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Questions and Answers
Which factor most directly decreases hepatic blood flow?
Which factor most directly decreases hepatic blood flow?
Which statement regarding liver reserves is accurate?
Which statement regarding liver reserves is accurate?
What is a primary function of Kupffer cells in the liver?
What is a primary function of Kupffer cells in the liver?
Which condition is most likely to cause hepatomegaly?
Which condition is most likely to cause hepatomegaly?
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In the context of liver function, what is a significant impact of positive pressure ventilation?
In the context of liver function, what is a significant impact of positive pressure ventilation?
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Which zone of the liver acinus is most susceptible to ischemic injury?
Which zone of the liver acinus is most susceptible to ischemic injury?
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What is the primary function of liver sinusoidal endothelial cells?
What is the primary function of liver sinusoidal endothelial cells?
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Which component of the portal triad is responsible for transporting nutrients from the gastrointestinal tract?
Which component of the portal triad is responsible for transporting nutrients from the gastrointestinal tract?
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What is the primary function of Kupffer cells in the liver?
What is the primary function of Kupffer cells in the liver?
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What percentage of resting cardiac output is attributed to hepatic blood flow?
What percentage of resting cardiac output is attributed to hepatic blood flow?
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In which zone of the liver acinus does gluconeogenesis primarily occur?
In which zone of the liver acinus does gluconeogenesis primarily occur?
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What structures surround bile canaliculi in the liver lobules?
What structures surround bile canaliculi in the liver lobules?
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What is the primary function of the Space of Disse in the liver?
What is the primary function of the Space of Disse in the liver?
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What is the primary function of the portal vein in hepatic circulation?
What is the primary function of the portal vein in hepatic circulation?
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Which statement accurately describes the hepatic artery's function in relation to the liver?
Which statement accurately describes the hepatic artery's function in relation to the liver?
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What is the effect of sympathetic stimulation on hepatic blood flow?
What is the effect of sympathetic stimulation on hepatic blood flow?
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How does the hepatic artery buffer response function during changes in portal flow?
How does the hepatic artery buffer response function during changes in portal flow?
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What is a consequence of portal hypertension?
What is a consequence of portal hypertension?
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Which function is NOT associated with the liver?
Which function is NOT associated with the liver?
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What role do adenosine levels play in hepatic blood flow regulation?
What role do adenosine levels play in hepatic blood flow regulation?
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What is the primary effect of beta-2 receptor stimulation in the liver?
What is the primary effect of beta-2 receptor stimulation in the liver?
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Which of the following describes a change seen in cirrhosis?
Which of the following describes a change seen in cirrhosis?
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What is a common cause of Hepatitis B transmission?
What is a common cause of Hepatitis B transmission?
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Which zone of the liver acinus is primarily responsible for gluconeogenesis?
Which zone of the liver acinus is primarily responsible for gluconeogenesis?
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What is the main function of the liver sinusoidal endothelial cells?
What is the main function of the liver sinusoidal endothelial cells?
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Hepatic circulation accounts for what percentage of resting cardiac output?
Hepatic circulation accounts for what percentage of resting cardiac output?
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Which component of the portal triad does NOT contribute to blood oxygenation in the liver lobules?
Which component of the portal triad does NOT contribute to blood oxygenation in the liver lobules?
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In the liver acinus, which zone is most susceptible to ischemic injury?
In the liver acinus, which zone is most susceptible to ischemic injury?
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What is the primary role of Kupffer cells in liver function?
What is the primary role of Kupffer cells in liver function?
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Which statement accurately describes the function of the Space of Disse in the liver?
Which statement accurately describes the function of the Space of Disse in the liver?
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Cirrhosis can negatively impact which organ system due to portal hypertension?
Cirrhosis can negatively impact which organ system due to portal hypertension?
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What factor is most closely associated with decreased hepatic perfusion pressure?
What factor is most closely associated with decreased hepatic perfusion pressure?
