CirculationCirculationThe movement of the blood as it is pumped through the cardiovascular system.ABCDE Assessment is the movement of blood throughout the body through one continuous circuit of blood vessels. Different organs have unique functions and, therefore, have different requirements, circulatory patterns, and regulatory mechanisms. Several of the most vital organs (including the brainBrainThe part of central nervous system that is contained within the skull (cranium). Arising from the neural tube, the embryonic brain is comprised of three major parts including prosencephalon (the forebrain); mesencephalon (the midbrain); and rhombencephalon (the hindbrain). The developed brain consists of cerebrum; cerebellum; and other structures in the brain stem.Nervous System: Anatomy, Structure, and Classification, heart, and kidneysKidneysThe 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, the kidneys are responsible for blood filtration and excretion of water-soluble waste in the urine.Kidneys: Anatomy) have autoregulatory properties, meaning that they are able to maintain a relatively constant blood flowBlood flowBlood flow refers to the movement of a certain volume of blood through the vasculature over a given unit of time (e.g., mL per minute).Vascular Resistance, Flow, and Mean Arterial Pressure despite fluctuations in mean arterial pressureMean Arterial PressureMean arterial pressure (MAP) is the average systemic arterial pressure and is directly related to cardiac output (CO) and systemic vascular resistance (SVR). The SVR and MAP are affected by the vascular anatomy as well as a number of local and neurohumoral factors.Vascular Resistance, Flow, and Mean Arterial Pressure (MAP). In other cases, locally produced factors (such as adenosineAdenosineA nucleoside that is composed of adenine and d-ribose. Adenosine or adenosine derivatives play many important biological roles in addition to being components of DNA and RNA. Adenosine itself is a neurotransmitter.Class 5 Antiarrhythmic Drugs, CO2, or NO) can produce local vasoconstrictionVasoconstrictionThe physiological narrowing of blood vessels by contraction of the vascular smooth muscle.Vascular Resistance, Flow, and Mean Arterial Pressure or vasodilationVasodilationThe physiological widening of blood vessels by relaxing the underlying vascular smooth muscle.Pulmonary Hypertension Drugs, regulating blood flowBlood flowBlood flow refers to the movement of a certain volume of blood through the vasculature over a given unit of time (e.g., mL per minute).Vascular Resistance, Flow, and Mean Arterial Pressure under specific physiologic conditions.
Overview of Systemic Circulation and Capillary Exchange
Anatomy review of systemic and pulmonary circulationCirculationThe movement of the blood as it is pumped through the cardiovascular system.ABCDE Assessment
Blood flows through the heart and lungsLungsLungs are the main organs of the respiratory system. Lungs are paired viscera located in the thoracic cavity and are composed of spongy tissue. The primary function of the lungs is to oxygenate blood and eliminate CO2. Lungs: Anatomy in one direction, sequentially through the following structures:
Right atrium (RA) → tricuspid valveTricuspid valveThe valve consisting of three cusps situated between the right atrium and right ventricle of the heart.Heart: Anatomy → right ventricle (RV) → pulmonary valvePulmonary valveA valve situated at the entrance to the pulmonary trunk from the right ventricle.Heart: Anatomy →
Pulmonary trunkPulmonary TrunkTruncus Arteriosus → pulmonary arteriesArteriesArteries 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: Histology → lungsLungsLungs are the main organs of the respiratory system. Lungs are paired viscera located in the thoracic cavity and are composed of spongy tissue. The primary function of the lungs is to oxygenate blood and eliminate CO2. Lungs: Anatomy:
Thin-walled capillariesCapillariesCapillaries 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 allows gas exchangeGas exchangeHuman cells are primarily reliant on aerobic metabolism. The respiratory system is involved in pulmonary ventilation and external respiration, while the circulatory system is responsible for transport and internal respiration. Pulmonary ventilation (breathing) represents movement of air into and out of the lungs. External respiration, or gas exchange, is represented by the O2 and CO2 exchange between the lungs and the blood.Gas Exchange → oxygenation of blood
Very-low-pressure system
Oncotic pressureOncotic PressureEdema in the lungsLungsLungs are the main organs of the respiratory system. Lungs are paired viscera located in the thoracic cavity and are composed of spongy tissue. The primary function of the lungs is to oxygenate blood and eliminate CO2. Lungs: Anatomy > hydrostatic pressureHydrostatic pressureThe pressure due to the weight of fluid.Edema
strongly favors absorptionAbsorptionAbsorption involves the uptake of nutrient molecules and their transfer from the lumen of the GI tract across the enterocytes and into the interstitial space, where they can be taken up in the venous or lymphatic circulation.Digestion and Absorption of fluid (prevents fluid accumulation in the alveolar walls and lumens, which would impede gas exchangeGas exchangeHuman cells are primarily reliant on aerobic metabolism. The respiratory system is involved in pulmonary ventilation and external respiration, while the circulatory system is responsible for transport and internal respiration. Pulmonary ventilation (breathing) represents movement of air into and out of the lungs. External respiration, or gas exchange, is represented by the O2 and CO2 exchange between the lungs and the blood.Gas Exchange)
Clinical relevance: ↑ left-sided heart pressures (e.g., mitral valveMitral valveThe valve between the left atrium and left ventricle of the heart.Heart: AnatomystenosisStenosisHypoplastic Left Heart Syndrome (HLHS)) may increase pulmonary pressures and lead to pulmonary edemaPulmonary edemaPulmonary edema is a condition caused by excess fluid within the lung parenchyma and alveoli as a consequence of a disease process. Based on etiology, pulmonary edema is classified as cardiogenic or noncardiogenic. Patients may present with progressive dyspnea, orthopnea, cough, or respiratory failure.Pulmonary Edema and hypoxiaHypoxiaSub-optimal oxygen levels in the ambient air of living organisms.Ischemic Cell Damage.
Pulmonary veinsPulmonary veinsThe veins that return the oxygenated blood from the lungs to the left atrium of the heart.Lungs: Anatomy → left atrium (LA) → mitral valveMitral valveThe valve between the left atrium and left ventricle of the heart.Heart: Anatomy → left ventricle (LV) → aortic valveAortic valveThe valve between the left ventricle and the ascending aorta which prevents backflow into the left ventricle.Heart: Anatomy →
AortaAortaThe main trunk of the systemic arteries.Mediastinum and Great Vessels: Anatomy → systemic arteriesArteriesArteries 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: Histology → capillariesCapillariesCapillaries 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 (blood is deoxygenated) → veinsVeinsVeins 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 → SVC/IVCIVCThe venous trunk which receives blood from the lower extremities and from the pelvic and abdominal organs.Mediastinum and Great Vessels: Anatomy → back to the heart
Circulation of blood through the body: Deoxygenated blood enters the right side of the heart and passes through the pulmonary trunk to the lungs, where it is oxygenated. The blood then returns to the left side of the heart via the pulmonary veins, where it is pumped into the aorta and distributed throughout the body. The blood travels through systemic capillaries, where it is deoxygenated again, and travels back to the heart via the superior and inferior vena cava. LA: left atrium LV: left ventricle RA: right atrium RV: right ventricle
At rest, the majority of cardiac outputCardiac outputThe volume of blood passing through the heart per unit of time. It is usually expressed as liters (volume) per minute so as not to be confused with stroke volume (volume per beat).Cardiac Mechanics flows to:
LiverLiverThe 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: approximately 25%
KidneysKidneysThe 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, the kidneys are responsible for blood filtration and excretion of water-soluble waste in the urine.Kidneys: Anatomy: approximately 20%
Skeletal muscle: approximately 20%
BrainBrainThe part of central nervous system that is contained within the skull (cranium). Arising from the neural tube, the embryonic brain is comprised of three major parts including prosencephalon (the forebrain); mesencephalon (the midbrain); and rhombencephalon (the hindbrain). The developed brain consists of cerebrum; cerebellum; and other structures in the brain stem.Nervous System: Anatomy, Structure, and Classification: approximately 15%
SkinSkinThe skin, also referred to as the integumentary system, is the largest organ of the body. The skin is primarily composed of the epidermis (outer layer) and dermis (deep layer). The epidermis is primarily composed of keratinocytes that undergo rapid turnover, while the dermis contains dense layers of connective tissue.Skin: Structure and Functions: approximately 7%
BrainBrainThe part of central nervous system that is contained within the skull (cranium). Arising from the neural tube, the embryonic brain is comprised of three major parts including prosencephalon (the forebrain); mesencephalon (the midbrain); and rhombencephalon (the hindbrain). The developed brain consists of cerebrum; cerebellum; and other structures in the brain stem.Nervous System: Anatomy, Structure, and Classification: although it has the ability to increase flowFlowBlood flows through the heart, arteries, capillaries, and veins in a closed, continuous circuit. Flow is the movement of volume per unit of time. Flow is affected by the pressure gradient and the resistance fluid encounters between 2 points. Vascular resistance is the opposition to flow, which is caused primarily by blood friction against vessel walls.Vascular Resistance, Flow, and Mean Arterial Pressure, of all the organs, keeps flowFlowBlood flows through the heart, arteries, capillaries, and veins in a closed, continuous circuit. Flow is the movement of volume per unit of time. Flow is affected by the pressure gradient and the resistance fluid encounters between 2 points. Vascular resistance is the opposition to flow, which is caused primarily by blood friction against vessel walls.Vascular Resistance, Flow, and Mean Arterial Pressure the most constant
Distribution of blood flow at rest
Image by Lecturio.
