liver

Question 1

What is excretion?

Answer 1

excretion is removal of waste products of metabolism from the body. (CO2 and nitrogenous waste (urea).

Question 2

What is the purpose of excretion?

Answer 2

It helps maintain normal metabolism. Helps to maintain homeostasis by keeping levels of certain substances in the blood roughly constant.

Question 3

What are the main metabolic waste products in the body and where do they come from?

Answer 3

CO2 - waste product from cellular respiration
Urea/nitrogenous waste - formed from breakdown of excess amino acids by liver
bile pigments - breakdown products of haemoglobin from old red blood cells in liver

Question 4

What is the structure of the liver?

Answer 4

• made out of many lobules. Each lobule is made of liver cells called hepatocytes. They are arranged in rows radiating out from the centre.
• in the centre of each lobule is a central vein called the hepatic vein which takes deoxygenated blood away from the body (to the vena cava).
• there are branches of bile duct, hepatic artery, hepatic portal vein connected to each lobule.
• the hepatic artery and hepatic portal vein are connected to central vein by capillaries called sinusoids.

Question 5

What does the hepatic artery do?

Answer 5

It supplies liver with oxygenated blood from the heart so there is plenty of oxygen for respiration so plenty of energy.

Question 6

What does the hepatic portal vein do?

Answer 6

it brings blood from duodenum and ileum (parts of small intestine) so its rich in products of digestion. so any ingested harmful substances are filtered out and broken down straight away.

Question 7

What does the bile duct do?

Answer 7

Take bile (substances produced by liver to emulsify fats) to the gall bladder to be stored.
hepatocytes secrete bile from breakdown of old red blood cells into canaliculi. Bile drains into bile duct to be stored in gall bladder. 
-bile emulsifies fats by giving enzymes larger surface area to work with.

Question 8

What happens at the sinusoids?

Answer 8

• blood runs through sinusoids past hepatocytes.
• hepatocytes remove harmful substances and oxygen form blood.
• hepatocytes break down harmful substances to less harmful ones which re-enter blood
• blood runs to the central vein. all central veins form all the lobules connect to form hepatic vein.
• Kupffer cells are attached to walls of sinusoids which remove bacteria and break down old red blood cells.
• bile duct is connected to central vein by tubes called canaliculi.

Question 9

What are the function of the liver?

Answer 9

• deamination of amino acids
• formation of urea (ornithine cycle)
• transamination
• storage of glycogen
• detoxification
• regulating blood glucose levels

Question 10

How does liver regulate blood glucose levels?

Answer 10

• insulin levels increase as blood glucose levels decrease by stimulating hepatocytes to convert glucose to glycogen via glycogenesis.
• glucagon helps to increase blood glucose levels if they are too low. hepatocytes are stimulated and glycogen is broken down via glycogenolysis and glucose is formed from amino acids and glycerol (fatty acids) via gluconeogenesis.

Question 11

What is deamination?

Answer 11

it is the removal of an amine group from an amino acid. The products of this reaction are ammonia and keto acid. Ammonia is toxic if left to accumulate. This leads on to the ornithine cycle.

Question 12

How is urea formed in the ornithine cycle?

Answer 12

keto acid is organic so can be respired to form ATP or converted to carbohydrate and stored as glycogen.

• in the mitochondria, ammonia is combined with CO2 to form less harmful substance.
• in the cytoplasm, it forms 3 substances and water is added to make urea. in a set of enzyme-controlled reactions.
• urea is released by liver into the blood which is filtered by kidneys and excreted from body as urine.

Question 13

What is detoxification?

Answer 13

it is the conversion of toxic molecules into less toxic or non-toxic molecules.
contain enzymes which have detoxification functions such as catalase

Question 14

Describe detoxification of alcohol ethanol?

Answer 14

Ethanol is converted into ethanal using ethanol dehydrogenase and oxidised NAD is reduced.
Ethanal is converted into ethanoic acid using ethanal dehydrogenase and NAD is reduced. Ethanoic acid combines with co-enzyme A to form acetyl-coenzyme A which enters link reaction or krebs cycle to be respired.

Question 15

What is transamination and why is it important?

Answer 15

• it is the conversion of one amino aid to another.

- it is important as diet doesnt always contain the required balance of amino acids.