Control of cardiac output

Question 1

Define stroke volume.

Answer 1

The volume of blood ejected from each ventricle during each ventricle contraction
SV = EDV - ESV

Question 2

Define cardiac output.

Answer 2

Volume of blood pumped by each ventricle per minute (litres per minute)
CO = SV x HR

Question 3

What is difference between preload and afterload?

Answer 3

Preload is the initial stretching of the cardiac myocytes (muscle cells) prior to contraction. It is related to ventricular filling. Afterload is the force or load against which the heart has to contract to eject the blood.

Question 4

Describe the effects of vagus nerve and sympathetic cardiac nerves on heart rate.

Answer 4

Vagus n - parasympathetic - dec HR (Acetylcholine)

Sympathetic cardiac n - inc HR and force of contraction (noradrenaline)

Question 5

Where are the arterial baroreceptors located?

Answer 5

In the carotid sinus and the aortic arch

Question 6

Describe the baroreceptor reflex after the carotid sinus and aortic arch baroreceptors detect inc BP.

Answer 6

Inc BP -> Inc firing of IX and X nerves (afferent) -> Inc firing of vagal nerve (efferent) -> Dec firing of sympathetic nerves to veins and arteries -> vasodilation

Question 7

Describe the atrial receptor (bainbridge) reflex.

Answer 7

Inc in atrial pressure -> detected by atrial stretch receptors -> inc firing of vagal afferents -> dec parasymp efferent firing -> inc symp efferent firing (inc HR)

Question 8

Describe the chemoreceptor reflex.

Answer 8

Aortic arch/ carotid body chemoreceptors detect change in CO2 levels -> Inc firing of IX and X nerves (afferent) -> Dec firing of X nerve (efferent) -> Inc firing of symp nerves

Question 9

What factors can cause increased preload/ventricular filling?

Answer 9

Inc aortic pressure
Inc atrial contractility
Inc ventricular compliance
Inc central venous pressure
Dec HR
Dec venous compliance

Question 10

What is the starling law? (SV and EDV)

Answer 10

The law states that the stroke volume of the heart increases in response to an increase in the volume of blood in the ventricles, before contraction, when all other factors remain constant.

Question 11

Do positive/negative agents decrease or increase contractility?

Answer 11

Positive Inotropic agents increase contractility

Negative Inotropic agents decrease contractility

Question 12

Vessels are usually classified according to function, what are these 4 classifications?

Answer 12

Capacitance
Exchange
Resistance
Distribution