15.4 The Liver

Question 1

define excretion

Answer 1

the removal of waste products of metabolism from the body

Question 2

what are the 3 main metabolic waste products in mammals

Answer 2

• CO2
• bile pigments
• nitrogenous waste products (urea)

Question 3

what is CO2 a waste product of

Answer 3

cellular respiration which is excreted from the lungs

Question 4

how are bile pigments formed

Answer 4

from the breakdown of haemoglobin from old RBCs in the liver

Question 5

where are bile pigments excreted from and into

Answer 5

the liver into the small intestine via the gall bladder and bile duct

Question 6

how are nitrogenous waste products formed

Answer 6

from the breakdown of excess amino acids by the liver

Question 7

what is the nitrogenous waste product in mammals

Answer 7

urea

Question 8

what is the nitrogenous waste product in fish

Answer 8

ammonia

Question 9

what is the nitrogenous waste product in birds and insects

Answer 9

uric acid

Question 10

explain the blood supply to the liver

Answer 10

• oxygenated blood is supplied by the hepatic artery and removed by the hepatic vein
• the hepatic portal vein carries blood with products from digestion from the intestine to the liver
• 75% comes via the hepatic portal vein

Question 11

explain the characteristics of hepatocytes

Answer 11

• large nuclei
• prominent Golgi apparatus
• lots of mitochondria
• divide and replicate very quickly

Question 12

what are sinusoids

Answer 12

spaces where blood from the hepatic artery and the hepatic portal vein get mixed (increases oxygen content of blood from the HPV)

Question 13

what do sinusoids contain

Answer 13

Kupffer cells

Question 14

what do Kupffer cells do

Answer 14

act as resident macrophages by ingesting foreign particles and protecting it against disease

Question 15

what do the hepatocytes secrete

Answer 15

• bile from the breakdown of blood into spaces called canaliculi
• then bile drains into the bile ductule which go to the gall bladder

Question 16

what are the 3 main function of the liver

Answer 16

• carbohydrate metabolism
• deamination of excess amino acids
• detoxification

Question 17

explain carbohydrate metabolism (blood glucose rises)

Answer 17

• blood glucose levels rise = insulin levels rise = hepatocytes convert glucose –> glycogen (storage)

Question 18

what is transamination

Answer 18

conversion of one amino acid into another

Question 19

why is transamination important

Answer 19

overcomes the problems of the diet which doesn’t always contain the required balance of amino acids

Question 20

what is deamination

Answer 20

the removal of an amine group from a molecule

Question 21

explain the process of deamination

Answer 21

• hepatocytes remove the amino group and convert amino acids –> ammonia –> urea

Question 22

what happens to the remaining amino acids after deamination

Answer 22

• fed into cellular respiration

- converted into lipids for storage

Question 23

what does the ornithine cycle do

Answer 23

convert ammonia into urea

Question 24

how is hydrogen peroxide broken down

Answer 24

hepatocytes contain catalase which splits the hydrogen peroxide into oxygen+water

Question 25

how does the liver detoxify ethanol

Answer 25

• hepatocytes contain alcohol dehydrogenase that breaks down ethanol –> ethanal
• ethanal is converted to ethanoate (used to build up fatty acids/in cellular respiration)

Question 26

what is cirrhosis

Answer 26

a disease where normal liver tissue is replaced by fibrous scar tissue

Question 27

what are the causes of cirrhosis

Answer 27

• genetic conditions
• hepatitis C
• excessive amounts of alcohol

Question 28

explain the 3 stages of alcoholic Iiver disease

Answer 28

1. alcoholic fatty liver disease (big fat-filled vesicles displace nuclei of hepatocytes and liver gets bigger)
2. alcoholic hepatitis (fatty liver, damaged hepatocytes, sinusoids and hepatic veins become narrow)
3. liver cirrhosis (hepatocytes die and are replaced by fibrous tissue so liver shrinks)

Question 29

explain carbohydrate metabolism (blood glucose falls)

Answer 29

• blood glucose levels fall = hepatocytes convert glycogen –> glucose under influence of the hormone glucagon