure or concentration to a point of lower pressure or concentration and to distribute itself throughout the available space. Diffusion, especially facilitated diffusion, is a major mechanism of biological transport. Peritoneal Dialysis and Hemodialysis
• Moved out into the interstitial space by a different transport protein located in the basolateral membrane:
  • GLUT2:
    • Can move all 3 primary monosaccharides Monosaccharides Single chain carbohydrates that are the most basic units of carbohydrates. They are typically colorless crystalline substances with a sweet taste and have the same general formula CNH2NON. Basics of Carbohydrates: glucose Glucose A primary source of energy for living organisms. It is naturally occurring and is found in fruits and other parts of plants in its free state. It is used therapeutically in fluid and nutrient replacement. Lactose Intolerance, galactose Galactose An aldohexose that occurs naturally in the d-form in lactose, cerebrosides, gangliosides, and mucoproteins. Deficiency of galactosyl-1-phosphate uridyltransferase causes an error in galactose metabolism called galactosemia, resulting in elevations of galactose in the blood. Lactose Intolerance, and fructose
    • Works via facilitated diffusion Diffusion The tendency of a gas or solute to pass from a point of higher pressure or concentration to a point of lower pressure or concentration and to distribute itself throughout the available space. Diffusion, especially facilitated diffusion, is a major mechanism of biological transport. Peritoneal Dialysis and Hemodialysis
• Absorbed into the capillaries Capillaries Capillaries are the primary structures in the circulatory system that allow the exchange of gas, nutrients, and other materials between the blood and the extracellular fluid (ECF). Capillaries are the smallest of the blood vessels. Because a capillary diameter is so small, only 1 RBC may pass through at a time. Capillaries: Histology from the interstitial space
• Capillaries Capillaries Capillaries are the primary structures in the circulatory system that allow the exchange of gas, nutrients, and other materials between the blood and the extracellular fluid (ECF). Capillaries are the smallest of the blood vessels. Because a capillary diameter is so small, only 1 RBC may pass through at a time. Capillaries: Histology drain into veins Veins Veins are tubular collections of cells, which transport deoxygenated blood and waste from the capillary beds back to the heart. Veins are classified into 3 types: small veins/venules, medium veins, and large veins. Each type contains 3 primary layers: tunica intima, tunica media, and tunica adventitia. Veins: Histology → portal vein Portal vein A short thick vein formed by union of the superior mesenteric vein and the splenic vein. Liver: Anatomy → liver Liver The liver is the largest gland in the human body. The liver is found in the superior right quadrant of the abdomen and weighs approximately 1.5 kilograms. Its main functions are detoxification, metabolism, nutrient storage (e.g., iron and vitamins), synthesis of coagulation factors, formation of bile, filtration, and storage of blood. Liver: Anatomy for metabolism

Digestion and Absorption of Proteins

Digestion

• Protein digestion Protein digestion The digestive system breaks down proteins into individual amino acids that are absorbed by the cells to build other proteins and macromolecules. Proteins and Peptides mainly occurs in the stomach Stomach The stomach is a muscular sac in the upper left portion of the abdomen that plays a critical role in digestion. The stomach develops from the foregut and connects the esophagus with the duodenum. Structurally, the stomach is C-shaped and forms a greater and lesser curvature and is divided grossly into regions: the cardia, fundus, body, and pylorus. Stomach: Anatomy and duodenum Duodenum The shortest and widest portion of the small intestine adjacent to the pylorus of the stomach. It is named for having the length equal to about the width of 12 fingers. Small Intestine: Anatomy.
• Recall: Peptide bonds join the amino terminus of AA AA Amyloidosis to the carboxy terminus of the next AA AA Amyloidosis.
• Protein digestion Protein digestion The digestive system breaks down proteins into individual amino acids that are absorbed by the cells to build other proteins and macromolecules. Proteins and Peptides occurs via enzymatic hydrolysis Hydrolysis The process of cleaving a chemical compound by the addition of a molecule of water. Proteins and Peptides of peptide bonds, breaking down proteins Proteins Linear polypeptides that are synthesized on ribosomes and may be further modified, crosslinked, cleaved, or assembled into complex proteins with several subunits. The specific sequence of amino acids determines the shape the polypeptide will take, during protein folding, and the function of the protein. Energy Homeostasis into:
  • Small peptides composed of short AA AA Amyloidosis chains
  • Individual AAs
• Enzymes Enzymes Enzymes are complex protein biocatalysts that accelerate chemical reactions without being consumed by them. Due to the body’s constant metabolic needs, the absence of enzymes would make life unsustainable, as reactions would occur too slowly without these molecules. Basics of Enzymes involved are:
  • Secreted by the stomach Stomach The stomach is a muscular sac in the upper left portion of the abdomen that plays a critical role in digestion. The stomach develops from the foregut and connects the esophagus with the duodenum. Structurally, the stomach is C-shaped and forms a greater and lesser curvature and is divided grossly into regions: the cardia, fundus, body, and pylorus. Stomach: Anatomy and pancreas Pancreas The pancreas lies mostly posterior to the stomach and extends across the posterior abdominal wall from the duodenum on the right to the spleen on the left. This organ has both exocrine and endocrine tissue. Pancreas: Anatomy (see table)
  • Bound to the brush border Brush border Tubular System of enterocytes:
    • Aminopeptidases Aminopeptidases A subclass of exopeptidases that act on the free n terminus end of a polypeptide liberating a single amino acid residue. Proteins and Peptides break down small peptides from their amino end (i.e., N-terminus).
    • Dipeptidases Dipeptidases Exopeptidases that specifically act on dipeptides. Proteins and Peptides break peptide bonds between 2 AAs → 2 single AAs

Absorption

• Absorption occurs in the small intestine Small intestine The small intestine is the longest part of the GI tract, extending from the pyloric orifice of the stomach to the ileocecal junction. The small intestine is the major organ responsible for chemical digestion and absorption of nutrients. It is divided into 3 segments: the duodenum, the jejunum, and the ileum. Small Intestine: Anatomy.
• Only AAs, dipeptides, and tripeptides can be absorbed across the apical membrane into the enterocytes.
• Only individual AAs can be absorbed across the basolateral membrane into the interstitial space.
• Individual AAs:
  • Absorbed into the enterocytes across the apical membrane via specialized Na⁺/ AA AA Amyloidosis cotransporters:
    • Uses the Na⁺ gradient created by the Na⁺/K⁺ ATPase pump Pump ACES and RUSH: Resuscitation Ultrasound Protocols on the basolateral membrane 
    • [Na⁺] is high in the lumen but low in the enterocytes → Na⁺ moves down its concentration gradient into the cell, transporting an AA AA Amyloidosis with it
  • Absorbed across the basolateral membrane by specialized transporters (different types of transporters for different types of AAs)
• Dipeptides and tripeptides:
  • Absorbed by the enterocytes across the apical membrane via specialized H⁺/PepT cotransporters
  • Uses the H⁺ gradient created by the H⁺/Na⁺ exchanger on the apical membrane (which pumps 1 H⁺ ion into the lumen and brings 1 Na⁺ into the enterocytes)
  • Peptides are broken down into individual AAs by peptidases within the enterocytes.
  • Absorbed across the basolateral membrane in the same manner as AAs
• Once in the interstitial space, AAs are absorbed into the venous circulation Circulation The movement of the blood as it is pumped through the cardiovascular system. ABCDE Assessment → transported through portal circulation Portal circulation A system of vessels in which blood, after passing through one capillary bed, is conveyed through a second set of capillaries before it returns to the systemic circulation. It pertains especially to the hepatic portal system. Systemic and Special Circulations to the liver Liver The liver is the largest gland in the human body. The liver is found in the superior right quadrant of the abdomen and weighs approximately 1.5 kilograms. Its main functions are detoxification, metabolism, nutrient storage (e.g., iron and vitamins), synthesis of coagulation factors, formation of bile, filtration, and storage of blood. Liver: Anatomy

Digestion and Absorption of Fats

Digestion

There are 3 primary types of fats Fats The glyceryl esters of a fatty acid, or of a mixture of fatty acids. They are generally odorless, colorless, and tasteless if pure, but they may be flavored according to origin. Fats are insoluble in water, soluble in most organic solvents. They occur in animal and vegetable tissue and are generally obtained by boiling or by extraction under pressure. They are important in the diet (dietary fats) as a source of energy. Energy Homeostasis that are digested and absorbed: triglycerides Triglycerides Fatty Acids and Lipids ( triacylglycerols Triacylglycerols Fatty Acids and Lipids, or TAGs), phospholipids Phospholipids Lipids containing one or more phosphate groups, particularly those derived from either glycerol (phosphoglycerides) or sphingosine (sphingolipids). They are polar lipids that are of great importance for the structure and function of cell membranes and are the most abundant of membrane lipids, although not stored in large amounts in the system. Lipid Metabolism, and cholesterol Cholesterol The principal sterol of all higher animals, distributed in body tissues, especially the brain and spinal cord, and in animal fats and oils. Cholesterol Metabolism esters. All 3 types contain ester bonds (R₁‒(C=O)‒O ‒R₂) that are broken during digestion.

