Kidneys

The kidneys are a pair of bean-shaped organs located retroperitoneally against the posterior wall of the abdomen on either side of the spine. As part of the urinary tract Urinary tract The urinary tract is located in the abdomen and pelvis and consists of the kidneys, ureters, urinary bladder, and urethra. The structures permit the excretion of urine from the body. Urine flows from the kidneys through the ureters to the urinary bladder and out through the urethra. Urinary Tract, the kidneys are responsible for blood filtration and excretion of water-soluble waste in the urine. The kidneys also play a major role in homeostatic processes, including electrolyte concentration, blood pressure, and acid–base regulation. Grossly, they consist of an outer cortex and inner medulla. Microscopic functional units known as nephrons filter the blood through a structure called the glomerulus, and this filtrate is then modified and concentrated as it moves through a complex tubular system. The renal arteries Arteries Arteries are tubular collections of cells that transport oxygenated blood and nutrients from the heart to the tissues of the body. The blood passes through the arteries in order of decreasing luminal diameter, starting in the largest artery (the aorta) and ending in the small arterioles. Arteries are classified into 3 types: large elastic arteries, medium muscular arteries, and small arteries and arterioles. Arteries supply the kidneys via a central opening, known as the renal hilum, on its medial side; large renal 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 empty directly into the vena cava.

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Editorial responsibility: Stanley Oiseth, Lindsay Jones, Evelin Maza

Table of Contents

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Embryology

The kidney develops from embryonic mesoderm in 3 successive forms from the nephrogenic cords as they elongate in a cranial-to-caudal direction.

Pronephros

  • Appears in week 4 as a cluster of a few cells that disintegrate shortly thereafter
  • Rudimentary and nonfunctional

Mesonephros

  • Begins to develop in the thoracolumbar region around week 5 as pronephros regresses
  • Regresses by week 10 
  • Consists of:
    • A longitudinal mesonephric duct (also known as the wolffian duct)
    • A series of tubules coming off the main duct and growing anteriorly toward the aorta 
  • Begins filtering blood → filtrate travels down the mesonephric tubule → mesonephric duct → cloaca → allantois
  • Functions as the primitive urinary system, while the metanephros develops into the permanent kidney
  • The mesonephric ducts persist and form part of the male reproductive system.
Graphical summary of the developing kidney

Graphical summary of the developing kidney:
The ureteric bud grows off of the mesonephric duct and into a collection of intermediate mesoderm cells known as the metanephric blastema. Together, this is known as the mesonephros, which develops into the kidney. The mesonephric tubules regress. In males, the mesonephric duct persists in the ejaculatory system.

Image by Lecturio.

Metanephros

The permanent kidney is formed from the metanephros.

  • Develops starting around the 5th week of gestation
  • Cells in the intermediate mesoderm in the pelvic region begin to differentiate into a structure called the metanephric blastema, which:
    • Ultimately becomes the cells making up the nephrons
    • Releases growth factors that stimulate the development of an outpouching off the caudal portion of the mesonephric duct called the ureteric buds
  • Ureteric buds grow toward and invade the metanephric blastema:
    • Elongating stalk of the ureteric bud develops into the ureter.
    • Within the metanephric blastema, the ureteric buds undergo a series of branchings to form the:
      • Renal pelvis Pelvis The pelvis consists of the bony pelvic girdle, the muscular and ligamentous pelvic floor, and the pelvic cavity, which contains viscera, vessels, and multiple nerves and muscles. The pelvic girdle, composed of 2 "hip" bones and the sacrum, is a ring-like bony structure of the axial skeleton that links the vertebral column with the lower extremities. Pelvis
      • Major calyces
      • Minor calyces
      • Collecting tubules
  • Metanephric mesodermal cap: 
    • Mesoderm from the metanephric blastema sitting on top of the developing collecting ducts
    • Elongates, forming the tubular system The tubular system The kidneys regulate water and solute homeostasis through the processes of filtration, reabsorption, secretion, and excretion. After the filtration of blood through the glomeruli, the tubular system takes over and is responsible for adjusting the urine composition throughout the remainder of the nephron. The Tubular System of the nephrons → becomes known as the metanephric tubules
    • The metanephric tubule fuses with the collecting tubule, creating one continuous system.
  • Bowman capsule: forms off the growing end of the metanephric tubule
  • Glomerular 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:
    • Develop off the common iliac arteries Arteries Arteries are tubular collections of cells that transport oxygenated blood and nutrients from the heart to the tissues of the body. The blood passes through the arteries in order of decreasing luminal diameter, starting in the largest artery (the aorta) and ending in the small arterioles. Arteries are classified into 3 types: large elastic arteries, medium muscular arteries, and small arteries and arterioles. Arteries
    • Become associated with Bowman capsule at the end of the metanephric tubules → begin creating “urine” (Note: True waste products are removed from the fetus via the placenta Placenta The placenta consists of a fetal side and a maternal side, and it provides a vascular communication between the mother and the fetus. This communication allows the mother to provide nutrients to the fetus and allows for removal of waste products from fetal blood. Placenta, Umbilical Cord, and Amniotic Cavity.)
  • Nephrons are formed until birth.
  • Nephron maturation continues after birth.