Changes in blood flow to the systemic organs during maximal vasodilation
Image by Lecturio.
Blood flowBlood flowBlood flow refers to the movement of a certain volume of blood through the vasculature over a given unit of time (e.g., mL per minute).Vascular Resistance, Flow, and Mean Arterial Pressure through and around capillariesCapillariesCapillaries 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
Blood enters the capillary bedsCapillary bedsGroups of 10–100 individual capillary vessels supplied by a single metarteriole.Capillaries: Histology through the arteriolesArteriolesThe smallest divisions of the arteries located between the muscular arteries and the capillaries.Arteries: Histology → metarteriolesMetarteriolesShort vessels linking arterioles and capillaries.Arteries: Histology → capillariesCapillariesCapillaries 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
Regulates the amount of blood flowBlood flowBlood flow refers to the movement of a certain volume of blood through the vasculature over a given unit of time (e.g., mL per minute).Vascular Resistance, Flow, and Mean Arterial Pressure into the capillary bed
When sphincters are closed, blood bypasses the capillariesCapillariesCapillaries 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 flows straight through the thoroughfare channelThoroughfare ChannelCapillaries: Histology.
Numerous in the dermisDermisA layer of vascularized connective tissue underneath the epidermis. The surface of the dermis contains innervated papillae. Embedded in or beneath the dermis are sweat glands; hair follicles; and sebaceous glands.Skin: Structure and Functions: help regulate body heatHeatInflammation
Capillary bed demonstrating arteriole, metarteriole, precapillary sphincters, thoroughfare channel, and venule
Image: “Capillary bed” by OpenStax College. License: CC BY 3.0
Physiology of capillariesCapillariesCapillaries 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
Functions:
Gas exchangeGas exchangeHuman cells are primarily reliant on aerobic metabolism. The respiratory system is involved in pulmonary ventilation and external respiration, while the circulatory system is responsible for transport and internal respiration. Pulmonary ventilation (breathing) represents movement of air into and out of the lungs. External respiration, or gas exchange, is represented by the O2 and CO2 exchange between the lungs and the blood.Gas Exchange:
O2 leaves the RBCsRBCsErythrocytes, or red blood cells (RBCs), are the most abundant cells in the blood. While erythrocytes in the fetus are initially produced in the yolk sac then the liver, the bone marrow eventually becomes the main site of production.Erythrocytes: Histology.
CO2 enters the RBCsRBCsErythrocytes, or red blood cells (RBCs), are the most abundant cells in the blood. While erythrocytes in the fetus are initially produced in the yolk sac then the liver, the bone marrow eventually becomes the main site of production.Erythrocytes: Histology.
Nutrient delivery
Blood picks up cellular and interstitial waste.
Starling forcesStarling ForcesCapillaries: Histology applied to capillariesCapillariesCapillaries 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:
Relatively higher hydrostatic pressureHydrostatic pressureThe pressure due to the weight of fluid.Edema in the arteriolesArteriolesThe smallest divisions of the arteries located between the muscular arteries and the capillaries.Arteries: Histology pushes fluid, nutrients, and other cellular material into the surrounding extracellular fluidExtracellular fluidThe fluid of the body that is outside of cells. It is the external environment for the cells.Body Fluid Compartments (ECF).
PlasmaPlasmaThe residual portion of blood that is left after removal of blood cells by centrifugation without prior blood coagulation.Transfusion ProductsproteinsProteinsLinear 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 generally cannot pass through the capillary walls → plasmaPlasmaThe residual portion of blood that is left after removal of blood cells by centrifugation without prior blood coagulation.Transfusion Productsoncotic pressureOncotic PressureEdema ↑ toward the venous end of the capillary
Relatively higher oncotic pressureOncotic PressureEdema in the venulesVenulesThe minute vessels that collect blood from the capillary plexuses and join together to form veins.Veins: Histologyallow waste to be absorbed into the vessels.
Clinical relevance of increased hydrostatic pressureHydrostatic pressureThe pressure due to the weight of fluid.Edema within capillariesCapillariesCapillaries 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:
Any condition that prevents blood flowBlood flowBlood flow refers to the movement of a certain volume of blood through the vasculature over a given unit of time (e.g., mL per minute).Vascular Resistance, Flow, and Mean Arterial Pressure from moving forward on the venous side can lead to an increase in hydrostatic pressureHydrostatic pressureThe pressure due to the weight of fluid.Edema within the capillariesCapillariesCapillaries 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, which will result in more fluid and substrateSubstrateA substance upon which the enzyme acts.Basics of Enzymes moving into the ECF.
Heart failureHeart FailureA heterogeneous condition in which the heart is unable to pump out sufficient blood to meet the metabolic need of the body. Heart failure can be caused by structural defects, functional abnormalities (ventricular dysfunction), or a sudden overload beyond its capacity. Chronic heart failure is more common than acute heart failure which results from sudden insult to cardiac function, such as myocardial infarction.Total Anomalous Pulmonary Venous Return (TAPVR) (HF): ineffective pumping by the heart; results in venous congestion because blood does not move through the heart effectively. Presentation is with dyspneaDyspneaDyspnea is the subjective sensation of breathing discomfort. Dyspnea is a normal manifestation of heavy physical or psychological exertion, but also may be caused by underlying conditions (both pulmonary and extrapulmonary). Dyspnea on exertion and/or at rest, orthopneaOrthopneaPulmonary Edema, and peripheral edemaPeripheral edemaPeripheral edema is the swelling of the lower extremities, namely, legs, feet, and ankles.Edema.
CirrhosisCirrhosisCirrhosis 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: late stage of hepatic necrosisNecrosisThe death of cells in an organ or tissue due to disease, injury or failure of the blood supply.Ischemic Cell Damage and scarringScarringInflammation causing venous congestion in the portal veinsVeinsVeins 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
Lower-extremity deep vein thrombosisThrombosisFormation and development of a thrombus or blood clot in the blood vessel.Epidemic Typhus (DVTDVTDeep vein thrombosis (DVT) usually occurs in the deep veins of the lower extremities. The affected veins include the femoral, popliteal, iliofemoral, and pelvic veins. Proximal DVT is more likely to cause a pulmonary embolism (PE) and is generally considered more serious. Deep Vein Thrombosis):occlusion of a deep vein by a thrombosisThrombosisFormation and development of a thrombus or blood clot in the blood vessel.Epidemic Typhus, most commonly occurring in the calvesCalvesErythema Nodosum, causing venous congestion behind the occlusion
Starling forces: Starling forces within a capillary determine the flow of molecules into and out of the vessel.