TAGs:

• Structure:
  • Glycerol backbone: 3-carbon chain with each carbon attached to an alcohol group
  • Fatty acids Acids Chemical compounds which yield hydrogen ions or protons when dissolved in water, whose hydrogen can be replaced by metals or basic radicals, or which react with bases to form salts and water (neutralization). An extension of the term includes substances dissolved in media other than water. Acid-Base Balance: hydrocarbon chain with a carboxyl group at 1 end
  • Each carbon on the glycerol backbone is bound to the carboxy end of a fatty-acid chain by an ester bond.
• Ester bonds are hydrolyzed by lipases Lipases An enzyme of the hydrolase class that catalyzes the reaction of triacylglycerol and water to yield diacylglycerol and a fatty acid anion. It is produced by glands on the tongue and by the pancreas and initiates the digestion of dietary fats. Lipid Metabolism:
  • Lingual lipase Lipase An enzyme of the hydrolase class that catalyzes the reaction of triacylglycerol and water to yield diacylglycerol and a fatty acid anion. It is produced by glands on the tongue and by the pancreas and initiates the digestion of dietary fats. Malabsorption and Maldigestion (from salivary glands Salivary glands The salivary glands are exocrine glands positioned in and around the oral cavity. These glands are responsible for secreting saliva into the mouth, which aids in digestion. There are 3 major paired salivary glands: the sublingual, submandibular, and parotid glands. Salivary Glands: Anatomy)
  • Gastric lipase Lipase An enzyme of the hydrolase class that catalyzes the reaction of triacylglycerol and water to yield diacylglycerol and a fatty acid anion. It is produced by glands on the tongue and by the pancreas and initiates the digestion of dietary fats. Malabsorption and Maldigestion (from chief cells Chief cells Epithelial cells that line the basal half of the gastric glands. Chief cells synthesize and export an inactive enzyme pepsinogen which is converted into the highly proteolytic enzyme pepsin in the acid environment of the stomach. Stomach: Anatomy)
  • Pancreatic lipase Pancreatic Lipase An enzyme of the hydrolase class that catalyzes the reaction of triacylglycerol and water to yield diacylglycerol and a fatty acid anion. It is produced by glands on the tongue and by the pancreas and initiates the digestion of dietary fats. Pancreatic Parameters (from exocrine pancreas Pancreas The pancreas lies mostly posterior to the stomach and extends across the posterior abdominal wall from the duodenum on the right to the spleen on the left. This organ has both exocrine and endocrine tissue. Pancreas: Anatomy, the most important)

Phospholipids Phospholipids Lipids containing one or more phosphate groups, particularly those derived from either glycerol (phosphoglycerides) or sphingosine (sphingolipids). They are polar lipids that are of great importance for the structure and function of cell membranes and are the most abundant of membrane lipids, although not stored in large amounts in the system. Lipid Metabolism:

• Similar structure to TAGs, but the glycerol backbone contains a phosphate Phosphate Inorganic salts of phosphoric acid. Electrolytes group
• Phosphate Phosphate Inorganic salts of phosphoric acid. Electrolytes group confers more polarity.
• Ester bonds are hydrolyzed by phospholipase A₂.

Cholesterol Cholesterol The principal sterol of all higher animals, distributed in body tissues, especially the brain and spinal cord, and in animal fats and oils. Cholesterol Metabolism esters:

• Cholesterol Cholesterol The principal sterol of all higher animals, distributed in body tissues, especially the brain and spinal cord, and in animal fats and oils. Cholesterol Metabolism bound to a fatty acid by an ester bond
• Ester bonds are hydrolyzed by cholesterol Cholesterol The principal sterol of all higher animals, distributed in body tissues, especially the brain and spinal cord, and in animal fats and oils. Cholesterol Metabolism ester hydrolase.

Substances required for lipase Lipase An enzyme of the hydrolase class that catalyzes the reaction of triacylglycerol and water to yield diacylglycerol and a fatty acid anion. It is produced by glands on the tongue and by the pancreas and initiates the digestion of dietary fats. Malabsorption and Maldigestion activity/digestion of lipids Lipids Lipids are a diverse group of hydrophobic organic molecules, which include fats, oils, sterols, and waxes. Fatty Acids and Lipids:

• Bile Bile An emulsifying agent produced in the liver and secreted into the duodenum. Its composition includes bile acids and salts; cholesterol; and electrolytes. It aids digestion of fats in the duodenum. Gallbladder and Biliary Tract: Anatomy:
  • Emulsifier produced by the liver Liver The liver is the largest gland in the human body. The liver is found in the superior right quadrant of the abdomen and weighs approximately 1.5 kilograms. Its main functions are detoxification, metabolism, nutrient storage (e.g., iron and vitamins), synthesis of coagulation factors, formation of bile, filtration, and storage of blood. Liver: Anatomy and stored and secreted by the gallbladder Gallbladder The gallbladder is a pear-shaped sac, located directly beneath the liver, that sits on top of the superior part of the duodenum. The primary functions of the gallbladder include concentrating and storing up to 50 mL of bile. Gallbladder and Biliary Tract: Anatomy
  • Contains lecithin Lecithin A complex mixture of phospholipids; glycolipids; and triglycerides; with substantial amounts of phosphatidylcholines; phosphatidylethanolamines; and phosphatidylinositols, which are sometimes loosely termed as 1, 2-diacyl-3-phosphocholines. Lecithin is a component of the cell membrane and commercially extracted from soybeans and egg yolk. The emulsifying and surfactant properties are useful in food additives and for forming organogels (gels). Fatty Acids and Lipids (a phospholipid) and bile Bile An emulsifying agent produced in the liver and secreted into the duodenum. Its composition includes bile acids and salts; cholesterol; and electrolytes. It aids digestion of fats in the duodenum. Gallbladder and Biliary Tract: Anatomy salts
  • Forms smaller fat droplets Droplets Varicella-Zoster Virus/Chickenpox, providing the water-soluble lipases Lipases An enzyme of the hydrolase class that catalyzes the reaction of triacylglycerol and water to yield diacylglycerol and a fatty acid anion. It is produced by glands on the tongue and by the pancreas and initiates the digestion of dietary fats. Lipid Metabolism more surface area to digest lipids Lipids Lipids are a diverse group of hydrophobic organic molecules, which include fats, oils, sterols, and waxes. Fatty Acids and Lipids
• Colipase: helps lipases Lipases An enzyme of the hydrolase class that catalyzes the reaction of triacylglycerol and water to yield diacylglycerol and a fatty acid anion. It is produced by glands on the tongue and by the pancreas and initiates the digestion of dietary fats. Lipid Metabolism bind BIND Hyperbilirubinemia of the Newborn to (and digest) the emulsified fat droplets Droplets Varicella-Zoster Virus/Chickenpox

Micelles Micelles Particles consisting of aggregates of molecules held loosely together by secondary bonds. The surface of micelles are usually comprised of amphiphatic compounds that are oriented in a way that minimizes the energy of interaction between the micelle and its environment. Liquids that contain large numbers of suspended micelles are referred to as emulsions. Malabsorption and Maldigestion:

As lipids Lipids Lipids are a diverse group of hydrophobic organic molecules, which include fats, oils, sterols, and waxes. Fatty Acids and Lipids are broken down, they (along with components from the bile Bile An emulsifying agent produced in the liver and secreted into the duodenum. Its composition includes bile acids and salts; cholesterol; and electrolytes. It aids digestion of fats in the duodenum. Gallbladder and Biliary Tract: Anatomy) arrange themselves in structures called micelles Micelles Particles consisting of aggregates of molecules held loosely together by secondary bonds. The surface of micelles are usually comprised of amphiphatic compounds that are oriented in a way that minimizes the energy of interaction between the micelle and its environment. Liquids that contain large numbers of suspended micelles are referred to as emulsions. Malabsorption and Maldigestion:

• Tiny spherical droplets Droplets Varicella-Zoster Virus/Chickenpox:
  • Interior portion is lipophilic.
  • Exterior portion is hydrophilic Hydrophilic Aminoglycosides.
  • Surrounded by phospholipids Phospholipids Lipids containing one or more phosphate groups, particularly those derived from either glycerol (phosphoglycerides) or sphingosine (sphingolipids). They are polar lipids that are of great importance for the structure and function of cell membranes and are the most abundant of membrane lipids, although not stored in large amounts in the system. Lipid Metabolism from bile Bile An emulsifying agent produced in the liver and secreted into the duodenum. Its composition includes bile acids and salts; cholesterol; and electrolytes. It aids digestion of fats in the duodenum. Gallbladder and Biliary Tract: Anatomy
• Contain all fat-soluble components to be absorbed:
  • Free fatty acids Acids Chemical compounds which yield hydrogen ions or protons when dissolved in water, whose hydrogen can be replaced by metals or basic radicals, or which react with bases to form salts and water (neutralization). An extension of the term includes substances dissolved in media other than water. Acid-Base Balance
  • Monoacylglycerides
  • Cholesterol Cholesterol The principal sterol of all higher animals, distributed in body tissues, especially the brain and spinal cord, and in animal fats and oils. Cholesterol Metabolism
  • Phospholipids Phospholipids Lipids containing one or more phosphate groups, particularly those derived from either glycerol (phosphoglycerides) or sphingosine (sphingolipids). They are polar lipids that are of great importance for the structure and function of cell membranes and are the most abundant of membrane lipids, although not stored in large amounts in the system. Lipid Metabolism
  • Fat-soluble vitamins: A, D, E, and K
• Micelles Micelles Particles consisting of aggregates of molecules held loosely together by secondary bonds. The surface of micelles are usually comprised of amphiphatic compounds that are oriented in a way that minimizes the energy of interaction between the micelle and its environment. Liquids that contain large numbers of suspended micelles are referred to as emulsions. Malabsorption and Maldigestion carry the lipid components to the enterocyte walls for absorption.