Position of the kidney and changes in vascularization

  • The kidneys are initially located in the pelvic region.
  • As the caudal portion of the body grows downward, the relative location of the kidneys “ascends” into the upper quadrants of the abdomen (failure to ascend results in a pelvic kidney).
  • As the kidneys ascend, the original blood supply degenerates.
  • New vessels (higher up) develop off the aorta and invade the kidneys, becoming the mature renal arteries Arteries Arteries are tubular collections of cells that transport oxygenated blood and nutrients from the heart to the tissues of the body. The blood passes through the arteries in order of decreasing luminal diameter, starting in the largest artery (the aorta) and ending in the small arterioles. Arteries are classified into 3 types: large elastic arteries, medium muscular arteries, and small arteries and arterioles. Arteries.
  • If the original vessels fail to regress, they may persist as additional renal arteries Arteries Arteries are tubular collections of cells that transport oxygenated blood and nutrients from the heart to the tissues of the body. The blood passes through the arteries in order of decreasing luminal diameter, starting in the largest artery (the aorta) and ending in the small arterioles. Arteries are classified into 3 types: large elastic arteries, medium muscular arteries, and small arteries and arterioles. Arteries or 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.
Ascent of the kidneys and corresponding change in vascular supply

Ascent of the kidneys and corresponding change in vascular supply

Image by Lecturio.

Gross Anatomy

Location

  • Retroperitoneal organs
  • Located along the posterior abdominal wall on either side of the vertebral column Vertebral column The human spine, or vertebral column, is the most important anatomical and functional axis of the human body. It consists of 7 cervical vertebrae, 12 thoracic vertebrae, and 5 lumbar vertebrae and is limited cranially by the skull and caudally by the sacrum. Vertebral Column in the paravertebral gutter
  • In front of the T12–L3 transverse processes
  • The superior pole rests against the 11th and 12th ribs.
  • The lower pole is directed laterally and anteriorly.
  • The presence of 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 on the right side forces the right kidney to be slightly lower than the left.

Anatomical relations

Table: Anatomic relations of the kidneys
Direction (in relation to the kidney) Right Left
Superior Right adrenal gland Left adrenal gland
Anterior
  • Upper portion: 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
  • Lower portion: hepatic flexure of 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
  • Upper portion: 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
  • Mid portion: 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
  • Lower portion: jejunum
Lateral Liver
  • Upper portion: Spleen
  • Lower portion: Descending 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
Posterior
  • Muscles:
    • Posterosuperior: diaphragm Diaphragm The diaphragm is a large, dome-shaped muscle that separates the thoracic cavity from the abdominal cavity. The diaphragm consists of muscle fibers and a large central tendon, which is divided into right and left parts. As the primary muscle of inspiration, the diaphragm contributes 75% of the total inspiratory muscle force. Diaphragm
    • Posteromedial: psoas muscle
    • Directly posterior: quadratus lumborum
  • Nerves:
    • Subcostal
    • Iliohypogastric
    • Ilioinguinal

Size and shape

  • Bean-shaped organs
  • Dimensions:
    • Length: 10–12 cm
    • Width: 5–7 cm
    • Depth: 2–3 cm
  • Weight: approximately 150 g

Outer layers

Surrounding the kidneys are several layers of adipose and connective tissue Connective tissue Connective tissues originate from embryonic mesenchyme and are present throughout the body except inside the brain and spinal cord. The main function of connective tissues is to provide structural support to organs. Connective tissues consist of cells and an extracellular matrix. Connective Tissue (from outside in):

  • Paranephric fat:
    • Located posterior to the kidney, between the renal fascia and the back muscles 
    • Anchors kidneys to the posterior abdominal wall
    • Provides some protection and warmth
  • Renal fascia, which also encloses the adrenal gland 
  • Perinephric fat
  • Fibrous capsule
Layers of adipose and connective tissue surrounding the kidneys (transverse section)

Layers of adipose and connective tissue Connective tissue Connective tissues originate from embryonic mesenchyme and are present throughout the body except inside the brain and spinal cord. The main function of connective tissues is to provide structural support to organs. Connective tissues consist of cells and an extracellular matrix. Connective Tissue surrounding the kidneys (transverse section)

Image by Lecturio.

Surface features

  • Superior and inferior poles
  • Convex lateral surface
  • Concave medial surface, which creates a cavity called the renal sinus
  • The renal sinus contains:
    • Renal neurovasculature, including:
      • Arteries and 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
      • Lymphatics
      • Nerves
    • Renal pelvis Pelvis The pelvis consists of the bony pelvic girdle, the muscular and ligamentous pelvic floor, and the pelvic cavity, which contains viscera, vessels, and multiple nerves and muscles. The pelvic girdle, composed of 2 "hip" bones and the sacrum, is a ring-like bony structure of the axial skeleton that links the vertebral column with the lower extremities. Pelvis (terminal portion of the renal collecting system)
    • Adipose tissue Adipose tissue Adipose tissue is a specialized type of connective tissue that has both structural and highly complex metabolic functions, including energy storage, glucose homeostasis, and a multitude of endocrine capabilities. There are three types of adipose tissue, white adipose tissue, brown adipose tissue, and beige or "brite" adipose tissue, which is a transitional form. Adipose Tissue (continuous with the perinephric fat surrounding the kidney)
  • Renal hilum: the entrance to the renal sinus

