5.1.2 - EXCRETION

Question 1

Define excretion

Answer 1

The removal of waste products from the body

Question 2

Describe the importance of excretion

Answer 2

• All chemical reactions in our cells make up our metabolism
  ^— metabolism produces waste products (substances not needed by cells - e.g. carbon dioxide + nitrogenous waste)
  ^— if they build up, they cause damage to other metabolic reactions (because they are toxic)
• Excretion removes these waste products of metabolism (maintains metabolism)

E.g. carbon dioxide is a waste product of respiration + too much in the blood is toxic so the LUNGS remove it (in mammals) - excretory organ

Question 3

Describe the role of the liver in the storage of glycogen

Answer 3

• Glucose needed for energy
  ^— liver converts excess glucose in the blood to glycogen + stores it as granules in its cells until the glucose is needed for energy

Question 4

Describe the role of the liver in the formation of urea from ammonia reacting with carbon dioxide

Answer 4

• Liver gets ride of excess amino acids produced by eating + digesting protein
• Amino acids contain nitrogen in amino groups —> nitrogenous substances can’t usually be stored by the body
  ^— excess amino acids can be damaging to the body, so they must be used or broken down + excreted:
• Nitrogen-containing amino groups are removed from any excess amino acids, forming ammonia + organic acids (deamination)
• Organic acids can be respired to give ATP or converted to carbohydrate + stored as glycogen
• Ammonia is too toxic for mammals to excrete directly, so it’s combines with/ carbon dioxide in the ornithine cycle to create urea
• Urea is released from the liver into the blood - kidneys then filter the blood + remove the urea as urine

Question 5

Describe the role of the liver in detoxification

Answer 5

• Alcohol (ethanol) - toxic + can damage cells | broken down by the liver into ethanal, which is broken down into a less harmful substance called acetic acid | excess alcohol over a long period can lead to cirrhosis of the liver (liver cells die + scar tissue blocks blood flow
• Paracetamol - common painkiller broken down by the liver | excess paracetamol in the blood can lead to liver + kidney failure
• Insulin - hormone controlling blood glucose concentration —> broken down by the liver as excess insulin can cause problems with blood sugar levels

Question 6

Describe the vessels connected to the liver

Answer 6

• Hepatic artery supplies the liver w/ oxygenated blood from the heart so liver has good oxygen supply for respiration, providing plenty of energy
• Hepatic vein takes deoxygenated blood away from liver
• Hepatic portal vein brings blood from duodenum + ileum (parts of small intestine) so it’s rich in the products of digestion —> means any ingested harmful substances are filtered out + broken down straight away
• Bile duct takes bile (substance produced by liver to emulsify fats) to the gall bladder to be stored

Question 7

Describe the structure of the liver

Question 8

What are liver lobules?

Question 9

What are Kupffer cells?

Answer 9

Cells attached to the walls of the sinusoids
^— remove bacteria + break down old red blood cells

Question 10

What are Hepatocytes?

Answer 10

Main liver cells which are highly metabolically active which divide and replicate