only becomes important when the body is exposed to extreme external conditions.

depends upon the interaction of receptors, integrating centres, and effectors.

usually involves positive feedback loops.

All of the above are correct.

The total resistance of the pulmonary circulation is much less than that of the systemic circulation.

The volume of blood flowing into the aorta per minute is much larger than that flowing into the pulmonary artery.

Blood flowing in all the veins of the body has a low oxygen content.

Blood flows in parallel through the systemic and pulmonary circulations.

Calcium enters the cell from the extracellular space via voltage sensitive calcium channels

Calcium enters from the extracellular space via the sarcoplasmic reticulum

Both (a) and (b)

Calcium enters the cytoplasm from intracellular stores within the sarcoplasmic reticulum

a fall in the arterial pressure as a result of the increase in venous pressure.

an increase in the total volume of blood within the veins.

all of the above.

an increase in the venous return of blood to the heart

the phase of isovolumetric ventricular relaxation.

the peak of ventricular ejection.

contraction of the atria.

the phase of passive ventricular filling.

requires the heart to have an intact sympathetic innervation.

relies on circulating adrenaline to increase cardiac contractility.

allows cardiac output to be matched to venous return.

allows the heart to maintain a constant cardiac output despite large variations in venous return.

Local chemical factors are released which cause the smooth muscle of the capillaries to relax.

There is an increase in activity in the sympathetic nerves which innervate the arterioles.

Local chemical factors are released which cause the smooth muscle of the arterioles to relax.

The veins leaving the organ dilate, allowing more blood to enter them.

Binding to tropomyosin to remove the blocking action of troponin on cross bridge formation

Changing the conformation of the myosin (thick filament) heads to initiate cross-bridge movement

Binding to troponin to remove the blocking action of tropomyosin on cross bridge formation

Hyperpolarising the cell membrane

QRS complex: repolarization of the ventricles

P wave: depolarization of the ventricles

T wave: repolarization of the atria

QRS complex: depolarization of the ventricles

the total blood volume would not change but there would be less red blood cells per millilitre of blood.

the resistance to blood flow through the vasculature would increase.

the viscosity of the blood would be decreased.

the red blood cells would become swollen due to the increased haemoglobin content within them.