Renal parenchyma

The parenchyma consists of:

  • Renal cortex:
    • The outermost part of the kidney, approximately 1 cm thick
    • Located underneath the renal capsule
    • Projections medially form the renal columns (of Bertin).
    • Microscopic structures located in the cortex:
      • Bowman capsule
      • Proximal and distal tubules
      • Upper portions of the collecting ducts
  • Renal medulla:
    • Divided into units known as renal pyramids
    • 6–10 renal pyramids separated by the columns of Bertin
    • Base of pyramid toward the cortex
    • The apex:
      • Projects toward the renal sinus 
      • Is called a papilla
      • Collecting tubules drain out of the papilla into the minor calyces.
    • Microscopic structures located in the medulla/pyramids:
      • Loops of Henle 
      • Collecting ducts
  • Collecting system:
    • Collects the newly formed urine and directs it to the ureter
    • Each papilla drains into a minor calyx.
    • 2–3 minor calyces drain into a single major calyx.
    • 2–3 major calyces converge to form the renal pelvis Pelvis The pelvis consists of the bony pelvic girdle, the muscular and ligamentous pelvic floor, and the pelvic cavity, which contains viscera, vessels, and multiple nerves and muscles. The pelvic girdle, composed of 2 "hip" bones and the sacrum, is a ring-like bony structure of the axial skeleton that links the vertebral column with the lower extremities. Pelvis, which: 
      • Is a funnel-shaped structure that is continuous with the ureter
      • Occupies most of the renal sinus
      • Transitions to the ureter at the ureteropelvic junction  
Diagram depicting renal anatomy

Diagram depicting the renal anatomy

Image: “Human Kidney Anatomy” by Blausen.com staff. License: CC BY 3.0, cropped by Lecturio.

Microscopic Anatomy

Nephrons are the functional units of the kidney; there are approximately 1.2 million nephrons in each kidney. The nephron is divided into 2 main parts: the renal corpuscle and the renal tubule, which has multiple defined segments.

Renal corpuscle

The renal corpuscle is where the blood plasma is filtered.

Glomerular (Bowman) capsule: 

  • A ball-shaped structure surrounding a web of arterial 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
  • Has an outer parietal layer made up of simple squamous epithelial cells
  • Has an inner visceral layer:
    • Directly surrounds the glomerular 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
    • Made up of specialized epithelial cells known as podocytes 
  • Bowman space: 
    • The space between the parietal and visceral layers of Bowman capsule 
    • Collects the filtrate (urine)
    • Drains into the proximal convoluted tubule (PCT)
Structure of the renal corpuscle

Structure of the renal corpuscle

Image by Lecturio.

Blood vessels associated with the renal corpuscle:

  • Afferent arteriole: 
    • Brings blood into the glomerulus 
    • Relatively large diameter 
  • Glomerulus (also called glomerular 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): 
    • A web of small arterial 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 between the afferent and efferent arterioles 
    • Where filtration occurs
  • Efferent arteriole: 
    • Carries filtered blood out of the glomerulus 
    • Small diameter (as compared with the afferent arteriole)
  • Filtration occurs primarily because of the high hydrostatic pressure in the glomerular 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 created by the large inlet (afferent arteriole) and small outlet (efferent arteriole).

Filtration membrane:

  • Constitutes the main blood filter between the glomerular 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 and Bowman space
  • Consists of 3 layers:
    • Fenestrated endothelium lining the glomerular 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
    • Glomerular basement membrane (GBM): made up of a negatively charged proteoglycan gel (repels larger negatively charged molecules)
    • Podocytes ( 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): 
      • Form the visceral layer of Bowman capsule
      • Multiple interdigitating foot processes wrap around the vessels, creating filtration slits between foot processes.
      • Slits are covered by a membrane called the slit diaphragm Diaphragm The diaphragm is a large, dome-shaped muscle that separates the thoracic cavity from the abdominal cavity. The diaphragm consists of muscle fibers and a large central tendon, which is divided into right and left parts. As the primary muscle of inspiration, the diaphragm contributes 75% of the total inspiratory muscle force. Diaphragm (a unique form of intercellular junction consisting of multiple proteins).
  • Not permeable to large molecules in blood, such as plasma proteins (e.g., albumin)
  • Permeable to small molecules, generally < 3 nm, including:
    • Water
    • 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 (e.g., sodium, potassium)
    • Glucose
    • Amino and fatty acids 
    • Vitamins
  • Can be damaged by infection and trauma
Filtration apparatus in the glomerulus

Filtration apparatus in the glomerulus

Image by Lecturio.