Image: “Net filtration” by Phil Schatz. License: CC BY 4.0
Arterial supply to the liverLiverThe 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
Abdominal aortaAbdominal AortaThe aorta from the diaphragm to the bifurcation into the right and left common iliac arteries.Posterior Abdominal Wall: Anatomy → celiac trunk → common hepatic arteryHepatic arteryA branch of the celiac artery that distributes to the stomach, pancreas, duodenum, liver, gallbladder, and greater omentum.Liver: Anatomy
Carries oxygenated blood and nutrients to hepatocytesHepatocytesThe main structural component of the liver. They are specialized epithelial cells that are organized into interconnected plates called lobules.Liver: Anatomy
Approximately 25% of the liverLiverThe 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’s blood supply
Portal circulationCirculationThe movement of the blood as it is pumped through the cardiovascular system.ABCDE Assessment
The portal veinPortal veinA short thick vein formed by union of the superior mesenteric vein and the splenic vein.Liver: Anatomy carries deoxygenated blood from the abdominal organs to the liverLiverThe 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 1st-pass metabolism of everything absorbed from the GI tract.
Pathway from the heart to the liverLiverThe 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:
Celiac, superior and inferior mesenteric arteriesArteriesArteries 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: Histology (SMA, IMA) →
Smaller named arteriesArteriesArteries 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: Histology →
CapillariesCapillariesCapillaries 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 in GI villi →
Smaller veinsVeinsVeins 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 veinPortal veinA short thick vein formed by union of the superior mesenteric vein and the splenic vein.Liver: Anatomy → portal venulesVenulesThe minute vessels that collect blood from the capillary plexuses and join together to form veins.Veins: Histology within the liverLiverThe 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
Blood from the portal venulesVenulesThe minute vessels that collect blood from the capillary plexuses and join together to form veins.Veins: Histology is filtered through hepatic sinusoidsSinusoidsLiver: Anatomy lined by hepatocytesHepatocytesThe main structural component of the liver. They are specialized epithelial cells that are organized into interconnected plates called lobules.Liver: Anatomy:
Many substances absorbed via the GI tract are metabolized here by hepatocytesHepatocytesThe main structural component of the liver. They are specialized epithelial cells that are organized into interconnected plates called lobules.Liver: Anatomy.
Blood from the arterial supply also filters through hepatic sinusoidsSinusoidsLiver: Anatomy.
Blood flows into the central vein of a hepatic lobule → hepatic veinsVeinsVeins 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 → IVCIVCThe venous trunk which receives blood from the lower extremities and from the pelvic and abdominal organs.Mediastinum and Great Vessels: Anatomy
Anatomy of a hepatic lobule:
Blood to be filtered enters through the portal venules and flows through the sinusoids and into the central vein. From there, the blood flows out through the hepatic veins and into the inferior vena cava.
Image: “Microscopic Anatomy of the Liver” by OpenStax College. License: CC BY 4.0
Portosystemic anastomoses
Portosystemic anastomoses are points where 2 veinsVeinsVeins 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 connect with one another; in these cases, blood from 1 vein normally drains into the portal system, while blood from the other vein normally drains into systemic venous circulationCirculationThe movement of the blood as it is pumped through the cardiovascular system.ABCDE Assessment (i.e., the IVCIVCThe venous trunk which receives blood from the lower extremities and from the pelvic and abdominal organs.Mediastinum and Great Vessels: Anatomy).
Ensures venous drainage of abdominal organs even if blockage occurs in portal system (e.g., cirrhosisCirrhosisCirrhosis 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)
Clinically important portosystemic anastomosis sites include:
Left gastric veinsVeinsVeins 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 and lower esophageal veinsVeinsVeins 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
Superior rectal veinsVeinsVeins 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 and the inferior and middle rectal veinsVeinsVeins 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
Paraumbilical veinsVeinsVeins 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 and small epigastric veinsVeinsVeins 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
Intraparenchymal hepatic branches of right division of portal veinPortal veinA short thick vein formed by union of the superior mesenteric vein and the splenic vein.Liver: Anatomy and retroperitonealRetroperitonealPeritoneum: AnatomyveinsVeinsVeins 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
Omental and colonic veinsVeinsVeins 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 with retroperitonealRetroperitonealPeritoneum: AnatomyveinsVeinsVeins 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
Clinical relevance: portal hypertensionPortal hypertensionPortal hypertension is increased pressure in the portal venous system. This increased pressure can lead to splanchnic vasodilation, collateral blood flow through portosystemic anastomoses, and increased hydrostatic pressure. There are a number of etiologies, including cirrhosis, right-sided congestive heart failure, schistosomiasis, portal vein thrombosis, hepatitis, and Budd-Chiari syndrome. Portal Hypertension
When pressures in the portal system rise, the portal veinPortal veinA short thick vein formed by union of the superior mesenteric vein and the splenic vein.Liver: Anatomy (and the veinsVeinsVeins 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 leading to it) become backed up.
Clinically may result in:
Esophageal varices (which may rupture, resulting in life-threatening hemorrhage)
HemorrhoidsHemorrhoidsHemorrhoids are normal vascular cushions in the anal canal composed of dilated vascular tissue, smooth muscle, and connective tissue. They do not cause issues unless they are enlarged, inflamed, thrombosed, or prolapsed. Patients often present with rectal bleeding of bright red blood, or they may have pain, perianal pruritus, or a palpable mass. Hemorrhoids
AscitesAscitesAscites is the pathologic accumulation of fluid within the peritoneal cavity that occurs due to an osmotic and/or hydrostatic pressure imbalance secondary to portal hypertension (cirrhosis, heart failure) or non-portal hypertension (hypoalbuminemia, malignancy, infection).Ascites
HypersplenismHypersplenismCondition characterized by splenomegaly, some reduction in the number of circulating blood cells in the presence of a normal or hyperactive bone marrow, and the potential for reversal by splenectomy.Splenomegaly (↑ pressure in the splenic vein)
Esophageal varices, splenomegaly, and rectal varices resulting from backup of blood flow due to elevated pressures within the portal vein
Blood flows to and through the kidneysKidneysThe 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, the kidneys are responsible for blood filtration and excretion of water-soluble waste in the urine.Kidneys: Anatomy via the following path:
Peritubular and vasa rectaVasa rectaGlomerular FiltrationcapillariesCapillariesCapillaries 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
These vessels are the beginning of venous circulationCirculationThe movement of the blood as it is pumped through the cardiovascular system.ABCDE Assessment and are important in adjusting the contents of the urine →
Interlobular vein → arcuate vein → interlobar vein → renal veinRenal veinShort thick veins which return blood from the kidneys to the vena cava.Glomerular Filtration → IVCIVCThe venous trunk which receives blood from the lower extremities and from the pelvic and abdominal organs.Mediastinum and Great Vessels: Anatomy
Renal circulation
Image by Lecturio.
Regulation of glomerular filtrationGlomerular filtrationThe kidneys are primarily in charge of the maintenance of water and solute homeostasis through the processes of filtration, reabsorption, secretion, and excretion. Glomerular filtration is the process of converting the systemic blood supply into a filtrate, which will ultimately become the urine. Glomerular Filtration
The kidney has multiple levels of regulatory mechanisms that affect renal blood flowRenal blood flowThe amount of the renal blood flow that is going to the functional renal tissue, i.e., parts of the kidney that are involved in production of urine.Glomerular Filtration (RBF) and the glomerular filtration rateGlomerular filtration rateThe volume of water filtered out of plasma through glomerular capillary walls into Bowman’s capsules per unit of time. It is considered to be equivalent to inulin clearance.Kidney Function Tests (GFRGFRThe volume of water filtered out of plasma through glomerular capillary walls into Bowman’s capsules per unit of time. It is considered to be equivalent to inulin clearance.Kidney Function Tests):
Relative constriction and dilation of the afferentAfferentNeurons which conduct nerve impulses to the central nervous system.Nervous System: Histology and efferentEfferentNeurons which send impulses peripherally to activate muscles or secretory cells.Nervous System: HistologyarteriolesArteriolesThe smallest divisions of the arteries located between the muscular arteries and the capillaries.Arteries: Histology:
Constriction: ↓ RBF → ↓ hydrostatic pressureHydrostatic pressureThe pressure due to the weight of fluid.Edema in the glomerular capillariesGlomerular capillariesKidneys: Anatomy → ↓ GFRGFRThe volume of water filtered out of plasma through glomerular capillary walls into Bowman’s capsules per unit of time. It is considered to be equivalent to inulin clearance.Kidney Function Tests
Dilation: ↑ RBF → ↑ hydrostatic pressureHydrostatic pressureThe pressure due to the weight of fluid.Edema in the glomerular capillariesGlomerular capillariesKidneys: Anatomy → ↑ GFRGFRThe volume of water filtered out of plasma through glomerular capillary walls into Bowman’s capsules per unit of time. It is considered to be equivalent to inulin clearance.Kidney Function Tests
Constriction: ↑ hydrostatic pressureHydrostatic pressureThe pressure due to the weight of fluid.Edema in glomerular capillariesGlomerular capillariesKidneys: Anatomy → ↑ GFRGFRThe volume of water filtered out of plasma through glomerular capillary walls into Bowman’s capsules per unit of time. It is considered to be equivalent to inulin clearance.Kidney Function Tests but ↓ RBF
Dilation: ↓ hydrostatic pressureHydrostatic pressureThe pressure due to the weight of fluid.Edema in glomerular capillariesGlomerular capillariesKidneys: Anatomy → ↓ GFRGFRThe volume of water filtered out of plasma through glomerular capillary walls into Bowman’s capsules per unit of time. It is considered to be equivalent to inulin clearance.Kidney Function Tests but ↑ RBF
Autoregulation of the renal blood flowRenal blood flowThe amount of the renal blood flow that is going to the functional renal tissue, i.e., parts of the kidney that are involved in production of urine.Glomerular Filtration (RBF):
Maintains relatively constant RBF within a range of normal mean arterial blood pressures (the autoregulatory range)
Stable RBF allows the other regulatory mechanisms (rather than systemic BP) to regulate the GFRGFRThe volume of water filtered out of plasma through glomerular capillary walls into Bowman’s capsules per unit of time. It is considered to be equivalent to inulin clearance.Kidney Function Tests.
