ECF Volume Regulation 1&2

Question 1

Which ions are the major ECF osmoles?

Answer 1

Sodium and chlorine

Question 2

Which ion is the major ICF osmole?

Answer 2

Potassium

Question 3

How is ECF volume regulated?

Answer 3

Regulation of body sodium

Question 4

How is the total body water (42L) regulated?

Answer 4

ECF = 14L (Plasma = 3L and interstitial = 11L)
ICF = 28L

Question 5

How is sodium regulated?

Answer 5

High and low P baroreceptors

Question 6

What happens when there is salt and water loss

Answer 6

Plasma volume decreases leading to a decrease in blood pressure and a decrease in carotid sinus baroreceptor inhibition of sympathetic discharge

Question 7

What happens when there is an increase in sympathetic discharge?

Answer 7

There is an increase in vasoconstriction which increases the blood pressure towards nornal

Question 8

What effect does an increase in sympathetic discharge have on the kidneys?

Answer 8

it increases the renal VC nerve activity which increases renal arteriolar

Question 9

What happens when there is an increase in renin?

Answer 9

It causes an increase in angiotensin Ii which decreases the peritubular capillary hydrostatic pressure and increases sodium reasbsorption

Question 10

Why is there an increase in sodium reabsorption caused by angiotensin II

Answer 10

Because there is greater reabsorptiveforces in the peritubular capillaries

Question 11

What is the reabsorptive range in the proximal tubule?

Answer 11

65% in volume excess to 75% in volume deficit

Question 12

What affect does a change in reabsorption have on the GFR?

Answer 12

Very little: autoregulation maintains the GFR and VC of afferent and efferent means there is little effect unless it is large enough to cause a change in MBP

Question 13

Which hormone regulates sodium reabsorption in the distal tubule?

Answer 13

Aldosterone

Question 14

How is aldosterone secretion controlled?

Answer 14

Reflexes involving the kidneys themselves

Question 15

What are juxtaglomerular cells?

Answer 15

Large epithelial cells with plentiful granules

Question 16

What forms the juxtaglomerular apparatus?

Answer 16

Juxtaglomerular cells + macula densa

Question 17

Which hormone is secreted by the juxtaglomerular cells?

Answer 17

Renin: proteolytic enzyme which acts on angiotensin 1

Question 18

Which enzyme converts angiotensin I to angiotensin II?

Answer 18

Angiotensin converting enzyme (ACE)

Question 19

Where are angiotensin converting enzymes found?

Answer 19

Vascular endothelium especially in the pulmonary circuit

Question 20

What is the function of Angiotesin II?

Answer 20

It stimulates the aldosterone secreting cells in the zona glomerulosa of the adrenal cortex

Question 21

Which step in the RAAS system is the rate limiting step?

Answer 21

Release of Renin

Question 22

What causes an increase in renin release?

Answer 22

A decrease in pressure in the afferent arteriole at the juxtaglomerular cells
Sympathetic nerve activity (on beta 1 cells) and decreased NaCl delivery

Question 23

What causes a decrease in renin release?

Answer 23

Angiotensin II feedback inhibits renin and ADH inhibits renin release

Question 24

How does Angiotensin II respond to hypovolaemia?

Answer 24

It stimulates aldosterone, it is a potent vasoconstrictor, it stimulates ADH secretion and it stimulates the thirst mechanism and salt appetite

Question 25

In the case of a person who has lost both salt and water, what takes priority: ECF volume or ECF osmolarity?

Answer 25

ECF volume: emergency mechanism to save perfusion to the brain

Question 26

What is the management of large losses of salt and water?

Answer 26

Infuse/drink saline

DO NOT give pure water

Question 27

Which hormone promotes sodium reabsorption?

Answer 27

Aldosterone

Question 28

What is ANP and what does it do?

Answer 28

Atrial Natriuretic Peptide: promotes sodium excretion

Question 29

What affect does aldosterone have on potassium secretion?

Answer 29

It increases the secretion

Question 30

Which cells secrete ANP?

Answer 30

Atrial cells

Question 31

Why does renal disruption in uncontrolled diabetes lead to a hyperglycaemic coma?

Answer 31

1) glucose remains in the tubule exerting an osmotic effect
2) Sodium conc. in the lumen is decreased and as sodium enters the proximal tubule sodium reabsorption will be decreased
3) As glucose shares a transporter with sodium, glucose reabsorption is decreased
4) Movement of water out of the tubule is reduced meaning fluid in the descending limb is not so concentrated: interstitial gradient is abolished
5) Large volumes of urine are produced and if ingestion is not adequate then the resulting hypotension may be severe enough to cause a hyperglycaemic coma (due to inadequate blood flow to the brain)