Integration of the Cardiovascular Mechanisms Flashcards Preview

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Flashcards in Integration of the Cardiovascular Mechanisms Deck (30)
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1
Q

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

A

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

2
Q

What is the resistance to blood flow mainly controlled by?

A

Vascular smooth muscles through changes in arteriolar radius.

3
Q

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

A

16 times.

4
Q

What causes the vasomotor tone in vascular smooth muscles?

A

Tonic discharge of sympathetic nerves.

5
Q

Where is there parasympathetic stimulation of smooth muscles?

A

In the penis and clitoris.

6
Q

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

A

Yes, and the predominant type of receptor.

7
Q

What receptors does adrenaline bind to for vasoconstriction and vasodilation?

A

a1 for vasoconstriction, B2 for vasodilation.

8
Q

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

A

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

9
Q

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

A

The intrinsic mechanisms can override the extrinsic mechanisms.

10
Q

What factors do intrinsic control of vascular smooth muscle include?

A

Local chemical and physical factors.

11
Q

What is metabolic hyperaemia?

A

Increased blood flow due to a metabolic cause.

12
Q

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

A

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

13
Q

What are local humoral agents?

A

Local chemical released within an organ.

14
Q

When are local humoral agents released?

A

In reponse to tissue injury and inflammation.

15
Q

GIve 3 examples of humoral agents that cause vasodilation.

A

Histamine, bradykinin, nitric oxide (NO).

16
Q

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

A

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

17
Q

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

A

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

18
Q

What is receptor stimulated NO formation?

A

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

19
Q

Give 4 examples of humoral agents that cause vasoconstriction.

A

Serotonin, thromboxane A2, leukotrienes, endothelin.

20
Q

What are the common features of endothelial producted vasodilators?

A

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

21
Q

What are the common features of endothelial cell produced vasoconstrictors?

A

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

22
Q

How can temperature affect vascular smooth muscles?

A

Cold causes vasoconstriction, warmth causes vasodilation.

23
Q

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

A

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.

24
Q

How does dilation of arterioles affect arteries upstream?

A

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

25
Q

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

A

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

26
Q

What factors will increase the venous return?

A

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

27
Q

How does increased venous return increase the stroke volume?

A

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

28
Q

What nerve fibres are venous smooth muscle cells supplied with?

A

Sympathetic nerve fibres.

29
Q

What are the acute CVS responses to exercise?

A
  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.
30
Q

What are the chronic cardiovascular responses to exercise?

A
  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).