Impact of mean arterial blood pressure on the flow rate of renal blood flow (RBF) and glomerular filtration rate (GFR): Notice that within the autoregulatory range, GFR and RBF remain relatively constant.
MaculaMaculaAn oval area in the retina, 3 to 5 mm in diameter, usually located temporal to the posterior pole of the eye and slightly below the level of the optic disk. It is characterized by the presence of a yellow pigment diffusely permeating the inner layers, contains the fovea centralis in its center, and provides the best phototropic visual acuity. It is devoid of retinal blood vessels, except in its periphery, and receives nourishment from the choriocapillaris of the choroid.Eye: Anatomy densa (MD) cells within the tubules can sense tubular flowFlowBlood flows through the heart, arteries, capillaries, and veins in a closed, continuous circuit. Flow is the movement of volume per unit of time. Flow is affected by the pressure gradient and the resistance fluid encounters between 2 points. Vascular resistance is the opposition to flow, which is caused primarily by blood friction against vessel walls.Vascular Resistance, Flow, and Mean Arterial Pressure and adjust secretionSecretionCoagulation Studies of substances that affect GFRGFRThe volume of water filtered out of plasma through glomerular capillary walls into Bowman’s capsules per unit of time. It is considered to be equivalent to inulin clearance.Kidney Function Tests:
MaculaMaculaAn oval area in the retina, 3 to 5 mm in diameter, usually located temporal to the posterior pole of the eye and slightly below the level of the optic disk. It is characterized by the presence of a yellow pigment diffusely permeating the inner layers, contains the fovea centralis in its center, and provides the best phototropic visual acuity. It is devoid of retinal blood vessels, except in its periphery, and receives nourishment from the choriocapillaris of the choroid.Eye: Anatomy densa cells (located in distal tubules):
Sense the relative flowFlowBlood flows through the heart, arteries, capillaries, and veins in a closed, continuous circuit. Flow is the movement of volume per unit of time. Flow is affected by the pressure gradient and the resistance fluid encounters between 2 points. Vascular resistance is the opposition to flow, which is caused primarily by blood friction against vessel walls.Vascular Resistance, Flow, and Mean Arterial Pressure of NaCl, which correlates directly with GFRGFRThe volume of water filtered out of plasma through glomerular capillary walls into Bowman’s capsules per unit of time. It is considered to be equivalent to inulin clearance.Kidney Function Tests
↑ NaCl flowFlowBlood flows through the heart, arteries, capillaries, and veins in a closed, continuous circuit. Flow is the movement of volume per unit of time. Flow is affected by the pressure gradient and the resistance fluid encounters between 2 points. Vascular resistance is the opposition to flow, which is caused primarily by blood friction against vessel walls.Vascular Resistance, Flow, and Mean Arterial Pressure = ↑ GFRGFRThe volume of water filtered out of plasma through glomerular capillary walls into Bowman’s capsules per unit of time. It is considered to be equivalent to inulin clearance.Kidney Function Tests
MD cells can:
Secrete adenosineAdenosineA nucleoside that is composed of adenine and d-ribose. Adenosine or adenosine derivatives play many important biological roles in addition to being components of DNA and RNA. Adenosine itself is a neurotransmitter.Class 5 Antiarrhythmic Drugs
Independently stimulate juxtaglomerular cells to secrete reninReninA highly specific (leu-leu) endopeptidase that generates angiotensin I from its precursor angiotensinogen, leading to a cascade of reactions which elevate blood pressure and increase sodium retention by the kidney in the renin-angiotensin system.Renal Sodium and Water Regulation
AdenosineAdenosineA nucleoside that is composed of adenine and d-ribose. Adenosine or adenosine derivatives play many important biological roles in addition to being components of DNA and RNA. Adenosine itself is a neurotransmitter.Class 5 Antiarrhythmic Drugs: ↓ GFRGFRThe volume of water filtered out of plasma through glomerular capillary walls into Bowman’s capsules per unit of time. It is considered to be equivalent to inulin clearance.Kidney Function Tests by constricting afferentAfferentNeurons which conduct nerve impulses to the central nervous system.Nervous System: HistologyarteriolesArteriolesThe smallest divisions of the arteries located between the muscular arteries and the capillaries.Arteries: Histology
ReninReninA highly specific (leu-leu) endopeptidase that generates angiotensin I from its precursor angiotensinogen, leading to a cascade of reactions which elevate blood pressure and increase sodium retention by the kidney in the renin-angiotensin system.Renal Sodium and Water Regulation: ↑ GFRGFRThe volume of water filtered out of plasma through glomerular capillary walls into Bowman’s capsules per unit of time. It is considered to be equivalent to inulin clearance.Kidney Function Tests by activating the RAASRAASA blood pressure regulating system of interacting components that include renin; angiotensinogen; angiotensin converting enzyme; angiotensin i; angiotensin ii; and angiotensinase. Renin, an enzyme produced in the kidney, acts on angiotensinogen, an alpha-2 globulin produced by the liver, forming angiotensin I. Angiotensin-converting enzyme, contained in the lung, acts on angiotensin I in the plasma converting it to angiotensin II, an extremely powerful vasoconstrictor. Angiotensin II causes contraction of the arteriolar and renal vascular smooth muscle, leading to retention of salt and water in the kidney and increased arterial blood pressure. In addition, angiotensin II stimulates the release of aldosterone from the adrenal cortex, which in turn also increases salt and water retention in the kidney. Angiotensin-converting enzyme also breaks down bradykinin, a powerful vasodilator and component of the kallikrein-kinin system.Adrenal Hormones
↑ ReninReninA highly specific (leu-leu) endopeptidase that generates angiotensin I from its precursor angiotensinogen, leading to a cascade of reactions which elevate blood pressure and increase sodium retention by the kidney in the renin-angiotensin system.Renal Sodium and Water Regulation → ↑ angiotensin I → ↑ angiotensin IIAngiotensin IIAn octapeptide that is a potent but labile vasoconstrictor. It is produced from angiotensin I after the removal of two amino acids at the c-terminal by angiotensin converting enzyme. The amino acid in position 5 varies in different species. To block vasoconstriction and hypertension effect of angiotensin II, patients are often treated with ace inhibitors or with angiotensin II type 1 receptor blockers.Renal Sodium and Water Regulation → ↑ aldosteroneAldosteroneA hormone secreted by the adrenal cortex that regulates electrolyte and water balance by increasing the renal retention of sodium and the excretion of potassium.Hyperkalemia
RAASRAASA blood pressure regulating system of interacting components that include renin; angiotensinogen; angiotensin converting enzyme; angiotensin i; angiotensin ii; and angiotensinase. Renin, an enzyme produced in the kidney, acts on angiotensinogen, an alpha-2 globulin produced by the liver, forming angiotensin I. Angiotensin-converting enzyme, contained in the lung, acts on angiotensin I in the plasma converting it to angiotensin II, an extremely powerful vasoconstrictor. Angiotensin II causes contraction of the arteriolar and renal vascular smooth muscle, leading to retention of salt and water in the kidney and increased arterial blood pressure. In addition, angiotensin II stimulates the release of aldosterone from the adrenal cortex, which in turn also increases salt and water retention in the kidney. Angiotensin-converting enzyme also breaks down bradykinin, a powerful vasodilator and component of the kallikrein-kinin system.Adrenal Hormones activation results in:
