Control of arterial blood pressure - 2

Question 1

What are the components of the total body fluid?

Answer 1

• 2/3 are intracellular fluid

- 1/3 are extracellular fluid

Question 2

What makes up the extracellular fluid volume (ECFV)?

Answer 2

Plasma volume (PV) + interstitial fluid volume (IFV)

Question 3

What happens if plasma volume falls?

Answer 3

Compensatory mechanisms shifts fluid from the interstitial compartment to the plasma compartment

Question 4

What happens if ECFV is controlled?

Answer 4

Plasma volume (PV), blood volume and MAP would be controlled

Question 5

How do hormones act as effectors to regulate the extracellular fluid volume (including plasma volume)?

Answer 5

Regulating the water and salt balance in our bodies

Question 6

What is the water and salt balance in healthy people?

Answer 6

water input=water output

Question 7

What 3 hormones regulate extracellular fluid volume?

Answer 7

1. The renin-angiotensin- Aldosterone system- RAAS
2. Atrial natriuretic peptide -ANP
3. Antidiuretic hormone (arginine vasopressin)- ADH

Question 8

What is the role of renin-angiotensin-aldosterone system?

Answer 8

Regulates plasma volume and TPR and hence the regulation of MAP

Question 9

Where is renin released from?

Answer 9

Kidneys

Question 10

What does renin do?

Answer 10

Stimulates the formation of angiotensin I in the blood from angiotensinogen (produced by the liver)

Question 11

What converts angiotensin I to angiotensin II?

Answer 11

Angiotensin coverting enzyme -ACE

Question 12

What are the roles of angiotensin II?

Answer 12

1) stimulates the release of Aldosterone from the adrenal cortex
- Causes systemic vasoconstriction which increases TPR and BP
- Also stimulates thirst and ADH release - i.e. contributes to increasing plasma volume and BP

Question 13

What is the function of aldosterone?

Answer 13

• steroid hormone

- acts on kidneys to increase sodium and water retention which increases plasma volume

Question 14

What 2 main factors affect extracellular fluid volume?

Answer 14

1. water excess or deficit

2. Na+ excess or deficit

Question 15

What 3 mechanisms regulate the RAAS ?

Answer 15

(1) Renal artery hypotension -caused by systemic hypotension ( blood pressure)
(2) stimulation of renal sympathetic nerves
(3) Decreased [Na+] in renal tubular fluid – sensed by macula densa (specialised cells of kidney tubules

Question 16

What Is the rate limiting step for RAAS?

Answer 16

Rennin secretion

Question 17

What is the role of atrial natriuretic peptide and when is it secreted?

Answer 17

• released in response to atrial distension
• causes excretion of salt and water in the kidneys, thereby reducing blood volume and blood pressure
• decrease rennin release
• counter-regulatory mechanism for RAAS

Question 18

What is antidiuretic hormone (ADH)?

Answer 18

Peptide hormone derived from a prehormone precursor synthesised by the hypothalamus and stored in the posterior pituitary

Question 19

What is secretion of ADH stimulated by?

Answer 19

1) reduced extracellular fluid volume

2) increased exrtracellular fluid osmolarity (main stimulus)

Question 20

What is the normal osmolarity of extracellular fluid?

Answer 20

280 milli-osmoles/l

Question 21

What is plasma osmolarity is monitored by?

Answer 21

Osmoreceptors mainly in the brain in close proximity to hypothalamus -

Question 22

What does increased plasma osmolarity lead to?

Answer 22

stimulation the release of ADH

Question 23

What is the role of ADH?

Answer 23

-acts in the kidney tubules to increase the reabsorption of water (conserve water) which increase extracellular and plasma volume and hence CO and BP

Question 24

What effect does ADH have on blood vessels?

Answer 24

• cause vasoconstriction which increases TPR and BP

- the effect is small in normal people but becomes important in hypovolaemic shock

Question 25

How is short term moment to moment regulation of MAP achieved?

Answer 25

via baroreceptors reflex

Question 26

What does ADH regulate?

Answer 26

ECF (including plasma volume and osmolarity) to deal with fluid loads/deficits

Question 27

What does aldosterone regulate?

Answer 27

total body Na+ and with that,ECF volume in the longer term