Physiology 6- Integration of Mechanisms

Question 1

What is the function of capillaries?

Answer 1

Exchange of gas, nutrients and water between blood and tissues

Question 2

What are the major capacitance vessels with most of the blood at rest contained there?

Answer 2

Veins

Question 3

What is TPR regulated by?

Answer 3

Vascular smooth muscle

Question 4

Resistance to blood flow is directly proportional to what?

Answer 4

Blood viscosity and length of the blood vessel

Question 5

Resistance to blood flow is inversely proportional to what?

Answer 5

Radius of the blood vessel to the power 4

Question 6

Resistance is mainly controlled by vascular smooth muscle changing what?

Answer 6

The radius of the vessel

Question 7

In terms of extrinsic control, what is vascular smooth muscle controlled by?

Answer 7

Nerves and hormones

Question 8

In terms of nerve supply, vascular smooth muscle is supplied by ? through the neurotransmitter ? acting on ? adrenoceptors

Answer 8

Sympathetic fibres
Noradrenaline
Alpha receptors

Question 9

What is vasomotor tone?

Answer 9

Vascular smooth muscle being partially constricted at rest

Question 10

What causes vasomotor tone?

Answer 10

Discharge of sympathetic fibres continuously releasing noradrenaline

Question 11

What is there none of in arterial smooth muscle?

Answer 11

Parasympathetic innervation

Question 12

The main hormonal influence on TPR is what?

Answer 12

Adrenaline from adrenal cortex

Question 13

What results from adrenaline acting on alpha receptors?

Answer 13

Vasoconstriction

Question 14

What results from adrenaline acting on beta2 receptors?

Answer 14

Vasodilation

Question 15

Where are alpha receptors more common and hence vasoconstriction by adrenaline?

Answer 15

Skin, gut, kidney arterioles

Question 16

Where are beta2 receptors more common and hence vasodilation by adrenaline?

Answer 16

Cardiac and skeletal muscle arterioles

Question 17

What can override extrinsic control mechanisms of TPR?

Answer 17

Intrinsic control mechanisms

Question 18

What is metabolic hyperaemia?

Answer 18

Increased blood flow to tissues

Question 19

What metabolic factors can cause vasodilation and increased blood flow to tissues?

Answer 19

Low PO2 or high PCO2
Increased H+ (decreased pH)
Increased extracellular K+
Increased osmolarity of ECF
Adenosine release from ATP

Question 20

What are examples of local humoral agents (chemicals) which cause vasodilation?

Answer 20

Bradykinin, NO, histamine

Question 21

What are examples of local humoral agents (chemicals) which cause vasoconstriction?

Answer 21

Serotonin, thromboxane A2, leukotrienes

Question 22

Nitric oxide is produced by ? from the amino acid ? through the enzyme ?

Answer 22

• Vascular endothelium of arteries and arterioles
• L-arginine
• Nitric oxide synthase (NOS)

Question 23

How would you describe NO in terms of its effect on blood flow?

Answer 23

Potent vasodilator

Question 24

What does sheer stress on the endothelium (as a result of increased blood flow) cause release of?

Answer 24

Ca++ and NOS

Question 25

NO diffuses from the endothelium into the adjacent smooth muscle cells to activate what?

Answer 25

cGMP which signals vasodilation

Question 26

What is endothelin?

Answer 26

A potent vasoconstrictor which is released from endothelial cells

Question 27

What 5 factors influence venous return?

Answer 27

Increase venomotor tone, respiratory pump, skeletal muscle pump, blood volume and atrial pressure

Question 28

Venous smooth muscle are provided with what nerve fibres?

Answer 28

Sympathetic

Question 29

What is venomotor tone?

Answer 29

Stimulation of the sympathetic nerve fibres in venous smooth muscle gives contraction