↑ Tubular NaCl flowFlowBlood flows through the heart, arteries, capillaries, and veins in a closed, continuous circuit. Flow is the movement of volume per unit of time. Flow is affected by the pressure gradient and the resistance fluid encounters between 2 points. Vascular resistance is the opposition to flow, which is caused primarily by blood friction against vessel walls.Vascular Resistance, Flow, and Mean Arterial Pressure → MD senses ↑ flowFlowBlood flows through the heart, arteries, capillaries, and veins in a closed, continuous circuit. Flow is the movement of volume per unit of time. Flow is affected by the pressure gradient and the resistance fluid encounters between 2 points. Vascular resistance is the opposition to flow, which is caused primarily by blood friction against vessel walls.Vascular Resistance, Flow, and Mean Arterial Pressure → releases adenosineAdenosineA nucleoside that is composed of adenine and d-ribose. Adenosine or adenosine derivatives play many important biological roles in addition to being components of DNA and RNA. Adenosine itself is a neurotransmitter.Class 5 Antiarrhythmic Drugs (and inhibits reninReninA highly specific (leu-leu) endopeptidase that generates angiotensin I from its precursor angiotensinogen, leading to a cascade of reactions which elevate blood pressure and increase sodium retention by the kidney in the renin-angiotensin system.Renal Sodium and Water Regulation) → GFRGFRThe volume of water filtered out of plasma through glomerular capillary walls into Bowman’s capsules per unit of time. It is considered to be equivalent to inulin clearance.Kidney Function Tests ↓ (normalizes)
↓ Tubular NaCl flowFlowBlood flows through the heart, arteries, capillaries, and veins in a closed, continuous circuit. Flow is the movement of volume per unit of time. Flow is affected by the pressure gradient and the resistance fluid encounters between 2 points. Vascular resistance is the opposition to flow, which is caused primarily by blood friction against vessel walls.Vascular Resistance, Flow, and Mean Arterial Pressure → MD senses ↓ flowFlowBlood flows through the heart, arteries, capillaries, and veins in a closed, continuous circuit. Flow is the movement of volume per unit of time. Flow is affected by the pressure gradient and the resistance fluid encounters between 2 points. Vascular resistance is the opposition to flow, which is caused primarily by blood friction against vessel walls.Vascular Resistance, Flow, and Mean Arterial Pressure → stimulates the release of reninReninA highly specific (leu-leu) endopeptidase that generates angiotensin I from its precursor angiotensinogen, leading to a cascade of reactions which elevate blood pressure and increase sodium retention by the kidney in the renin-angiotensin system.Renal Sodium and Water Regulation (and inhibits adenosineAdenosineA nucleoside that is composed of adenine and d-ribose. Adenosine or adenosine derivatives play many important biological roles in addition to being components of DNA and RNA. Adenosine itself is a neurotransmitter.Class 5 Antiarrhythmic Drugs) → GFRGFRThe volume of water filtered out of plasma through glomerular capillary walls into Bowman’s capsules per unit of time. It is considered to be equivalent to inulin clearance.Kidney Function Tests ↑ (normalizes)
Fine-tuning mechanisms:
Paracrine mechanismsParacrine mechanismsCellular signaling in which a factor secreted by a cell affects other cells in the local environment. This term is often used to denote the action of intercellular signaling peptides and proteins on surrounding cells.Glomerular Filtration: local release of vasoactive substances
Vasoconstrictors (e.g., endothelinsEndothelins21-amino-acid peptides produced by vascular endothelial cells and functioning as potent vasoconstrictors. The endothelin family consists of three members, endothelin-1; endothelin-2; and endothelin-3. All three peptides contain 21 amino acids, but vary in amino acid composition. The three peptides produce vasoconstrictor and pressor responses in various parts of the body. However, the quantitative profiles of the pharmacological activities are considerably different among the three isopeptides.Hemostasis): ↓ RBF
VasodilatorsVasodilatorsDrugs used to cause dilation of the blood vessels.Thromboangiitis Obliterans (Buerger Disease) (e.g., nitric oxideNitric OxideA free radical gas produced endogenously by a variety of mammalian cells, synthesized from arginine by nitric oxide synthase. Nitric oxide is one of the endothelium-dependent relaxing factors released by the vascular endothelium and mediates vasodilation. It also inhibits platelet aggregation, induces disaggregation of aggregated platelets, and inhibits platelet adhesion to the vascular endothelium. Nitric oxide activates cytosolic guanylate cyclase and thus elevates intracellular levels of cyclic gmp.Pulmonary Hypertension Drugs, prostaglandinsProstaglandinsA group of compounds derived from unsaturated 20-carbon fatty acids, primarily arachidonic acid, via the cyclooxygenase pathway. They are extremely potent mediators of a diverse group of physiological processes.Eicosanoids): ↑ RBF
RAASRAASA blood pressure regulating system of interacting components that include renin; angiotensinogen; angiotensin converting enzyme; angiotensin i; angiotensin ii; and angiotensinase. Renin, an enzyme produced in the kidney, acts on angiotensinogen, an alpha-2 globulin produced by the liver, forming angiotensin I. Angiotensin-converting enzyme, contained in the lung, acts on angiotensin I in the plasma converting it to angiotensin II, an extremely powerful vasoconstrictor. Angiotensin II causes contraction of the arteriolar and renal vascular smooth muscle, leading to retention of salt and water in the kidney and increased arterial blood pressure. In addition, angiotensin II stimulates the release of aldosterone from the adrenal cortex, which in turn also increases salt and water retention in the kidney. Angiotensin-converting enzyme also breaks down bradykinin, a powerful vasodilator and component of the kallikrein-kinin system.Adrenal Hormones
Natriuretic peptidesNatriuretic peptidesPeptides that regulate the water-electrolyte balance in the body, also known as natriuretic peptide hormones. Several have been sequenced (atrial natriuretic factor; brain natriuretic peptide; c-type natriuretic peptide).Arterial Pressure Regulation
Prevents many harmful substancesHarmful substancesElements, compounds, mixtures, or solutions that are considered severely harmful to human health and the environment. They include substances that are toxic, corrosive, flammable, or explosive.Esophagitis (e.g., toxins, bacteriaBacteriaBacteria 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) from affecting brainBrainThe part of central nervous system that is contained within the skull (cranium). Arising from the neural tube, the embryonic brain is comprised of three major parts including prosencephalon (the forebrain); mesencephalon (the midbrain); and rhombencephalon (the hindbrain). The developed brain consists of cerebrum; cerebellum; and other structures in the brain stem.Nervous System: Anatomy, Structure, and Classification parenchyma
Allows passage of ions and nutrients
Structurally created by:
Foot-like processes of astrocytesAstrocytesA class of large neuroglial (macroglial) cells in the central nervous system – the largest and most numerous neuroglial cells in the brain and spinal cord. Astrocytes (from ‘star’ cells) are irregularly shaped with many long processes, including those with ‘end feet’ which form the glial (limiting) membrane and directly and indirectly contribute to the blood-brain barrier. They regulate the extracellular ionic and chemical environment, and ‘reactive astrocytes’ (along with microglia) respond to injury.Nervous System: Histology wrapping around cerebral capillariesCapillariesCapillaries 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, limiting substances that can escapeEscapeWith constant immune mechanisms holding unstable tumor cells in equilibrium, tumor-cell variants may emerge. These cancer cells may express fewer antigens on their surfaces or lose their MHC class I expression.Variants may also protect themselves from T-cell attack via expression of IC molecules on their surfaces, like normal cells.Creation of an immunosuppressive state in the microenvironment is another way to grow without immunologic interference.Cancer Immunotherapy the vasculature
No fenestrations in capillariesCapillariesCapillaries 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
Tight junctionsTight junctionsCell-cell junctions that seal adjacent epithelial cells together, preventing the passage of most dissolved molecules from one side of the epithelial sheet to the other.The Cell: Cell Junctions prevent paracellularParacellularRenal Potassium RegulationdiffusionDiffusionThe 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
The blood–brain barrier
Image by Lecturio.
