Short term control of blood pressure

Question 1

What is MAP (mean arterial pressure

Answer 1

MAP is the driving force pushing blood through the circulation
- MAP has to be regulated

Question 2

What occurs if MAP is too low?

Answer 2

Fainting (syncope)

Question 3

What occurs if MAP is too high?

Answer 3

Hypertension

Question 4

What is the arterial baroreflex?

Answer 4

The baroreflex is one of the body’s homeostatic mechanisms that helps to maintain blood pressure at nearly constant levels.

Question 5

What are baroreceptors?

Answer 5

Baroreceptors are stretch receptors and respond to the pressure induced stretching of the blood vessel in which they are found.

Question 6

Mechanism of the baroreflex

Answer 6

The baroreflex provides a rapid negative feedback loop in which an elevated blood pressure reflexively causes the heart rate to decrease and also causes blood pressure to decrease.
- Decreased blood pressure decreases baroreflex activation and causes heart rate to increase and to restore blood pressure levels.

Question 7

What structures is the arterial baroreflex composed of?

Answer 7

• Glossopharyngeal nerve
• Carotid sinus baroreceptors
• Vagus nerve
• Aortic arch baroreceptors
• Medullary cardiovascular centres
• Parasympathetic (vagus)
• Sympathetic nerves
• Adrenal medulla

Question 8

Where are baroreceptors mainly located?

Answer 8

Aortic arch and Carotid sinuses but they can also be found elsewhere

Question 9

What are other outputs to the medullary cardiovascular centres?

Answer 9

• Cardiopulmonary baroreceptors
• Central chemoreceptors
• Chemoreceptors in muscle
• Joint receptors
• Higher centres

Question 10

Features of cardiopulmonary baroreceptors

Answer 10

• They are low pressure receptors/volumoreceptors: right atrium, left atrium, cardiac ventriculi and pulmonary vessels
• They respond to distention, provoke changes in the sympathetic vaso-constrictor outflow and act in the regulation of volume of body fluids
• They exert a greater control over skin and muscle resistance and smaller control over splanchnic vasculature
• Low pressure receptors contribute an important role to minimise arterial pressure changes in response to changes in blood volume

Question 11

Features of central chemoreceptors

Answer 11

Central chemoreceptors are sensitive to the pH of their environment

• These act to detect the changes in pH of nearby cerebrospinal fluid (CSF) that are indicative of altered oxygen or carbon dioxide concentrations available to brain tissues.
• An increase in carbon dioxide causes tension of the arteries, often resulting from decreased CO2 output (hypercapnia), indirectly causes the blood to become more acidic

Question 12

Where are higher centres locate?

Answer 12

In the hypothalamus

Question 13

Features of regulation of blood pressure in the long term

Answer 13

• Cannot be by the arterial baroreceptors
• Revolves around blood volume
• Main sensors are the cardio-pulmonary baroreceptors
• Effects tend to be hormonal
• Act on blood vessels and kidneys

Question 14

Mechanisms for the regulation of blood pressure in the long term

Answer 14

• Renin-Angiotensin-Aldosterone system
• Vasopressin (=antidiuretic hormone)
• Atrial natriuretic pepetide & brain na

Question 15

Basic function of renin-angiotensin-aldosterone system

Answer 15

• Angiotensin II causes arteriolar constriction, and therefore increases TPR.
• Increases water permeabillity of collecting duct, and increases plasma volume.

Question 16

Basic function of Vasopressin

Answer 16

• Causes arteriolar constriction, and therefore increases TPR.
• Increases water permeability of collecting duct, and therefore increases plasma volume.

Question 17

Basic function of Atrial natriuretic peptide & Brain natriuretic peptide

Answer 17

• Causes arteriolar dilation, therefore decreases TPR.

- Increases Na+ excretion (natriuresis)

Question 18

Effect of standing on MAP

Answer 18

• Increased hydrostatic pressure causes pooling of blood in veins/venules of feet/legs.
• This causes decreased: VR, EDV, preload, SV, CO, MAP, baroreceptor firing rate.

Question 19

How does the reflex response affect vagal tone?

Answer 19

Decreased vagal tone causes increased heart rate and increased cardiac output

Question 20

How does the reflex response affect sympathetic tone

Answer 20

• Increases sympathetic tone by:
• increasing SV and CO
• Increased contractility- due to increased SV & CO
• Increased Venoconstriction- due to increased VR, EDV, SV ,CO
• Increased arteriolar constriction- due to increased TPr

Question 21

What part of the heart does the vagus nerve innervate?

Answer 21

The sinoatrial node

Question 22

What receptors does the heart mainly contain?

Answer 22

Beta 1 receptors in the SA node and Ventricular muscle

Beta 2 receptors in coronary arteries

Question 23

What occurs to pacemaker cells when heart rate is increased?

Answer 23

Pacemaker cells depolarise faster allowing for an increase in heart rate.

Question 24

What receptors are used for contraction?

Answer 24

Alpha 1 receptors

- However one does not follow this rule

Question 25

What is the valsalva manoevre

Answer 25

Forced expiration against closed glottis.

- Increases intra-thoracic pressure, making it harder for blood to get back to the heart.

Question 26

In the valsalva manoevre, what changes occurs?

Answer 26

• Increased thoracic pressure is transmitted through to aorta.
• This causes decrease in: VR, EDV, SV, CO, MAP.
• Decrease in MAP is detected by baroreceptors which initiate reflex, increase in CO and TPR.
• Decrease in thoracic pressure is transmitted through to the aorta
• VR is restored so Increase in SV, but reflex effects not worn off.