the cardiac cycle Flashcards
what is the cardiac cycle?
consists of two phases of the beating of the heart systole (contraction) and diastole (relaxation).
what happens during diastole?
atria relaxed, ventricles relaxed:
blood flows into atria due to high pressure in the pulmonary vein and vena cava, the pressure of atria increases, and is greater than that of the ventricles, forcing AV valves to open (allows blood to passively flow into the ventricles without atrial contraction).
what happens during atrial systole?
atria contract, ventricles relaxed:
atrial walls contract, the pressure of the atria is greater than that of the ventricles, so remaining blood flows into ventricles - a slight increase in ventricular pressure
what happens during ventricular systole?
atria relaxed, ventricles contract:
ventricle walls contract, the pressure of the ventricles increases, and is greater than that of atria so AV valves close), preventing backflow. The pressure of ventricles further increases and is greater than that of the pulmonary artery and aorta, forcing semi-lunar valves open and blood leaves the heart.
what creates the ‘lub’ and ‘dub’ sound of the heartbeat?
closing of ventricles
which way will blood always move?
from a region of high pressure to a region of low pressure.
what is the use of valves?
to prevent backflow
what are AV valves?
between atrium and ventricle, prevent backflow when the contraction of the ventricles means that ventricular pressure exceeds atrial pressure.
what are semi-lunar valves?
in the aorta and pulmonary artery, prevent backflow when the pressure in these vessels exceeds ventricular pressure.
what are pocket valves?
in veins that occur throughout the venous system. They ensure that when veins are squeezed e.g. when skeletal muscles contract, blood flows back towards the heart rather than away from it.
how are valves designed?
the number of flaps of fibrous tissue - cusp-shaped - like deep bowls - pressure greater on the convex side of the cusps, rather than the concave side, they move apart to let blood pass between the cusps, but when the pressure greater on the concave side, blood collects within the cusps.
