3.3 Regulation of Arterial Pressure and Flow

Question 1

Using Ohm’s law, logically derive the two main control mechanisms that influence blood pressure

Answer 1

• Control of cardiac output (flow/current)
• Control of systemic vascular resistance

Question 2

Which chambers/nodes of the heart do the sympa/parasympathetic nervous system innervate?

Answer 2

Para: Atria, SA node, AV node
Sympa: Atria, ventricles, SA node, AV node

Question 3

Which branch of the autonomic nervous system can more rapidly alter heart rate?

Answer 3

Parasympathetic

Question 4

Is the operating point of the baroreflex pre-determined?

Answer 4

• No.
• It can be altered by chronic changes in blood pressure
• This is how we can increase our blood pressure during exercise

Question 5

What is pressure diuresis?

Answer 5

Increase fluid output due to increased BP

Question 6

What is pressure natriuresis?

Answer 6

Increases sodium excretion in response to increased BP

Question 7

Describe longer term, natural mechanisms of BP control

Answer 7

In response to increased blood pressure, pressure natriuresis and pressure diuresis increase, thus reducing blood pressure.

Question 8

Describe the direct effects of angiotensin II on fluid and salt retention

Answer 8

• Renal artery constriction
• Reduced renal flow
• Increased fluid retention

Question 9

Describe the indirect effects of angiotensin II on fluid and salt retention

Answer 9

Aldosterone increase sodium reabsorption and thus increases blood volume and pressure

Question 10

In terms of sympathetic nerve function, what factor controls the degree of systemic arterial constriction?

Answer 10

Higher rate of firing -> more constriction
Lower rate of firing -> less constriction

Question 11

Describe metabolic factors that contribute to control of blood flow

Answer 11

• Oxygen/CO2 removal
• Nutrient delivery
• H+ removal
• Hormone transport

Question 12

Effect of increased metabolic rate on blood flow is…

Answer 12

Increase

Question 13

Describe how tissue-derived vasodilators control local blood flow

Answer 13

Substances such as adenosine, ADP, ATP and K+ all promote local vasodilation in response to increased metabolic activity

Question 14

What is the main endothelium derived vasodilator? How does it modulate local blood flow? Under what main circumstance is it released?

Answer 14

• Nitric oxide
• Potent vasodilator; released in response to shear stress or receptor-dependent activation to increase flow

Question 15

Why is it difficult to isolate which tissue-derived local factors are most important in regulating blood flow? What is this concept known as?

Answer 15

• Known as redundancy
• If one factor is eliminated, others will increase their effect to compensate

Question 16

Describe the myogenic mechanism by which cerebral blood flow is controlled

Answer 16

• As pressure increased, mechanically-gated calcium channels facilitate smooth muscle contraction in response to arterial stretch
• Allows flow to remain constant

Question 17

Define “autoregulation” of blood flow

Answer 17

The intrinsic ability of an organ to maintain constant blood flow despite changes in perfusion pressure

Question 18

What is the role of the cardiovascular centre in regulating blood pressure?

Answer 18

This is the central location (specifically, within the medulla), where the afferent inputs are sent during the baroreceptor reflex, before sympathetic outflow modulates the response.