osmoregulation

Question 1

1. a. Alport syndrome (AS) is an inherited disorder that affects kidney glomeruli of
   both men and women. Affected individuals have proteinuria (high quantities of
   protein in their urine).
   (a) Suggest how AS could cause proteinuria. (2)

Answer 1

1. Affects/damages basement membrane
2. Proteins can pass into the (glomerular) filtrate/tubule;

Question 2

(b) AS results from a sex-linked mutation.
In a male with AS, where would the sex-linked mutation be located? (1)

Answer 2

The non-homologous section of an X chromosome

Question 3

Q2.
(a) Describe how ultrafiltration occurs in a glomerulus. (3)

Answer 3

1. High blood/hydrostatic pressure;
2. Two named small substances pass out eg water, glucose,
3. (Through small) gaps/pores/fenestrations in (capillary)
   endothelium;
4. through (capillary) basement membrane;

Question 4

3. (d) Furosemide inhibits the absorption of sodium and chloride ions from the filtrate produced in the nephrons.
   Explain how furosemide causes an increase in the volume of urine produced. (3)

Answer 4

1. Water potential of filtrate/tubule decreased;
2. Less water (reabsorbed) by osmosis (from filtrate/tubule);
3. Collecting duct (is where osmosis occurs);

Question 5

6. (a) Give the location of osmoreceptors in the body of a mammal (1)

Answer 5

hypothalamus

Question 6

(b) When a person is dehydrated, the cell volume of an osmoreceptor decreases.
Explain why. (2)

Answer 6

1. Water potential of blood will decrease;
2. Water moves from osmoreceptor into blood by osmosis.

Question 7

(c) Stimulation of osmoreceptors can lead to secretion of the hormone ADH.
Describe and explain how the secretion of ADH affects urine produced by the kidneys. (4)

Answer 7

1. Permeability of membrane / cells (to water) is increased;
2. More water absorbed from / leaves distal tubule / collecting duct
3. Smaller volume of urine;
4. Urine becomes more concentrated.

Question 8

(e) Creatinine is a breakdown product of creatine found in muscle tissues.
Apart from age and gender, give two factors that could affect the
concentration of creatinine in the blood (2)

Answer 8

• ethnicity
• muscle mass
• exercise
• kidney disease

Question 9

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 9

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 10

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

Answer 10

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 11

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 11

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 12

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

Answer 12

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 13

Describe how ultrafiltration produces glomerular filtrate (5)

Answer 13

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 14

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 14

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