cardiac cycle

arteries:

• thick walls made up of: more collagen, elastic fibres, and smooth muscle to withstand high pressure

• narrow lumen to maintain high blood pressure - more muscle tissue to maintain pressure in the aorta

• smooth endothelium reduces resistance to blood flow

• no valves because blood is always being forced forwards by the heart an elastic recoil of the arteries

• outer layer of connective tissue with fibres of collagen, a fibrous protein that makes the outer wall tough

veins:

• thin walls made up of: less collagen, elastic fibres, smooth muscle to withstand low pressure

• wide lumen ( thin layer of elastic tissue) to maintain low blood pressure

• smooth endothelium reduces resistance to blood flow

• valves to prevent backflow of blood. blood in the veins is pushed forwards by the contraction of nearby skeletal muscle. when they stop pressing on the vein the blood would tend to flow backwards if there were no valves

• outer layer of connective tissue with fibres of collagen, a fibrous protein that makes the outer wall tough

capillaries

• one cell thick - short diffusion distance

• low pressure no valves

• oxygenated and deoxygenated depending on location

• more elastic tissue to allow recoil

what happens in atrial systole

• volume of atria decreases, so pressure of atria increases

• pressure against the atrioventricular valves pushes them open,

• the atria contract, forcing more blood into the ventricles

• semilunar valves closed: not enough pressure

what happens in ventricular systole

• happens immediately after atrial systole

• ventricles contract from the base of the heart upwards

• semilunar valves are open

• blood is pushed up and out through the arteries

• pressure also closes the atrioventricular valves preventing backflow

what happens in diastole

• both atria and ventricles relax

• elastic recoil lowers pressure in atria and ventricles

• blood drawn back

  • arteries ( semilunar valves) close to prevent backflow

  • veins - blood is drawn into the aorta

when looking at the cardiac cycle in a graph - why is the representation on the left side

its easier to measure pressure