Cardiovascular System - Control of Arterial Blood Pressure

Question 1

Define arterial blood pressure.

Answer 1

Force exerted by the blood against the walls of the arteries as it is pumped from the heart throughout the circulatory system. It is typically measured in millimeters of mercury (mmHg) and consists of two main components: systolic pressure and diastolic pressure.

Question 2

What is systolic pressure?

Answer 2

Systolic pressure represents the highest pressure in the arteries, occurring during ventricular contraction (systole) when blood is ejected from the heart into the arteries.
Normal systolic blood pressure in adults is typically around 90 to 120 mmHg

Question 3

What is diastolic pressure?

Answer 3

Diastolic pressure represents the lowest pressure in the arteries, occurring during ventricular relaxation (diastole) when the heart refills with blood.
Normal diastolic blood pressure in adults is typically around 60 to 80 mmHg

Question 4

How do you calculate mean arterial blood pressure?

Answer 4

Diastolic pressure + one third the difference between systolic and diastolic pressure (pulse pressure)

Question 5

Describe the changes in cardiac output with baroreceptor activity.

Answer 5

Blood pressure is monitored by stretch receptors in the carotid sinus and aortic arch
These detect the absolute level of pressure (tonic) and changes in pressure (phasic) in both of these blood vessels. They project via the IX and X nerve afferents to the medulla oblongata where they mediate an integrated response that keeps blood pressure within normal ranges.
Afferents from the baroreceptors reach the nucleus of the tractus solitarius in the medulla oblongata where they synapse with neurons that inhibit sympathetic outflow to the heart, thus reducing cardiac ouput

Question 6

Describe the role of the vasomotor centre in cardiac output.

Answer 6

Groups of neurones that project to noradrenergic sympathetic efferents that constrict blood vessels.
Baroreceptor stimulation acts to inhibit output from the vasomotor centre, thereby increasing the caliber of the resistance vessels, reducing peripheral resistance and blood pressure

Question 7

What happens if blood pressure rises?

Answer 7

If blood pressure rises, then barorecptor activation inhibits sympathetic outflow to the heart and the blood vessels.
Vagal outflow to the heart is increased.
This acts to decrease cardiac output, reduce peripheral resistance and so bring blood pressure back to normal levels

Question 8

Describe the effects of hormones on blood pressure.

Answer 8

Noradrenaline and adrenaline secreted by the adrenal medulla act as vasoconstrictor hormones.
Angiotensin causes vasoconstriction and sodium absorption via the renin/ angiotensin/ aldosterone axis
Kinins act to dilate blood vessels
Atrial Natriuretic peptide, released by the atria when fluid volume increases causes sodium diuresis and an inhibition of vasoconstriction
Endothelium secretes - endothelin which causes vasoconstriction and EDRF which causes smooth muscle relaxation and vasodilation.

Question 9

What are other reflexes involved in controlling blood pressure?

Answer 9

Those from low blood pressure side of circulation - walls of right and left atria, entrance of superior and inferior vena cava and pulmonary veins
They mediate a fall in blood pressure via vasodilation if stimulated