Lecture 1: Liver Anatomy and Physiology Flashcards
Describe the general anatomy of the liver… lobules etc
8 Segements made into lobules
Each lobule is represented as a hexagonal cluster of hepatocytes which is connected to a central vein, hepatic portal vein, bile duct, hepatic artery.
Draw a diagram of a liver lobule labelled correctly
Lecture slides
Describe AND draw a flow diagram of the DUAL blood flow through the liver and Bile flow
Blood is conveyed to the lobules by branches of the hepatic portal vein and the hepatic artery.
It then flows through sinuses, bathing the hepatocytes, to the central vein of the lobule, a branch of the Hepatic vein which drains into the Inferior Vena Cava.
The hepatocytes secrete bile into bile canuliculi running between the hepatocytes, and these drain into branches of the bile duct.
Refer to lecture slides for diagram
What is the challenge with liver cells
Lonely cells, very temperamental when outside the body
Cells die immediately and function is lost in order of hours.
What are the cells that reside in the liver?
hepatocyte
stellate fat storing cell
Kupffer cell
liver endothelial cell
Describe/explain hepatocyte cell functions
Also called parenchymal cells.
Make up 70 to 80 percent of the liver’s cytoplasmic mass.
Are involved in synthesizing protein, cholesterol, bile salts, fibrinogen, phospholipids and glycoproteins.
Describe/explain endothelial cell functions
Transportation of WBC and increasing immune tolerance.
Secrete cytokines, which is a forem of cellular communication signal.
Describe/explain kupffer cell functions
Reticuloendothelial cells of the liver
Secrete mediators of immune response system
Phagocytize bacteria, foreign material
Blood flowing through intestinal capillaries picks up many bacteria in intestines
Describe/explain stellate cell functions
Exist in the space between parenchymal cells and sinusoidal endothelial cells
Vitamin A-storing cells, lipocytes, interstitial cells, fat-storing cells, promote ion movement and proliferation of chemical responses to stress.
General functions of liver
Production of bile
Production of cholesterol, carbohydrate, proteins
Regulate blood levels of amino acids
Processing of haemoglobin for use of its iron content
Conversion of ammonia to urea
Detoxification of drugs
Regulate blood clotting
What is Carbohydrate Metabolism regulation?
storage of glycogen
gluconeogenesis site
role in glucose homeostasis.
What is Fat Metabolism regulation?
The liver is central to the processing of dietary fats to lipoproteins
What is Protein Metabolism regulation?
De-animation of amino acids
What is the function of protein metabolism?
Deamination of amino acids, conversion of the non-nitrogenous part of those molecules to glucose or lipids.
Formation of urea for removal of ammonia from the body fluids
Formation of plasma proteins – not gamma globulins
Interconversions of the various amino acids and synthesis of other compound from amino acids
What is the function of proteins metabolism? IN HEPATIC DISEASE
Ammonia detoxification disorder and failure of urea formation
(ammonia comes from bacterial degradation of nitrogen substances in intestines, from intestine mucosa during glutamine degradation, from degradation of amino acids in kidneys and muscles)
Hyperamonemia
increase of ammonia blood concentration (>50 μmol/l)
Hepatic encephalopathy Toxic effect of ammonia in the brain (Binding of ammonia to glutamate = glutamine) Mental changes (capriciousness, disorientation, sleeping disorders, chaotic speech, personality changes) Motoric changes (increased in muscle reactivity, hyperreflexion, tremor)
Hepatic coma to death
Endogenous = viral hepatitis and poisoning (hepatic cells desintegration)
Exogenous = final status of chronic cirrhosis (ammonia and other toxic substances bypass the liver through the extrahepatic anastomoses)
Draw the diagram of Liver and Amino acid metabolism
Lecture slides
Function of carbohydrate metabolism
Storage of glycogen
Glucose buffer function = removing excess of glucose from blood, storage, fast return when the blood concentration decreases
Conversion of galactose/fructose to glucose
What is glycogenolysis, glycogenesis, gluconeogenesis?
glycogenesis:
Excess glucose entering the blood after a meal is rapidly taken up by the liver and sequestered as the large polymer, glycogen
glycogenolysis:
When blood concentrations of glucose begin to decline, the liver activates other pathways which lead to depolymerization of glycogen to glucose
gluconeogenesis:
Synthesizing glucose out of such things as amino acids and non-hexose carbohydrates
Carbohydrate metabolism in hepatic disease
Hyperglycaemia:
in patients with cirrhosis after carbohydrate rich meal.
liver insufficiency → decrease of glucose utilization → hyperglycemia → hyperinsulinemia → down-regulation of insulin receptors → insulin resistance
Hypoglycemia in alcohol abusers – alcohol suppresses citrate cycle and thereby impairs gluconeogenesis from amino acids. After depletion of glycogen storages comes hypoglycemia that threatens the patient’s life
Fat metabolism function
Oxidation of fatty acids to supply energy for other body function
Synthesis of large quantities of cholesterol (80% of cholesterol synthesized in the liver is converted into bile salts), phospholipids, and most lipoproteins
Inactivation of steroids and their excretion of the body
Synthesis of lipoproteins, fat from proteins and carbohydrates
Remainder is excreted in bile as cholesterol or after conversion to bile acids.
In bile formation there are two stages of secretion.
Initial portion is from hepatocytes (contains bile acids, cholesterol, organic constituents).Mostly bile acids
Additional secretion is a watery solution of sodium and bicarbonate – secreted by secretory epithelial cells lining the ductules and ducts. Neutralising gastric acid
Bile composition
Water, electrolytes, cholestrol, phospholipids, bile acids, bilirubin
Bile acid purpose
- Fat emulsifation/absorption
2. Neutralisation of gastric acid
what controls bile secretions?
Cholecystokinin (CCK)
Most potent stimulant for bile secretion
Stimulus for release = fat in duodenum
Secretin
Stimulated in response to acid in duodenum
Stimulates bile duct (and pancreas) to secrete bicarb and H20
Expands volume of bile and bile flow increases
Acetylcholine secreting nerve fibers
Not as potent, from vagi and enteric nervous system
ie smell food gastric system kicks in and pH drops, releases bicarbonate
Process of Haem elimination
To be eliminated haem is changed to bilirubin in phagocytic cells, bound to albumin
Stripped off albumin in hepatocytes
Conjugated by addition of glucouronic acid
Excreted in stool as sterobilin
Purpose of bile acids
Synthesized in the liver from cholesterol
Critical for absorption of fats and vitamins
Composition depends on species, but must be conjugated to taurine or glycine to be excreted
Is cholesterol made into bile acids?
Yes.
When fat is consumed this is taken into as bile and this bile goes to the liver. Bile emulsifies the fat. Without Bile acids fat can not be transported to liver or absorbed in the body
Bile in enterohepatic recirculation
95% bile acids are reabsorbed in ileum and circulated back to liver
Hepatocytes reabsorb essentially all bile acids in portal vein in healthy situation
In hepatocyte disease – decreased ability of cells to extract bile acids from portal system
Canilicular disease can result in leakage of bile acids back into systemic circulation
In shunting, bypass hepatocytes so don’t get reabsorbed and are elevated in systemic circulation (into blood system)
