liver function

Question 1

what are the functions of the liver

Answer 1

• metabolism
• synthesis (plasma proteins, cholesterol, bile acids, urea)
• waste management
• +++

Question 2

What is the role of the liver in energy metabolism?

Answer 2

• Convert amino acids into energy (glycolysis)
• Store glucose as glycogen

Question 3

What are the liver enzymes involved in energy metabolism?

Answer 3

• Aspartate aminotransferase (AST)
• Alanine aminotransferase (ALT)

Question 4

What is the function of aspartate aminotransferase (AST) in energy metabolism in the liver?

Answer 4

Glycolysis
- Role in the malate-asparate shuttle
Aspartate can be converted to malate in a reversible reaction (intermediate = oxaloacetate)
- Malate is produced in the cytoplasm and then converted back to aspartate in the mitochondria
- Malate -> oxaloacetate in the mitochondria produces NADH
- NADH is then used to produce ATP by oxidative phosphorylation
- AST catalyses the conversion between aspartate and oxaloacetate

Question 5

What is the role of alanine aminotransferase (ALT) in energy metaolism in the liver?

Answer 5

Gluconeogenesis
- Amino acid catabolism
- Alanine reacts with alpha-ketoglutarate to form glutamate and pyruvate (catalyzed by ALT)
- Pyruvate can be used to produce glucose or enter the Kreb’s cycle

Question 6

How can liver enzymes be used to diagnose liver damage?

Answer 6

AST and ALT are only found in the blood when liver damage is present

Question 7

list plasma proteins made by the liver

Answer 7

• serum albumin (highly abundant carrier protein that maintains osmotic pressure)
• very low density lipoprotine
• high density lipoprotein
• fibrinogen
• prothrombin
• trasnferrin
• complement proteins

Question 8

what is important about hypoalbuminemia

Answer 8

albumin synthesized exclusively by hepatocytes BUT
hypoalbuminemia is not specific for liver disease as can be low in cases of malnutrition etc

Question 9

what do lipoproteins do

Answer 9

move insoluble fat around
- triglycerides
- phospholipids
- cholesterol esters

Question 10

lipoproteins are linked to which kind of protein

Answer 10

apolipoproteins

Question 11

what are the functions of apolipoproteins

Answer 11

• activate enzymes
• bind receptors
• stabilise lipoprotein

Question 12

Describe the synthesis of cholesterol in the liver

Answer 12

1. Acetyl-CoA + actetoacetyl-CoA
2. Carbon chain lengthens
3. Decarboxylation => cholesterol
4. Cholesterol can then be converted to bile salts in the liver or moved to endocrine glands to become steroid hormones

Question 13

How are bile salts formed in the liver?

Answer 13

• Bile acids are cholesterol derivatives
• Cholic acid (main bile acid) conjugates with amino acids to reduce the pK (reduce acidity) of amino acids so they exist in ionised forms as bile salts

Question 14

what are micelles in the liver

Answer 14

• bile salts in aqueous solution tend to form aggregates or micelles
• amphiphilic (+ve inside, -ve outside)
• bile salts are conjugated with cholesterol and phospholipids
• the -ve external charge prevents them from coalescing

Question 15

what is the purpose of bile

Answer 15

• acts as a detergent to emulsify fats (increases their surface area by breaking them into small bits)
• emulsification occurs by associating the hydrophobic side with lipids and the hydrophilic side with water. since the bile increases the absorption of fats it is an important part of the absorption of fat soluble vitamins (A, D, E and K)
• phospholipids are hydrolysed by pancreatic phospholipase A2 and cholesterol by esterase

Question 16

Describe the route of bile acids

Answer 16

• Absorbed in ileum
• travel to liver via hepatic portal vein
  conjugate with cholesterol to form conjugated bile acids
• travel to gall bladder then into the duodenum where they cause fat absorption
• travel down to ileum and reabsorbed

Question 17

How is fat absorbed in the small intestine?

Answer 17

• Bile salts and pancreatic lipase break large fat droplets down
• Micelles formed as bile salts form aggregates, conjugated with phospholipids and cholesterol
• Micelles release into epithelial cells/enterocytes
• Free fatty acids and monoglycerides within mycelle diffuse into enterocyte
• Triglycerides resynthesised and chylomicrons formed in enterocyte (chylomicrons are exocytosed into lymph vessel)

Question 18

Describe the detoxification of foreign chemicals in the liver

Answer 18

2 phases:
phase 1 = relies on cytochrome P450 to modify the chemical
phase 2 = conjugation reactions

Question 19

how does the liver manage endogenous waste

Answer 19

Bilirubin Metabolism: Converting heme breakdown products to conjugated bilirubin for excretion.
Ammonia Detoxification: Converting ammonia to urea via the urea cycle.
Hormone Metabolism: Inactivating and excreting hormone metabolites.
Detoxification of Metabolic Intermediates: Converting lactate and ketone bodies to usable forms or excreting them.
Handling ROS: Using antioxidants to neutralize reactive oxygen species.
Autophagy: Recycling cellular components through autophagic processes.