Renal tubule

The renal tubule is a long continuous tube that adjusts the contents of the filtrate received from the renal corpuscle. The tubules ultimately drain through the papilla into the calyces. Segments of the tubule, in order, are:

  • PCT:
    • Located in the cortex
    • Major site of reabsorption, especially for:
      • 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: Na+, Cl, K+, Ca2+, Mg2+, HCO3, PO43– 
      • Glucose
      • Amino acids and peptides
    • Lined with simple cuboidal 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 with prominent microvilli known as a brush border lining the tubule lumen (↑ the surface area for reabsorption)
    • H&E stain: dark pink owing to high amounts of mitochondria (↑ rates of reabsorption requires ↑ energy for active transport)
  • Proximal straight tubule (PST):
    • Major site of secretion of:
      • Organic anions (e.g., bile salts, urate, drugs)
      • Organic cations (e.g., creatinine, dopamine, drugs)
    • H&E stain: dark pink 
  • Loop of Henle (located in the cortex and medulla), further divided into:
    • Thin descending and thin ascending limbs 
      • Both made of simple squamous 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
      • Involved in passive transport of water or electrolytes, which establish the large osmotic gradient in the medulla
    • Thick ascending limb (TAL): 
      • Cuboidal 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
      • Heavily involved in active transport of electrolytes
  • Distal convoluted tubule (DCT)
    • Located in the cortex
    • Responsible for “fine tuning” the components of the urine
    • Lined with simple cuboidal 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 without microvilli
    • H&E stain: pale pink owing to fewer mitochondria
    • Last part of the nephron functional unit
  • Collecting duct (CD)
    • Located in the cortex and medulla
    • Simple cuboidal 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
    • Multiple DCTs from different nephrons come together and drain into a CD.
Segments of the nephron

Segments of the nephron

Image by Lecturio.

Juxtaglomerular apparatus (JGA)

A specialized group of 3 cell types in close proximity to the glomerulus. The JGA plays an important role in maintaining blood pressure and fluid homeostasis.

  • Juxtaglomerular (JG) cells:
    • Enlarged smooth muscle cells primarily in the afferent (and some in the efferent) arterioles
    • Can dilate or constrict the arterioles, adjusting the pressure within the glomerulus
    • Secrete renin in response to hypovolemia and hypotension Hypotension Hypotension is defined as low blood pressure, specifically < 90/60 mm Hg, and is most commonly a physiologic response. Hypotension may be mild, serious, or life threatening, depending on the cause. Hypotension
  • Macula densa (MD) cells: 
    • Specialized slender, closely spaced epithelial cells in the DCT that are adjacent to the JG cells
    • Detect sodium concentration of the fluid in the DCT
    • Signals JG cells to dilate or constrict arterioles, adjusting the GFR in order to maintain homeostasis
  • Mesangial cells: 
    • Flat and elongated cells in the cleft between the afferent and efferent arterioles
    • Connected to MD and JG cells by gap junctions
    • Role is still unclear, but potentially mediate communication between MD and JG cells
Structure of a renal corpuscle and the juxtaglomerular apparatus

Structure of a renal corpuscle and the juxtaglomerular apparatus:
A: Renal corpuscle
B: Proximal tubule
C: Distal convoluted tube
D: Juxtaglomerular apparatus
1: Basement membrane
2: Bowman capsule, parietal layer
3: Bowman capsule, visceral layer
3a: Podocyte pedicles
3b: Podocyte
4: Bowman space (urinary space)
5a: Mesangium—intraglomerular mesangial cells
5b: Mesangium—extraglomerular mesangial cells
6: Juxtaglomerular cells
7: Macula densa
8: Myocytes (cells of smooth muscle)
9: Afferent arteriole
10: Glomerulus 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
11: Efferent arteriole.

Image by Lecturio.

Types of nephrons

Nephrons are divided into cortical and juxtamedullary nephrons based on their location. 

  • Cortical nephrons:
    • Located almost entirely in the cortex
    • Loops of Henle have a short course inside the medulla.
  • Juxtamedullary nephrons:
    • Located close to the corticomedullary junction
    • Loop of Henle traverses deep into the medulla.
    • Responsible for maintaining high osmotic gradient within medulla
    • Allow for stronger concentration of urine
Nephron anatomy

Nephron anatomy:
The left side shows a juxtamedullary nephron, while the right side shows a cortical nephron.

Image by Lecturio.

Neurovasculature

Renal and segmental arteries Arteries Arteries are tubular collections of cells that transport oxygenated blood and nutrients from the heart to the tissues of the body. The blood passes through the arteries in order of decreasing luminal diameter, starting in the largest artery (the aorta) and ending in the small arterioles. Arteries are classified into 3 types: large elastic arteries, medium muscular arteries, and small arteries and arterioles. Arteries

  • Each kidney is perfused by a renal artery:
    • Branch off the abdominal aorta below the superior mesenteric artery ( SMA SMA Spinal muscular atrophy (SMA) is a spectrum of autosomal recessive syndromes characterized by progressive proximal muscle weakness and atrophy, possibly due to degeneration of the anterior horn cells in the spinal cord and motor nuclei in the lower brainstem. Spinal Muscular Atrophy (SMA))
    • Right renal artery passes posterior to the vena cava.
  • The renal arteries Arteries Arteries are tubular collections of cells that transport oxygenated blood and nutrients from the heart to the tissues of the body. The blood passes through the arteries in order of decreasing luminal diameter, starting in the largest artery (the aorta) and ending in the small arterioles. Arteries are classified into 3 types: large elastic arteries, medium muscular arteries, and small arteries and arterioles. Arteries divide into 5 segmental arteries Arteries Arteries are tubular collections of cells that transport oxygenated blood and nutrients from the heart to the tissues of the body. The blood passes through the arteries in order of decreasing luminal diameter, starting in the largest artery (the aorta) and ending in the small arterioles. Arteries are classified into 3 types: large elastic arteries, medium muscular arteries, and small arteries and arterioles. Arteries, which irrigate separate segments of the kidney (no anastomosis between the segments).
  • Renal segments:
    • Superior
    • Anterior superior
    • Anterior inferior
    • Inferior
    • Posterior
Segments of the kidney

Segments of the kidney

Image by Lecturio.

