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Questions and Answers
What is the daily secretion volume of bile from the liver?
What is the daily secretion volume of bile from the liver?
What role does bile play in fat digestion?
What role does bile play in fat digestion?
Which of the following substances is NOT excreted by bile?
Which of the following substances is NOT excreted by bile?
What is the main function of secretin in biliary secretion?
What is the main function of secretin in biliary secretion?
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What stimulates the gallbladder to empty its bile?
What stimulates the gallbladder to empty its bile?
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How is the concentrated bile in the gallbladder primarily formed?
How is the concentrated bile in the gallbladder primarily formed?
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What is the capacity of the gallbladder for bile storage?
What is the capacity of the gallbladder for bile storage?
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What secondary absorption occurs in the gallbladder following the active transport of sodium ions?
What secondary absorption occurs in the gallbladder following the active transport of sodium ions?
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What is one of the primary functions of bile salts in the digestive process?
What is one of the primary functions of bile salts in the digestive process?
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What is the result of bile salts being absent in the digestive system?
What is the result of bile salts being absent in the digestive system?
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Which of the following lipids are absorbed with the help of bile salts?
Which of the following lipids are absorbed with the help of bile salts?
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What could be a possible consequence of a high-fat diet over a prolonged period?
What could be a possible consequence of a high-fat diet over a prolonged period?
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What role does enterohepatic circulation play in the body?
What role does enterohepatic circulation play in the body?
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How does the quantity of fat consumed affect the composition of bile?
How does the quantity of fat consumed affect the composition of bile?
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What is primarily lost from the body when bile salts are not present?
What is primarily lost from the body when bile salts are not present?
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What physiological condition is linked to restricted bile flow?
What physiological condition is linked to restricted bile flow?
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Study Notes
Liver and Biliary Secretion
- Bile is secreted by the liver, approximately 600-1000 ml/day.
- Bile is stored in the gallbladder.
- Bile aids in fat digestion and absorption by emulsifying large fat particles into smaller ones.
- Bile aids in the absorption of digested fat end products through the intestinal mucosal membrane.
- Bile serves as a means for excretion of waste products such as bilirubin and cholesterol.
- Bilirubin is an end product of hemoglobin destruction.
- The gallbladder can hold up to 30-60 ml of bile, but in 12 hours, up to 450ml can be stored.
- Water, sodium, chloride, and other electrolytes are continually absorbed through the gallbladder mucosa.
- The end result of this absorption is concentrated bile.
- Gallbladder contraction and sphincter of Oddi relaxation are stimulated by CCK when fatty foods reach the duodenum about 30 minutes after a meal.
- The gallbladder is also stimulated less strongly by acetylcholine
Composition of Bile
- Bile is mostly water (97.5 g/dL in liver bile)
- Bile salts constitute approximately at 1.1 g/dL in liver bile and 6.0 g/dL in gallbladder bile
- Bilirubin accounts for approximately 0.04 g/dL in liver and 0.3 g/dL in gallbladder bile.
- Cholesterol is another component, ranging from 0.1 g/dL to 1.2 g/dl depending if it is from liver or gallbladder.
- Fatty acids have a wide range, from 0.12 g/dL in liver bile and between 0.3 and 1.2 depending on the measurement.
- Lecithin has 0.04 g/dl in liver bile and around 0.3 g/dl in gallbladder bile.
Biliary Secretion
- A second portion of liver secretion is added to the initial bile in the bile ducts.
- This additional secretion is a watery solution of Na and HCO3 ions.
- Epithelial cells line the ductules and ducts that secrete the solution.
- This additional secretion increases the total volume of bile by up to 100%.
- Secretion is stimulated by secretin, which releases more HCO3 ions to neutralize acid from the stomach that empties into the duodenum.
Biliary Secretion (Diagram)
- Bile ducts and small ducts carry bile from liver cells into the gallbladder or duodenum.
- The large ducts of the gallbladder and pancreas connect.
- The illustration shows the flow of bile.
Regulation of Biliary Secretion
- Bile acids stimulate the parathyroid secretion; for example, blood stream stimulates liver ducts.
- Vagal stimulation causes weak contraction of the gallbladder to secrete bile.
- Hormones in the blood, such as secretin and cholecystokinin, stimulate various secretion processes and contractions of the gallbladder and relaxation of the sphincter of Oddi.
Bile Salts
- Bile salts aid in fat digestion and absorption, forming micelles that emulsify fat globules into minute sizes.
- Bile salts also help absorb fatty acids, monoglycerides, cholesterol, and other lipids from the gastrointestinal tract.
Why Do We Need Bile?
- Bile is needed for fat digestion and absorption because without it, up to 40% of ingested fats could be lost in feces.
- Bile plays a key role in the absorption of fats, reducing the loss and thus preventing metabolic deficits and ensuring nutrient absorption.