Autoregulatory ability
The brainBrainThe part of central nervous system that is contained within the skull (cranium). Arising from the neural tube, the embryonic brain is comprised of three major parts including prosencephalon (the forebrain); mesencephalon (the midbrain); and rhombencephalon (the hindbrain). The developed brain consists of cerebrum; cerebellum; and other structures in the brain stem.Nervous System: Anatomy, Structure, and Classification can regulate its own cerebral blood flowBlood flowBlood flow refers to the movement of a certain volume of blood through the vasculature over a given unit of time (e.g., mL per minute).Vascular Resistance, Flow, and Mean Arterial Pressure (CBF) in response to changes in blood pressure, CO2 levels, and activity levels of different brainBrainThe part of central nervous system that is contained within the skull (cranium). Arising from the neural tube, the embryonic brain is comprised of three major parts including prosencephalon (the forebrain); mesencephalon (the midbrain); and rhombencephalon (the hindbrain). The developed brain consists of cerebrum; cerebellum; and other structures in the brain stem.Nervous System: Anatomy, Structure, and Classification regions.
Myogenic autoregulatory ability in response to changes in mean arterial pressures (MAPs) (similar to the kidneysKidneysThe 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, the kidneys are responsible for blood filtration and excretion of water-soluble waste in the urine.Kidneys: Anatomy):
↑ Systemic MAPs : cerebral arteriesArteriesArteries 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: Histology vasoconstrict, limiting flowFlowBlood flows through the heart, arteries, capillaries, and veins in a closed, continuous circuit. Flow is the movement of volume per unit of time. Flow is affected by the pressure gradient and the resistance fluid encounters between 2 points. Vascular resistance is the opposition to flow, which is caused primarily by blood friction against vessel walls.Vascular Resistance, Flow, and Mean Arterial Pressure
↓ Systemic MAPs: cerebral arteriesArteriesArteries 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: Histology vasodilate, maintaining perfusion
Autoregulatory ability functions between MAPs of 60 and 150 mm Hg
< 60 mm Hg: CBF ↓ because there simply is not enough pressure to perfuse the brainBrainThe part of central nervous system that is contained within the skull (cranium). Arising from the neural tube, the embryonic brain is comprised of three major parts including prosencephalon (the forebrain); mesencephalon (the midbrain); and rhombencephalon (the hindbrain). The developed brain consists of cerebrum; cerebellum; and other structures in the brain stem.Nervous System: Anatomy, Structure, and Classification
> 150 mm Hg: CBF ↑ because the pressure overwhelms the autoregulatory system
↓ Perfusion → CO2 accumulates → ↓ pHpHThe quantitative measurement of the acidity or basicity of a solution.Acid-Base Balance → triggers vasodilationVasodilationThe physiological widening of blood vessels by relaxing the underlying vascular smooth muscle.Pulmonary Hypertension Drugs → ↑ flowFlowBlood flows through the heart, arteries, capillaries, and veins in a closed, continuous circuit. Flow is the movement of volume per unit of time. Flow is affected by the pressure gradient and the resistance fluid encounters between 2 points. Vascular resistance is the opposition to flow, which is caused primarily by blood friction against vessel walls.Vascular Resistance, Flow, and Mean Arterial Pressure
Hypocapnia (i.e., ↓ CO2) → ↑ pHpHThe quantitative measurement of the acidity or basicity of a solution.Acid-Base Balance → vasoconstrictionVasoconstrictionThe physiological narrowing of blood vessels by contraction of the vascular smooth muscle.Vascular Resistance, Flow, and Mean Arterial Pressure → ↓ flowFlowBlood flows through the heart, arteries, capillaries, and veins in a closed, continuous circuit. Flow is the movement of volume per unit of time. Flow is affected by the pressure gradient and the resistance fluid encounters between 2 points. Vascular resistance is the opposition to flow, which is caused primarily by blood friction against vessel walls.Vascular Resistance, Flow, and Mean Arterial Pressure
Clinical relevance: hyperventilationHyperventilationA pulmonary ventilation rate faster than is metabolically necessary for the exchange of gases. It is the result of an increased frequency of breathing, an increased tidal volume, or a combination of both. It causes an excess intake of oxygen and the blowing off of carbon dioxide.Respiratory Alkalosis
Exhaling CO2 faster than the body produces it
Results in hypocapnia → cerebral vasoconstrictionVasoconstrictionThe physiological narrowing of blood vessels by contraction of the vascular smooth muscle.Vascular Resistance, Flow, and Mean Arterial Pressure → ischemiaIschemiaA hypoperfusion of the blood through an organ or tissue caused by a pathologic constriction or obstruction of its blood vessels, or an absence of blood circulation.Ischemic Cell Damage, dizzinessDizzinessAn imprecise term which may refer to a sense of spatial disorientation, motion of the environment, or lightheadedness.Lateral Medullary Syndrome (Wallenberg Syndrome), and potentially syncopeSyncopeSyncope is a short-term loss of consciousness and loss of postural stability followed by spontaneous return of consciousness to the previous neurologic baseline without the need for resuscitation. The condition is caused by transient interruption of cerebral blood flow that may be benign or related to a underlying life-threatening condition. Syncope
Redistribution of blood flowBlood flowBlood flow refers to the movement of a certain volume of blood through the vasculature over a given unit of time (e.g., mL per minute).Vascular Resistance, Flow, and Mean Arterial Pressure throughout the brainBrainThe part of central nervous system that is contained within the skull (cranium). Arising from the neural tube, the embryonic brain is comprised of three major parts including prosencephalon (the forebrain); mesencephalon (the midbrain); and rhombencephalon (the hindbrain). The developed brain consists of cerebrum; cerebellum; and other structures in the brain stem.Nervous System: Anatomy, Structure, and Classification according to tasks being performed
For example, motorMotorNeurons which send impulses peripherally to activate muscles or secretory cells.Nervous System: Histology versus sensorySensoryNeurons which conduct nerve impulses to the central nervous system.Nervous System: Histology versus cognitive functions
Occurs in a matter of seconds
Due to effects of local metabolites
Blood flow redistribution in the brain according to the task being performed:
Redistribution depends heavily on the metabolic activity of the different portions of the cerebral tissue.
Coronary circulationCirculationThe movement of the blood as it is pumped through the cardiovascular system.ABCDE Assessment
The heart does notreceive significant O2 and nutrients from the blood flowing through it. Coronary circulationCirculationThe movement of the blood as it is pumped through the cardiovascular system.ABCDE Assessment describes the flowFlowBlood flows through the heart, arteries, capillaries, and veins in a closed, continuous circuit. Flow is the movement of volume per unit of time. Flow is affected by the pressure gradient and the resistance fluid encounters between 2 points. Vascular resistance is the opposition to flow, which is caused primarily by blood friction against vessel walls.Vascular Resistance, Flow, and Mean Arterial Pressure of blood through the vessels supplying the heart muscle itself.
There are 2 primary coronary arteriesArteriesArteries 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: Histology:
Posterior interventricular artery (i.e., posterior descending artery (PDAPDAThe ductus arteriosus (DA) allows blood to bypass pulmonary circulation. After birth, the DA remains open for up to 72 hours and then constricts and involutes, becoming the ligamentum arteriosum. Failure of this process to occur results in patent ductus arteriosus (PDA), a condition that causes up to 10% of congenital heart defects. Patent Ductus Arteriosus (PDA)))
Right marginal artery
Both the LCA and the RCA originate from the aortaAortaThe main trunk of the systemic arteries.Mediastinum and Great Vessels: Anatomy, just above the aortic valveAortic valveThe valve between the left ventricle and the ascending aorta which prevents backflow into the left ventricle.Heart: Anatomy.
