homeostasis

Question 1

Humans can produce urine which is more concentrated than their blood plasma.

Explain the role of the loop of Henle in the absorption of water from the filtrate (6)

Answer 1

1. In the ascending limb sodium(ions) actively removed;
2. Ascending limb impermeable to water;
3. In descending limb sodium(ions) diffuse in;
4. Descending limb water moves out
5. Low water potential in the medulla / tissue fluid;
6. The longer the loop the lower the water potential in medulla / tissue fluid;
7. Water leaves collecting duct
8. By osmosis

Question 2

Explain the role of ADH in the production of concentrated urine (4)

Answer 2

1. When water potential of the blood too low;
2. Detected by receptors in the hypothalamus;
3. Pituitary secretes / releases (more) ADH;
4. ADH increases the permeability / recruitment of aquaporins / opens channels for water in the DCT / collecting duct;
5. More water is reabsorbed / leaves the nephron moves into the blood;
6. By osmosis down the water potential gradient;

Question 3

The kidney plays an important part in the regulation of blood water potential. This involves control of the amount of water reabsorbed from the filtrate produced in the kidney tubules. The amount of water reabsorbed affects the volume of urine produced, the rate at which the bladder fills and how often it has to be emptied.

Explain how the loop of Henle maintains the gradient of ions which allows water to be reabsorbed from filtrate in the collecting duct (5)

Answer 3

1. (epithelial cell) of tubule cells carry out active transport;
2. transport chloride / sodium ions out (of filtrate);
3. against concentration gradient;
4. into surrounding tissue / tissue fluid;
5. creates / maintains water potential gradient for water reabsorption;
6. countercurrent multiplier;

Question 4

Explain how ADH is involved in the control of the volume of urine produced (4)

Answer 4

1. if water potential of blood falls, detected by receptors in hypothalamus;
2. leads to ADH released from pituitary gland;
3. ADH makes cells of collecting duct permeable to water;
4. water leaves filtrate by osmosis;
5. smaller volume of urine produced;

Question 5

Describe how ultrafiltration produces glomerular filtrate (5)

Answer 5

1. hydrostatic pressure;
2. Small molecules / named example;
3. Pass through basement membrane /
4. Protein too large to go through / large so stays behind;
5. Presence of pores in capillaries

Question 6

Some people who have diabetes do not secrete insulin. Explain how a lack of insulin affects reabsorption of glucose in the kidneys of a person who does not secrete insulin (4)

Answer 6

1. High concentration of glucose in blood;
2. High concentration in filtrate;
3. Reabsorbed by facilitated diffusion / active transport;
4. Requires proteins / carriers;
5. These are working at maximum rate / are saturated;
6. Not all glucose is reabsorbed

Question 7

Some desert mammals have long loops of Henle and secrete large amounts of antidiuretic hormone (ADH).

Explain how these two features are adaptations to living in desert conditions (6)

Answer 7

1. More water (from filtrate) reabsorbed
2. By osmosis;
3. From collecting duct
4. Due to longer loop of Henle;

For loop of Henle, maximum 2 marks:
5. Sodium ions absorbed from filtrate in ascending limb;

6. Gradient established in medulla

For ADH, maximum 2 marks:
7. Acts on collecting duct

8. Makes cells more permeable