The Kidneys

Question 1

What originally enters the kidneys?

Answer 1

Blood

Question 2

What is the glomerulus?

Answer 2

A bundle of capillaries looped inside a ball - Bowman’s capsule.

Question 3

Where does ultrafiltration occur?

Answer 3

In the glomerulus in Bowman’s capsule.

Question 4

What does the afferent arteriole do?

Answer 4

Takes blood into each glomerulus

Question 5

What does the efferent arteriole do?

Answer 5

Filters blood away from the glomerulus

Question 6

What is the difference between the afferent and efferent arteriole?

Answer 6

Efferent has a smaller diameter, so the blood in the glomerulus is under higher pressure.

Question 7

What does the high pressure from the efferent arteriole do?

Answer 7

Forces liquids and small molecules in the blood out of the capillary and into the Bowman’s capsule.

Question 8

What happens to larger molecules eg proteins and blood cells in the kidney?

Answer 8

They pass though 3 layers to get into the Bowman’s capsule and then enter the nephron tubules

Question 9

What are the 3 layers that the liquid and small molecules pass through to get into the Bowman’s capsule?

Answer 9

The capillary wall, basement membrane, epithelium of Bowman’s capsule.

Question 10

Outline ultrafiltration.

Answer 10

1. Blood from the afferent arteriole passes into the glomerulus, which creates a high hydrostatic blood pressure, which forces small molecules out of the blood (eg glucose, urea, AAs, water).
2. The small molecules pass into the Bowman’s capsule across three layers (endothelium, basement membrane, podocyte cells)

Question 11

Outline the podocytes involved in ultrafiltration.

Answer 11

Have foot processes called pedicels which create gaps for molecules to move through.

Question 12

Outline the reabsorption of glucose and water by PCT.

Answer 12

1. All glucose / AAs, some water / salts, no urea pass back into the blood.
2. 99% of glomerular filtrate is reabsorbed back into the blood.

Question 13

Outline the loop of helne.

Answer 13

From the PCT, water moves out of the loop by osmosis. Because the descending limb is permeable to H2O. Therefore at the bottom of the loop, filtrate is more conc (lower WP).

The ascending limb is impermeable to H2O, so NaCl diffuses (high - low) out of the loop, then even higher up, NaCl actively transports (low - high). Therefore WP is high. Leaves DCT.

Question 14

Outline the DCT.

Answer 14

• if WP of blood is high, this is detected by osmosreceptors in hypothalamus, so less ADH is released from pituitary gland so the wall of the collection fiction is less permeable, so less water leaves in urine.
  Large amount of dilute urine is produced.
• if WP of blood is low, this is detected by osmoreceptors in hypothalamus, so the posterior pituitary gland is stimulated to release more ADH into blood. This means the DCT and collecting duct become more permeable so more water is reabsorbed into blood by osmosis.
  A small amount of highly conc urine is lost.

Question 15

Beta cells secrete _________ into the blood.

Answer 15

Insulin

Question 16

Alpha cells secrete _________ into the blood.

Answer 16

Glucagon

Question 17

Outline what insulin does.

Answer 17

1. Insulin binds to specific receptors on the cell membranes of liver cells and muscle cells.
2. This increases permeability of muscle cell membranes to glucose, so the cell takes up more glucose by increasing the no of channel proteins.
3. Insulin also activates enzymes in liver and muscle cells that convert glucose to glycogen (glycogenesis).
4. This lowers blood glucose conc when it’s too high.

Question 18

What does glycogen do?

Answer 18

1. Binds to specific receptors on the cell membranes of liver cells.
2. Glucagon activates enzymes in liver cells that break down glycogen into glucose (glycogenolysis).
3. Also activates enzymes that are involved in the formation of glycerol to glucose (gluconeogenesis).
4. This raises blood glucose conc when it’s too low.

Question 19

Outline type 1 diabetes.

Answer 19

The immune system attacks B cells in islets of langerhans so they can’t produce insulin.

After the blood glucose level rises, it stays high (hyperglycaemia). The kidneys can’t reabsorbed all this glucose so some of its excreted.

Question 20

Outline type 2 diabetes.

Answer 20

Occurs when B cells don’t produce enough insulin

Or body cells don’t respond properly to insulin due to insulin receptors on the membrane don’t work properly so don’t take up enough glucose. Their blood conc is higher than normal.