Control of Arterial Tone

Question 1

What are resistance vessels major contributors to?

Answer 1

Regulation of arterial blood pressure and regulation of local blood flow

Question 2

What is pressure equal to?

Answer 2

Pressure = Flow X Resistance

Question 3

What is TPR mainly determined by?

Answer 3

Resistance arteries

Question 4

Define resistance vessels?

Answer 4

Arteries and arterioles that contribute most substantially to TPR.

Question 5

What are arterioles made of?

Answer 5

1-2 layers of smooth muscle in the media layer

Question 6

What are extrinsic factors?

Answer 6

Autonomic nerves and Humoral Stimuli

Question 7

What are intrinsic factors?

Answer 7

Autacoids and autoregulation

Question 8

Which factor controls large arteries and veins?

Answer 8

Extrinsic control

Question 9

Which factor controls arterioles?

Answer 9

Both extrinsic and intrinsic control

Question 10

What vessels don’t have a contractile function and why?

Answer 10

Capillaries and postcapillary venules due to having no smooth muscle layer

Question 11

What is the effect of widespread resistance artery constriction?

Answer 11

Raised TPR which causes raised upstream pressure and downstream pressure falls.

Question 12

What is the effect of local resistance artery constriction?

Answer 12

Limited effect on TPR and local downstream pressure falls

Question 13

Define autoregulation.

Answer 13

A (nearly) constant flow in the face of changing pressure.

Question 14

What is the role of autoregulation?

Answer 14

Stabilizes tissue perfusion, capillary pressure and therefore water movement across capillary walls.

Question 15

What is the Myogenic Response?

Answer 15

The active change in diameter subsequent to a change in lumenal pressure.

Question 16

What is myogenic contraction dependent on?

Answer 16

Ca2+ entry into smooth muscle

Question 17

What is Hyperaemia?

Answer 17

Increased blood flow due to increased vasodilator metabolite production.

Question 18

What is reactive hyperaemia?

Answer 18

Increased blood flow due to release of an obstruction.

Question 19

What are autacoids?

Answer 19

Local vasoactive chemicals eg. histamine, bradykinin and prostaglandins

Question 20

What are endothelium vasoconstrictors?

Answer 20

ET-1 and PGH2

Question 21

What are endothelium vasodilators?

Answer 21

EDRFs, NO, PGI2, EDHF

Question 22

What is the effect of Protein Kinase G

Answer 22

cGMP activation -> vascular relaxation by: K+ channel activation with hyperpolarisation and Ca2+ channel closure.
Ca2+ ATPase activity increased
Decreased Ca2+ sensitivity of contractile apparatus

Question 23

What activates K+ channels directly

Answer 23

NO

Question 24

What does K+ do?

Answer 24

Activates KIR channels and stimulates Na+/K+ATPase

Question 25

How does ADRF act?

Answer 25

A paracrine fashion and activates K+ channels in vascular smooth muscle cells

Question 26

Describe sympathetic adrenergic nerves.

Answer 26

Nerve fibres that are tonically active and mostly vasoconstrictor in effect eg. noradrenaline

Question 27

Describe parasympathetic nerves.

Answer 27

Nerve fibres that are not tonically active eg. ACH, VIP and NO

Question 28

Name a sympathetic cholinergic nerve and its function.

Answer 28

ACh. Vasodilation via muscarinic receptors on endothelium (release of EDRFs)

Question 29

Where does sympathetic tone originate from?

Answer 29

The medulla oblongata

Question 30

What increases sympathetic tone?

Answer 30

Fall in arterial blood pressure sensed by baroreceptors and low PO2 and pH and high PCO2 sensed by chemoreceptors

Question 31

What does NA act via?

Answer 31

Adrenoreceptors

Question 32

What is pharmacomechanical coupling?

Answer 32

Depolarisation-independent contraction eg. PLC, PIP2 and DAG

Question 33

What is electrochemical coupling?

Answer 33

Depolarisation-dependent contraction