Regulation Of Blood Pressure

Question 1

What are the mechanisms that control blood vessel diameter ?

Answer 1

• intrinsic control
• extrinsic control

Question 2

What is meant by intrinsic control of blood vessels ?

Answer 2

Response to local and physiological effects on the smooth muscle layer of the blood vessels such as stretch, temperature and local mediators

Question 3

What are local mediators ?

Answer 3

Agents that affect blood flow

Question 4

What is meant by extrinsic control of blood vessels ?

Answer 4

Extrinsic control is a more integrated control mechanism
- involves the autonomic nervous system and hormones such as noradrenaline
- a significant control mechanism of the major arteries and veins except the aorta

Question 5

Describe autoregulation as an intrinsic control mechanism

Answer 5

• if there are minor changes in blood pressure then there will be a minor effect on the flow of blood through that vessel
• if there is a sudden increase in blood pressure then there is an increase in blood flow but after a short amount of time the flow is reduced to control levels within the autoregulatory range
• the same happens when there is a sudden decrease in pressure
• if there is a larger than normal increase in blood pressure there would be larger fluctuations in pressure and the transient flow of blood will increase but the ability to return to normal begins to get lost

Question 6

What is the myogenic response ?

Answer 6

When over a very narrow range a steady state flow can still be established despite small changes in pressure

Question 7

Describe metabolic active hyperaemia as an intrinsic control mechanism

Answer 7

This is when there is an increase in organ blood flow associated with an increase in metabolic activity of an organ or tissue
e.g. blood flow increases due to an increase in oxygen consumption during muscle contraction which stimulates the production of vasoactive substances which dilate the blood vessels in the skeletal muscle and vasodilation increases blood flow due to an overall decrease in total peripheral resistance

Question 8

What is reactive hyperaemia ?

Answer 8

A combination of active hyperaemia and autoregulation results in reactive hyperaemia
e.g. when measuring blood pressure and the brachial artery is occluded this causes a build up of metabolic byproducts but when the occlusion is removed there is an increase in blood flow

Question 9

How do local hormones influence blood pressure ?

Answer 9

• histamines lower blood pressure and anti histamines increase blood pressure
• prostaglandins can increase or decrease blood pressure
• vascular endothelium produces nitric oxide which is a vasodilator so decreases blood pressure
• vascular endothelium produces endothelin which is a vasoconstrictor so increases blood pressure

Question 10

Summarise how extrinsic control of blood vessels works

Answer 10

during exercise the body redistributes most of the blood to the skeletal muscles but an adequate supply of blood to the brain is also needed and so extrinsic control provides that variable distribution and is a key regulator of arterial blood pressure

Question 11

Describe how the autonomic nervous system affects vasculature

Answer 11

There is nervous control of vasculature by vasoconstrictor or vasodilator nerve fibres and it is affected by adrenaline

Question 12

Describe how the autonomic nervous system affects the heart

Answer 12

It is affected by time dependent effects (chronotropic effects) such as heart rate - tachycardia/bradycardia - or the strength of contraction (inotropic effects)

Question 13

Describe nervous control of vasculature

Answer 13

• extrinsic control mechanism
• vasoconstrictor nerve fibres are from the sympathetic part of the ANS
• at rest the sympathetic nerve fibres ensure that blood vessels are partially constricted because of this tonic activity
• useful in exercise and fight or flight
• vasodilator nerve fibres are from both the sympathetic and parasympathetic parts of the ANS
• in the parasympathetic part these nerve fibres are involved in rest and digest
• these parasympathetic fibres innervate the salivary glands and the GI tract
• these nerve fibres are not tonically active but promote blood flow during rest
• the sympathetic fibres innervate sweat glands

Question 14

Summarise hormonal control of blood vessels

Answer 14

• adrenaline - vasodilation and vasoconstriction
• vasopressin - vasoconstriction
• atrial natriuretic peptide - vasodilation
• angiotensin II - vasoconstriction

Question 15

What is the role of the baroreceptor reflex ?

Answer 15

It maintains or regulates blood pressure when there is massive blood loss during a haemorrhage

Question 16

Summarise the baroreceptor reflex

Answer 16

• receptors monitor blood pressure in different parts of the body
• they send signals to the control system which is in the medulla oblongata
• the control system integrates that information and provide an output through the ANS to the heart and blood vessels depending on the body’s needs
• this affects cardiac output and total peripheral resistance
• the baroreceptor reflex is a short term regulator of arterial blood pressure

Question 17

Why are two different receptors needed in the reflex ?

Answer 17

One receptor is needed in the high pressure part of circulation and one receptor is needed in the low pressure part of circulation
- baroreceptors monitor high pressure in the aorta and carotid arteries
- volume receptors monitor low pressure in the atria and ventricles

Question 18

Where are baro receptors located ?

Answer 18

They are located in the elastic walls of the carotid arteries and aortic arch

Question 19

What is the role of mechanoreceptors ?

Answer 19

• they respond to changes in stretch
• more pressure leads to more stretch
• send signals to the control system via the glossopharyngeal nerve and vagus nerve
• an increase in stretch and increased pressure leads to an increase in action potentials

Question 20

What is a phasic signal ?

Answer 20

A stream of action potentials associated with a sudden rise in pressure

Question 21

How does the signal in the carotid sinus vary ?

Answer 21

• low blood pressure is associated with phasic activity but low tonic signals
• high blood pressure is associated with phasic activity and a rise in tonic signals due to a higher frequency of discharge

Question 22

Summarise the central control system involved in the baroreceptor reflex

Answer 22

• receives signals from the carotid sinus and the aortic arch
• located in the medulla oblongata
• it is a polysynaptic area and has output to different regions

Question 23

Describe sympathetic and parasympathetic activity of the heart

Answer 23

• a sharp rise in blood pressure leads to an increase in stretch of the blood vessels
• increased impulses are sent to control centres
• this means there is increased level of inhibition in the sympathetic activity to the heart and vasculature
• this means there is increased level of parasympathetic activity to the heart
• this leads to bradycardia and a decrease in vascular tone and vasodilation
• therefore leads to a decrease in total peripheral resistance

Question 24

What are the effectors of the baroreceptor reflex ?

Answer 24

• vasculature
• heart