X. Anatomy and Physiology

Circulatory system

Blood

The body contains about 5 liters of blood which consists basically of four constituents:

plasma; red cells; white cells; and platelet cells. The plasma is the liquid component of

the blood which circulates to all the tissue cells throughout the body. It distributes food,

water, salts and heat and collects waste products which are subsequently excreted. The

red cells predominate and give the blood its color. This color is derived from a complex

iron compound (hemoglobin) which is the main oxygen carrier. The white cells give

protection against infection by attacking and killing bacteria and also by producing

substances which are necessary for building up resistance to further infections. The

main purpose of platelets is to assist in the blood clotting mechanism.

The heart and blood vessels

The heart is a thick-walled muscular pump about the size of a clenched fist. It is divided

in the mid line into two sides which do not communicate. Each side has upper and lower

chambers which communicate through heart valves. The separate chambers are each

served by a major blood vessel that either brings blood to the chamber or carries it

away. Blood enters the right atrium from the systemic circulation through the superior

and inferior vena cava. Most of the blood flowing in the right atrium enters to the right

ventricle while the right ventricle relaxes following the previous contraction. Before the

end of ventricular relaxation, the right atrium contracts and enough blood are pushed

from the right atrium into the ventricle which completes the right ventricular filling.

Contraction of the right ventricle pushes blood against the tricuspid valve, forcing it

closed. After pressure within the right ventricle increases, the pulmonary semilunar

valve is forced to open, and blood flows to pulmonary trunk. As the right ventricle

relaxes, its pressure falls rapidly, and pressure in the pulmonary trunk becomes greater

than in the right ventricle. The pulmonary trunk branches to form right and left

pulmonary arteries, which carries deoxygenated blood that will be delivered to lungs for

exchange of carbon dioxide and waste to nutrients and oxygen. After the exchange of

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products in the lung capillaries the blood will go to the pulmonary vein. The pulmonary

veins carry the oxygenated blood into the left atrium. The left atrium contracts forcing it

to open bicuspid valve and filling of blood into the left ventricle. Contraction of left

ventricle cause the bicuspid valve to closed to avoid back-flow and forcing the aortic

valve to open. From the aortic valve it will go to the aortic arch which has three

branches consisting aorta, coronary artery and carotid artery. Blood flowing to the aorta

is distributed to the body except to lungs because it is being supplied by the pulmonary

blood vessel. The heart is being supplied by the coronary artery and the carotid artery

supplies the head part.