L28 Regulation of Salt Balance

Question 1

What effect does excessive fluid ingestion have on ECF osmolality?

Answer 1

Excess fluid intake = ↓osmolality of ECF

Question 2

What are some examples of events that ↑ ECF osmolality?

Answer 2

Fluid deprivation, excess solute ingestion, diarrhoea etc.

Question 3

Which hypothalamic osmoreceptors detect ECF osmolality?

Answer 3

Supraoptic and paraventricular nuclei (regulate ADH)

Lateral preoptic (controls thirst)

Question 4

True or false: The kidneys can produce up to 23 litres of urine per day

Answer 4

True.

Question 5

True or false: The kidneys can produce as little as 300ml of urine per day

Answer 5

True.

Question 6

What determines osmolality of ECF?

A) Water content
B) Salt content
C) Both A and B
D) Neither A nor B

Answer 6

C) Both A and B

Osmolality is determined not only by water content, but also by salt content

Question 7

What is the major cation in ECF?

Answer 7

Na

Question 8

True or false: Hypernatremia can result in hypotension

Answer 8

False.

↑Na = ↑H2O, therefore hypernatremia leads to hypertension

Question 9

True or false hyponatremia can result in hypovolaemia

Answer 9

True.

↓Na = ↓H2O

This leads to hypovolaemia and hypotension

Question 10

Why does water follow sodium?

Answer 10

Sodium increases osmolality of the fluid, so ↑Na in ECF will lead to ↑osmosis of water.

Water will diffuse out of a hypotonic solution into a hypertonic solution.

Hypertonic = greater osmolality = more solute

Question 11

Increase ECF osmolality will lead to what response from the body?

Answer 11

↑ osmolality = ↑ Na

Therefore, need to increase water in ECF.

Responses: ADH secretion (↑ water retention) and thirst (↑ fluid intake)

Question 12

Decrease ECF osmolality will lead to what response from the body?

Answer 12

↓ osmolality = ↓ Na

Therefore, ↓ water in ECF.

Responses: ADH suppression (↑ water excretion)

Question 13

Define ‘effective circulating volume’

Answer 13

The component of blood which is perfusing the tissues

Not necessarily identical to the intravascular blood volume - e.g. congestive heart failure

Question 14

True or false: Renin is an enzyme

Answer 14

True

Question 15

Where is renin synthesised and stored?

Answer 15

Juxtaglomerular apparatus

Question 16

True or false: Increasing the effective circulating volume stimulates release of renin

Answer 16

False.

↑ sympathetic activity

↓ afferent arteriolar pressure

↓ Na delivery at macula densa (end of the loop of Henle/start of distal tubule)

These are all reflective of a decrease in ECV (caused by ↓Na)

Question 17

There are two mechanism of renin release:

1. The __1__ releases __2__, which stimulates granular cells to release renin into blood.
2. __3__ nerves via __4__ receptors

Answer 17

1. macula densa
2. prostaglandin I2 (PGI2)
3. Sympathetic
4. beta-adrenergic

Question 18

Which agent in the RAA system is a decapeptide messenger?

Answer 18

Angiotensin I

Question 19

Which agent in the RAA system is a plasma protein that is cleaved by renin?

Answer 19

Angiotensinogen

Question 20

Which plasma endothelial enzyme converts angiotensin I to angiotensin II?

Answer 20

Angiotensin converting enzyme (ACE)

Question 21

Which agent in the RAA system is an octapeptide, and the primary hormone in Na regulation?

Answer 21

Angiotensin II

Question 22

What is angiotensin II broken down into?

Answer 22

Angiotensin III and inactive products. Broken down by plasma peptidases

Question 23

In what ways does angiotensin II increase blood pressure?

Answer 23

1. Vasoconstriction
2. ↑Na reabsorption from proximal tubule
3. Stimulates aldosterone secretion - ↑Na reabsorption from distal tubule
4. Thirst
5. ADH release (water retention)

Question 24

Removal of which organ results in:

1. ↑NaCl excretion via urine
2. ↓Na in ECF
3. ↓ ECF volume
4. Circulatory collapse

Answer 24

Adrenal glands - loss of aldosterone

Death can be avoided by high Na diet and aldosterone replacement therapy

Question 25

Which agent in the RAA system is synthesised and secreted from zona glomerulosa?

Answer 25

Aldosterone

Question 26

Aldosterone is: ``` A) a glucocorticoid B) a mineralocorticoid C) an androgen D) synthesised from cholesterol E) Both B and D ```

Answer 26

E) Both B and D Remember that it regulates body minerals, therefore is a mineralocorticoid.

Question 27

Which of the following is a trigger for release of aldosterone? ``` A) ↑ plasma [K] B) ↓ plasma [K] C) ↑ plasma [Na] D) ↓ ECV E) Both B and C F) B, C and D G) Both A and D ```

Answer 27

G) Both A and D Stimuli for aldosterone release include: ↑ plasma K concentration ↓ plasma Na concentration ↓ ECV

Question 28

Aldosterone promotes: ``` A) Na reabsorption in collecting duct B) K secretion in collecting duct C) H secretion in collecting duct D) Na reabsorption in gut and sweat glands E) All of the above ```

Answer 28

E) All of the above

Question 29

What are principal cells and intercalated cells?

Answer 29

Cells in collecting duct epithelium. Principal cells: main Na reabsorbing cells. Site of action for aldosterone, K-sparing diuretics and spironolactone. Intercalated cells: H secretion, bicarbonate reabsorption

Question 30

Which 28 amino acid hormone is released in response to hypovolaemia?

Answer 30

Atrial natriuretic peptide Atrial = released from atrial cell in response to atrial stretch Natriuretic = causes ↑ Na excretion in urine

Question 31

Which 32 amino acid hormone is produced in the kidney and has natriuretic properties?

Answer 31

Urodilatin Almost identical to ANP (4 extra AAs), same actions, but is produced in kidney not the atria.

Question 32

What are the actions of ANP and urodilatin?

Answer 32

1. Inhibit collecting duct Na-K ATPase 2. Inhibit aldosterone secretion 3. Reduce renin secretion 4. Promotes vasodilation of afferent arteriole to ↑ GFR (more filtrate = more Na lost)

Question 33

Which natriuretic agent is synthesised in the proximal tubule and inhibits Na-K ATPase and Na-H antiport? ``` A) ANP B) BNP C) Urodilatin D) Dopamine E) Kinins F) Adrenomedullin ```

Answer 33

D) Dopamine

Question 34

Which 52 amino acid peptide is synthesised in the kidney, increases GFR and decreases Na tubular reabsorption? ``` A) ANP B) BNP C) Urodilatin D) Dopamine E) Kinins F) Adrenomedullin ```

Answer 34

F) Adrenomedullin

Question 35

Which of the following counteracts ADH and is produced by the enzyme kallikrein? ``` A) ANP B) BNP C) Urodilatin D) Dopamine E) Kinins F) Adrenomedullin ```

Answer 35

E) Kinins