Clinical relevance: occlusion of these vessels (typically via a thrombus), results in rapid ischemiaIschemiaA hypoperfusion of the blood through an organ or tissue caused by a pathologic constriction or obstruction of its blood vessels, or an absence of blood circulation.Ischemic Cell Damage and potential necrosisNecrosisThe death of cells in an organ or tissue due to disease, injury or failure of the blood supply.Ischemic Cell Damage of surrounding myocardial tissue; this is known as a myocardial infarctionMyocardial infarctionMI is ischemia and death of an area of myocardial tissue due to insufficient blood flow and oxygenation, usually from thrombus formation on a ruptured atherosclerotic plaque in the epicardial arteries. Clinical presentation is most commonly with chest pain, but women and patients with diabetes may have atypical symptoms.Myocardial Infarction (MIMIMI is ischemia and death of an area of myocardial tissue due to insufficient blood flow and oxygenation, usually from thrombus formation on a ruptured atherosclerotic plaque in the epicardial arteries. Clinical presentation is most commonly with chest pain, but women and patients with diabetes may have atypical symptoms.Myocardial Infarction; i.e., heart attackHeart attackMi is ischemia and death of an area of myocardial tissue due to insufficient blood flow and oxygenation, usually from thrombus formation on a ruptured atherosclerotic plaque in the epicardial arteries. Clinical presentation is most commonly with chest pain, but women and patients with diabetes may have atypical symptoms.Myocardial Infarction)
The heart is primarily irrigated during diastoleDiastolePost-systolic relaxation of the heart, especially the heart ventricles.Cardiac Cycle (relaxation of the heart muscle):
During systoleSystolePeriod of contraction of the heart, especially of the heart ventricles.Cardiac Cycle, the small vessels perforating/supplying the cardiac muscleCardiac muscleThe muscle tissue of the heart. It is composed of striated, involuntary muscle cells connected to form the contractile pump to generate blood flow.Muscle Tissue: Histology are compressed.
The faster the heart beats = shorter diastoleDiastolePost-systolic relaxation of the heart, especially the heart ventricles.Cardiac Cycle = less time heart has for irrigation
Autoregulation: like the brainBrainThe part of central nervous system that is contained within the skull (cranium). Arising from the neural tube, the embryonic brain is comprised of three major parts including prosencephalon (the forebrain); mesencephalon (the midbrain); and rhombencephalon (the hindbrain). The developed brain consists of cerebrum; cerebellum; and other structures in the brain stem.Nervous System: Anatomy, Structure, and Classification and kidneysKidneysThe 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, the kidneys are responsible for blood filtration and excretion of water-soluble waste in the urine.Kidneys: Anatomy, the heart has the ability to vasodilate and/or vasoconstrict coronary vessels across a range of MAPs to maintain a steady flow rateFlow ratemaximum flow the ventilator will deliver a set tidal volume in liters per minuteInvasive Mechanical Ventilation.
Cardiac irrigation during diastole:
During ventricular contraction (systole) flow to cardiac tissue diminishes (down). During ventricular relaxation (diastole), flow to the heart increases.
Image by Lecturio.
Skeletal muscle circulationCirculationThe movement of the blood as it is pumped through the cardiovascular system.ABCDE Assessment
Actively contracting muscles increase their own blood flowBlood flowBlood flow refers to the movement of a certain volume of blood through the vasculature over a given unit of time (e.g., mL per minute).Vascular Resistance, Flow, and Mean Arterial Pressure.
Sympathetic activation via the sympathetic nervous systemNervous systemThe nervous system is a small and complex system that consists of an intricate network of neural cells (or neurons) and even more glial cells (for support and insulation). It is divided according to its anatomical components as well as its functional characteristics. The brain and spinal cord are referred to as the central nervous system, and the branches of nerves from these structures are referred to as the peripheral nervous system.Nervous System: Anatomy, Structure, and Classification (SNS):
Responsible for maintaining arterial blood pressure under resting circumstances
Via:
Sympathetic nerves
Circulating catecholaminesCatecholaminesA general class of ortho-dihydroxyphenylalkylamines derived from tyrosine.Adrenal Hormones (epinephrineEpinephrineThe active sympathomimetic hormone from the adrenal medulla. It stimulates both the alpha- and beta- adrenergic systems, causes systemic vasoconstriction and gastrointestinal relaxation, stimulates the heart, and dilates bronchi and cerebral vessels.Sympathomimetic Drugs and norepinephrineNorepinephrinePrecursor of epinephrine that is secreted by the adrenal medulla and is a widespread central and autonomic neurotransmitter. Norepinephrine is the principal transmitter of most postganglionic sympathetic fibers, and of the diffuse projection system in the brain that arises from the locus ceruleus.Receptors and Neurotransmitters of the CNS) released from the adrenal medullaAdrenal MedullaThe inner portion of the adrenal gland. Derived from ectoderm, adrenal medulla consists mainly of chromaffin cells that produces and stores a number of neurotransmitters, mainly adrenaline (epinephrine) and norepinephrine. The activity of the adrenal medulla is regulated by the sympathetic nervous system.Adrenal Glands: Anatomy
AdenosineAdenosineA nucleoside that is composed of adenine and d-ribose. Adenosine or adenosine derivatives play many important biological roles in addition to being components of DNA and RNA. Adenosine itself is a neurotransmitter.Class 5 Antiarrhythmic Drugs
Blood flowBlood flowBlood flow refers to the movement of a certain volume of blood through the vasculature over a given unit of time (e.g., mL per minute).Vascular Resistance, Flow, and Mean Arterial Pressure to skeletal musclesSkeletal musclesA subtype of striated muscle, attached by tendons to the skeleton. Skeletal muscles are innervated and their movement can be consciously controlled. They are also called voluntary muscles.Muscle Tissue: Histology can increase > 20-fold during strenuous exerciseStrenuous exercisePhysical activity which is usually regular and done with the intention of improving or maintaining physical fitness or health. Contrast with physical exertion which is concerned largely with the physiologic and metabolic response to energy expenditure.Cardiovascular Response to Exercise.
Like cardiac muscleCardiac muscleThe muscle tissue of the heart. It is composed of striated, involuntary muscle cells connected to form the contractile pump to generate blood flow.Muscle Tissue: Histology, flowFlowBlood flows through the heart, arteries, capillaries, and veins in a closed, continuous circuit. Flow is the movement of volume per unit of time. Flow is affected by the pressure gradient and the resistance fluid encounters between 2 points. Vascular resistance is the opposition to flow, which is caused primarily by blood friction against vessel walls.Vascular Resistance, Flow, and Mean Arterial Pressure is restricted during muscle contraction owing to compressionCompressionBlunt Chest Trauma of smaller vessels.
Isometric contractionsIsometric contractionsMuscular contractions characterized by increase in tension without change in length.Cardiovascular Response to Exercise cause fatigueFatigueThe 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 more quickly than intermittent isotonicIsotonicSolutions having the same osmotic pressure as blood serum, or another solution with which they are compared.Renal Sodium and Water Regulation contractions.
IsotonicIsotonicSolutions having the same osmotic pressure as blood serum, or another solution with which they are compared.Renal Sodium and Water Regulation contractions: change in muscle length producing limb motion
Regulating vascular flowFlowBlood flows through the heart, arteries, capillaries, and veins in a closed, continuous circuit. Flow is the movement of volume per unit of time. Flow is affected by the pressure gradient and the resistance fluid encounters between 2 points. Vascular resistance is the opposition to flow, which is caused primarily by blood friction against vessel walls.Vascular Resistance, Flow, and Mean Arterial Pressure to the skinSkinThe skin, also referred to as the integumentary system, is the largest organ of the body. The skin is primarily composed of the epidermis (outer layer) and dermis (deep layer). The epidermis is primarily composed of keratinocytes that undergo rapid turnover, while the dermis contains dense layers of connective tissue.Skin: Structure and Functions is critical to thermoregulationThermoregulationBody temperature can be divided into external temperature, which involves the skin, and core temperature, which involves the CNS and viscera. While external temperature can be variable, the core temperature is maintained within a narrow range of 36.5-37.5ºC (97.7-99.5ºF).Body Temperature Regulation because heatHeatInflammation is dissipated as blood flows near the surface of the skinSkinThe skin, also referred to as the integumentary system, is the largest organ of the body. The skin is primarily composed of the epidermis (outer layer) and dermis (deep layer). The epidermis is primarily composed of keratinocytes that undergo rapid turnover, while the dermis contains dense layers of connective tissue.Skin: Structure and Functions.
