gas exchange and the heart

counter current flow

water and blood flow in opposite directions, blood always meets water with a higher concentration of oxygen so diffusion gradient is maintained

parallel flow

water and blood flow in the same direction halfway across blood and water reach same oxygen concentration equilibrium

trachea

fine tubes that have a wall of single layered epithelial cells

open circulatory system

blood is pumped at a low pressure into a fluid filled cavity the haemocoel

closed circulatory system

blood is enclosed in blood vessels tissues are not in direct contact with the blood blood pumps at a higher pressure

single circulatory system

the blood stays in vessels on a single pathway around the body and only passes through the heart once

double circulatory system

blood goes through the heart twice

diastole

relaxation of the muscle

systole

contraction of the muscle

sino atrial node

hearts internal pacemaker

p wave

depolarisation/ contraction of atria atrial systole

QRS complex

depolarisation/ contraction of ventricles ventricular systole

T wave

repolarisation/ relaxation of ventricles ventricular diastole

artery

takes high pressure blood away from heart

vein

returns low pressure blood to heart

capillary

allows for exchange with surrounding tissues via diffusion