Revision 6: Control of the CVS

Question 1

effects of TPR and CO on arterial and venous pressure

Answer 1

TPR: inc -> art. press. inc and ven. press. dec.

CO: inc -> art. press inc. and ve. press. dec.

Question 2

define end systolic and diastolic volume, and stroke volume

Answer 2

ESV: volume of blood in ventricles at the end of systole

EDV: volume of blood in ventriles at end of diastole

SV: difference between ESV and EDV

Question 3

define pre- and after-load

Answer 3

pre-load: stretch of myocardium at the end of diastole, determined by venous pressure

after-load: force necessary to expel blood from ventricles into arteries

Question 4

define contractility and desc. how the Starling Curve is changed by factors inc. the contractility of the ventricular myocardium

Answer 4

contractility is simply the SV obtained compared to the venous press., i.e. the line on a Starling curve

the line shifts to the left if the SyNS causes the force of contraction to inc.

Question 5

effect of changing venous and arterial pressure on CO

Answer 5

inc venous: -> inc. SV (starling’s law) and inc. HR -> inc. CO

dec. arterial: -> inc SV (SyNS from baroreceptos and direct effect) and inc. HR -> inc. CO

Question 6

What would happen if the HR was suddenly inc. (eg due to a faulty pacemaker)

Answer 6

HR inc. -> CO inc. -> dec. ven. press. -> dec. diastolic filling -> dec. SV

Overall, inc. HR, dec. SV -> =CO

Question 7

What would happen to CVS if a meal was eaten?

Answer 7

activity of gut -> release of metabolites -> inc. vasodilatation -> dec. TPR -> inc. ven and dec. art. press. -> inc. CO -> dec. ven. and inc. art. press.

-> System is stabilised

Question 8

The CVS during exercise

Answer 8

If there was no response by ANS: massive vasodilatation by arterioles supplying muscles rapidly dec. TPR and inc. ven. press -> drives heart to top of Starling curve, reducing its capacity to control the CO

However, at the start of exercise, the SyNS acts to rapidly inc. the HR -> prevents ven. press. spikes by pumping any extra blood quickly into arteries, presents at the start of exercise with large changes in arterial and venous press.

Question 9

The CVS when standing up

Answer 9

blood pools in the great/short saphenous (superficial) veins of the legs -> dec. ven. press. -> dec. CO -> dec. art. press.

both art. and ven. press. are low which is bad -> baroreceptors detect dec. art. press. -> inc. HR (ven press. is still low)

body inc. TPR in skin, gut to maintain the inc. art. press.

Sometimes these reflexes don’t work, leading to postural hypotension

Question 10

The CVS in haemorrhages

Answer 10

Consequence of haemorrhage: less blood in capacitance -> dec. ven. press. -> dec. CO -> dec. art. press.

Immediate rxn from body: baroreceptors inc. HR, inc. TPR -> very rapid, very weak pulse w/ low SV (as venous press. is v. low)

Solution: venoconstriction to inc. ven. press., fluid moves from EC space to circulation (autotransfusion)

Question 11

The CVS in a sustained blood volume increase eg changes in kidneys or diet

Answer 11

inc. ven. press. -> inc. CO -> art. press. inc. -> more blood into tiss. -> autoregulation leads to inc. TPR -> CO returns nearly to normal, but permanent hypertension in arteries occur

can be partially solved by diuretics to reduce the blood vol.