Nonglabrous skinSkinThe skin, also referred to as the integumentary system, is the largest organ of the body. The skin is primarily composed of the epidermis (outer layer) and dermis (deep layer). The epidermis is primarily composed of keratinocytes that undergo rapid turnover, while the dermis contains dense layers of connective tissue.Skin: Structure and Functions
Nonglabrous skinSkinThe skin, also referred to as the integumentary system, is the largest organ of the body. The skin is primarily composed of the epidermis (outer layer) and dermis (deep layer). The epidermis is primarily composed of keratinocytes that undergo rapid turnover, while the dermis contains dense layers of connective tissue.Skin: Structure and Functions is thin skinSkinThe skin, also referred to as the integumentary system, is the largest organ of the body. The skin is primarily composed of the epidermis (outer layer) and dermis (deep layer). The epidermis is primarily composed of keratinocytes that undergo rapid turnover, while the dermis contains dense layers of connective tissue.Skin: Structure and Functions with hair on it.
Under stable temperatures: flowFlowBlood flows through the heart, arteries, capillaries, and veins in a closed, continuous circuit. Flow is the movement of volume per unit of time. Flow is affected by the pressure gradient and the resistance fluid encounters between 2 points. Vascular resistance is the opposition to flow, which is caused primarily by blood friction against vessel walls.Vascular Resistance, Flow, and Mean Arterial Pressure is low and stable.
In response to systemic cold (i.e., whole-body cold thermal stress):
Via epinephrineEpinephrineThe active sympathomimetic hormone from the adrenal medulla. It stimulates both the alpha- and beta- adrenergic systems, causes systemic vasoconstriction and gastrointestinal relaxation, stimulates the heart, and dilates bronchi and cerebral vessels.Sympathomimetic Drugs on α1– and α2-adrenergic receptorsReceptorsReceptors are proteins located either on the surface of or within a cell that can bind to signaling molecules known as ligands (e.g., hormones) and cause some type of response within the cell.Receptors
In response to local cold:
VasoconstrictionVasoconstrictionThe physiological narrowing of blood vessels by contraction of the vascular smooth muscle.Vascular Resistance, Flow, and Mean Arterial Pressure is mediated through local translocation of α2c-adrenergic receptorsReceptorsReceptors are proteins located either on the surface of or within a cell that can bind to signaling molecules known as ligands (e.g., hormones) and cause some type of response within the cell.Receptors to the cell surface.
Not mediated via systemic sympathetic activation
In response to systemic heatHeatInflammation (i.e., whole-body hot thermal stress):
Activation of vasodilationVasodilationThe physiological widening of blood vessels by relaxing the underlying vascular smooth muscle.Pulmonary Hypertension Drugs → allows more blood near the skinSkinThe skin, also referred to as the integumentary system, is the largest organ of the body. The skin is primarily composed of the epidermis (outer layer) and dermis (deep layer). The epidermis is primarily composed of keratinocytes that undergo rapid turnover, while the dermis contains dense layers of connective tissue.Skin: Structure and Functions surface to dissipate the heatHeatInflammation
Via acetylcholineAcetylcholineA neurotransmitter found at neuromuscular junctions, autonomic ganglia, parasympathetic effector junctions, a subset of sympathetic effector junctions, and at many sites in the central nervous system.Receptors and Neurotransmitters of the CNS and an unknown molecule (thought to be related to NO, which causes smooth muscle dilation)
Axon reflex: triggers a rapid increase in vasodilationVasodilationThe physiological widening of blood vessels by relaxing the underlying vascular smooth muscle.Pulmonary Hypertension Drugs
NO: sustains maximal vasodilationVasodilationThe physiological widening of blood vessels by relaxing the underlying vascular smooth muscle.Pulmonary Hypertension Drugs
Glabrous skinSkinThe skin, also referred to as the integumentary system, is the largest organ of the body. The skin is primarily composed of the epidermis (outer layer) and dermis (deep layer). The epidermis is primarily composed of keratinocytes that undergo rapid turnover, while the dermis contains dense layers of connective tissue.Skin: Structure and Functions
Glabrous skinSkinThe skin, also referred to as the integumentary system, is the largest organ of the body. The skin is primarily composed of the epidermis (outer layer) and dermis (deep layer). The epidermis is primarily composed of keratinocytes that undergo rapid turnover, while the dermis contains dense layers of connective tissue.Skin: Structure and Functions is thicker skinSkinThe skin, also referred to as the integumentary system, is the largest organ of the body. The skin is primarily composed of the epidermis (outer layer) and dermis (deep layer). The epidermis is primarily composed of keratinocytes that undergo rapid turnover, while the dermis contains dense layers of connective tissue.Skin: Structure and Functions without hair on it (e.g., palms, soles, ear lobes):
Tonic sympathetic activation → almost always vasoconstricted, but can be increased
Mediated via:
NorepinephrineNorepinephrinePrecursor of epinephrine that is secreted by the adrenal medulla and is a widespread central and autonomic neurotransmitter. Norepinephrine is the principal transmitter of most postganglionic sympathetic fibers, and of the diffuse projection system in the brain that arises from the locus ceruleus.Receptors and Neurotransmitters of the CNS
Neuropeptide Y
Has AV anastomoses:
Shunts that bypass the capillary bedsCapillary bedsGroups of 10–100 individual capillary vessels supplied by a single metarteriole.Capillaries: Histology closer to the surface of the skinSkinThe skin, also referred to as the integumentary system, is the largest organ of the body. The skin is primarily composed of the epidermis (outer layer) and dermis (deep layer). The epidermis is primarily composed of keratinocytes that undergo rapid turnover, while the dermis contains dense layers of connective tissue.Skin: Structure and Functions
Glabrous skinSkinThe skin, also referred to as the integumentary system, is the largest organ of the body. The skin is primarily composed of the epidermis (outer layer) and dermis (deep layer). The epidermis is primarily composed of keratinocytes that undergo rapid turnover, while the dermis contains dense layers of connective tissue.Skin: Structure and Functions has no active vasodilationVasodilationThe physiological widening of blood vessels by relaxing the underlying vascular smooth muscle.Pulmonary Hypertension Drugs: flowFlowBlood flows through the heart, arteries, capillaries, and veins in a closed, continuous circuit. Flow is the movement of volume per unit of time. Flow is affected by the pressure gradient and the resistance fluid encounters between 2 points. Vascular resistance is the opposition to flow, which is caused primarily by blood friction against vessel walls.Vascular Resistance, Flow, and Mean Arterial Pressure increases by releasing vasoconstrictionVasoconstrictionThe physiological narrowing of blood vessels by contraction of the vascular smooth muscle.Vascular Resistance, Flow, and Mean Arterial Pressure.
In response to local heatHeatInflammation or cold: opening and closing the AV anastomoses allows for alterations in blood flowBlood flowBlood flow refers to the movement of a certain volume of blood through the vasculature over a given unit of time (e.g., mL per minute).Vascular Resistance, Flow, and Mean Arterial Pressure.
Arteriovenous anastomosis in the dermal layers of glabrous skin, allowing for increased blood flow without loss of heat in these areas NE: norepinephrine
A localized skinSkinThe skin, also referred to as the integumentary system, is the largest organ of the body. The skin is primarily composed of the epidermis (outer layer) and dermis (deep layer). The epidermis is primarily composed of keratinocytes that undergo rapid turnover, while the dermis contains dense layers of connective tissue.Skin: Structure and Functions response occurring in response to an allergen (e.g., allergyAllergyAn abnormal adaptive immune response that may or may not involve antigen-specific IgEType I Hypersensitivity Reaction testing and mosquito bites)
Mohrman, D. E., Heller, L. J. (2018). Overview of the cardiovascular system. Chapter 1 of Cardiovascular Physiology, 9th ed. McGraw-Hill Education. Retrieved November 16, 2021, from accessmedicine.mhmedical.com/content.aspx?aid=1153946098