Physiology: Blood Flow and Vascular System

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Blood flow:

Enters right atrium, and flows through valve. Fills ventricles.

Atria contract, any remaining blood moves to ventricle. 

Ventricles contract, deoxygenated blood to lungs via pulmonary artery.

When ventricles contract, no backflow wanted, so valves shut. Blood forced to lungs. 

Pulmonary semilunar valve shuts. Heart starts to relax.

Gas exchange occurs in the lungs. 

Pulmonary vein, oxygenated blood, relaxed heart. Left atria fills. Left ventricle fills too.

Left atria contracts, moves blood to ventricle. 

Ventricle contracts, bicuspid valve shuts. 

Major aorta takes blood to body.

Aortic semilunar valve shuts to stop backflow.

Left side of the heart has thicker walls as more pressure is needed to send blood to the body.

Vascular system: arteries, capillaries and veins.

Large artery walls are elastic. They withstand high pressures and have elastic rebound, recoil. 

Smooth muscle cells in ateries and arterioles contract and relax, varying the vessel diameters. 

Diamerter changes: resistance to flow changes. Blood distributed to different tissues. 

Smooth muscles under neuronal and hormonal control. 

Arteries and arterioles called resistance vessels. 

Blood vessels: 


Endothelium, basal lamina, elastic layer, smooth muscle, elastic layer, connective tissue.


Valve, endothelium, basal lamina, smooth muscle, connective tissue. 

Starling's forces: 

Capillary walls: single layer of endothelial cells. Fine holes called fenestrations. 

Small molecules leak through, but larger protein molecules are held back. 

Water balance in capillary beds result…


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