Short Term Control of Blood Pressure

Question 1

Why does the mean arterial pressure need to be regulated?

Answer 1

It is the driving force pushing blood through the circulation, if it falls too low it causes syncope and if it becomes too high it causes hypertension

Question 2

What is the function of the arterial baroreflex?

Answer 2

Acts rapidly to minimise fluctuations in the MABP

Question 3

What are baroreceptors?

Answer 3

Afferent nerve endings in the walls of the carotid sinuses and aortic arch

Question 4

What is the function of the baroreceptors?

Answer 4

Sense alterations in wall-stretch caused by pressure changes, and respond to these by modifying the frequency at which they fire action potentials

Question 5

What effect do pressure elevations have?

Answer 5

Increase wall stretch and increase AP impulse frequency from the baroreceptors (vice versa for pressure decreases)

Question 6

When MAP falls, what does the reduction in baroreceptor impulse frequency cause the brain to do?

Answer 6

Reduce the firing of vagal efferents which supply the sinoatrial node, resulting in tachycardia

Question 7

When MAP falls and the brain reduces the firing of vagal efferents, what happens to the activity of the sympathetic nerves innervating the heart and blood vessels?

Answer 7

Activity increases, resulting in increased cardiac contractility and the constriction of arteries and veins

Question 8

What does stimulation of the renal sympathetic nerves cause?

Answer 8

Increase in renin release and consequently angiotensin II production and aldosterone secretion, resulting in fluid retention

Question 9

Tachycardia, vasoconstriction and fluid retention act together to do what?

Answer 9

Raise MAP

Question 10

What are the main differences between A-fibres and C-fibres?

Answer 10

A-fibres have large unmyelinated axons and are activated over lower levels of pressure
C-fibres have small unmyelinated axons and respond over higher levers of pressure

Question 11

Baroreceptor A and C fibres provide input to what?

Answer 11

The brain

Question 12

The brain is most sensitive to pressure changes between which range?

Answer 12

60 and 150mmHg

Question 13

How does the brain allow increases in MAP to occur?

Answer 13

It is able to reset the baroreflex

Question 14

What causes a decrease in arterial wall compliance?

Answer 14

Ageing
Hypertension
Atherosclerosis

Question 15

When are alterations in frequency of baroreceptor firing greatest? When do these alterations tend to moderate?

Answer 15

While pressure is changing

Tend to moderate when a new steady-state pressure is established

Question 16

What happens if the baroreflex is unable to prevent a change in MAP?

Answer 16

It will reset within several hours to the new level of pressure

Question 17

What are the other inputs to the medullary cardiovascular centres?

Answer 17

Cardiopulmonary baroreceptors 
Central chemoreceptors 
Chemoreceptors in muscles
Joint receptors 
Higher centres

Question 18

Regulation of blood pressure in the long term can’t be done by the arterial baroreceptors, what does it revolve around instead?

Answer 18

Blood volume

Question 19

What are the main sensors involved in the long-term regulation of blood pressure?

Answer 19

Cardiopulmonary baroreceptors - effects tend to be hormonal, act on blood vessels and kidneys

Question 20

What does angiotensin II cause?

Answer 20

Arteriolar construction, and increased TPR

Question 21

What does aldosterone cause?

Answer 21

Increase Na+ reabsorption and increased plasma volume

Question 22

What does vasopressin cause?

Answer 22

Arteriolar constriction and increased TPR

Increased water permeability of the collecting duct and increased plasma volume

Question 23

What do ANP and BNP cause?

Answer 23

Arteriolar dilation and decreased TPR

Increased Na+ excretion and decreased blood volume

Question 24

What effect does standing have on hydrostatic pressure?

Answer 24

Increases hydrostatic pressure causing pooling of blood in the veins and venules of the feet and legs

Question 25

What effect does standing have on venous return, EDV, preload, SV, CO, MAP and baroreceptor firing rate?

Answer 25

Decreases these

Question 26

What effect does decreased vagal tone have on HR and CO?

Answer 26

Increases these

Question 27

What does increased sympathetic tone cause?

Answer 27

Increased;
HR
CO 
Contractility 
SV 
Venoconstriction 
Venous return 
EDV 
Arteriolar constriction 
TPR

Question 28

What is the Valsalva manoeuvre?

Answer 28

Forced expiration against a closed glottis

Question 29

The Valsalva manoeuvre causes increased thoracic pressure, this decreases what?

Answer 29

Venous return 
EDV
CO 
SV 
MAP

Question 30

What detects decreased MAP?

Answer 30

Baroreceptors - these initiate the reflex to increase CO and TPR