- Bile salts are important in digestion, dissolving fat globules for better absorption, and in the excretion of cholesterol and bilirubin.
Enterohepatic Circulation
- The liver synthesizes bile salts which are stored in the gallbladder, secreted, and reabsorbed numerous times (enterohepatic circulation).
- About 3 grams of bile recirculates through the system in the pool, between 4 to 12 times daily.
- Bile salts are continually absorbed, reentering the systemic circulation through the liver to be recycled and reused.
Gross Anatomical Lobes
- The liver has right lobe, quadrate lobe, caudate lobe, and left lobe.
- The right lobe is the largest.
- The quadrate and caudate lobes are smaller.
- The left lobe is the smaller of the two main lobes. The liver shows different functional patterns.
Couinaud Segments
- The liver has functional segments (Couinaud segments) that have different functions and locations.
- Segments I, II, and III comprise the functional left lobe.
- Segments V, VI, VII, and VIII comprise the functional right lobe.
- Segment I is analogous to the caudate lobe, while IV is analogous to the quadrate lobe.
Blood Supply
- The liver receives blood from the hepatic artery (about 30%) and the portal vein (about 70%).
- The portal vein carries deoxygenated blood rich in nutrients from the digestive system to the liver.
Porta Hepatis
- Porta hepatis is an area of the inferior surface of the liver where the neurovascular and biliary structures enter and leave the liver, excluding hepatic veins.
- It's located between the quadrate lobe and the caudate process.
- Right and left hepatic ducts emerge from the porta hepatis region.
- Structures in this area are enveloped in a perivascular fibrous capsule (called Glisson's capsule).
Cells of the Liver
- The liver contains hepatocytes, hepatic stellate cells (Ito cells), sinusoidal endothelial cells, macrophages (Kupffer cells), and cells of the biliary tree (cuboidal to columnar epithelium).
- Connective tissue cells reside in the capsule and portal tracts.
Liver Functions
- Removing metabolic waste products, hormones, drugs, and toxins.
- Producing bile to aid in digestion.
- Processing nutrients absorbed from the digestive tract.
- Storing glycogen, certain vitamins, and minerals.
- Maintaining normal blood sugar.
- Synthesizing plasma proteins, albumin, and clotting factors.
- Producing immune factors and removing bacteria.
- Removing senescent red blood cells from circulation.
- Execreting bilirubin.
Liver Physiology
- The liver performs multiple functions, including protein metabolism, carbohydrate metabolism, lipid metabolism, bile secretion and bile acid metabolism, hormone and drug inactivation, and immunological function.
Protein Metabolism
- The liver is the primary site for synthesizing all circulating proteins, including albumin, globulins, and fibrinogen.
- Albumin functions to maintain intravascular oncotic pressure and carries water-insoluble substances.
- The liver produces proteins essential for blood clotting, components of the complement system, and stores vitamins.
Carbohydrate Metabolism
- The liver maintains blood glucose homeostasis.
- In fasting states, glucose is maintained by glycogenolysis (glycogen breakdown) or gluconeogenesis (glucose synthesis).
- Gluconeogenesis utilizes lactate, pyruvate, amino acids, and glycerol.
Lipid Metabolism
- Fats are transported in the plasma as protein-lipid complexes (lipoproteins).
- The liver plays a role in lipoprotein metabolism, synthesizing VLDLs and HDLs.
- Hepatic lipase converts VLDLs to LDLs, which are later degraded by the liver.
- Fatty acid oxidation occurs in the liver based on dietary fat availability.
Phase 1 & Phase 2 Liver Detoxification.
- Phase 1 detoxification adds or subtracts electrons to toxins to alter their electric charge.
- Phase 2 detoxifies by conjugating toxins to other molecules to make them soluble.
Drug Metabolism
- Most drugs undergo hepatic biotransformation in the liver, following two or three pathways.
- Phase I modifies active drug groups, Phase II conjugates metabolites to water-soluble substrates, and Phase III aids in excretion through hepatic blood flow or into the bile.
Hormone and Drug Inactivation and Immunological Function
- The liver is involved in the metabolism of hormones and drugs, transforming them into more easily excreted forms.
- The liver's reticuloendothelial system plays a vital role in immunity.
Blood-Cleansing
- Kupffer cells in the liver's sinusoids are part of the mononuclear phagocytic system.
- Liver Kupffer cells engage in phagocytosis, antigen processing, and mediator release.
- Liver Kupffer and endothelial cells remove bacteria & endotoxins from the portal circulation.
Other Information.
- The liver's anatomical structure is organized into hexagonal lobules, radiating from central veins to the periphery. Sinusoids are in between the hepatocyte rows.
- Substances from the gastrointestinal tract enter the portal vein and are delivered to the liver's sinusoids.
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