liver

Question 1

excretion

Answer 1

removal of waste products of metabolism from the body

Question 2

what are the main metabolic waste products in mammals

Answer 2

• carbon dioxide
• bile pigments formed from breakdown of haemoglobin from old RBCs in liver and excreted in bile into small intestine via gall bladder and bile duct
• nitrogenous waste products (urea) formed from breakdown of excess amino acids in liver

Question 3

liver description

Answer 3

• major body organs in homeostasis
• reddish-brown organ
• makes up about 5% of total body mass
• largest internal organ
• lies just below diaphragm and made of several lobes
• liver is fast growing and damaged areas generally regenerate very quickly

Question 4

how is blood supplied to liver

Answer 4

• liver has very rich blood supply - 1dm^3 flows through it every minute
• oxygenated blood is supplied via hepatic artery
• blood removed from liver and returned to heart in hepatic vein
• liver is supplied with blood by second vessel - hepatic portal vein
• this carries blood loaded with products of digestion straight from intestines to liver and is starting point for many metabolic activities of liver
• up to 75% of blood flowing through liver comes via hepatic portal vein

Question 5

hepatocytes

Answer 5

• liver cells
• have large nuclei, prominent Golgi apparatus, lots of mitochondria
• metabolically active cells
• they divide and replicate- even if 65% of the liver is lost, it will regenerate in months

Question 6

sinusoids

Answer 6

• where the blood from hepatic artery and hepatic portal vein is mixed
• surrounded by hepatocytes
• mixing increases oxygen content of blood from hepatic portal vein, supplying the hepatocytes with enough oxygen for their needs

Question 7

Kupffer cells

Answer 7

• in sinusoids
• act as resident macrophages of the liver
• they ingest foreign particles and help protect against disease

Question 8

canaliculi

Answer 8

• hepatocytes secrete bile from breakdown of blood into these spaces
• from these canaliculi, the bile drains into the bile ductules which take it to the gall bladder

Question 9

central vein

Answer 9

blood flows from here into hepatic vein

Question 10

liver carbohydrate metabolism

Answer 10

• hepatocytes closely involved in homeostatic control of glucose levels in blood by their interaction with insulin and glucagon
• it stores glucose as glycogen
• when blood glucose levels rise, insulin levels rise and stimulate hepatocytes to convert glucose to glycogen
• when blood sugar levels fall, hepatocytes convert glycogen to glucose with hormone glucagon

Question 11

liver deamination of excess amino acids

Answer 11

-hepatocytes synthesise most the plasma proteins
- hepatocytes carry out transamination which is important because diet does not always contain required balance of amino acids
- deamination is the removal of amine group from a molecule
- amino acids are deaminated to toxic ammonia then urea in the ornithine cycle

Question 12

deamination process (ornithine cycle)

Answer 12

• amine group (NH2) is removed from amino acids
• H atom is removed
• these combine to form ammonia (NH3) which forms ammonium ions (NH4+) in cytoplasm
• remaining keto acid may enter Krebs cycle in mitochondria to be respired and converted to glucose or glycogen

Question 13

detoxification

Answer 13

• level of toxins in body increases always e.g. urea, alcohol, drugs, other metabolic pathways
• most of these substances are detoxified and made harmless in the liver
• e.g. breakdown of hydrogen peroxide by catalase stored in hepatocytes which goes to oxygen and water
• e.g. detoxifying ethanol from alcoholic drinks. hepatocytes contain enzyme alcohol dehydrogenase that breaks it down to ethanal then converted to ethanoate to build up fatty acids/used in respiration