Core N - Excretion

Question 0

Describe the events in the kidneys, after ultrafiltration, that result in the increasing quantity of glucose in a diabetics urine. (3)

Answer 0

• Initially, glucose reabsorbed by proximal convoluted tubule
• Co-transported with sodium ions by facilitated diffusion / protein carrier
• Above a certain concentration, no further reabsorption
• Because carriers in PCT saturated

Question 1

Suggest what is meant by the term renal threshold. (1)

Answer 1

The concentration of blood glucose above which some glucose appears in the urine.

Question 2

Define the term excretion. (2)

Answer 2

• Removal or elimination of waste products
• Of metabolism
• Which are toxic
• Or substances excess to requirements

Question 3

Outline the role of negative feedback in osmoregulation. (4)

Answer 3

• Homeostasis
• Change in water potential
• Detected by osmoreceptors
• In hypothalamus
• Response via effector
• ADH released
• Effect on collecting duct
• Return to norm / set point

Question 4

Cold diuresis is when a person who remains in a cold environment for more than 15 minutes has increased urine production.
Suggest how exposure to cold can lead to called diuresis. (2)

Answer 4

• Blood diverted away from skin
• Less sweating
• More water retained in body (high water potential in body)
• Less water reabsorbed from collecting duct