Integration of the Cardiovascular Mechanisms

Question 1

What is the equation of the resistance to flow in a blood vessel?

Answer 1

R alpha (n.L)/R to the power of 4. (n is blood viscosity).

Question 2

What is the resistance to blood flow mainly controlled by?

Answer 2

Vascular smooth muscles through changes in arteriolar radius.

Question 3

How much will the flow increase if the radius is doubled?

Answer 3

16 times.

Question 4

What causes the vasomotor tone in vascular smooth muscles?

Answer 4

Tonic discharge of sympathetic nerves.

Question 5

Where is there parasympathetic stimulation of smooth muscles?

Answer 5

In the penis and clitoris.

Question 6

Is the effect of adrenaline organ specific and what does it depend on?

Answer 6

Yes, and the predominant type of receptor.

Question 7

What receptors does adrenaline bind to for vasoconstriction and vasodilation?

Answer 7

a1 for vasoconstriction, B2 for vasodilation.

Question 8

Where are a1 receptors and b2 receptors found in the body?

Answer 8

a1 receptors are predominant in skin, gut and kidney areterioles. B2 are predominant in cardiac and skeletal muscle arterioles.

Question 9

Can extrinsic mechanisms of vascular smooth muscle contraction override the intrinsic mechanisms or is it the other way around?

Answer 9

The intrinsic mechanisms can override the extrinsic mechanisms.

Question 10

What factors do intrinsic control of vascular smooth muscle include?

Answer 10

Local chemical and physical factors.

Question 11

What is metabolic hyperaemia?

Answer 11

Increased blood flow due to a metabolic cause.

Question 12

What metabolic factors cause relaxation of arteriolar smooth muscles and vasodilation?

Answer 12

Decreased local PO2, increased local PCO2, increased local [H+] conc, increased extracellular K+, increased osmolarity of ECF, adenosine release (from ATP).

Question 13

What are local humoral agents?

Answer 13

Local chemical released within an organ.

Question 14

When are local humoral agents released?

Answer 14

In reponse to tissue injury and inflammation.

Question 15

GIve 3 examples of humoral agents that cause vasodilation.

Answer 15

Histamine, bradykinin, nitric oxide (NO).

Question 16

How and when is nitric oxide produced by the vascular endothelium?

Answer 16

From amino acid L-arginine through enzymatic action of nitric oxide synthase (NOS). Produced continuously.

Question 17

What physical stimulus can cause release of calcium in endothelial cells and subsequent activation of NOS (flow dependent NO formation)?

Answer 17

Shear stress of vascular endothelium as a result of increased flow.

Question 18

What is receptor stimulated NO formation?

Answer 18

Where chemical stimuli induce NO formation (many vasoactive substances act through stimulation of NO formation).

Question 19

Give 4 examples of humoral agents that cause vasoconstriction.

Answer 19

Serotonin, thromboxane A2, leukotrienes, endothelin.

Question 20

What are the common features of endothelial producted vasodilators?

Answer 20

Anti-thrombotic, anti-inflammatory and anti-oxidants.

Question 21

What are the common features of endothelial cell produced vasoconstrictors?

Answer 21

Pro-thrombotic, pro-inflammatory and pro-oxidants.

Question 22

How can temperature affect vascular smooth muscles?

Answer 22

Cold causes vasoconstriction, warmth causes vasodilation.

Question 23

Describe the myogenic response to stretch and what tissues is this important in?

Answer 23

If MAP rises resistance vessels automatically constrict to limit flow, if MAP falls resistance vessels automatically dilate to increase flow. Important in brain and kidneys.

Question 24

How does dilation of arterioles affect arteries upstream?

Answer 24

Causes sheer stress making them dilate (increases blood flow to metabolically active tissues).

Question 25

Why does the brain not usually participate in the baroreceptor reflex and what actually regulates its blood pressure?

Answer 25

Sympathetic nerve stimulation does not have large effect. Myogenic response.

Question 26

What factors will increase the venous return?

Answer 26

Increased venomotor tone, blood volume, skeletal muscle pump and respiratory pump.

Question 27

How does increased venous return increase the stroke volume?

Answer 27

Increased venous return -> increased atrial pressure -> increased EDV -> increased stroke volume.

Question 28

What nerve fibres are venous smooth muscle cells supplied with?

Answer 28

Sympathetic nerve fibres.

Question 29

What are the acute CVS responses to exercise?

Answer 29

1. Sympathetic nerve activity increases.
2. HR and SV increase (increased CO).
3. Sympathetic vasomotor nerves reduce flow to kidneys and gut (vasoconstriction).
4. Skeletal and cardiac muscle: metabolic hyperaemia overcomes vasomotor drive (vasodilation).
5. Blood flow to skeletal and cardiac muscle increases in proportion to metabolic activity.
6. The increases in CO increases systolic BP. Metabolic hyperaemia decreases SVR and DBP (pulse pressure increases).
7. Post exercise hypotensive response.

Question 30

What are the chronic cardiovascular responses to exercise?

Answer 30

1. Helps reduce blood pressure (mechanism not fully understood and controversial).
2. Reduction in sympathetic tone and noradrenaline levels.
3. Increased parasympathetic tone to the heart.
4. Cardiac remodelling.
5. Reduction in plasma renin levels.
6. Improved endothelial function (upregulation of vasodilators and downregulation of vasoconstrictors, decrease arterial stiffening).