Absorption

While the majority of absorption occurs in the small intestine Small intestine The small intestine is the longest part of the GI tract, extending from the pyloric orifice of the stomach to the ileocecal junction. The small intestine is the major organ responsible for chemical digestion and absorption of nutrients. It is divided into 3 segments: the duodenum, the jejunum, and the ileum. Small Intestine: Anatomy, some absorption may begin in the stomach Stomach The stomach is a muscular sac in the upper left portion of the abdomen that plays a critical role in digestion. The stomach develops from the foregut and connects the esophagus with the duodenum. Structurally, the stomach is C-shaped and forms a greater and lesser curvature and is divided grossly into regions: the cardia, fundus, body, and pylorus. Stomach: Anatomy.

Long-chain fatty acids Acids Chemical compounds which yield hydrogen ions or protons when dissolved in water, whose hydrogen can be replaced by metals or basic radicals, or which react with bases to form salts and water (neutralization). An extension of the term includes substances dissolved in media other than water. Acid-Base Balance (LCFAs):

• Mixed micelles Micelles Particles consisting of aggregates of molecules held loosely together by secondary bonds. The surface of micelles are usually comprised of amphiphatic compounds that are oriented in a way that minimizes the energy of interaction between the micelle and its environment. Liquids that contain large numbers of suspended micelles are referred to as emulsions. Malabsorption and Maldigestion package LCFAs and bring them to the enterocyte border.
• pH pH The quantitative measurement of the acidity or basicity of a solution. Acid-Base Balance change near the brush border Brush border Tubular System breaks open the micelles Micelles Particles consisting of aggregates of molecules held loosely together by secondary bonds. The surface of micelles are usually comprised of amphiphatic compounds that are oriented in a way that minimizes the energy of interaction between the micelle and its environment. Liquids that contain large numbers of suspended micelles are referred to as emulsions. Malabsorption and Maldigestion.
• Lipid components (e.g., fatty acids Acids Chemical compounds which yield hydrogen ions or protons when dissolved in water, whose hydrogen can be replaced by metals or basic radicals, or which react with bases to form salts and water (neutralization). An extension of the term includes substances dissolved in media other than water. Acid-Base Balance and monoglycerides Monoglycerides Glycerol esterified with a single Acyl (fatty acids) chain. Lipid Metabolism) travel across the membrane to enter the cytosol Cytosol A cell’s cytoskeleton is a network of intracellular protein fibers that provides structural support, anchors organelles, and aids intra- and extracellular movement. The Cell: Cytosol and Cytoskeleton of enterocytes.
• Lipid components are:
  • Lipid soluble Lipid Soluble Chloramphenicol → can cross the phospholipid membrane without specialized transport molecules
  • Resynthesized via esterification Esterification The process of converting an acid into an alkyl or aryl derivative. Most frequently the process consists of the reaction of an acid with an alcohol in the presence of a trace of mineral acid as catalyst or the reaction of an Acyl chloride with an alcohol. Esterification can also be accomplished by enzymatic processes. Lipid Metabolism in the ER
  • Repackaged as chylomicrons in the golgi apparatus
• Chylomicrons exit the enterocytes on their basolateral side → enter lymphatic circulation Circulation The movement of the blood as it is pumped through the cardiovascular system. ABCDE Assessment

Short-chain fatty acids Acids Chemical compounds which yield hydrogen ions or protons when dissolved in water, whose hydrogen can be replaced by metals or basic radicals, or which react with bases to form salts and water (neutralization). An extension of the term includes substances dissolved in media other than water. Acid-Base Balance (SCFAs) and medium-chain fatty acids Acids Chemical compounds which yield hydrogen ions or protons when dissolved in water, whose hydrogen can be replaced by metals or basic radicals, or which react with bases to form salts and water (neutralization). An extension of the term includes substances dissolved in media other than water. Acid-Base Balance (MCFAs):

• In the small intestine Small intestine The small intestine is the longest part of the GI tract, extending from the pyloric orifice of the stomach to the ileocecal junction. The small intestine is the major organ responsible for chemical digestion and absorption of nutrients. It is divided into 3 segments: the duodenum, the jejunum, and the ileum. Small Intestine: Anatomy:
  • SCFAs and MCFAs travel across the enterocytes without assistance.
  • SCFAs and MCFAs are absorbed into venous circulation Circulation The movement of the blood as it is pumped through the cardiovascular system. ABCDE Assessment → hepatic portal vein Portal vein A short thick vein formed by union of the superior mesenteric vein and the splenic vein. Liver: Anatomy → liver Liver The liver is the largest gland in the human body. The liver is found in the superior right quadrant of the abdomen and weighs approximately 1.5 kilograms. Its main functions are detoxification, metabolism, nutrient storage (e.g., iron and vitamins), synthesis of coagulation factors, formation of bile, filtration, and storage of blood. Liver: Anatomy
• In the large intestine Large intestine The large intestines constitute the last portion of the digestive system. The large intestine consists of the cecum, appendix, colon (with ascending, transverse, descending, and sigmoid segments), rectum, and anal canal. The primary function of the colon is to remove water and compact the stool prior to expulsion from the body via the rectum and anal canal. Colon, Cecum, and Appendix: Anatomy, SCFAs use the sodium Sodium A member of the alkali group of metals. It has the atomic symbol na, atomic number 11, and atomic weight 23. Hyponatremia monocarboxylate transporter (SMCT) 1:
  • Na⁺/SCFA cotransporter
  • Uses the Na⁺ gradient generated by the basolateral Na⁺/K⁺ pump Pump ACES and RUSH: Resuscitation Ultrasound Protocols
  • The pump Pump ACES and RUSH: Resuscitation Ultrasound Protocols also assists in the absorption of water in the large intestine Large intestine The large intestines constitute the last portion of the digestive system. The large intestine consists of the cecum, appendix, colon (with ascending, transverse, descending, and sigmoid segments), rectum, and anal canal. The primary function of the colon is to remove water and compact the stool prior to expulsion from the body via the rectum and anal canal. Colon, Cecum, and Appendix: Anatomy.

Digestion and Absorption of Micronutrients

Calcium Calcium A basic element found in nearly all tissues. It is a member of the alkaline earth family of metals with the atomic symbol ca, atomic number 20, and atomic weight 40. Calcium is the most abundant mineral in the body and combines with phosphorus to form calcium phosphate in the bones and teeth. It is essential for the normal functioning of nerves and muscles and plays a role in blood coagulation (as factor IV) and in many enzymatic processes. Electrolytes ( Ca CA Condylomata acuminata are a clinical manifestation of genital HPV infection. Condylomata acuminata are described as raised, pearly, flesh-colored, papular, cauliflower-like lesions seen in the anogenital region that may cause itching, pain, or bleeding. Condylomata Acuminata (Genital Warts)²⁺) absorption

