urine production

Question 1

Define filtration

Answer 1

Filtration means that water and small molecules pass (under high pressure) from the blood into the nephron

Question 2

What is the first step of filtration?

Answer 2

1. Blood entering the nephron in the afferent arteriole contains waste products

Question 3

What is the 2nd step of filtration?

Answer 3

Small molecules (such as glucose, amino acids, vitamins, some hormones, urea, salts and water) are forced out of the plasma and into the Bowman’s capsule. Here they form a dilute solution called glomerular filtrate.

Question 4

Where does filtration take place?

Answer 4

Filtration takes place in the glomerulus.

Question 5

What is the 3rd step of filtration? (how does the structure of the glomerulus help filtration? (3))

Answer 5

1. The pressure of the glomerulus is greater than normal blood pressure. filtration in the Bowman’s capsule is called ultra-filtration because of the high pressure.
2. The surface area of the capillaries in the glomerulus is large. This increases the area for filtration.
3. The walls of the glomerular capillaries are more porous than normal capillaries. The cell wall of the Bowman’s capsule is only one cell thick.

Question 6

How is the pressure in the glomerulus greater than normal blood pressure?

Answer 6

This is caused by the already high pressure of the afferent arteriole being increased due to to the efferent arteriole being narrower.

Question 7

What is the 4th step of filtration?

Answer 7

4. larger substances do not enter the glomerular filtrate. These include red and white blood cells, platelets, antibodies, clotting proteins and some hormones.

Question 8

How much of the glomerular filtrate is reabsorbed?

Answer 8

99% is reabsorbed leaving about 1.5 litres of urine to be excreted in a normal day.

Question 9

1. Reabsorption: What happens in the proximal convoluted tubule? (3)

Answer 9

1. Most of the water is reabsorbed by osmosis.
2. All of the useful molecules (glucose, amino acids, vitamins, etc) are reabsorbed by a combination of diffusion and active transport.
3. Most of the salts are reabsorbed by active transport or diffusion.

Question 10

Define reabsorption

Answer 10

Reabsorption means that molecules pass from the nephron back into the blood

Question 11

Define active transport

Answer 11

Active transport means that energy (in the form of ATP) is used to move molecules, often against a concentration gradient, i.e. from low to high concentrations.

Question 12

Define diffusion

Answer 12

Diffusion is the spreading out of molecules from a region of high concentration to a region of low concentration

Question 13

Do diffusion and osmosis require energy?

Answer 13

No

Question 14

Does active transport require energy?

Answer 14

yes

Question 15

What features does the proximal tubule have in order to aid in reabsorption

Answer 15

1. It is thin-walled (one cell thick).
2. Is long (14mm).
3. Has numerous infoldings (called microvilli) in its cells.
4. Has a high concentration of mitochondria to provide energy for active transport.

Question 16

Where is a small amount of water reabsorbed (other than in the proximal convoluted tubule where most is)? What is also reabsorbed with this?

Answer 16

The descending limb of the loop of Henle is permeable to water. In this section of the loop of Henle a small amount of the water is reabsorbed by osmosis. Also, some minerals are reabsorbed.

Question 17

What happens in the ascending limb of the loop of Henle?

Answer 17

The ascending limb of the loop of Henle is permeable to salts. So, salts move out of the nephron into the fluid of the medulla. Initially, this happens by diffusion, but at the top of the ascending limb sodium is pumped out by active transport.

Question 18

Where is sodium pumped out by active transport and into the fluid of the medulla?

Answer 18

at the top of the ascending limb of the loop of Henle

Question 19

The addition of salts (from the ascending limb of the loop of Henle) makes the medulla more concentrated than the fluid in the tubule. what does this cause?

Answer 19

This helps to remove water (by osmosis) from both the descending limb of the loop of Henle and the collecting ducts.

Question 20

What is the function of the loop of Henle?

Answer 20

to reabsorb water

Question 21

What is the distal convoluted tubule involved in?

Answer 21

The control of the water, salt and pH values of the blood

Question 22

What is reabsorbed into the blood in the region of the distal convoluted tubule?

Answer 22

Some water and salts can be reabsorbed from the tubule into the blood in this region.

Question 23

is the collection duct impermeable to water or permeable?

Answer 23

It is permeable to water

Question 24

What is reabsorbed from the filtrate in the collecting duct? How does this occur?

Answer 24

a small amount of water is reabsorbed from the filtrate. This occurs by osmosis, due to the high salt concentration in the medulla.

Question 25

What is the liquid passing from the collecting duct called?

Answer 25

urine

Question 26

Where does urine flow to from the collecting duct?

Answer 26

It flows into the pelvis of the kidney and on to the bladder through the ureters.

Question 27

where does secretion take place?

Answer 27

In the distal tube

Question 28

What is secreted in the distal tube?

Answer 28

potassium ions (K+) and hydrogen ions (H+)

Question 29

The secretion of potassium ions (K+) and hydrogen ions (H+) in the distal tube help to maintain what?

Answer 29

the pH of blood

Question 30

Define secretion

Answer 30

Secretion means that some substances pass from the blood into the nephron

Question 31

How much water is reabsorbed in the proximal convoluted tubule? What else is reabsorbed here and how much?

Answer 31

Most water.
Most salts, glucose, amino acids and vitamins

Question 32

How much water is reabsorbed in the loop of Henle(descending limb)? What else is reabsorbed here and how much?

Answer 32

A little water.
Some minerals

Question 33

How much water is reabsorbed in the loop of Henle(ascending limb)? What else is reabsorbed here and how much?

Answer 33

No water, some salts

Question 34

How much water is reabsorbed in the distal convoluted tubule? What else is reabsorbed here and how much?

Answer 34

Some water.
Some salts

Question 35

How much water is reabsorbed in thecollecting duct? What else is reabsorbed here and how much?

Answer 35

A little water.
Nothing else

Question 36

How does glomerular filtrate differ from urine? (2)

Answer 36

1. It has more water (i.e. is more dilute) than urine.
2. It contains many useful molecules like glucose and amino acids that are not normally found in urine.