Control of Blood Pressure

Question 1

What are the normal ranges of pulse pressure?

Answer 1

Between 20 and 50mmHg.

Question 2

How many Korotkoff sounds are there and when is diastolic pressure recorded?

Answer 2

5, the 5th (point at which sound disappears).

Question 3

How would you calculate the pressure gradient between the aorta and the right atrium?

Answer 3

Mean arterial pressure (MAP) - central venous pressure (CVP).

Question 4

What are the 2 ways of calculating mean arterial blood pressure (MAP)?

Answer 4

(2x diastolic + systolic pressure)/3. DBP + 1/3 x pulse pressure.

Question 5

What is the normal mean arterial blood pressure ranges?

Answer 5

70-105mmHg.

Question 6

What is the lowest MAP required to perfuse coronary arteries, brain and kidneys?

Answer 6

60mmHg.

Question 7

What are the equations involving MAP, SV, HR and SVR?

Answer 7

MAP = SV x HR x SVR.

Question 8

What cranial nerves carry impulses from the aortic and carotid baroreceptors?

Answer 8

Aortic - vagus nerve (Xth). Carotid - glossopharyngeal (IXth).

Question 9

What is the response produced when the MAP increases and the carotid sinus afferent nerve fibres fire more?

Answer 9

Cardiac vagal efferent nerve fibre activity will increase, cardiac sympathetic efferent nerve fibre activity will decrease and the sympathetic vasoconstrictor nerve fibre activity will decrease. (Opposite for decrease of MAP).

Question 10

Give an example of when the baroreceptor response is useful in moment-to-moment regulation of MAP?

Answer 10

Prevention of postural hypotension.

Question 11

What is there a slight increase in when healthy people stand from a lying position and what is this caused by?

Answer 11

Diastolic blood pressure, increase in SVR.

Question 12

Why can baroreceptors only respond to acute changes in blood pressure?

Answer 12

Firing decreases if high blood pressure is sustained.

Question 13

What do compensatory mechanisms do if plasma volume falls?

Answer 13

Shift fluid from the interstitial compartment to the plasma compartment.

Question 14

How much of the body’s fluid is extracellular fluid?

Answer 14

About 1/3rd.

Question 15

What are the 2 main factors affecting the ECFV?

Answer 15

1. Water excess or deficit.

2. Na+ excess or deficit.

Question 16

How do hormones regulate ECFV?

Answer 16

By regulating the water and salt balance in our bodies.

Question 17

What constitutes a stable water and salt balance?

Answer 17

Water input = water output.

Question 18

What are 3 hormones which regulate ECFV?

Answer 18

1. Renin-angiotensin-aldosterone system (RAAS).
2. Natriuretic peptides - NPs.
3. ADH (arginine vasopressin/anti-diuretic hormone).

Question 19

Where is renin released from and what does it stimulate the formation of?

Answer 19

The kidenys, angiotensin I from angiotensinogen (produced by liver).

Question 20

What converts angiotensin I into angiotensin II and where is this found?

Answer 20

Angiotensin converting enzyme (ACE, mainly produced by pulmonary vascular epithelium).

Question 21

What are the 3 effects of angiotensin II on the body?

Answer 21

1. Stimulates release of aldosterone from the adrenal cortex.
2. Causes systemic vasoconstriction.
3. Stimulates thirst and release of ADH.

Question 22

What type of hormone is aldosterone, where does it act and what does it do?

Answer 22

Steroid, acts on kidneys to increase sodium and water retention so increases plasma volume.

Question 23

What is the rate limiting step for RAAS?

Answer 23

Renin secretion.

Question 24

What 3 mechanisms stimulate renin release?

Answer 24

1. Renal artery hypotension (caused by systemic hypotension).
2. Stimulation of renal sympathetic nerves.
3. Decreases sodium conc in renal tubular fluid (sensed by macula densa [specialised cells of kidney tubules]).

Question 25

Where is renin released from in the kidney?

Answer 25

The juxtaglomerular apparatus.

Question 26

What is the juxtaglomerular apparatus?

Answer 26

A region comprising the macula densa, extragolmerular mesangial cells and granular cells (release renin).

Question 27

Where are natriuretic hormones synthesised?

Answer 27

Heart (also brain and other organs).

Question 28

When are natriuretic peptides released?

Answer 28

In response to cardiac distension or neurohormonal stimuli.

Question 29

What are the 3 mechanisms of action of natriuretic peptides?

Answer 29

1. Cause excretion of salt and water in kidneys thereby reducing blood volume and pressure.
2. Decrease renin release.
3. Act as vasodilators so decrease SVR and blood pressure.

Question 30

What are the 2 types of natriuretic peptide released by the heart?

Answer 30

1. Atrial natriuretic peptide (ANP).

2. Brain-type natriuretic peptide (BNP).

Question 31

What size is ANP and where is it stored?

Answer 31

28 amino acids, in atrial myocytes.

Question 32

When is ANP released?

Answer 32

In response to atrial distension (hypervolaemic states).

Question 33

What size is BNP and where is it synthesised?

Answer 33

32 amino acids. Heart ventricles, the brain and other organs.

Question 34

Describe the formation of BNP.

Answer 34

Prepro-BNP -> pro-BNP (108 amino acids) -> BNP (32 amino acids).

Question 35

What can be measured in patients with suspected heart failure?

Answer 35

Serum BNP and the N-terminal piece of pro-BNP (NT-pro-BNP, 76 amino acids).

Question 36

What is ADH derived from and where is it stored?

Answer 36

Prehormone precursor synthesised by hypothalamus. Stored in posterior pituitary gland.

Question 37

What is secretion of ADH stimulated by?

Answer 37

1. Reduced extracellular volume. 2. Increased extracellular fluid osmolarity (main stimulus).

Question 38

What is plasma osmolarity monitored by?

Answer 38

Osmoreceptors mainly in the brain in close proximity to hypothalamus.

Question 39

What are the 2 functions of ADH?

Answer 39

1. Acts in kidney tubules to increase reabsorption of water.
2. Acts on blood vessels to cause vasoconstriction (small effect in normal people but important in hypovolaemic shock e.g. haemorrhage).