Smaller arteries Arteries Arteries are tubular collections of cells that transport oxygenated blood and nutrients from the heart to the tissues of the body. The blood passes through the arteries in order of decreasing luminal diameter, starting in the largest artery (the aorta) and ending in the small arterioles. Arteries are classified into 3 types: large elastic arteries, medium muscular arteries, and small arteries and arterioles. Arteries, 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, and 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

  • Segmental arteries Arteries Arteries are tubular collections of cells that transport oxygenated blood and nutrients from the heart to the tissues of the body. The blood passes through the arteries in order of decreasing luminal diameter, starting in the largest artery (the aorta) and ending in the small arterioles. Arteries are classified into 3 types: large elastic arteries, medium muscular arteries, and small arteries and arterioles. Arteries branch into interlobar arteries Arteries Arteries are tubular collections of cells that transport oxygenated blood and nutrients from the heart to the tissues of the body. The blood passes through the arteries in order of decreasing luminal diameter, starting in the largest artery (the aorta) and ending in the small arterioles. Arteries are classified into 3 types: large elastic arteries, medium muscular arteries, and small arteries and arterioles. Arteries, which run between renal pyramids.
  • Interlobar arteries Arteries Arteries are tubular collections of cells that transport oxygenated blood and nutrients from the heart to the tissues of the body. The blood passes through the arteries in order of decreasing luminal diameter, starting in the largest artery (the aorta) and ending in the small arterioles. Arteries are classified into 3 types: large elastic arteries, medium muscular arteries, and small arteries and arterioles. Arteries branch into arcuate arteries Arteries Arteries are tubular collections of cells that transport oxygenated blood and nutrients from the heart to the tissues of the body. The blood passes through the arteries in order of decreasing luminal diameter, starting in the largest artery (the aorta) and ending in the small arterioles. Arteries are classified into 3 types: large elastic arteries, medium muscular arteries, and small arteries and arterioles. Arteries, which run along the base of the renal pyramids in the renal cortex.
  • Arcuate arteries Arteries Arteries are tubular collections of cells that transport oxygenated blood and nutrients from the heart to the tissues of the body. The blood passes through the arteries in order of decreasing luminal diameter, starting in the largest artery (the aorta) and ending in the small arterioles. Arteries are classified into 3 types: large elastic arteries, medium muscular arteries, and small arteries and arterioles. Arteries send off small branches called interlobular arteries Arteries Arteries are tubular collections of cells that transport oxygenated blood and nutrients from the heart to the tissues of the body. The blood passes through the arteries in order of decreasing luminal diameter, starting in the largest artery (the aorta) and ending in the small arterioles. Arteries are classified into 3 types: large elastic arteries, medium muscular arteries, and small arteries and arterioles. Arteries.
  • Interlobar arteries Arteries Arteries are tubular collections of cells that transport oxygenated blood and nutrients from the heart to the tissues of the body. The blood passes through the arteries in order of decreasing luminal diameter, starting in the largest artery (the aorta) and ending in the small arterioles. Arteries are classified into 3 types: large elastic arteries, medium muscular arteries, and small arteries and arterioles. Arteries branch into afferent arterioles, which lead into Bowman capsules.
  • After blood leaves the glomerulus via the efferent arterioles, it travels to either the peritubular 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 or the vasa recta.
  • Peritubular 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: supply the cortical tubules (e.g., PCT and DCT)
  • Vasa recta:
    • Capillary networks that surround the loops of Henle in the medulla
    • Highly permeable to solute and water
    • Vital in maintaining the osmotic gradient in the medulla
  • Blood from the peritubular and vasa recta 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 drain into interlobular 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.
  • Interlobular 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 → arcuate 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 → interlobar 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 → segmental 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 → renal vein
  • Each kidney has a single renal vein. These 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: 
    • Drain directly into the inferior vena cava
    • Run anterior to the arteries Arteries Arteries are tubular collections of cells that transport oxygenated blood and nutrients from the heart to the tissues of the body. The blood passes through the arteries in order of decreasing luminal diameter, starting in the largest artery (the aorta) and ending in the small arterioles. Arteries are classified into 3 types: large elastic arteries, medium muscular arteries, and small arteries and arterioles. Arteries 
    • The left renal vein passes anterior to the abdominal aorta.

Summary of blood flow through the kidney

Renal circulation

Renal circulation

Image by Lecturio.

