5.2

Question 1

What is excretion?

Answer 1

The removal of metabolic waste

Question 2

What products must be excreted? (3)

Answer 2

• co2
• nitrogenous waste (urea)
• other compounds such as bile pigments(bilirubin)

Question 3

How is CO2 transported in the blood?

Answer 3

CO2 + H20 —-> H2CO3
H2CO3 —-> H+ + HCO3-

• Hydrogencarbonate in plasma (85%)
• bonded to Hb to form carboaminohaemoglobin (10%)
• dissolved directly into blood plasma (5%)

Question 4

Removal of excess amino acids

Answer 4

• deamination: amino acid + oxygen –> lactic acid + ammonia

- formation of urea : 2NH3 + CO2 —-> (NH2)2CO (urea) + H2O

Question 5

What are the excertory organs and their functions?

Answer 5

Lungs = CO2 - Mostly in form of hco3-
Liver = deamination and excretion of bilirubin
Kidney = urea removal + urine production
Skin = 
-sweat excretion
-UREA, URIC ACID + AMMONIA Removal
- loss of water and salts
- water potential and blood temperature regulation

Question 6

Why does the liver need a good blood supply?

Answer 6

To assure efficient filtering of the blood and removal of toxins found in the blood

Question 7

The liver has 2 blood sources, what are they?

Answer 7

Hepatic artery:
Oxygenated blood from the heart used for respiration

Hepatic portal vein:
Deoxygenated blood from intestines to remove toxins and control concentration of nutrients that have been absorbed

Question 8

How does blood leave the liver?

Answer 8

Through the hepatic vein to the vena cava

Question 9

Describe the histology of a lobule within the liver

Answer 9

• Contains a central hepatic vein which is intralobular vessel
• contains 2 interlobular vessels; hepatic portal vein and hepatic artery which allow blood from both sources to flow past the sinusoid cells along hepatocytes which remove waste and return useful nutrients to the blood.
• bile is transported from the bile canaliculi which join together to form the bile duct to the gall bladder
• kupffer cells are specialised macrophages within the sinusoidal and their primary function is to break down and recycle old erythrocytes. This is where bilirubin is produced and excreted as part of the bile.

Question 10

Give specific features of hepatocytes (3)

Answer 10

• Dense cytoplasm
• high number of certain organelles such as mitochondria
• has microvilli on cell surface

Question 11

Give the metabolic functions of the liver (7)

Answer 11

• control of blood sugar, amino acid and lipid levels
• synthesis of bile, plasma proteins and cholesterol
• synthesis of erythrocytes in the fetus
• storage of vitamin A, B12, D, iron and glycogen
• detoxification of alcohol and drugs
• breakdown of hormones
• recycling of erythrocytes

Question 12

How is glycogen stored in hepatocytes?

Answer 12

As glycogen granules

Question 13

Give the function of catalase

Answer 13

Converts hydrogen peroxide into water and oxygen

Question 14

Give the function of cytochrome p450. Why can some medicinal drugs cause side effects?

Answer 14

The group of enzymes break down drugs such as cocaine or medicinal drugs. Cytochrome P450 is used in the ETC in respiration. Sometimes their role in metabolising drugs can interfere with other metabolic roles and produce unwanted waste products that cause side effects