Question 20

Describe the role of the liver in the detoxification of endogenous and exogenous substances. Include specific examples of how the liver processes hormones and drugs.

Answer 20

The liver detoxifies hormones such as insulin and glucagon by breaking them down. It also metabolizes drugs through the cytochrome P450 enzyme system, converting lipophilic substances into more water-soluble forms for excretion.

Question 21

Explain the process by which the liver converts ammonia to urea. Why is this process important for the body?

Answer 21

The liver converts ammonia to urea via the urea cycle, involving enzymes such as carbamoyl phosphate synthetase. This process is crucial to prevent ammonia toxicity.

Question 22

Discuss the role of the liver in protein synthesis. Identify at least three types of plasma proteins synthesized by the liver and their functions.

Answer 22

the liver synthesizes albumin (maintains oncotic pressure), clotting factors (e.g., fibrinogen for coagulation), and transport proteins (e.g., transferrin for iron transport).

Question 23

Explain the processes of deamination and transamination in the liver. How do these processes contribute to amino acid metabolism?

Answer 23

Deamination removes amino groups from amino acids, producing ammonia, while transamination transfers amino groups to form new amino acids. These processes help in amino acid catabolism and synthesis.

Question 24

Describe the urea cycle and its significance in amino acid metabolism. What are the consequences of urea cycle disorders?

Answer 24

The urea cycle converts toxic ammonia into urea for excretion by the kidneys. Disorders in this cycle can lead to hyperammonemia, causing neurological damage.

Question 25

Outline the steps involved in the de novo synthesis of cholesterol in the liver. What role does HMG-CoA reductase play in this pathway?

Answer 25

Cholesterol synthesis in the liver starts with acetyl-CoA and involves several steps, with HMG-CoA reductase being the rate-limiting enzyme.

Question 26

Explain how the liver regulates cholesterol levels in the body. Include the roles of synthesis, uptake, and excretion.

Answer 26

The liver regulates cholesterol levels by synthesizing cholesterol, taking up LDL from the blood, and excreting cholesterol in bile. Statins inhibit HMG-CoA reductase to lower cholesterol levels.

Question 27

Describe the liver’s role in lipid metabolism, including the synthesis and transport of lipoproteins. How do VLDL, LDL, and HDL differ in their functions?

Answer 27

The liver synthesizes VLDL to transport triglycerides, LDL to deliver cholesterol to cells, and HDL to transport cholesterol back to the liver for excretion.

Question 28

Explain the liver’s role in glycogen storage and release. How does the liver maintain blood glucose levels through glycogenesis and glycogenolysis?

Answer 28

The liver stores glucose as glycogen (glycogenesis) and breaks it down to release glucose (glycogenolysis), maintaining blood glucose levels during fasting and feeding.

Question 29

Describe the composition and function of bile produced by the liver. How is bile involved in the digestion and absorption of fats?

Answer 29

Bile contains bile acids, bilirubin, cholesterol, and phospholipids. It emulsifies fats, aiding in their digestion and absorption in the intestine.

Question 30

Discuss the immune function of the liver, focusing on the role of Kupffer cells. How do these cells contribute to the body's defense mechanisms?

Answer 30

Kupffer cells are liver macrophages that phagocytose pathogens, dead cells, and debris, playing a crucial role in immune surveillance and response.

Question 31

List and describe five key substances synthesized by the liver. What are their primary functions in the body?

Answer 31

The liver synthesizes albumin (oncotic pressure), clotting factors (coagulation), bile acids (fat digestion), lipoproteins (lipid transport), and glucose (gluconeogenesis).

Question 32

Explain the process of gluconeogenesis in the liver. Which substrates can be used by the liver to produce glucose during fasting?

Answer 32

During fasting, the liver produces glucose from non-carbohydrate sources like amino acids, glycerol, and lactate through gluconeogenesis.

Question 33

Discuss the importance of the liver in vitamin storage. Which vitamins are stored in the liver, and what are their roles in the body?

Answer 33

The liver stores vitamins A, D, E, K (fat-soluble) and B12 (water-soluble), essential for vision, bone health, antioxidant function, blood clotting, and neurological function, respectively.