Topic 6I: Homeostasis and Control of Blood Water Potential

Question 1

Describe how ultrafiltration occurs at the glomerulus. [4]

Answer 1

1. High hydrostatic pressure;
2. Two named small substances pass out, e.g. water, glucose, ions, urea;
3. (Through small) fenestrations in (capillary) endothelium;
4. (And) through (capillary) basement membrane

Question 2

AS is a disorder that affects kidney glomeruli. Affected individuals have proteinuria (high quantities of protein in their urine).

Suggest how AS could cause proteinuria. [2]

Answer 2

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

Question 3

Creatinine is formed by the breakdown of phosphocreatine in muscles.

Suggest and explain to characteristics of a patient that could alter the creatinine concentration in the blood. [4]

Answer 3

1. Age;
2. (because) kidney function declines with age;
3. Gender;
4. (because) men and women have different muscle mass;
5. Diet;
6. (because this will) affect levels of, (phospho)creating (in muscles)

Question 4

Compare and contrast ultrafiltration and the formation of tissue fluid. [5]

Answer 4

Similarities:
1. Ions are filtered from blood;
2. Both processes occur in capillaries;
3. Proteins/cells remain in the blood;
4. High hydrostatic pressure in both processes;
5. Mainly molecules are reabsorbed back into capillaries;
6. Hydrostatic pressure gradient greater then water potential gradient in both;

Differences:
7. Filtrate enters the Bowman’s capsule in the kidney, but tissue fluid bathes cells;
8. Molecules that are not reabsorbed by capillaries form urine in the kidney, but molecules that are not reabsorbed from tissue fluid form lymph;
9. Knot of capillaries in ultrafiltration but network of capillaries in formation of tissue fluid

Question 5

Describe how glucose is reabsorbed into the blood at the proximal convoluted tubule. [4]

Answer 5

1. Sodium ions removed (from epithelial cell) by active transport into blood;
2. Maintains sodium ion concentration gradient (between tubule lumen and epithelial cell);
3. Sodium ions and glucose absorbed by co-transport
4. via carrier proteins;
5. Sodium ions enter epithelial cells by facilitated diffusion taking glucose with them (from tubule);
6. Glucose moved by facilitated diffusion into blood (from epithelial cells)

Question 6

Why do untreated diabetic people often have glucose in their urine? [3]

Answer 6

1. High concentration of glucose in blood/filtrate/tubule;
2. Not all the glucose is (re)absorbed at the proximal convoluted tubule;
3. Not enough carrier/co-transport proteins to absorb all the glucose

Question 7

Species of mammal that live in drier environments tend to have a greater proportion of their kidneys taken up by the medulla. Suggest why. [3]

Answer 7

1. Thicker medulla means a longer loop (of Henle);
2. (The longer the loop of Henle means) higher sodium ion concentration (in medulla)
   OR
   Sodium ion gradient maintained for **longer/deeper (in medulla);
   OR
   More sodium ions are moved out (into medulla);
3. (Therefore) water potential gradient maintained (for longer), so more water reabsorbed from collecting duct (back into blood);
   OR
   More water reabsorbed from collecting duct by osmosis (back into blood)

Question 8

Name the part of the body that contains osmoreceptors that regulate ADH secretion. [1]

Answer 8

1. Hypothalamus

Question 9

Name the part of the body which releases antidiuretic hormone (ADH) into the blood. [1]

Answer 9

1. Posterior pituitary

Question 10

Describe the effect of ADH on the distal convolted tubules and collecting ducts in the kidneys. [3]

Answer 10

1. (Stimulates) addition of (water) channel proteins into membrane;
2. Increases permeability to water
   OR
   (More) water reabsorbed;
3. By osmosis

Question 11

Untreated diabetic people often have glucose in their urine.

Why do these people produce unusually large volumes of urine? [3]

Answer 11

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

Question 12

Alcohol decreases the release of ADH into the blood.

Suggest two signs or symptoms which many result from a decrease in ADH. [2]

Answer 12

1. Dehydration/thirst;
2. Frequent urination
   OR
   Increase in volume of urine;
3. Less concentrated urine

Question 13

Antidiuretic hormone (ADH) binds to V receptors found in cell-surface membranes in two parts of a nephron.

Name the two parts of a nephron when V receptors are found. [1]

Answer 13

1. Distal (convoluted) tubule and collecting duct

Question 14

Antidiuretic hormone (ADH) binds to V receptors found in cell-surface membranes in two parts of a nephron.

V receptors only bind with ADH.

Suggest and explain why. [2]

Answer 14

1.Has a (specific) tertiary structure/shape;
2. (Structures are) complementary

Question 15

A decrease in blood pressure stimulates the release of ADH.

Give the location of the receptors that detect a decrease in blood pressure and explain how the release of ADH will affect blood pressure. [3]

Answer 15

1. Aorta
   OR
   Carotid arteries;
2. (ADH) increases reabsorbtion of water;
3. Increases volume of blood and pressure increases/returns to normal

Question 16

More than 99% of biological molecules are reabsorbed from the filtrate in the proximal convoluted tubule.
Despite this, the concentration of the fluid in this tubule remains constant.
Explain why. [1]

Answer 16

1. Water is also reabsorbed

Question 17

Suggest how an increase in urination results in a decrease in blood pressure. [1]

Answer 17

1. Lower volume of blood

Question 18

Alpert 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).

Suggest how AS could cause proteinuria. [2]

Answer 18

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