Physiology 6 - Integration of CV Mechanisms

Question 1

What are the major resistance vessels in the circulation?

Answer 1

The arterioles

Question 2

What vessels contain most of the blood volume during rest?

Answer 2

The veins (the capacitance vessels)

Question 3

What is the main regulator of the HR?

Answer 3

Autonomic nervous system

Question 4

What are the main regulators of the stroke volume? (3)

Answer 4

Pre-loadAfter-loadMyocardial contractility

Question 5

Where is the main site of TPR?

Answer 5

Arterioles

Question 6

How is resistance to blood flow related to blood viscosity and length of blood vessel?

Answer 6

Directly proportional to blood viscosity and length of blood vessel

Question 7

How is resistance to blood flow related to the radius of the blood vessel?

Answer 7

Inversely proportional to the radius of the blood vessel to the power of 4

Question 8

Equation for what resistance to blood flow is related to?

Answer 8

blood viscosity X length of blood vessel divided by radius of blood vessel to the power of 4

Question 9

How is the resistance to blood flow mainly controlled?

Answer 9

By vascular smooth muscle that changes the radius of arterioles

Question 10

What is involved in the extrinsic control of vascular smooth muscle?

Answer 10

Hormones and nerves

Question 11

What branch of the autonomic nervous system supplies the vascular smooth muscle?What receptors on the smooth muscle does the released neurotransmitter act on?

Answer 11

SympatheticAlpha 1 (noradrenaline)There is no significant parasympathetic innervation of arterial smooth muscle except in the penis and clitoris

Question 12

what is the state of the vascular smooth muscle at rest?Why?

Answer 12

It is partially constricted due to the vasomotor tone - tonic discharge of sympathetic nerves resulting in continuous release of noradrenaline

Question 13

What effect does increased sympathetic stimulation have on vascular smooth muscle?

Answer 13

Increased vasomotor tone = increase vasoconstriction and vice versa

Question 14

What hormones are involved in the control of vascular smooth muscle? (3)

Answer 14

AdrenalineAngiotensin 2Vasopressin (ADH)All cause vasoconstriction

Question 15

What effect dies adrenaline have on vascular smooth muscle?

Answer 15

Adrenal is released from the adrenal medullaAdrenal acting on B2 adrenoceptors causes vasodilation (cardiac and skeletal muscle arterioles) Adrenaline acting on alpha 1 adrenoceptors causes vasoconstriction (predominant in skin, gut and kidney arterioles)

Question 16

What is the purpose of intrinsic controls of vascular smooth muscle?

Answer 16

To match the blood flow of different tissues to their metabolic needs (they can over red the extrinsic control mechanisms)They include local chemical and physical factors

Question 17

What local metabolites (chemicals) cause vasodilation? (6)

Answer 17

Decreased local pO2Increased local pCO2Increased local [H+] (decreased pH)Increased extra-cellular [K+]increased osmolarity of ECFadenosine release (from ATP)

Question 18

What are local humoral agents released in response to?

Answer 18

Tissue injury or inflammation

Question 19

What are examples of local humoral agents which cause relaxation of arteriolar smooth muscle resulting in vasodilation? (3)

Answer 19

HistamineBradykinNO

Question 20

Where is NO released from?What causes its release?

Answer 20

Continuously produced by the vascular endothelium from the amino acid L-arginine through enzymatic action of nitric oxide synthase (NOS)Shear stress on vascular endothelium as a result of increased flow causes release of of calcium in vascular endothelial cells and the subsequent activation of NOSChemical stimuli can also induce NO formation

Question 21

How does NO causes vasodilation?

Answer 21

NO diffuses from the vascular endothelium into the adjacent smooth muscles where it activates the formation of cGMP that serves as a second messenger for signalling smooth muscle relaxation

Question 22

Examples of humoral factors that cause vasocontraction? (4)

Answer 22

SerotoninThromboxane A2leukotrienesEndothelin

Question 23

In terms for thrombotic, inflammatory and oxidant effect, what are endothelial produced vasodilators?

Answer 23

Anti-thrombotic, anti-inflammatory, anti-oxidants (and vice versa for endothelial produced vasoconstrictors

Question 24

Apart from chemicals, what else can intrinsically control vascular smooth muscle?

Answer 24

Physical factors:Sheer stresstemperatureMyogenic response to stretch

Question 25

What effect does temperature have on vascular smooth muscle?

Answer 25

Cold = vasoconstrictionWarmth = vasodilation

Question 26

What is the myogenic response to stretch?

Answer 26

If MAP rises, resistance vessels automatically constrict to limit flowIf MAP falls resistance vessels automatically dilate dilate to increase flow (especially important in tissues lie the brain and kidneys)

Question 27

When is the maximal force generated in myocytes?

Answer 27

At optimal fibre length

Question 28

What 5 factors increase venous return? (5)

Answer 28

Increased venomotor tone Increased skeletal muscle pumpIncreased respiratory pumpIncreased stroke volume = increased arterial pressureIncreased blood volume

Question 29

What branch of the autonomic nervous system supplies your blood vessels?

Answer 29

Sympathetic

Question 30

What does increased venomotor tone cause?

Answer 30

Due to increased sympathetic stimulation - increased venous constructionBlood driven to the right atrium increases (venous return), SV and MAP also increase

Question 31

What does increased muscle activity cause in terms of venous return?

Answer 31

Increased venous return to the heart due to skeletal muscle pump

Question 32

What effect does exercise have on the CVS?

Answer 32

Sympathetic nerve activity increasesHR and SV increase = increased COSympathetic vasomotor nerves reduce flow to kidneys and gut = vasoconstrictionIn skeletal and cardiac muscle, metabolic hyperaemia overcomes vasomotor tone = vasodilationIncrease in CO increases systolic BP The increase in CO increases systolic BP and the metabolic hyperaemia decreases TPR and decreases DBP (pulse pressure increases)Post exercise hypotensive response