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Which function does the liver perform related to blood storage?
Which function does the liver perform related to blood storage?
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Which statement accurately characterizes the regenerative capacity of the liver?
Which statement accurately characterizes the regenerative capacity of the liver?
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Which condition is likely to contribute to hepatomegaly through changes in liver hemodynamics?
Which condition is likely to contribute to hepatomegaly through changes in liver hemodynamics?
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What is the primary impact of sympathetic nervous system (SNS) stimulation on hepatic blood flow?
What is the primary impact of sympathetic nervous system (SNS) stimulation on hepatic blood flow?
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What percentage of the liver's oxygen requirements is supplied by the hepatic artery?
What percentage of the liver's oxygen requirements is supplied by the hepatic artery?
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Which factor contributes to increased hepatic blood flow during sympathetic stimulation?
Which factor contributes to increased hepatic blood flow during sympathetic stimulation?
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Which statement accurately describes the flow of blood through the liver?
Which statement accurately describes the flow of blood through the liver?
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What is the primary purpose of the hepatic artery buffer response?
What is the primary purpose of the hepatic artery buffer response?
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Which condition is least likely to interfere with the hepatic artery buffer response?
Which condition is least likely to interfere with the hepatic artery buffer response?
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What role does adenosine play in the regulation of hepatic blood flow?
What role does adenosine play in the regulation of hepatic blood flow?
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What is a primary effect of beta blockers on hepatic circulation?
What is a primary effect of beta blockers on hepatic circulation?
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Which hepatic blood supply pathway originates from the SMA and IMA?
Which hepatic blood supply pathway originates from the SMA and IMA?
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Which physiological change can cause decreased hepatic blood flow?
Which physiological change can cause decreased hepatic blood flow?
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How is hepatic venous drainage primarily achieved?
How is hepatic venous drainage primarily achieved?
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Study Notes
Liver Sinusoidal Endothelial Cells
- Interface between blood cells, hepatocytes and stellate cells
- Permeable barrier
- Regulation of hepatic vascular tone
Liver Lobules
- Anatomic unit of the liver
- 50,000 - 100,000 lobules per liver
- Each lobule contains a portal triad, plate of hepatocytes, and a central vein (CV)
- Blood flows from aorta (HA) and GI tract (PV) into sinusoids
- Blood mixes in the sinusoids
- Sinusoid lining has large pores allowing plasma and proteins to flow into the Space of Disse
- Space of Disse is where blood is cleaned, filtered, and excess fluid and waste products are drained via the lymphatic duct
- Space of Disse is located between sinusoidal capillaries and hepatocytes
- Contains stellate cells with vitamin A and Kupffer cells (filter)
Liver Acinus
- Functional unit of the liver
- Zone 1: periportal
- Hepatocytes are closest to blood supply, well oxygenated
- Responsible for 'high' oxidative activities: gluconeogenesis, oxidation of fatty acids, cholesterol synthesis, bile production
- Zone 2: midzone
- Centrally-located hepatocytes
- Zone 3: perivenous or pericentral
- Hepatocytes are furthest from blood supply, closer to central veins
- Most susceptible to ischemic injury
- Responsible for glycolysis, lipogenesis, detoxification, and biotransformation of drugs
Hepatic Blood Flow
- 25% of resting cardiac output (800-1200 ml/min)
- Total hepatic blood flow = portal vein blood flow + hepatic artery blood flow
- Maintains oxygen supply to the liver
- Portal venous changes do not affect the liver's ability to function
Extrinsic Determinants of Hepatic Blood Flow
- Hepatic perfusion pressure: MAP - Hepatic Vein Pressure
- Splanchnic Vascular Resistance: splanchnic vessels innervated by the SNS
- SNS stimulation increases splanchnic vascular resistance, decreasing hepatic blood flow
Hepatic Blood Flow is Reduced With:
- Anything that stimulates the SNS: pain/surgical stimulation, hypoxia, increased catecholamines, volatile anesthetics, regional anesthesia, positive pressure ventilation, excess fluid administration, insufflation
Functions of the Liver
- Body's "chemical factory" - estimated 500 separate functions
- Liver has substantial reserves, can lose 80% and still maintain normal function
- Liver regenerates
- Filtration and storage of blood:
- Liver normally stores 450 ml of blood
- Liver is expandable and can store up to 1L as a reservoir in hypervolemia (excess IVFs, renal and heart failure)
- Moderates hypotensive response to hemorrhage/hypovolemia
- Forms 50% of body's lymph
- Kupffer cells are effective phagocytic macrophages
Dual Afferent Blood Supply
- Hepatic artery:
- Arises from celiac artery (80% of the time) or SMA (20% of the time)
- Pressure = aortic pressure (90 mmHg)
- 25-30% of blood supply
- 50-70% of oxygen requirements
- Portal vein:
- Drains from GI tract, rich in nutrients and bacteria
- Arises from SMA, IMA, and aorta
- Pressure is lower (6-10 mmHg)
- 70-75% of blood supply
- 30-50% of oxygen requirements
How does blood exit the liver?
