Module 6 - Control of blood water potential

Question 1

What is the cortex of the kidneys?

Answer 1

The outer layer

Question 2

What is ultrafiltration?

Answer 2

The process of substances being filtered out of the blood into long tubules that surround the capillaries.

Question 3

What is selective reabsorption?

Answer 3

This is the uptake of glucose and the right amount of water being taken back into the blood.

Question 4

What is a nephron?

Answer 4

These are what the long tubules and the bundle of capillaries are called.

Question 5

In 5 steps explain how blood is filtered in the nephron

Answer 5

1. Blood enters the arteriole in the cortex from the renal artery which then splits into many arterioles known as the glomerulus.
2. The blood that leaves the glomerulus is known as the efferent arteriole which creates high pressure and will force small molecules and liquid out.
3. The liquid will be forced through the capillary wall, basement membrane and bowman capsule membrane
4. The larger molecules remain inside the blood forming the glomerular filtrate.
5. The glomerular filtrate passes along the rest of the nephron

Question 6

Explain the first stage of ultrafiltration in the nephrons

Answer 6

Blood enters from the renal artery into the arterioles in the cortex. The arterioles split into more arterioles known as the glomerulus which is a bundle of capillaries inside a hollow-ball known as the bowman’s capsule.

Question 7

Explain the second stage of ultrafiltration in the nephrons.

Answer 7

The arteriole that carries blood to the glomerulus is known as the afferent arteriole and the one that takes it away is the efferent. The efferent arteriole has high pressure because it has a small diameter meaning, it forces liquid and small molecules out of it into the bowman’s capsule.

Question 8

Explain the third stage of ultrafiltration in the nephrons.

Answer 8

The liquid and small molecules pass through the 3 layers to get into the bowman’s capsule and enter the nephron tubules. These are the capillary wall, a basement membrane and epithelium of the bowman’s capsule.

Question 9

Explain the fourth stage of ultrafiltration in the nephrons.

Answer 9

Larger molecules like proteins and blood cells cannot pass through and so they remain inside the blood. This is known as the glomerular filtrate.

Question 10

Explain the fifth stage of ultrafiltration in the nephrons.

Answer 10

The glomerular filtrate passes along the nephron and useful substances are reabsorbed along the way. It will also flow through the collecting duct and passes out of the kidneys along the ureter.

Question 11

Where does selective reabsorption take places?

Answer 11

Proximal convoluted duct, loop of henle and the distal convoluted duct.

Question 12

How does selective reabsorption take place in the PCT?

Answer 12

The epithelium of the wall of the PCT has microvilli to provide a large surface area for the reabsorption of useful materials for the glomerular filtrate. Glucose is reabsorbed along the PCT by active transport and facilitated diffusion. Water enters the blood via osmosis because the water potential of the blood is lower.

Question 13

What is urine usually made up of?

Answer 13

Water, urea, other substances like hormones and dissolved salts

Question 14

What is urine not usually made up of?

Answer 14

Proteins and blood cells and glucose

Question 15

How does the body regulate water potential in the blood when it is too low?

Answer 15

More water is reabsorbed by osmosis into the blood from the tubules of the nephrons. This means that urine is more concentrated

Question 16

How does the body regulate water potential in the blood when it is too high?

Answer 16

less water is reabsorbed by osmosis in the blood from the tubules of the nephrons. The urine will be more dilute

Question 17

Describe the loop of henle.

Answer 17

It is located in the medulla. It is made up of two limbs - the descending and ascending limb. The limbs control the movement of sodium ions so that the water can be reabsorbed by the blood.

Question 18

Explain the 4 stages that takes place in the loop of henle

Answer 18

1. At the ascending limb, Na+ ions are pumped into the medulla. It is impermeable to water, so the water stays inside the tubule. Low conc gradient in the medulla
2. Water moves out into the medulla in the descending limb by osmosis. The filtrate is more conc and the water is reabsorbed into the capillaries.
3. Near the bottom of the ascending limb, the Na+ ions diffuse out into the medulla, further lowering the water potential.
4. Water moves out by distal convoluted tubule by osmosis

Question 19

What is the water potential of the cells monitored by?

Answer 19

Osmoreceptors in the hypothalamus.

Question 20

What happens to blood ADH levels when you are hydrated or dehydrated?

Answer 20

When you are hydrated, ADH falls and when you are dehydrated, ADH rises

Question 21

Explain the process of being dehydrated

Answer 21

The water potential in the blood drops which is detected by the osmoreceptors in the hypothalamus. The posterior pituitary gland is stimulated and then releases ADH into the blood. More ADH means the DCT and collecting duct become more permeable, so more water is reabsorbed by blood by osmosis.

Question 22

Explain the process of being hydrated

Answer 22

The water content of blood rises which is detected by osmoreceptors in the hypothalamus. The posterior releases less ADH into the blood. This means the DCT and collecting duct become less permeable and so less water is reabsorbed into the blood by osmosis.

Question 23

Why do aquatic organisms not have a loop of henle?

Answer 23

They do not need to conserve water because they live in water environments

Question 24

How many desert animals have an adapted loop of henle?

Answer 24

They may have a longer loop of henle so more ions can diffuse out, decreasing the water potential further and allowing more water to be reabsorbed by the capillaries

Question 25

Explain how the ADH makes a membrane more permeable to water?

Answer 25

The ADH will bind to complementary receptors on the membrane on collecting duct cells. The aquaporins inside the cells will become phosphorylated and cause the vesicles to fuse with the membrane. This will cause water through aquaporins, down the concentration gradient into the blood plasma

Question 26

What are symptoms of drinking alcohol which decreases the release of ADH?

Answer 26

1. Dehydration/ more thirsty
2. More frequent urination
3. Less concentrated urine