The Liver Flashcards
What are the two major vessels that supply the liver
Hepatic artery and hepatic portal vein
Describe the movement of blood in the liver
High blood flow and low vascular resistance
What does the hepatic portal vein carry
Water soluble products of digestion absorbed from enterocytes into the villi capillaries
What is the basic functional unit of the liver
The liver lobule
Describe the structure of a lobule
Consists of hepatic cellular plates (2 cells thick) and has a central vein ( branch of hepatic vein carrying blood to vena cava) in centre, blood flows between hepatocytes from HPV via sinusoids (capillaries) and small bile canaliculi that empty in to bile ducts lie between adjacent cells
What is a triad in a lobule
At the corner of each lobule a triad of 3 vessels exist as branches of the portal vein, hepatic artery and bile duct
What are Kupffer cells
Macrophages within the liver
What are the 3 main types of cells that the liver consists of
Hepatocytes, endothelial cells and kupffer cells
What is the function of the liver
Energy metabolism and storage
What 8 processes are controlled by the liver
Glycogenesis, gkycogenolysis, gluconeogenesis, lipogenesis, lipolysis, transanimation and deanimation and excretion
Why must the liver maintain a store of glucose (glycogen store)
Glucose cannot be synthesised directly from fat stores in the liver
How does circulating glucose enter liver cells
GLUT-2 glucose transporter
How is glucose store in cells
As granules
How are TAG carried in the blood
Hydrophobic so carried as lipoproteins (bound to protein albumin)
What are drawbacks of glucose and protein storage
Carry large weight penalty
What is the rate of glucose turnover
2mg/kg/min
What is the rate of fatty acid turnover
1.7 mg/kg/min
How much energy does glucose yield (kJ/g)
17
How much energy does fatty acids yield (kJ/g)
38
What % of total contribution to energy is from glucose
32%
What % of total contribution to energy is from fatty acids
66%
What hormones are released from the pancreas into the hepatic portal vein
Insulin and glucagon
When is insulin released from the pancreas
When plasma glucose is above 5mmol/L
What does the binding of insulin to the receptors on liver cell membranes stimulate
Glycogenesis, lipogenesis
What is the function of glucagon
Elevate blood glucose when lower than 3 mmol/L by glycogenolysis in the liver
What is the role of cortisol in liver function
Released from adrenal glands to stimulate liver gluconeogenesis so more blood glucose for brain
What is the role of adrenaline (epinephrine) in liver function
Released form adrenal glands to stimulate glycogenolysis and lipolysis
What are the 3 main ways glucose enters the blood stream
Absorption from small intestine (SGLUT1, GLUT2), glycogenolysis and gluconeogenesis in the liver
What is gluconeogenesis
Synthesis of glucose from other precursors (amino acids, lactate and glycerol to maintain supply to brain
What is lipolysis
Beta-oxidation of fatty acid
What is de novo lipogenesis
Synthesis of endogenous TAG exported from liver into plasma as VLDL lipoproteins (adipose)
How does the liver play a role in protein metabolism
First organ to receive dietary amino acids via hepatic portal vein and only organ capable of eliminating nitrogen from amino acids (deanimation/ eliminating amine group) to form ammonia and synthesis urea
What hormone activates amino acid transporters to increase uptake
Glucagon
What happens in the liver when we exercise
Increased glycogenolysis and gluconeogenesis
Increased adipose tissue lipolysis and FFA mobilisation
What happens to insulin and glucagon concentrations during exercise
Insulin falls so the glucagon to insulin ratio rises
What is effect of an increased glucagon/insulin ratio during exercise
Adipose tissue releases fatty acid transporters (oxidation of fatty acids for local energy demands)
What happens to protein during exercise
Increased protein breakdown from skeletal muscle or GI tract, so more AA is circulation as minor direct fuel for muscle (recycled in liver to make glucose)
What happens to the associated nitrogen in broken down proteins when AA are recycled in the liver to make glucose during exercise
Converted and excreted as urea via kidney
Why is liver metabolism not dominant during exercise
Reduced blood flow to liver
What are the adaptations of the liver to exercise training
More effective at fat utilisation for fuel
Reduces liver fat content
How can the liver synthesis cholesterol (endogenous cholesterol)
From multiple molecules of acetyl-CoA
What are bile salts composed of
Bile acids, phosphatidylcholine and cholesterol
How are bile salts synthesised in the liver
Cholesterol is converted into cholic acid and chenodeoxyxholic acid (primary bile acids) in hepatocytes, primary bile acids ar conjugated to glycine or taurine
Describe active reuptake of conjugated bile salts
In the terminal ileum via sodium dependent bile salt transporter into the portal vein to hepatocytes
Describe lipoprotein synthesis
Remaining cholestrol synthesised in liver and phospholipids synthesised in the liver is incorporated into lipoproteins
How are lipoproteins transported
Via blood to peripheral cells
What are the functions of phospholipids
-lipoprotein synthesis and lipid transport in blood
- membrane structure
- thromboplastin synthesis
- Sphingomyelin synthesis
What are the other metabolic functions of the liver
Storage of vitamins A, D and B12
Storage of iron
Synthesis of blood clotting proteins
Detoxification
Hormone excretion