- Hepatic veins → IVC
Sympathetic Stimulation
- Increases hepatic artery vasoconstriction and vasoconstriction of splanchnic circulation (end result: decreased hepatic blood flow)
- Beta-2 stimulation → vasodilation, relaxation of smooth muscle, relaxation of GI smooth muscle, increases liver's ability to make glucose, increases hepatic blood flow via vasodilation of hepatic artery
- Beta blockers → reduce hepatic artery blood flow and decrease portal pressure
- Vasopressin → reduces splanchnic blood flow and decreases portal venous pressure
Intrinsic Determinants of Hepatic Blood Flow
- Hepatic artery buffer response:
- Adjusts to changes in portal flow, mediated by adenosine
- Hepatic artery flow can increase as much as 100% to maintain oxygen delivery
- Decrease in portal vein flow → low pH, low CO2, elevated CO2, increased adenosine, hepatic artery vasodilates
- Volatiles and cirrhosis interfere with this response
- Portal vein does NOT compensate for changes in hepatic artery supply
Liver Sinusoidal Endothelial Cells
- Interface between blood cells and hepatocytes and stellate cells
- Permeable barrier
- Helps regulate hepatic vascular tone
Liver Lobules
- Anatomic unit of the liver
- Liver consists of 50,000 to 100,000 lobules
- Each lobule is composed of:
- Portal triad:
- Branch of hepatic artery
- Branch of portal vein
- Bile ducts
- Plate of Hepatocytes
- Central Vein (CV)
- Portal triad:
- Each lobule is constructed around a central vein; cellular plates radiate from the central vein like spokes on a wheel
- Cellular plates surround bile canaliculi, which empty into the bile duct
- Blood flows into sinusoids, where it mixes, and then into the Space of Disse; the lining of the sinusoids contain large pores allowing free passage of plasma and proteins
- Space of Disse:
- Between sinusoidal capillaries and hepatocytes
- Nutrient exchange (contains stellate cells with vitamin A)
- Kupffer cells (filter)
- Blood exits the central vein, then the hepatic vein, then the IVC, and finally, the RA
Liver Acinus
- Functional unit of the liver
- Zone 1 (periportal):
- Hepatocytes closest to blood supply (well-oxygenated)
- Responsible for 'high' oxidative activities - gluconeogenesis, oxidation of fatty acids, cholesterol synthesis, and bile formation
- Zone 2 (midzone):
- Centrally-located hepatocytes
- Zone 3 (perivenous or pericentral):
- Hepatocytes furthest away from blood supply (closer to central veins)
- MOST susceptible to ischemic injury
- Responsible for glycolysis, lipogenesis, detoxification, and biotransformation of drugs
Hepatic Blood Flow
- 25% of resting cardiac output (800-1200 ml/min)
- Total hepatic blood flow = portal vein blood flow + hepatic artery blood flow
- Two main purposes:
- Maintain oxygen supply to the liver
- Provide all the services to the rest of the body
Extrinsic Determinants of Hepatic Blood Flow
- Hepatic perfusion pressure:
- Calculated by MAP - Hepatic Vein Pressure
- OR
- Splanchnic Vascular Resistance
- Splanchnic vessels are innervated by the SNS
- SNS stimulation increases splanchnic vascular resistance and decreases hepatic blood flow
- Hepatic blood flow is reduced by anything that stimulates the SNS:
- Pain and/or surgical stimulation
- Hypoxia
- Increased catecholamines
- Volatile anesthetics and regional anesthesia
- Positive pressure ventilation
- Excess fluid administration
- Insufflation
Functions of the Liver
- The liver is the body's "chemical factory" - estimated 500 separate functions to maintain homeostasis
- The liver has substantial reserves; you could lose 80% of the organ and still maintain normal function, and it can regenerate.