Nerves

Renal innervation includes both afferent and efferent nerves through the renal nerve plexus. Innervation is via the autonomic nervous system Autonomic nervous system The ANS is a component of the peripheral nervous system that uses both afferent (sensory) and efferent (effector) neurons, which control the functioning of the internal organs and involuntary processes via connections with the CNS. The ANS consists of the sympathetic and parasympathetic nervous systems. Autonomic Nervous System, primarily through sympathetic fibers:

  • Sympathetic efferent nerves:
    • Primarily via splanchnic nerves
    • Only efferent innervation to the nephrons and renal vasculature
    • Concentrated most heavily around the afferent arterioles, TAL, and DCT
    • Stimulation can activate the RAAS.
  • Sensory afferent nerves: involved in blood pressure regulation
  • Visceral afferent nerves: transmit pain Pain Pain has accompanied humans since they first existed, first lamented as the curse of existence and later understood as an adaptive mechanism that ensures survival. Pain is the most common symptomatic complaint and the main reason why people seek medical care. Physiology of Pain signals to spinal cord Spinal cord The spinal cord is the major conduction pathway connecting the brain to the body; it is part of the CNS. In cross section, the spinal cord is divided into an H-shaped area of gray matter (consisting of synapsing neuronal cell bodies) and a surrounding area of white matter (consisting of ascending and descending tracts of myelinated axons). Spinal Cord segments T11–L2 

Functions

Functions of the kidneys include:

  • Filter the blood and excrete water-soluble waste in the urine
  • Regulate total body water by appropriately concentrating the urine according to the body’s osmotic status
  • Regulate hemodynamic/blood pressure via the RAAS
  • Regulate acid–base status
  • Maintain bone metabolism Bone metabolism Bone is the primary storage site of calcium in the body; thus, bone metabolism plays a critical role in maintaining normal calcium levels. Bone metabolism (and thus calcium levels) are primarily regulated by 3 hormones, namely, calcitonin, parathyroid hormone (PTH), and vitamin D. Bone Metabolism via selective excretion/reabsorption of calcium and phosphate
  • Produce RBCs via secretion of erythropoietin

