25. Excretion of waste products

Question 1

Where does most of the reabsorption in the nephron take place?

Answer 1

Proximal convoluted tubule

Question 2

What does the loop of Henle cause urine to become?

Answer 2

• Become more concentrated as it produces a concentration gradient in the surrounding medullary tissue
• Urine is hyper osmotic to the blood

Question 3

What are the three parts of the renal tubule?

Answer 3

• Thin descending limb
• Thick ascending limb
• Thin ascending limb

Question 4

What does the thick ascending limb do?

Answer 4

Actively pumps out NaCl

Question 5

Is the thick ascending limb permeable to water?

Answer 5

No, the thick ascending limb is impermeable to water so water does not follow

Question 6

What does NaCl that has been actively pumped out by the thick ascending limb do?

Answer 6

It raises the solute concentration in the surrounding interstitial fluid of the renal medulla

Question 7

Are there aquaporins in the thick ascending limb?

Answer 7

No aquaporins at this point

Question 8

What is the thin descending limb permeable to?

Answer 8

Highly permeable to water but not to Na+ or Cl-

Question 9

Where does water move in the thin descending limb?

Answer 9

• Water exits the descending loop by osmosis because the surrounding interstitial fluid tissue is more concentrated

Question 10

How does the concentration of the renal fluid in the descending limb change?

Answer 10

It becomes more concentrated

Question 11

In the distal convoluted tubule, what is the concentration of the renal fluid like?

Answer 11

The renal fluid is less concentrated that the interstitial fluid

Question 12

What is reabsorbed at the distal convoluted tubule?

Answer 12

• Reabsorption of salts, amino acids

- Some water moves out by osmosis

Question 13

Compare the concentration of the renal fluid with the interstitial fluid at the distal convoluted tubule?

Answer 13

Renal fluid becomes isosmotic with interstitial fluid

Question 14

What happens at the collecting duct?

Answer 14

As the renal fluid moves down the collecting duct it become highly concentrated as water is drawn out due to the high solute concentration in the interstitial fluid of the medulla

Question 15

What is the major solute in the renal fluid of the collecting duct?

Answer 15

Urea

Question 16

Where does urea movement occur?

Answer 16

• Some urea leaks from the collecting duct into the interstitial fluid of the medulla adding to increased osmotic concentration in renal medulla
• Urea diffuses back into the ascending limb and is returned to the collecting duct

Question 17

What does ADH do?

Answer 17

Also known as vasopressin, ADH controls the permeability of the collecting duct to water, thereby controlling the amount of water reabsorbed from urine

Question 18

How does ADH control permeability to water?

Answer 18

It stimulates the expression of aquaporin 2 which is a water channel in the collecting duct cell membranes

Question 19

What makes people thirsty?

Answer 19

When the brain receives signals that

• The amount of water in the body is too low or
• Some elements in the blood such as sodium are too concentrated

Question 20

What detects the rise in blood osmolarity?

Answer 20

Osmoreceptors detect increased osmolarity and stimulate ADH release

Question 21

What do the osmoreceptors stimulate and what does this do?

Answer 21

They stimulate the hypothalamus

Causes release of ADH in the bloodstream

Question 22

What does ADH do in the kidney?

Answer 22

Increases water permeability of the collecting duct and distal tubule

Question 23

What does increased water permeability do?

Answer 23

Reabsorption of water helps maintain blood volume and blood pressure

Question 24

What detects a rise in blood pressure?

Answer 24

Stretch receptors in the aorta and carotid artery detect increases in blood pressure and inhibit ADH release causing a fall in blood pressure

Question 25

What does low blood pressure cause?

Answer 25

This acts on the hypothalamus and promotes ADH release

Question 26

Where are aquaporins found?

Answer 26

They are found in the renal tubule epithelium

Question 27

How is AQP2 expressed?

Answer 27

• APQ2 is not expressed on the cell membrane
• When there is ADH (stimulus) then the ion channels move to the apical membrane and express themselves
• Water moves from the collecting duct to the tissue

Question 28

What is nephrogenic diabetes insipidus (NDI)?

Answer 28

A disease characterised by excessive urination and thirst

Question 29

What causes NDI?

Answer 29

A mutation in the vasopressin (ADH) gene meaning you drink and urinate excessively

Question 30

What happens during a hangover?

Answer 30

• High blood alcohol blocks production of vasopressin in the pituitary gland
• Cannot produce vasopressin
• Kidneys don’t return water to the blood
• Frequent trips to the bathroom to urinate

Question 31

What is the name of the system that regulates blood pressure?

Answer 31

Renin - Angiotensin - Aldosterone System (RAAS)

Question 32

What is the first step when blood pressure falls?

Answer 32

Renin release by the kidney

Question 33

What does renin do?

Answer 33

Cleaves angiotensinogen into angiotensin 1

Question 34

What happens to angiotensin 1?

Answer 34

Angiotensin 1 is converted to angiotensin 2 by angiotensin concerting enzyme (ACE)

Question 35

What does angiotensin concerting enzyme do?

Answer 35

• Constriction of peripheral blood vessels
• Release of aldosterone (which enhances Na+ reabsorption and hence water reabsorption in distal convoluted tubule and collecting duct)
• Stimulation of thirst and drinking

Question 36

What cells detect a decrease in blood pressure?

Answer 36

Juxtaglomerular cells detect low blood pressure