• Ca CA Condylomata acuminata are a clinical manifestation of genital HPV infection. Condylomata acuminata are described as raised, pearly, flesh-colored, papular, cauliflower-like lesions seen in the anogenital region that may cause itching, pain, or bleeding. Condylomata Acuminata (Genital Warts)²⁺ is absorbed across the apical membrane via Ca CA Condylomata acuminata are a clinical manifestation of genital HPV infection. Condylomata acuminata are described as raised, pearly, flesh-colored, papular, cauliflower-like lesions seen in the anogenital region that may cause itching, pain, or bleeding. Condylomata Acuminata (Genital Warts)²⁺ transporters (primarily TRPV6).
• Calbindin Calbindin Calcium-binding proteins that are found in distal kidney tubules, intestines, brain, and other tissues where they bind, buffer and transport cytoplasmic calcium. Calbindins possess a variable number of ef-hand motifs which contain calcium-binding sites. Some isoforms are regulated by vitamin d. Calcium Hemostasis and Bone Metabolism: an intracellular Ca CA Condylomata acuminata are a clinical manifestation of genital HPV infection. Condylomata acuminata are described as raised, pearly, flesh-colored, papular, cauliflower-like lesions seen in the anogenital region that may cause itching, pain, or bleeding. Condylomata Acuminata (Genital Warts)²⁺-binding protein that immediately binds all absorbed Ca CA Condylomata acuminata are a clinical manifestation of genital HPV infection. Condylomata acuminata are described as raised, pearly, flesh-colored, papular, cauliflower-like lesions seen in the anogenital region that may cause itching, pain, or bleeding. Condylomata Acuminata (Genital Warts)²⁺ and transports it to the basolateral membrane
  • Purpose:
    • Free Ca CA Condylomata acuminata are a clinical manifestation of genital HPV infection. Condylomata acuminata are described as raised, pearly, flesh-colored, papular, cauliflower-like lesions seen in the anogenital region that may cause itching, pain, or bleeding. Condylomata Acuminata (Genital Warts)²⁺ could act as an intracellular signaling molecule.
    • High levels of free Ca CA Condylomata acuminata are a clinical manifestation of genital HPV infection. Condylomata acuminata are described as raised, pearly, flesh-colored, papular, cauliflower-like lesions seen in the anogenital region that may cause itching, pain, or bleeding. Condylomata Acuminata (Genital Warts)²⁺ can be toxic.
  • Calbindin Calbindin Calcium-binding proteins that are found in distal kidney tubules, intestines, brain, and other tissues where they bind, buffer and transport cytoplasmic calcium. Calbindins possess a variable number of ef-hand motifs which contain calcium-binding sites. Some isoforms are regulated by vitamin d. Calcium Hemostasis and Bone Metabolism level in the cell determines how much Ca CA Condylomata acuminata are a clinical manifestation of genital HPV infection. Condylomata acuminata are described as raised, pearly, flesh-colored, papular, cauliflower-like lesions seen in the anogenital region that may cause itching, pain, or bleeding. Condylomata Acuminata (Genital Warts)²⁺ can be absorbed.
• Ca CA Condylomata acuminata are a clinical manifestation of genital HPV infection. Condylomata acuminata are described as raised, pearly, flesh-colored, papular, cauliflower-like lesions seen in the anogenital region that may cause itching, pain, or bleeding. Condylomata Acuminata (Genital Warts)²⁺ is absorbed across the basolateral membrane by:
  • Ca CA Condylomata acuminata are a clinical manifestation of genital HPV infection. Condylomata acuminata are described as raised, pearly, flesh-colored, papular, cauliflower-like lesions seen in the anogenital region that may cause itching, pain, or bleeding. Condylomata Acuminata (Genital Warts)²⁺ ATPase
  • Ca CA Condylomata acuminata are a clinical manifestation of genital HPV infection. Condylomata acuminata are described as raised, pearly, flesh-colored, papular, cauliflower-like lesions seen in the anogenital region that may cause itching, pain, or bleeding. Condylomata Acuminata (Genital Warts)²⁺/Na⁺ exchanger
• Note: A small amount of Ca CA Condylomata acuminata are a clinical manifestation of genital HPV infection. Condylomata acuminata are described as raised, pearly, flesh-colored, papular, cauliflower-like lesions seen in the anogenital region that may cause itching, pain, or bleeding. Condylomata Acuminata (Genital Warts)²⁺ can also be absorbed paracellularly.
• Regulation:
  • Production of the apical Ca CA Condylomata acuminata are a clinical manifestation of genital HPV infection. Condylomata acuminata are described as raised, pearly, flesh-colored, papular, cauliflower-like lesions seen in the anogenital region that may cause itching, pain, or bleeding. Condylomata Acuminata (Genital Warts)²⁺ transporter is induced by:
    • Vitamin D Vitamin D A vitamin that includes both cholecalciferols and ergocalciferols, which have the common effect of preventing or curing rickets in animals. It can also be viewed as a hormone since it can be formed in skin by action of ultraviolet rays upon the precursors, 7-dehydrocholesterol and ergosterol, and acts on vitamin D receptors to regulate calcium in opposition to parathyroid hormone. Fat-soluble Vitamins and their Deficiencies
    • Estrogens
  • Calbindin Calbindin Calcium-binding proteins that are found in distal kidney tubules, intestines, brain, and other tissues where they bind, buffer and transport cytoplasmic calcium. Calbindins possess a variable number of ef-hand motifs which contain calcium-binding sites. Some isoforms are regulated by vitamin d. Calcium Hemostasis and Bone Metabolism synthesis Synthesis Polymerase Chain Reaction (PCR) is induced by vitamin D Vitamin D A vitamin that includes both cholecalciferols and ergocalciferols, which have the common effect of preventing or curing rickets in animals. It can also be viewed as a hormone since it can be formed in skin by action of ultraviolet rays upon the precursors, 7-dehydrocholesterol and ergosterol, and acts on vitamin D receptors to regulate calcium in opposition to parathyroid hormone. Fat-soluble Vitamins and their Deficiencies.

Iron Iron A metallic element with atomic symbol fe, atomic number 26, and atomic weight 55. 85. It is an essential constituent of hemoglobins; cytochromes; and iron-binding proteins. It plays a role in cellular redox reactions and in the transport of oxygen. Trace Elements absorption

