CVS physiology

Question 1

Describe the stages of the cardiac cycle

Answer 1

late diastole - passive filling of atria and ventricles

atrial systole - contraction of atria, small ejection into ventricles, causing small increase in intra-atrial pressure.

Isometric/volumetric contraction of ventricles - closes mitral/tricuspid valves, pressure builds in ventricles but does not exceed that in aorta/pulmonary artery.

Ventricular ejection - pressure in ventricles exceeds that in arteries, pulmonary/aortic valves open, blood ejected from ventricles

Isometric relaxation of ventricles - contraction drops, pressure in arteries exceeds ventricles, pulmonary/aortic valves close.

Question 2

outline shape/process of pressure volume loop

Answer 2

1. mitral valve opens. increase in ventricular vol, slight pressure increase until 2. mitral closes. vertical increase in pressure, no vol change (isometric ventricular contraction) 3. aortic valve opens. pressure continues to increase, volume drops from 135 to 65 mls - normal SV = 70 4. aortic aortic valve closes. pressure drops from ~100 to near 0

Question 3

Describe changes in velocity and pressure through the vascular tree

Answer 3

Velocity highest in largest vessels i.e. aorta, arteries, pressure also highest (~90 in arteries, drops to 40 in arterioles) total cross sectional diameter is lowest

capillary pressure = 40-20
Venous pressure = 20-5

Question 4

List the factors effecting venous blood flow

Answer 4

Gravity - standing/lying
muscular pump - i.e. calves
respiratory pump - pressure in thorax decreases on inspiration, draws blood upwards
muscular tone of veins - capacitance vessel function
systemic artery pressure

Question 5

Outline arterial baroreceptor reflex

Answer 5

Baroreceptors in carotids and aorta. Constant firing of action potentials to CV medullary centres, via the vagus nerve for the aorta and the glossopharyngeal nerve for the carotids.

Increased MAP causes increased stretch and AP firing. Input summated in CV medullary centres, sympathetic or parasympathetic response modulated.

Sympathetic response is via sympathetic spinal nerves, acts on SA node and

Question 6

What are the main factors in blood clotting

Answer 6

Platelet aggregation and fibrin aggregation

Question 7

List the anti-clotting mechanisms of capillaries

Answer 7

Prostacyclin secretion and NO secretion -Inhibit platelet aggregation

Thrombomodulin, Heparin - inhibit fibrinogen to fibrin conversion

TFPI (tissue factor pathway inhibitor) - inhibits thrombin production

Plasmin and plasminogen activator - plasmin digests clots.

Question 8

Darcy’s law

Answer 8

flow = delta pressure/Resistance

Question 9

Pouseilles law

Answer 9

resistance = (viscosity x length x 8)/(Pi x r4)

Question 10

Equation for MAP

Answer 10

MAP - CVP = COxTPR

= > MAP = COxTPR

Question 11

List the three types of intrinsic blood pressure regulation

Answer 11

Active hyperaemia, Pressure autoregulation, Reactive hyperaemia

Question 12

Define active/metabolic hyperaemia, Pressure auto-regulation and reactive hyperaemia

Answer 12

active hyperaemia - metabolite buildup in tissue as result of metabolism, causes release of EDRF aka NO, which dilates capillaries, increasing blood flow to tissue ‘washes away’ increased metabolite conc., restoring balance.

Flow autoregulation - low flow to tissue results in metabolite build up. Same response as above. This is an adaption to ensure a tissue receives adequate blood supply regardless of MAP changes.

Reactive Hyperaemia - essentially an extreme form of active hyperaemia, in response to ischaemia

Question 13

What tissue displays excellent active hyperaemia response

Answer 13

The brain - high metabolic demand

Question 14

Give examples were strong pressure autoregulation is essential

Answer 14

In the kidneys, traumatic blood loss.

Question 15

Outline extrinsic control of arteriolar resistance

Answer 15

Sympathetic innervation, release of noradrenaline acting on a1 adrenoreceptors causes arteriolar restriction.

However, there is action on B2 receptors in tissues containing these i.e. skeletal and cardiac muscle have high numbers. This causes dilation.

Adrenaline also elicits these effects

The parasympthetic system has little effect.

Question 16

What occurs in the sympathetic response to the arterial baroreceptor reflex

Answer 16

Sympathetic response - release of noradrenaline from sympathetic fibres, release of adrenaline from adrenal medula

Acts on B1 receptors in atria, ventricles and veins/venioles.
Results in increased HR and contractile force, dilation of veins causing increased venous return.

Acts on B2 receptors in skeletal muscle and cardiac arteries, causing arteriolar dilation

Question 17

Outline cardiac response to exercise

Answer 17

Increased O2/nutrient demand by tissues causes dilation of arterioles to these tissues, requires greater cardiac output to meet demand.

Dilated arterioles cause MAP drop. Artery Baroreceptor response acts sympathetically to increase HR, contractility and B2 activation to maintain MAP and supply tissues.

Question 18

Describe the cardiac response to standing up from lying down.

Answer 18

Increased pooling of blood in veins in legs as a result of gravity causes drop in venous return, preload/EDV, SV and MAP. Arterial baroreceptor response to increase MAP: reduced vagal tone, increased sympathetic tone.

Question 19

Describe the effects of the Valsalva manoeuvre on the CVS

Answer 19

1. Initial forced expiration causes increased pressure on aorta, increasing MAP for a few seconds.
2. However this pressure compresses the VC, redugin venous return, therefore preload, SV and CO, causing MAP to fall.
3. Arterial baroreceptor response begins to raise MAP, may reach almost normal pressure.
4. Cessation of forced expiration causes sudden drop in intra-thoracic pressure, causing MAP to fall again
5. Baroreceptor response returns MAP to normal.

Question 20

What are the main hormones involved in long term BP control?

Answer 20

Renin-angiotensin-aldesterone axis
ADH/Vasopressin
BNP and ANP

Question 21

What cells release renin?

Answer 21

Juxtaglomerular cells of kidney

Question 22

What three inputs stimulate renin release?

Answer 22

Decreased afferent nephron arteriolar distension

Decreased Na/Cl concentration at Macula densa cells in ascending loop of Henle.

Sympathetic stimulation from CVS medullary centres in response to decreased MAP.

Question 23

Outline the cascade effects of renin

Answer 23

renin acts on angiotensinogen, converting it to angiotensin I

Angiotensin one is converted by ubiquitous ACE to angiotensin II. Angiotensin II:

1. Acts on pituitary gland, causing AADH release
2. Stimulates the adrenal cortex to produce aldesterone
3. Acts as a vasoconstrictor.

Question 24

What are the effects of ADH?

Answer 24

Increases collecting duct permeability, therefore reducing diuresis

Stimulates thirst

Increases TPR (vasopressin)

Question 25

What is the effect of aldesterone?

Answer 25

Acts on loop of Henle, increasing Na+ reabsorption and therefore water reabsorption

Question 26

Where are ANP and BNP released from?

Answer 26

The walls of the atria and ventricles respectively

Question 27

What stimulates ANP and BNP release?

Answer 27

Increased distension of ventricle/atrial walls by increased plasma volume.

Question 28

What are the functions of ANP and BNP

Answer 28

Act on loop of Henle, decreasing Na reabsorption

Act on CVS medullary centres, decreasing sympathetic output.

Inhibit Renin release