Clinical Relevance

  • Duplications of the collecting system: known as a “duplex system.” Duplications of the collecting system are the most common congenital anomaly of the urinary tract Urinary tract The urinary tract is located in the abdomen and pelvis and consists of the kidneys, ureters, urinary bladder, and urethra. The structures permit the excretion of urine from the body. Urine flows from the kidneys through the ureters to the urinary bladder and out through the urethra. Urinary Tract. In these cases, a kidney will have 2 separate pelvicaliceal systems and 2 ureters. Ureteral insertion into the bladder from the duplicated system is often abnormal as well. Most affected individuals are asymptomatic, though recurrent urinary tract Urinary tract The urinary tract is located in the abdomen and pelvis and consists of the kidneys, ureters, urinary bladder, and urethra. The structures permit the excretion of urine from the body. Urine flows from the kidneys through the ureters to the urinary bladder and out through the urethra. Urinary Tract infection (UTIs) or obstruction may occur.
  • Renal agenesis: congenital absence of a kidney, specifically, renal parenchymal tissue. Renal agenesis results from disruption of metanephric development. Most affected individuals are asymptomatic and diagnosed incidentally on imaging. Renal agenesis is often associated with additional congenital anomalies.
  • Polycystic kidney disease (PKD): genetic condition caused by either an autosomal recessive Autosomal recessive Autosomal inheritance, both dominant and recessive, refers to the transmission of genes from the 22 autosomal chromosomes. Autosomal recessive diseases are only expressed when 2 copies of the recessive allele are inherited. Autosomal Recessive and Autosomal Dominant Inheritance 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 in the PKHD1 gene (fibrocystin) or an autosomal dominant Autosomal dominant Autosomal inheritance, both dominant and recessive, refers to the transmission of genes from the 22 autosomal chromosomes. Autosomal dominant diseases are expressed when only 1 copy of the dominant allele is inherited. Autosomal Recessive and Autosomal Dominant Inheritance 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 in either the PKD1 or PKD2 gene (polycystin proteins). Autosomal recessive PKD is characterized by multiple microscopic cysts and can have serious effects in utero. Autosomal dominant PKD is characterized by multiple larger cysts and most commonly presents in adulthood with hematuria and hypertension Hypertension Hypertension, or high blood pressure, is a common disease that manifests as elevated systemic arterial pressures. Hypertension is most often asymptomatic and is found incidentally as part of a routine physical examination or during triage for an unrelated medical encounter. Hypertension.
  • Goodpasture syndrome Goodpasture Syndrome Goodpasture syndrome, also known as anti-glomerular basement membrane (GBM) disease, is an autoimmune disease characterized by circulating antibodies directed against glomerular and alveolar basement membranes. Affected individuals present with symptoms of rapidly progressive glomerulonephritis and alveolar hemorrhage. Goodpasture Syndrome: also known as anti–glomerular basement membrane (anti-GBM) disease. Goodpasture syndrome Goodpasture Syndrome Goodpasture syndrome, also known as anti-glomerular basement membrane (GBM) disease, is an autoimmune disease characterized by circulating antibodies directed against glomerular and alveolar basement membranes. Affected individuals present with symptoms of rapidly progressive glomerulonephritis and alveolar hemorrhage. Goodpasture Syndrome is an autoimmune disease characterized by circulating antibodies Antibodies Immunoglobulins (Igs), also known as antibodies, are glycoprotein molecules produced by plasma cells that act in immune responses by recognizing and binding particular antigens. The various Ig classes are IgG (the most abundant), IgM, IgE, IgD, and IgA, which differ in their biologic features, structure, target specificity, and distribution. Immunoglobulins directed against glomerular and alveolar basement membranes. Presentation is with signs and symptoms of rapidly progressive glomerulonephritis Rapidly Progressive Glomerulonephritis Rapidly progressive glomerulonephritis (RPGN) is a syndrome of severe glomerular disease with progressive loss of kidney function within weeks to months. Histologically, crescents (the proliferation of epithelial cells and the infiltration of monocytes/macrophages in the Bowman space) are found in the glomeruli and arise from immunologic injury. Rapidly Progressive Glomerulonephritis and alveolar hemorrhage. Management includes plasmapheresis and immunosuppressants Immunosuppressants Immunosuppressants are a class of drugs widely used in the management of autoimmune conditions and organ transplant rejection. The general effect is dampening of the immune response. Immunosuppressants. Renal transplantation is an option in individuals who develop end-stage renal failure. 
  • Alport syndrome Alport Syndrome Alport syndrome, also called hereditary nephritis, is a genetic disorder caused by a mutation in the genes encoding for the alpha chains of type IV collagen, resulting in the production of abnormal type IV collagen strands. Patients present with glomerulonephritis, hypertension, edema, hematuria, and proteinuria, as well as with ocular and auditory findings. Alport Syndrome: also called hereditary nephritis. Alport syndrome Alport Syndrome Alport syndrome, also called hereditary nephritis, is a genetic disorder caused by a mutation in the genes encoding for the alpha chains of type IV collagen, resulting in the production of abnormal type IV collagen strands. Patients present with glomerulonephritis, hypertension, edema, hematuria, and proteinuria, as well as with ocular and auditory findings. Alport Syndrome is a genetic disorder caused by a 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 in the genes coding for the alpha chains of type IV collagen, resulting in the production of abnormal type IV collagen strands. Presentation is with glomerulonephritis, hypertension Hypertension Hypertension, or high blood pressure, is a common disease that manifests as elevated systemic arterial pressures. Hypertension is most often asymptomatic and is found incidentally as part of a routine physical examination or during triage for an unrelated medical encounter. Hypertension, 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, hematuria, and proteinuria, as well as with ocular and auditory findings. A renal biopsy will show characteristic GBM splitting.