• Primarily absorbed in the duodenum Duodenum The shortest and widest portion of the small intestine adjacent to the pylorus of the stomach. It is named for having the length equal to about the width of 12 fingers. Small Intestine: Anatomy
• Fe³⁺ (the primary form of iron Iron A metallic element with atomic symbol fe, atomic number 26, and atomic weight 55. 85. It is an essential constituent of hemoglobins; cytochromes; and iron-binding proteins. It plays a role in cellular redox reactions and in the transport of oxygen. Trace Elements found in food) must be reduced to Fe²⁺ for absorption via duodenal cytochrome B (DcytB) located on the brush border Brush border Tubular System of enterocytes.
• Absorption across the apical membrane:
  • DMT ( divalent metal transporter Divalent metal transporter Transports Fe²⁺ (not Fe³⁺) from the apical surface of enterocytes to the interior of the cell. Heme Metabolism) 1: a specialized Fe²⁺/H⁺ cotransporter absorbing most nonheme iron Iron A metallic element with atomic symbol fe, atomic number 26, and atomic weight 55. 85. It is an essential constituent of hemoglobins; cytochromes; and iron-binding proteins. It plays a role in cellular redox reactions and in the transport of oxygen. Trace Elements
  • Within heme molecules (e.g., from meat)
• Within the cell:
  • Mobilferrin: an iron-binding protein that binds Fe²⁺ and transports it across the enterocyte to the basolateral membrane
  • Heme oxygenase Heme oxygenase A mixed function oxidase enzyme which during hemoglobin catabolism catalyzes the degradation of heme to ferrous iron, carbon monoxide and biliverdin in the presence of molecular oxygen and reduced NADPH. Heme Metabolism: releases Fe²⁺ from heme → Fe²⁺ is bound and transported by mobilferrin
• Release across the basolateral membrane:
  • Ferroportin Ferroportin Helps export iron from the intestinal cell. Heme Metabolism 1: a membrane-bound transport protein that releases Fe²⁺ into the interstitial space
  • Hephaestin Hephaestin A copper-containing membrane protein which has a ferroxidase activity. Heme Metabolism:
    • A copper-dependent membrane-bound ferroxidase
    • Oxidizes Fe²⁺ to Fe³⁺, which is necessary for iron Iron A metallic element with atomic symbol fe, atomic number 26, and atomic weight 55. 85. It is an essential constituent of hemoglobins; cytochromes; and iron-binding proteins. It plays a role in cellular redox reactions and in the transport of oxygen. Trace Elements to move into capillaries Capillaries Capillaries are the primary structures in the circulatory system that allow the exchange of gas, nutrients, and other materials between the blood and the extracellular fluid (ECF). Capillaries are the smallest of the blood vessels. Because a capillary diameter is so small, only 1 RBC may pass through at a time. Capillaries: Histology and bind BIND Hyperbilirubinemia of the Newborn transferrin Transferrin An iron-binding beta1-globulin that is synthesized in the liver and secreted into the blood. It plays a central role in the transport of iron throughout the circulation. Heme Metabolism ( plasma Plasma The residual portion of blood that is left after removal of blood cells by centrifugation without prior blood coagulation. Transfusion Products iron Iron A metallic element with atomic symbol fe, atomic number 26, and atomic weight 55. 85. It is an essential constituent of hemoglobins; cytochromes; and iron-binding proteins. It plays a role in cellular redox reactions and in the transport of oxygen. Trace Elements transport protein)
• Regulation:
  • Hepcidin Hepcidin Forms of hepcidin, a cationic amphipathic peptide synthesized in the liver as a prepropeptide which is first processed into prohepcidin and then into the biologically active hepcidin forms, including in human the 20-, 22-, and 25-amino acid residue peptide forms. Hepcidin acts as a homeostatic regulators of iron metabolism and also possesses antimicrobial activity. Hereditary Hemochromatosis:
    • Inactivates ferroportin Ferroportin Helps export iron from the intestinal cell. Heme Metabolism 1 (the primary negative regulatory outcome of intestinal iron Iron A metallic element with atomic symbol fe, atomic number 26, and atomic weight 55. 85. It is an essential constituent of hemoglobins; cytochromes; and iron-binding proteins. It plays a role in cellular redox reactions and in the transport of oxygen. Trace Elements absorption)
    • Clinical relevance: Mutation Mutation Genetic mutations are errors in DNA that can cause protein misfolding and dysfunction. There are various types of mutations, including chromosomal, point, frameshift, and expansion mutations. Types of Mutations/deficiency of hepcidin Hepcidin Forms of hepcidin, a cationic amphipathic peptide synthesized in the liver as a prepropeptide which is first processed into prohepcidin and then into the biologically active hepcidin forms, including in human the 20-, 22-, and 25-amino acid residue peptide forms. Hepcidin acts as a homeostatic regulators of iron metabolism and also possesses antimicrobial activity. Hereditary Hemochromatosis results in hereditary hemochromatosis Hemochromatosis A disorder of iron metabolism characterized by a triad of hemosiderosis; liver cirrhosis; and diabetes mellitus. It is caused by massive iron deposits in parenchymal cells that may develop after a prolonged increase of iron absorption. Hereditary Hemochromatosis.
  • Hypoxia-inducible factor Hypoxia-inducible factor Hypoxia-inducible factor 1, alpha subunit is a basic helix-loop-helix transcription factor that is regulated by oxygen availability and is targeted for degradation by VHL tumor suppressor protein. Von Hippel-Lindau Disease ( HIF HIF Hypoxia-inducible factor 1, alpha subunit is a basic helix-loop-helix transcription factor that is regulated by oxygen availability and is targeted for degradation by VHL tumor suppressor protein. Von Hippel-Lindau Disease)-2α induces synthesis Synthesis Polymerase Chain Reaction (PCR) of DMT1 DMT1 Transports Fe²⁺ (not Fe³⁺) from the apical surface of enterocytes to the interior of the cell. Heme Metabolism and DcytB → ↑ absorption
  • Hypoxia Hypoxia Sub-optimal oxygen levels in the ambient air of living organisms. Ischemic Cell Damage and anemia Anemia Anemia is a condition in which individuals have low Hb levels, which can arise from various causes. Anemia is accompanied by a reduced number of RBCs and may manifest with fatigue, shortness of breath, pallor, and weakness. Subtypes are classified by the size of RBCs, chronicity, and etiology. Anemia: Overview and Types → ↑ iron Iron A metallic element with atomic symbol fe, atomic number 26, and atomic weight 55. 85. It is an essential constituent of hemoglobins; cytochromes; and iron-binding proteins. It plays a role in cellular redox reactions and in the transport of oxygen. Trace Elements absorption via:
    • ↓ Hepcidin Hepcidin Forms of hepcidin, a cationic amphipathic peptide synthesized in the liver as a prepropeptide which is first processed into prohepcidin and then into the biologically active hepcidin forms, including in human the 20-, 22-, and 25-amino acid residue peptide forms. Hepcidin acts as a homeostatic regulators of iron metabolism and also possesses antimicrobial activity. Hereditary Hemochromatosis → ↑ activity of ferroportin Ferroportin Helps export iron from the intestinal cell. Heme Metabolism 1
    • ↑ HIF-2α
  • Ascorbic acid ( vitamin C Vitamin C A six carbon compound related to glucose. It is found naturally in citrus fruits and many vegetables. Ascorbic acid is an essential nutrient in human diets, and necessary to maintain connective tissue and bone. Its biologically active form, vitamin C, functions as a reducing agent and coenzyme in several metabolic pathways. Vitamin C is considered an antioxidant. Water-soluble Vitamins and their Deficiencies) enhances absorption.
  • Phosphates (present in teas, bran) inhibit absorption.

Digestion and absorption of other micronutrients

Fat-soluble vitamins:

• A, D, E, and K
• Absorbed with lipids Lipids Lipids are a diverse group of hydrophobic organic molecules, which include fats, oils, sterols, and waxes. Fatty Acids and Lipids → packaged in micelles Micelles Particles consisting of aggregates of molecules held loosely together by secondary bonds. The surface of micelles are usually comprised of amphiphatic compounds that are oriented in a way that minimizes the energy of interaction between the micelle and its environment. Liquids that contain large numbers of suspended micelles are referred to as emulsions. Malabsorption and Maldigestion
• Absorbed across the apical membrane → repackaged into chylomicrons
• Chylomicrons → released into the interstitial fluid Interstitial fluid Body Fluid Compartments → absorbed into lymphatic circulation Circulation The movement of the blood as it is pumped through the cardiovascular system. ABCDE Assessment

Water-soluble vitamins:

• Includes all B vitamins and vitamin C Vitamin C A six carbon compound related to glucose. It is found naturally in citrus fruits and many vegetables. Ascorbic acid is an essential nutrient in human diets, and necessary to maintain connective tissue and bone. Its biologically active form, vitamin C, functions as a reducing agent and coenzyme in several metabolic pathways. Vitamin C is considered an antioxidant. Water-soluble Vitamins and their Deficiencies
• Primarily absorbed in the small intestine Small intestine The small intestine is the longest part of the GI tract, extending from the pyloric orifice of the stomach to the ileocecal junction. The small intestine is the major organ responsible for chemical digestion and absorption of nutrients. It is divided into 3 segments: the duodenum, the jejunum, and the ileum. Small Intestine: Anatomy:
  • Via active transport Active transport The movement of materials across cell membranes and epithelial layers against an electrochemical gradient, requiring the expenditure of metabolic energy. The Cell: Cell Membrane:
    • Vitamin C Vitamin C A six carbon compound related to glucose. It is found naturally in citrus fruits and many vegetables. Ascorbic acid is an essential nutrient in human diets, and necessary to maintain connective tissue and bone. Its biologically active form, vitamin C, functions as a reducing agent and coenzyme in several metabolic pathways. Vitamin C is considered an antioxidant. Water-soluble Vitamins and their Deficiencies
    • Thiamine Thiamine Also known as thiamine or thiamin, it is a vitamin C12H17N4OSCl of the vitamin B complex that is essential to normal metabolism and nerve function and is widespread in plants and animals Water-soluble Vitamins and their Deficiencies (B1)
    • Pantothenic acid (B5)
    • Folate Folate Folate and vitamin B12 are 2 of the most clinically important water-soluble vitamins. Deficiencies can present with megaloblastic anemia, GI symptoms, neuropsychiatric symptoms, and adverse pregnancy complications, including neural tube defects. Folate and Vitamin B12 (B9)
    • Cobalamine (B12)
  • Via passive transport Passive transport The passive movement of molecules exceeding the rate expected by simple diffusion. No energy is expended in the process. It is achieved by the introduction of passively diffusing molecules to an environment or path that is more favorable to the movement of those molecules. Examples of facilitated diffusion are passive transport of hydrophilic substances across a lipid membrane through hydrophilic pores that traverse the membrane, and the sliding of a DNA binding protein along a strand of DNA. The Cell: Cell Membrane and/or facilitated diffusion Diffusion The tendency of a gas or solute to pass from a point of higher pressure or concentration to a point of lower pressure or concentration and to distribute itself throughout the available space. Diffusion, especially facilitated diffusion, is a major mechanism of biological transport. Peritoneal Dialysis and Hemodialysis:
    • Riboflavin (B2)
    • Niacin Niacin A water-soluble vitamin of the B complex occurring in various animal and plant tissues. It is required by the body for the formation of coenzymes nad and NADP. It has pellagra-curative, vasodilating, and antilipemic properties. Lipid Control Drugs (B3)
    • Pyridoxine (B6)
• Absorption of B12:
  • Vitamin B12 Vitamin B12 A cobalt-containing coordination compound produced by intestinal microorganisms and found also in soil and water. Higher plants do not concentrate vitamin B 12 from the soil and so are a poor source of the substance as compared with animal tissues. Intrinsic factor is important for the assimilation of vitamin B 12. Folate and Vitamin B12 is bound to proteins Proteins Linear polypeptides that are synthesized on ribosomes and may be further modified, crosslinked, cleaved, or assembled into complex proteins with several subunits. The specific sequence of amino acids determines the shape the polypeptide will take, during protein folding, and the function of the protein. Energy Homeostasis in food.
  • In the stomach Stomach The stomach is a muscular sac in the upper left portion of the abdomen that plays a critical role in digestion. The stomach develops from the foregut and connects the esophagus with the duodenum. Structurally, the stomach is C-shaped and forms a greater and lesser curvature and is divided grossly into regions: the cardia, fundus, body, and pylorus. Stomach: Anatomy:
    • Acid and pepsin Pepsin Pepsin breaks down proteins into proteoses, peptones, and large polypeptides. Proteins and Peptides release vitamin B12 Vitamin B12 A cobalt-containing coordination compound produced by intestinal microorganisms and found also in soil and water. Higher plants do not concentrate vitamin B 12 from the soil and so are a poor source of the substance as compared with animal tissues. Intrinsic factor is important for the assimilation of vitamin B 12. Folate and Vitamin B12 from dietary proteins Proteins Linear polypeptides that are synthesized on ribosomes and may be further modified, crosslinked, cleaved, or assembled into complex proteins with several subunits. The specific sequence of amino acids determines the shape the polypeptide will take, during protein folding, and the function of the protein. Energy Homeostasis.
    • Vitamin B12 Vitamin B12 A cobalt-containing coordination compound produced by intestinal microorganisms and found also in soil and water. Higher plants do not concentrate vitamin B 12 from the soil and so are a poor source of the substance as compared with animal tissues. Intrinsic factor is important for the assimilation of vitamin B 12. Folate and Vitamin B12 binds haptocorrin.
    • Parietal cells Parietal cells Rounded or pyramidal cells of the gastric glands. They secrete hydrochloric acid and produce gastric intrinsic factor, a glycoprotein that binds vitamin B12. Stomach: Anatomy release intrinsic factor Intrinsic factor A glycoprotein secreted by the cells of the gastric glands that is required for the absorption of vitamin B 12 (cyanocobalamin). Deficiency of intrinsic factor leads to vitamin B12 deficiency and anemia, pernicious. Gastritis (IF).
  • In the duodenum Duodenum The shortest and widest portion of the small intestine adjacent to the pylorus of the stomach. It is named for having the length equal to about the width of 12 fingers. Small Intestine: Anatomy:
    • Pancreatic proteases Proteases Proteins and Peptides remove haptocorrin from B12.
    • B12 binds IF.
  • The B12-IF complex is absorbed by receptor-mediated endocytosis Endocytosis Cellular uptake of extracellular materials within membrane-limited vacuoles or microvesicles. Endosomes play a central role in endocytosis. The Cell: Cell Membrane in the terminal ileum Ileum The distal and narrowest portion of the small intestine, between the jejunum and the ileocecal valve of the large intestine. Small Intestine: Anatomy.
  • Vitamin B12 Vitamin B12 A cobalt-containing coordination compound produced by intestinal microorganisms and found also in soil and water. Higher plants do not concentrate vitamin B 12 from the soil and so are a poor source of the substance as compared with animal tissues. Intrinsic factor is important for the assimilation of vitamin B 12. Folate and Vitamin B12 is secreted into the blood by active transport Active transport The movement of materials across cell membranes and epithelial layers against an electrochemical gradient, requiring the expenditure of metabolic energy. The Cell: Cell Membrane, where it binds to transcobalamin.
• Clinical relevance:
  • ↓ Vitamin C Vitamin C A six carbon compound related to glucose. It is found naturally in citrus fruits and many vegetables. Ascorbic acid is an essential nutrient in human diets, and necessary to maintain connective tissue and bone. Its biologically active form, vitamin C, functions as a reducing agent and coenzyme in several metabolic pathways. Vitamin C is considered an antioxidant. Water-soluble Vitamins and their Deficiencies → scurvy Scurvy An acquired blood vessel disorder caused by severe deficiency of vitamin C (ascorbic acid) in the diet leading to defective collagen formation in small blood vessels. Scurvy is characterized by bleeding in any tissue, weakness, anemia, spongy gums, and a brawny induration of the muscles of the calves and legs. Water-soluble Vitamins and their Deficiencies
  • ↓ Vitamin B1 Vitamin B1 Also known as thiamine or thiamin, it is a vitamin C12H17N4OSCl of the vitamin B complex that is essential to normal metabolism and nerve function and is widespread in plants and animals Water-soluble Vitamins and their Deficiencies → beriberi Beriberi A disease caused by a deficiency of thiamine (vitamin B1) and characterized by polyneuritis, cardiac pathology, and edema. The epidemic form is found primarily in areas in which white (polished) rice is the staple food, as in japan, china, the philippines, india, and other countries of southeast Asia. Water-soluble Vitamins and their Deficiencies; Wernicke-Korsakoff syndrome Wernicke-Korsakoff syndrome 2 different syndromes that are different stages of the same disease including Wernicke’s encephalopathy and Korsakoff psychosis.Wernicke-Korsakoff syndrome is seen in patients with alcohol use disorder 8–10 times more than in the general population. Wernicke Encephalopathy and Korsakoff Syndrome
  • ↓ Vitamin B3 Vitamin B3 A water-soluble vitamin of the B complex occurring in various animal and plant tissues. It is required by the body for the formation of coenzymes nad and NADP. It has pellagra-curative, vasodilating, and antilipemic properties. Water-soluble Vitamins and their Deficiencies → pellagra Pellagra A disease due to deficiency of niacin, a b-complex vitamin, or its precursor tryptophan. It is characterized by scaly dermatitis which is often associated with diarrhea and dementia (the three d’s). Water-soluble Vitamins and their Deficiencies
  • ↓ Folate Folate Folate and vitamin B12 are 2 of the most clinically important water-soluble vitamins. Deficiencies can present with megaloblastic anemia, GI symptoms, neuropsychiatric symptoms, and adverse pregnancy complications, including neural tube defects. Folate and Vitamin B12 and/or vitamin B12 Vitamin B12 A cobalt-containing coordination compound produced by intestinal microorganisms and found also in soil and water. Higher plants do not concentrate vitamin B 12 from the soil and so are a poor source of the substance as compared with animal tissues. Intrinsic factor is important for the assimilation of vitamin B 12. Folate and Vitamin B12 → megaloblastic anemia Megaloblastic anemia Megaloblastic anemia is a subset of macrocytic anemias that arises because of impaired nucleic acid synthesis in erythroid precursors. This impairment leads to ineffective RBC production and intramedullary hemolysis that is characterized by large cells with arrested nuclear maturation. The most common causes are vitamin B12 and folic acid deficiencies. Megaloblastic Anemia
  • ↓ Folate Folate Folate and vitamin B12 are 2 of the most clinically important water-soluble vitamins. Deficiencies can present with megaloblastic anemia, GI symptoms, neuropsychiatric symptoms, and adverse pregnancy complications, including neural tube defects. Folate and Vitamin B12 in early pregnancy Pregnancy The status during which female mammals carry their developing young (embryos or fetuses) in utero before birth, beginning from fertilization to birth. Pregnancy: Diagnosis, Physiology, and Care → neural-tube defects in infants
  • Gastric bypass Gastric bypass Surgical procedure in which the stomach is transected high on the body. The resulting small proximal gastric pouch is joined to any parts of the small intestine by an end-to-side surgical anastomosis, depending on the amounts of intestinal surface being bypasses. This procedure is used frequently in the treatment of morbid obesity by limiting the size of functional stomach, food intake, and food absorption. Gastroesophageal Reflux Disease (GERD) → may remove a majority of parietal cells Parietal cells Rounded or pyramidal cells of the gastric glands. They secrete hydrochloric acid and produce gastric intrinsic factor, a glycoprotein that binds vitamin B12. Stomach: Anatomy → ↓ IF → ↓ vitamin B12 Vitamin B12 A cobalt-containing coordination compound produced by intestinal microorganisms and found also in soil and water. Higher plants do not concentrate vitamin B 12 from the soil and so are a poor source of the substance as compared with animal tissues. Intrinsic factor is important for the assimilation of vitamin B 12. Folate and Vitamin B12 absorption
  • Surgical removal of the terminal ileum Ileum The distal and narrowest portion of the small intestine, between the jejunum and the ileocecal valve of the large intestine. Small Intestine: Anatomy → ↓ vitamin B12 Vitamin B12 A cobalt-containing coordination compound produced by intestinal microorganisms and found also in soil and water. Higher plants do not concentrate vitamin B 12 from the soil and so are a poor source of the substance as compared with animal tissues. Intrinsic factor is important for the assimilation of vitamin B 12. Folate and Vitamin B12 absorption