- Filtration and storage of blood:
- The liver normally stores approximately 450 ml of blood.
- The liver is expandable and can store up to 1 L, acting as a reservoir in hypervolemia (excess IVFs, renal and heart failure)
- This explains why we see hepatomegaly in CHF
- Moderates hypotensive response to hemorrhage/hypovolemia
- Forms approximately 50% of the body's lymph
- Kupffer cells are effective phagocytic macrophages
Dual Afferent Blood Supply
- Hepatic artery:
- Arises from the celiac artery (80% of the time) or SMA (20% of the time)
- Pressure = aortic pressure (90 mmHg)
- 25 - 30% of blood supply
- 50 - 70% oxygen requirements
- How is this different from other organs? Most organs receive all oxygen from the arterial supply.
- Why? Because not all of the blood going to the liver is there to provide oxygen/nutrients to the organ itself.
- Portal vein:
- Drains from the GI tract, rich in nutrients and bacteria
- Arises from the SMA, IMA, and aorta
- Lower pressure (6 - 10 mmHg)
- 70 - 75% of blood supply
- 30 - 50% of oxygen requirements
- This blood is lower in oxygen content but high in substances that must be transformed into a usable form or eliminated
How does blood exit the liver?
- Hepatic veins to IVC
Sympathetic Stimulation
- Increases hepatic artery vasoconstriction and vasoconstriction of splanchnic circulation → decreased hepatic blood flow
- Beta-2 stimulation:
- Vasodilation
- Relaxation of GI smooth muscle → increases the liver's ability to make glucose and increases hepatic blood flow via vasodilation of the hepatic artery
- Beta receptors are only in the hepatic artery (not the portal vein) → beta-2 stimulation does not change portal venous supply
- Beta blockers reduce hepatic artery blood flow and decrease portal pressure
- Vasopressin reduces splanchnic blood flow and decreases portal venous pressure
Intrinsic Determinants of Hepatic Blood Flow- Hepatic Artery Buffer Response
- In addition to "classic arterial autoregulation" where changes in blood pressure cause constriction or dilation of the hepatic artery, the liver can regulate its own blood supply via the hepatic artery with the hepatic artery buffer response.
- Hepatic artery tone adjusts to changes in portal flow, mediated by adenosine.
- Hepatic artery flow can increase as much as 100% to maintain oxygen delivery to the liver.
- Decrease in portal vein flow → low pH, low CO2, elevated CO2 → increased adenosine → hepatic artery vasodilates.
- Volatiles and cirrhosis interfere with this response (but it does work during laparoscopic cases)
- Portal vein does NOT compensate for changes in hepatic artery supply.
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Description
Test your knowledge on liver anatomy and the roles of liver sinusoidal endothelial cells, liver lobules, and the liver acinus. This quiz covers the functional units of the liver and their significance in hepatic physiology. Understand the complex interactions within the liver's structure and its vascular system.
