Paper 2 - Kidneys And Osmoregulation

Question 1

Why do people with diabetes end up with glucose in their urine?

Answer 1

Diabetes doesn’t produce enough insulin:

• blood glucose conc becomes too high
• so more glucose is filtered out of blood into filtrate
• all glucose can’t be reabsorbed because the carrier proteins needed for active transport become saturated

Question 2

Label the structure of the nephron

Answer 2

• Bowman’s capsule
• Glomerulus
• Renal capsule
• Afferent arteriole
• Efferent arteriole
• Proximal convoluted tubule (PCT)
• loop of Henle
• Distal convoluted tubule (DCT)
• Collecting duct

Question 3

Label the structure of the kidney

Answer 3

• Outer cortex
• Medulla
• Renal pelvis

Question 4

Describe the process of ultrafiltration in the production of glomerular filtrate

Answer 4

1. The hydrostatic pressure in the glomerulus is high due to the afferent arteriole being wider than the efferent
2. Water and small soluble molecules such as glucose are pushed from the glomerulus into the Bowman’s capsule.
3. Glomerular filtrate flows from the capsule into the proximal convoluted tubule
4. No cells or proteins are in the filtrate as they are too large to fit through

Question 5

Explain how PCT is adapted to maximise absorption

Answer 5

• Microvilli = large surface area
• Many mitochondria which produce ATP for active transport
• Many channel and carrier proteins for facilitated diffusion
• Many carrier proteins for active transport
• Many ribosomes that produce many transport proteins

Question 6

Explain the role of the loop of Henle in maintain a gradient of sodium ions in the medulla to cause reabsorption of water

Answer 6

1. The ascending limb is impermeable to water but the descending limb is permeable to water.
2. Na+ is actively transported out of the ascending limb into the tissue fluid
3. Some Na+ diffuse into the descending limb
4. This lowers the water potential of the tissue fluid
5. Water moves out of the collecting duct and DCT into the tissue fluid by osmosis, down a WP gradient
6. Water moves back into the capillaries by osmosis

Question 7

Explain how water potential is detected in the body and describe the effect this has on the permeability of the DCT and the collecting duct

Answer 7

When water potential is too low:

• Detected by osmoreceptors in the hypothalamus
• Hypothalamus sends impulses to posterior pituitary gland which release more ADH into the blood into the collecting duct and DCT
• More aquaporins are inserted into the membranes of cells = more permeable to water
• More water is reabsorbed from collecting duct by osmosis = increase in WP of the blood
• Small volume of concentrated urine produced

Question 8

Name the 3 layers of cells that water and small solutes pass through

Answer 8

• Endothelial cells - contain tiny pores
• Basement membrane - mesh that doesn’t let proteins through
• Podocytes (epithelial cells)