Clinical Relevance of Malabsorption and Maldigestion

Malabsorption Malabsorption General term for a group of malnutrition syndromes caused by failure of normal intestinal absorption of nutrients. Malabsorption and Maldigestion involves many disorders wherein the gut cannot absorb nutrients including water and/or electrolytes Electrolytes Electrolytes are mineral salts that dissolve in water and dissociate into charged particles called ions, which can be either be positively (cations) or negatively (anions) charged. Electrolytes are distributed in the extracellular and intracellular compartments in different concentrations. Electrolytes are essential for various basic life-sustaining functions. Electrolytes from the diet. Maldigestion Maldigestion Malabsorption involves many disorders in which there is an inability of the gut to absorb nutrients from dietary intake, potentially including water and/or electrolytes. A closely related term, maldigestion is the inability to break down large molecules of food into their smaller constituents. Malabsorption and maldigestion can affect macronutrients (fats, proteins, and carbohydrates), micronutrients (vitamins and minerals), or both. Malabsorption and Maldigestion is a closely related term, which is the inability of the gut to break down large food molecules into their smaller constituents.  Maldigestion Maldigestion Malabsorption involves many disorders in which there is an inability of the gut to absorb nutrients from dietary intake, potentially including water and/or electrolytes. A closely related term, maldigestion is the inability to break down large molecules of food into their smaller constituents. Malabsorption and maldigestion can affect macronutrients (fats, proteins, and carbohydrates), micronutrients (vitamins and minerals), or both. Malabsorption and Maldigestion can affect macronutrients ( fats Fats The glyceryl esters of a fatty acid, or of a mixture of fatty acids. They are generally odorless, colorless, and tasteless if pure, but they may be flavored according to origin. Fats are insoluble in water, soluble in most organic solvents. They occur in animal and vegetable tissue and are generally obtained by boiling or by extraction under pressure. They are important in the diet (dietary fats) as a source of energy. Energy Homeostasis, proteins Proteins Linear polypeptides that are synthesized on ribosomes and may be further modified, crosslinked, cleaved, or assembled into complex proteins with several subunits. The specific sequence of amino acids determines the shape the polypeptide will take, during protein folding, and the function of the protein. Energy Homeostasis, and carbohydrates Carbohydrates A class of organic compounds composed of carbon, hydrogen, and oxygen in a ratio of cn(H2O)n. The largest class of organic compounds, including starch; glycogen; cellulose; polysaccharides; and simple monosaccharides. Basics of Carbohydrates), micronutrients (vitamins, minerals Minerals Electrolytes), or both. Malabsorption Malabsorption General term for a group of malnutrition syndromes caused by failure of normal intestinal absorption of nutrients. Malabsorption and Maldigestion and maldigestion Maldigestion Malabsorption involves many disorders in which there is an inability of the gut to absorb nutrients from dietary intake, potentially including water and/or electrolytes. A closely related term, maldigestion is the inability to break down large molecules of food into their smaller constituents. Malabsorption and maldigestion can affect macronutrients (fats, proteins, and carbohydrates), micronutrients (vitamins and minerals), or both. Malabsorption and Maldigestion present with weight loss Weight loss Decrease in existing body weight. Bariatric Surgery, diarrhea Diarrhea Diarrhea is defined as ≥ 3 watery or loose stools in a 24-hour period. There are a multitude of etiologies, which can be classified based on the underlying mechanism of disease. The duration of symptoms (acute or chronic) and characteristics of the stools (e.g., watery, bloody, steatorrheic, mucoid) can help guide further diagnostic evaluation. Diarrhea, weakness, and fatigue Fatigue The state of weariness following a period of exertion, mental or physical, characterized by a decreased capacity for work and reduced efficiency to respond to stimuli. Fibromyalgia.

