Homeostasis

Question 1

What are the main metabolic waste products in mammals?

Answer 1

• Carbon dioxide
• Nitrogenous waste
• Bile pigments

Question 2

How are bile pigments formed?

Answer 2

Breakdown of haemoglobin from old red blood cells in the liver.

Question 3

What colours the faeces?

Answer 3

Bile pigments

Question 4

How is nitrogenous waste formed?

Answer 4

Breakdown of excess amino acids by the liver.

Question 5

How is oxygenated blood supplied to the liver?

Answer 5

Hepatic artery

Question 6

How is deoxygenated blood returned to the heart from the liver?

Answer 6

Hepatic vein

Question 7

What is the role of the hepatic portal vein?

Answer 7

Supplies blood to the liver loaded with the products of digestion from the intestines.

Question 8

What are the features of hepatocytes?

Answer 8

Large nuclei
Prominent Golgi apparatus
Lots of mitochondria

Question 9

What happens in sinusoids?

Answer 9

Blood from the hepatic artery and hepatic vein mix.

Question 10

What surrounds sinusoids?

Answer 10

Hepatocytes

Question 11

What is the purpose of mixing of the blood in the sinusoids?

Answer 11

Increases oxygen content of blood from the hepatic portal vein so the hepatocytes have enough oxygen.

Question 12

What is the purpose of the Kupffer cells in the sinusoids?

Answer 12

Ingest foreign particles.

Help protect against disease.

Question 13

What do hepatocytes secrete?

Answer 13

Bile

Question 14

Why do hepatocytes secrete bile?

Answer 14

Secrete bile into canaliculi and from these the bile drains into bile ducts which take it to the gall bladder.

Question 15

Where does detoxification happen?

Answer 15

Liver

Question 16

What is transamination?

Answer 16

Conversion of one amino acid into another.

Question 17

Why is transamination important?

Answer 17

Diet doesn’t always contain the required balance of amino acids.

Question 18

What is deamination?

Answer 18

Removal of an amine group from a molecule.

Question 19

What is ultrafiltration?

Answer 19

1) Blood from the renal artery is supplied to the glomerulus from the afferent arteriole.
2) Blood leaves through the narrower efferent arteriole which builds up pressure.
3) So blood is passed out through the capillary wall and then through the basement membrane. Red blood cells and proteins are retained in the capillary as they are too large.

Question 20

What are the role of podocytes in ultrafiltration?

Answer 20

Acts as an additional filter. They have extensions called pedicles that wrap around capillaries forming slits to ensure ay escaped large molecules from the basement membrane don’t pass into the tubule.

Question 21

What are the steps of reabsorption which occur in the PCT?

Answer 21

All glucose, amino acids, vitamins and hormomes are actively transported back into the blood. About 85% of Na ions move back by AT and Cl ions by passive diffusion.

Question 22

What are the adaptations of cells lining the PCT?

Answer 22

• Microvilli

- Many mitochondria

Question 23

What are the steps of reabsorption which occur in the loop of Henle?

Answer 23

Descending limb-
Lower part is permeable to water, so water moves out by osmosis. Impermeable to ions. At the hairpin, the fluid is very concentrated.

Ascending limb-
In the first section, many ions move out by diffusion. In the second part, ions are moved out by AT. Impermeable to water. So the fluid becomes increasingly dilute.

Question 24

What does the loop of Henle act as?

Answer 24

A countercurrent multiplier

Question 25

What are the roles of the DCT in reabsorption?

Answer 25

If the body lacks salts, ions will be pumped out down an electrochemical gradient. The cells lining the DCT have many mitochondria for AT. The permeability of the walls to water vary with the levels of ADH.

Question 26

What is the main purpose of the DCT and collecting duct?

Answer 26

Balancing of water needs.

Question 27

What happens when water is in short supply?

Answer 27

- Detected by osmoreceptors in the hypothalamus. - Send nerve impulses to the posterior pituitary gland which releases ADH. - ADH is picked up by receptors in the cells lining the collecting duct and increases the permeability to water. - So water enters the blood by osmosis.

Question 28

What happens when there is an excess of water in the body?

Answer 28

- Change is detected by the osmoreceptors in the hypothalamus. - Nerve impulses to the posterior pituitary are reduced so release of ADH is inhibited.

Question 29

What is the mechanism of ADH?

Answer 29

- Vesicles in the cells lining the collecting duct fuse with the cell surface membranes on the side of the cell in contact with the tissue fluid of the medulla. - Membranes of these vesicles contain aquaporins and make a cell surface membrane permeable to water. - This allows for the movement of water in the blood by osmosis.

Question 30

What is the ornithine cycle?

Answer 30

Ammonia combines with carbon dioxide to form urea and water.

Question 31

What is the purpose of the ornithine cycle?

Answer 31

Ammonia is too toxic to be excreted directly.

Question 32

What is the process of deamination?

Answer 32

NH2 are removed from excess amino acids forming ammonia and organic acids.

Question 33

What is done with the organic acids formed in deamination?

Answer 33

Used in respiration Stored as glycogen Converted to carbohydrate

Question 34

Which dialysis has AT?

Answer 34

Peritoneal

Question 35

Where does peritoneal dialysis take place?

Answer 35

Inside the body

Question 36

What is an advantage of peritoneal dialysis?

Answer 36

Can take place at home

Question 37

How does peritoneal dialysis work?

Answer 37

1) Dialysis fluid is introduced into the body using a catheter. 2) Left for hours so urea and excess mineral ions pass out of blood capillaries into the tissue fluid across the peritoneal membrane into the dialysis fluid.

Question 38

What machinery does haemodialysis use?

Answer 38

Dialysis machine

Question 39

How does haemodialysis work?

Answer 39

1) Blood leaves body from artery and flows into machine. 2) Blood flows between partially permeable dialysis membranes which mimic the basement membrane. 3) Patients lose excess mineral ions and urea.

Question 40

How is it ensured that patients don't lose useful substances in haemodialysis?

Answer 40

Dialysis fluid contains normal plasma levels of glucose.

Question 41

How is a steep concentration gradient of urea built up in haemodialysis?

Answer 41

Dialysis fluid doesn't contain any urea.