  • Hydronephrosis Hydronephrosis Hydronephrosis is dilation of the renal collecting system as a result of the obstruction of urine outflow. Hydronephrosis can be unilateral or bilateral. Nephrolithiasis is the most common cause of hydronephrosis in young adults, while prostatic hyperplasia and neoplasm are seen in older patients. Hydronephrosis: dilation of the renal collecting system as a result of the obstruction of urine outflow. Hydronephrosis Hydronephrosis Hydronephrosis is dilation of the renal collecting system as a result of the obstruction of urine outflow. Hydronephrosis can be unilateral or bilateral. Nephrolithiasis is the most common cause of hydronephrosis in young adults, while prostatic hyperplasia and neoplasm are seen in older patients. Hydronephrosis can be unilateral or bilateral. Nephrolithiasis Nephrolithiasis Nephrolithiasis is the formation of a stone, or calculus, anywhere along the urinary tract caused by precipitations of solutes in the urine. The most common type of kidney stone is the calcium oxalate stone, but other types include calcium phosphate, struvite (ammonium magnesium phosphate), uric acid, and cystine stones. Nephrolithiasis is the most common cause of hydronephrosis in young adults, while prostatic hyperplasia and neoplasm are seen in older individuals. Presentation can be with flank pain Pain Pain has accompanied humans since they first existed, first lamented as the curse of existence and later understood as an adaptive mechanism that ensures survival. Pain is the most common symptomatic complaint and the main reason why people seek medical care. Physiology of Pain, dysuria, urgency, fever Fever Fever is defined as a measured body temperature of at least 38°C (100.4°F). Fever is caused by circulating endogenous and/or exogenous pyrogens that increase levels of prostaglandin E2 in the hypothalamus. Fever is commonly associated with chills, rigors, sweating, and flushing of the skin. Fever, palpable abdominal mass, fever Fever Fever is defined as a measured body temperature of at least 38°C (100.4°F). Fever is caused by circulating endogenous and/or exogenous pyrogens that increase levels of prostaglandin E2 in the hypothalamus. Fever is commonly associated with chills, rigors, sweating, and flushing of the skin. Fever, and hypertension Hypertension Hypertension, or high blood pressure, is a common disease that manifests as elevated systemic arterial pressures. Hypertension is most often asymptomatic and is found incidentally as part of a routine physical examination or during triage for an unrelated medical encounter. Hypertension. Diagnosis includes imaging with ultrasonography, CT, or IV pyelography.
  • Nutcracker syndrome: occurs when the left renal vein is compressed, affecting the venous drainage (and subsequently the arterial supply) of the left kidney, the left adrenal gland, and the left testis (in men) or the left ovary (in women). Symptoms are often vague but may include intermittent flank pain Pain Pain has accompanied humans since they first existed, first lamented as the curse of existence and later understood as an adaptive mechanism that ensures survival. Pain is the most common symptomatic complaint and the main reason why people seek medical care. Physiology of Pain, hematuria, pelvic pain Pain Pain has accompanied humans since they first existed, first lamented as the curse of existence and later understood as an adaptive mechanism that ensures survival. Pain is the most common symptomatic complaint and the main reason why people seek medical care. Physiology of Pain, scrotal 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, varicocele, or pelvic congestion syndrome. 
  • Renal cell carcinoma Renal cell carcinoma Renal cell carcinoma (RCC) is a tumor that arises from the lining of the renal tubular system within the renal cortex. Renal cell carcinoma is responsible for 80%-85% of all primary renal neoplasms. Most RCCs arise sporadically, but smoking, hypertension, and obesity are linked to its development. Renal Cell Carcinoma ( RCC RCC Renal cell carcinoma (RCC) is a tumor that arises from the lining of the renal tubular system within the renal cortex. Renal cell carcinoma is responsible for 80%-85% of all primary renal neoplasms. Most RCCs arise sporadically, but smoking, hypertension, and obesity are linked to its development. Renal Cell Carcinoma): tumor that arises from the lining of the renal tubular system within the renal cortex. Renal cell carcinoma Renal cell carcinoma Renal cell carcinoma (RCC) is a tumor that arises from the lining of the renal tubular system within the renal cortex. Renal cell carcinoma is responsible for 80%-85% of all primary renal neoplasms. Most RCCs arise sporadically, but smoking, hypertension, and obesity are linked to its development. Renal Cell Carcinoma is responsible for 80%–85% of all primary renal neoplasms. Most RCCs arise sporadically, but smoking, hypertension Hypertension Hypertension, or high blood pressure, is a common disease that manifests as elevated systemic arterial pressures. Hypertension is most often asymptomatic and is found incidentally as part of a routine physical examination or during triage for an unrelated medical encounter. Hypertension, and obesity Obesity Obesity is a condition associated with excess body weight, specifically with the deposition of excessive adipose tissue. Obesity is considered a global epidemic. Major influences come from the western diet and sedentary lifestyles, but the exact mechanisms likely include a mixture of genetic and environmental factors. Obesity are linked to the development of the disease. The condition is usually asymptomatic. The classic clinical triad of RCC RCC Renal cell carcinoma (RCC) is a tumor that arises from the lining of the renal tubular system within the renal cortex. Renal cell carcinoma is responsible for 80%-85% of all primary renal neoplasms. Most RCCs arise sporadically, but smoking, hypertension, and obesity are linked to its development. Renal Cell Carcinoma is flank pain Pain Pain has accompanied humans since they first existed, first lamented as the curse of existence and later understood as an adaptive mechanism that ensures survival. Pain is the most common symptomatic complaint and the main reason why people seek medical care. Physiology of Pain, hematuria, and a palpable abdominal renal mass, but only in about 9% of cases. Renal cell carcinoma Renal cell carcinoma Renal cell carcinoma (RCC) is a tumor that arises from the lining of the renal tubular system within the renal cortex. Renal cell carcinoma is responsible for 80%-85% of all primary renal neoplasms. Most RCCs arise sporadically, but smoking, hypertension, and obesity are linked to its development. Renal Cell Carcinoma is usually diagnosed via CT scan.
  • Horseshoe kidney: developmental defect of kidneys in which inferior poles are fused together. As the kidney attempts to migrate superiorly during development, it is blocked by the superior mesenteric artery. The vascular supplies and collecting system of the kidney also tend to have various degrees of distortion. Affected individuals are typically asymptomatic; incidental diagnosis is made on imaging. Other presentations include infection, obstruction, hydronephrosis, and calculi. 

References

  1. Chalouhy, C. E. (2017). Kidney anatomy. Medscape. Retrieved September 3, 2021, from https://reference.medscape.com/article/1948775-overview
  2. Gulleroglu, K., Gulleroglu, B., Baskin, E. (2014). Nutcracker syndrome. World Journal of Nephrology 3:277–281. Retrieved September 3, 2021, from https://pubmed.ncbi.nlm.nih.gov/25374822/
  3. Soriano, R. M., Penfold, D., Leslie, S. W. (2021). Anatomy, abdomen and pelvis, kidneys. StatPearls. Retrieved September 3, 2021, from https://www.ncbi.nlm.nih.gov/books/NBK482385/
  4. Tadros, N. N. (2020). Horseshoe kidney. Medscape. Retrieved September 3, 2021, from https://reference.medscape.com/article/441510-overview
  5. Wallace, M. A. (1998). Anatomy and physiology of the kidney. AORN Journal 68:800–824. doi: 10.1016/s0001-2092(06)62377-6
  6. Saladin, K. S., Miller, L. (2004). Anatomy and physiology, 3rd ed., pp. 881–887. McGraw-Hill Education.

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