• Etiologies of maldigestion Maldigestion Malabsorption involves many disorders in which there is an inability of the gut to absorb nutrients from dietary intake, potentially including water and/or electrolytes. A closely related term, maldigestion is the inability to break down large molecules of food into their smaller constituents. Malabsorption and maldigestion can affect macronutrients (fats, proteins, and carbohydrates), micronutrients (vitamins and minerals), or both. Malabsorption and Maldigestion:
  • Abnormal milieu due to:
    • Small intestinal bacterial overgrowth Bacterial overgrowth Lactose Intolerance
    • Zollinger-Ellison syndrome Zollinger-ellison syndrome A syndrome that is characterized by the triad of severe peptic ulcer, hypersecretion of gastric acid, and gastrin-producing tumors of the pancreas or other tissue (gastrinoma). This syndrome may be sporadic or be associated with multiple endocrine neoplasia type 1. Esophagitis (hypersecretion of gastric acid Gastric acid Hydrochloric acid present in gastric juice. Gastroesophageal Reflux Disease (GERD) resulting in low pH pH The quantitative measurement of the acidity or basicity of a solution. Acid-Base Balance)
  • Abnormal motility Motility The motor activity of the gastrointestinal tract. Gastrointestinal Motility due to:
    • Diabetic gastroparesis Gastroparesis Chronic delayed gastric emptying. Gastroparesis may be caused by motor dysfunction or paralysis of stomach muscles or may be associated with other systemic diseases such as diabetes mellitus. Malabsorption and Maldigestion
    • Systemic sclerosis Systemic sclerosis Scleroderma (systemic sclerosis) is an autoimmune condition characterized by diffuse collagen deposition and fibrosis. The clinical presentation varies from limited skin involvement to diffuse involvement of internal organs. Scleroderma
    • Thyroid Thyroid The thyroid gland is one of the largest endocrine glands in the human body. The thyroid gland is a highly vascular, brownish-red gland located in the visceral compartment of the anterior region of the neck. Thyroid Gland: Anatomy dysfunction
  • Biliary obstruction and/or cholestasis
  • Bile Bile An emulsifying agent produced in the liver and secreted into the duodenum. Its composition includes bile acids and salts; cholesterol; and electrolytes. It aids digestion of fats in the duodenum. Gallbladder and Biliary Tract: Anatomy salt deficiency due to:
    • Hepatic cirrhosis Cirrhosis Cirrhosis is a late stage of hepatic parenchymal necrosis and scarring (fibrosis) most commonly due to hepatitis C infection and alcoholic liver disease. Patients may present with jaundice, ascites, and hepatosplenomegaly. Cirrhosis can also cause complications such as hepatic encephalopathy, portal hypertension, portal vein thrombosis, and hepatorenal syndrome. Cirrhosis
    • Primary biliary cirrhosis Cirrhosis Cirrhosis is a late stage of hepatic parenchymal necrosis and scarring (fibrosis) most commonly due to hepatitis C infection and alcoholic liver disease. Patients may present with jaundice, ascites, and hepatosplenomegaly. Cirrhosis can also cause complications such as hepatic encephalopathy, portal hypertension, portal vein thrombosis, and hepatorenal syndrome. Cirrhosis
  • Pancreatic diseases:
    • Exocrine pancreatic insufficiency Exocrine pancreatic insufficiency A malabsorption condition resulting from greater than 10% reduction in the secretion of pancreatic digestive enzymes (lipase; proteases; and amylase) by the exocrine pancreas into the duodenum. This condition is often associated with cystic fibrosis and with chronic pancreatitis. Malabsorption and Maldigestion
    • Cystic fibrosis Cystic fibrosis Cystic fibrosis is an autosomal recessive disorder caused by mutations in the gene CFTR. The mutations lead to dysfunction of chloride channels, which results in hyperviscous mucus and the accumulation of secretions. Common presentations include chronic respiratory infections, failure to thrive, and pancreatic insufficiency. Cystic Fibrosis
    • Chronic pancreatitis Chronic pancreatitis Chronic pancreatitis is due to persistent inflammation, fibrosis, and irreversible cell damage to the pancreas, resulting in a loss of endocrine and exocrine gland function. The most common etiologies are alcohol abuse and pancreatic duct obstruction. Patients often present with recurrent epigastric abdominal pain, nausea, and features of malabsorption syndrome (diarrhea, steatorrhea, and weight loss). Chronic Pancreatitis
    • Pancreatic cancer
  • Disaccharidase Disaccharidase Enzymes belonging to the class of glycoside hydrolases which break down disaccharides into simpler sugars, monosaccharides. Rotavirus deficiencies:
    • Lactase Lactase An enzyme which catalyzes the hydrolysis of lactose to d-galactose and d-glucose. Defects in the enzyme cause lactose intolerance. Digestion and Absorption of Carbohydrates deficiency (resulting in lactose intolerance Lactose intolerance Lactose intolerance (LI) describes a constellation of symptoms due to lactase deficiency (LD), the enzyme located in the brush border of the absorptive cells in the small intestine. Lactose is the disaccharide present in milk and requires hydrolysis by lactase to break it down into its 2 absorbable constituents, glucose and galactose. Lactose intolerance typically presents with bloating, abdominal cramping, diarrhea, and flatulence. Lactose Intolerance)
    • Sucrase deficiency Sucrase deficiency Malabsorption and Maldigestion
• Etiologies of malabsorption Malabsorption General term for a group of malnutrition syndromes caused by failure of normal intestinal absorption of nutrients. Malabsorption and Maldigestion:
  • Acutely abnormal epithelium Epithelium The epithelium is a complex of specialized cellular organizations arranged into sheets and lining cavities and covering the surfaces of the body. The cells exhibit polarity, having an apical and a basal pole. Structures important for the epithelial integrity and function involve the basement membrane, the semipermeable sheet on which the cells rest, and interdigitations, as well as cellular junctions. Surface Epithelium: Histology:
    • Acute intestinal infections Infections Invasion of the host organism by microorganisms or their toxins or by parasites that can cause pathological conditions or diseases. Chronic Granulomatous Disease such as giardiasis Giardiasis An infection of the small intestine caused by the flagellated protozoan giardia. It is spread via contaminated food and water and by direct person-to-person contact. Giardia/Giardiasis
    • Alcohol ingestion
  • Chronically abnormal epithelium Epithelium The epithelium is a complex of specialized cellular organizations arranged into sheets and lining cavities and covering the surfaces of the body. The cells exhibit polarity, having an apical and a basal pole. Structures important for the epithelial integrity and function involve the basement membrane, the semipermeable sheet on which the cells rest, and interdigitations, as well as cellular junctions. Surface Epithelium: Histology:
    • Celiac disease Celiac disease Celiac disease (also known as celiac sprue or gluten enteropathy) is an autoimmune reaction to gliadin, which is a component of gluten. Celiac disease is closely associated with HLA-DQ2 and HLA-DQ8. The immune response is localized to the proximal small intestine and causes the characteristic histologic findings of villous atrophy, crypt hyperplasia, and intraepithelial lymphocytosis. Celiac Disease
    • Inflammatory bowel disease (IBD): Crohn disease and ulcerative colitis Ulcerative colitis Ulcerative colitis (UC) is an idiopathic inflammatory condition that involves the mucosal surface of the colon. It is a type of inflammatory bowel disease (IBD), along with Crohn’s disease (CD). The rectum is always involved, and inflammation may extend proximally through the colon. Ulcerative Colitis
    • Intestinal ischemia Intestinal ischemia Intestinal ischemia occurs when perfusion fails to meet the demands of the intestines, resulting in ischemic tissue injury that can be life-threatening if bowel necrosis and/or perforation occurs. Symptoms can range from mild indigestion or diarrhea to severe abdominal pain. Intestinal Ischemia
    • Radiation Radiation Emission or propagation of acoustic waves (sound), electromagnetic energy waves (such as light; radio waves; gamma rays; or x-rays), or a stream of subatomic particles (such as electrons; neutrons; protons; or alpha particles). Osteosarcoma enteritis Enteritis Inflammation of any segment of the small intestine. Lactose Intolerance
    • Whipple disease
  • Infiltrative disease: can affect both motility Motility The motor activity of the gastrointestinal tract. Gastrointestinal Motility and absorptive ability
    • Lymphoma Lymphoma A general term for various neoplastic diseases of the lymphoid tissue. Imaging of the Mediastinum
    • Sarcoidosis Sarcoidosis Sarcoidosis is a multisystem inflammatory disease that causes noncaseating granulomas. The exact etiology is unknown. Sarcoidosis usually affects the lungs and thoracic lymph nodes, but it can also affect almost every system in the body, including the skin, heart, and eyes, most commonly. Sarcoidosis
    • Amyloidosis Amyloidosis Amyloidosis is a disease caused by abnormal extracellular tissue deposition of fibrils composed of various misfolded low-molecular-weight protein subunits. These proteins are frequently byproducts of other pathological processes (e.g., multiple myeloma). Amyloidosis
    • Systemic sclerosis Systemic sclerosis Scleroderma (systemic sclerosis) is an autoimmune condition characterized by diffuse collagen deposition and fibrosis. The clinical presentation varies from limited skin involvement to diffuse involvement of internal organs. Scleroderma
• Malabsorption Malabsorption General term for a group of malnutrition syndromes caused by failure of normal intestinal absorption of nutrients. Malabsorption and Maldigestion of carbohydrates Carbohydrates A class of organic compounds composed of carbon, hydrogen, and oxygen in a ratio of cn(H2O)n. The largest class of organic compounds, including starch; glycogen; cellulose; polysaccharides; and simple monosaccharides. Basics of Carbohydrates:
  • Most commonly due to deficiency of disaccharidases (e.g., lactase Lactase An enzyme which catalyzes the hydrolysis of lactose to d-galactose and d-glucose. Defects in the enzyme cause lactose intolerance. Digestion and Absorption of Carbohydrates)
  • Colonic bacteria Bacteria Bacteria are prokaryotic single-celled microorganisms that are metabolically active and divide by binary fission. Some of these organisms play a significant role in the pathogenesis of diseases. Bacteriology ferment unabsorbed carbohydrates Carbohydrates A class of organic compounds composed of carbon, hydrogen, and oxygen in a ratio of cn(H2O)n. The largest class of organic compounds, including starch; glycogen; cellulose; polysaccharides; and simple monosaccharides. Basics of Carbohydrates into gases and fatty acids Acids Chemical compounds which yield hydrogen ions or protons when dissolved in water, whose hydrogen can be replaced by metals or basic radicals, or which react with bases to form salts and water (neutralization). An extension of the term includes substances dissolved in media other than water. Acid-Base Balance.
  • Results in flatulence, bloating Bloating Constipation, and diarrhea Diarrhea Diarrhea is defined as ≥ 3 watery or loose stools in a 24-hour period. There are a multitude of etiologies, which can be classified based on the underlying mechanism of disease. The duration of symptoms (acute or chronic) and characteristics of the stools (e.g., watery, bloody, steatorrheic, mucoid) can help guide further diagnostic evaluation. Diarrhea
• Malabsorption Malabsorption General term for a group of malnutrition syndromes caused by failure of normal intestinal absorption of nutrients. Malabsorption and Maldigestion of proteins Proteins Linear polypeptides that are synthesized on ribosomes and may be further modified, crosslinked, cleaved, or assembled into complex proteins with several subunits. The specific sequence of amino acids determines the shape the polypeptide will take, during protein folding, and the function of the protein. Energy Homeostasis: Deficiency can result in muscle atrophy Atrophy Decrease in the size of a cell, tissue, organ, or multiple organs, associated with a variety of pathological conditions such as abnormal cellular changes, ischemia, malnutrition, or hormonal changes. Cellular Adaptation and edema Edema Edema is a condition in which excess serous fluid accumulates in the body cavity or interstitial space of connective tissues. Edema is a symptom observed in several medical conditions. It can be categorized into 2 types, namely, peripheral (in the extremities) and internal (in an organ or body cavity). Edema.
• Malabsorption Malabsorption General term for a group of malnutrition syndromes caused by failure of normal intestinal absorption of nutrients. Malabsorption and Maldigestion of lipids Lipids Lipids are a diverse group of hydrophobic organic molecules, which include fats, oils, sterols, and waxes. Fatty Acids and Lipids:
  • Deficiency in lipases Lipases An enzyme of the hydrolase class that catalyzes the reaction of triacylglycerol and water to yield diacylglycerol and a fatty acid anion. It is produced by glands on the tongue and by the pancreas and initiates the digestion of dietary fats. Lipid Metabolism prevents the effective breakdown of fats Fats The glyceryl esters of a fatty acid, or of a mixture of fatty acids. They are generally odorless, colorless, and tasteless if pure, but they may be flavored according to origin. Fats are insoluble in water, soluble in most organic solvents. They occur in animal and vegetable tissue and are generally obtained by boiling or by extraction under pressure. They are important in the diet (dietary fats) as a source of energy. Energy Homeostasis.
  • Most commonly due to pancreatic insufficiency
  • Results in:
    • Steatorrhea Steatorrhea A condition that is characterized by chronic fatty diarrhea, a result of abnormal digestion and/or intestinal absorption of fats. Diarrhea
    • Deficiencies of fat-soluble vitamins
    • Diarrhea Diarrhea Diarrhea is defined as ≥ 3 watery or loose stools in a 24-hour period. There are a multitude of etiologies, which can be classified based on the underlying mechanism of disease. The duration of symptoms (acute or chronic) and characteristics of the stools (e.g., watery, bloody, steatorrheic, mucoid) can help guide further diagnostic evaluation. Diarrhea (stimulation of water secretion Secretion Coagulation Studies in the colon Colon The large intestines constitute the last portion of the digestive system. The large intestine consists of the cecum, appendix, colon (with ascending, transverse, descending, and sigmoid segments), rectum, and anal canal. The primary function of the colon is to remove water and compact the stool prior to expulsion from the body via the rectum and anal canal. Colon, Cecum, and Appendix: Anatomy by unabsorbed bile Bile An emulsifying agent produced in the liver and secreted into the duodenum. Its composition includes bile acids and salts; cholesterol; and electrolytes. It aids digestion of fats in the duodenum. Gallbladder and Biliary Tract: Anatomy salts)