*Physiology 5 (lecture 5)

Question 1

What is the total body fluid made up of?

Answer 1

Intracellular fluid (2/3rds) and extracellular fluid (1/3rd)

Question 2

What makes up the extracellular fluid?

Answer 2

Plasma volume + interstitial fluid volume

Question 3

What happens if the plasma volume falls?

Answer 3

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

Question 4

What are the 2 main factors that affect extracellular fluid volume?

Answer 4

Water excess or deficit

Na+ excess or deficit

Question 5

How does the body control the extracellular fluid volume (water excess/ deficit and Na+ excess and deficit) therefore controlling MAP? (2)

Answer 5

Hormones act as effectors to regulate the extracellular fluid volume (including plasma volume) by regulating the water and salt balance in our bodies
Healthy people stay in a stable water and salt balance, where water input = water output

Question 6

What 3 hormones/ systems regulate extracellular fluid volume?

Answer 6

The renin-angiotensin-aldosterone system
Atrial natriuretic peptide (ANP)
Antidiuretic hormone (arginine vasopressin) -ADH

Question 7

What are the 3 important components of the Renin-angiotensin-aldosterone system (system helps to regulate plasma volume and TPR ad hence the regulation of MAP)?

Answer 7

Renin
Angiotensin
Aldosterone

Question 8

Where is renin released?

What does it do?

Answer 8

Kidney

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

Question 9

What happens to angiotensin I once it is produced?

Answer 9

It is converted to angiotensin II by angiotensin converting enzyme (ACE) which is produced in the pulmonary vascular endothelium

Question 10

What does angiotensin II do?

Answer 10

Stimulates the release of aldosterone from the adrenal cortex
Causes vasoconstriction (increases TPR and therefore BP)
Causes increased ADH release and increased thirst (Increased plasma volume = increased BP)

Question 11

When is renin released form the kidney?

Answer 11

When plasma volume drops causing a drop in blood pressure

Question 12

What effects does aldosterone have?

Answer 12

Causes increased sodium and water reabsorption in the kidneys
Causes an increased plasma volume
Causes an increased blood pressure

Question 13

What is the rate limiting step in the RAAS?

Answer 13

Renin secretion

Question 14

What 3 factors cause renin release?

Answer 14

Renal artery hypotension (caused by systemic hypotension)
Stimulation of renal sympathetic nerves
Decreased [Na+] in renal tubular fluid (sensed by macula densa)

Question 15

what in the renal tubules senses decreased [Na+]?

Answer 15

Macula densa

Question 16

What synthesis and stores the atrial natriuretic peptide?

Answer 16

28 amino acid peptide synthesised and stored by atrial muscle cells

Question 17

When is atrial natriuretic peptide released?

Answer 17

In response to atrial distension
Causes excretion of salt and water in the kidneys thereby reducing blood volume and blood pressure
Acts as a vasodilator
Decreases renin release

Question 18

What is another name for ADH?

Answer 18

Vasopressin

Question 19

Where is ADH synthesised and stored?

Answer 19

Synthesised by the hypothalmus and stored in the posterior pituitary

Question 20

What stimulates secretion of ADH?

Answer 20

Reduced extracellular fluid volume

Increased extracellular fluid osmolarity (main stimulus)

Question 21

How is plasma osmolarity monitored?

Answer 21

By osmoreceptors mainly in the brain in close proximity to the hypothalamus - increased plasma osmolarity will stimulate release of ADH

Question 22

Where does ADH act?

Answer 22

In the kidney tubules to increase the reabsorption of water
This leads to an increase in extracellular and plasma volume and hence cardiac output and blood pressure
ADH also acts on blood vessels to cause vasoconstriction

Question 23

What is short term moment to moment control of MAP achieved rapidly by?

Answer 23

Baroreceptors reflex

Question 24

What is long term control of MA achieved by?

Answer 24

Control of blood volumes by hormones