Circulatory system

The circulatory system has several functions:

the system comprises blood, the heart to pump the blood, and blood vessels through which blood may flow. A simplified diagram of the human circulatory system clearly demonstrates how the structure of the system relates to its function in providing oxygen for tissues; deoxygenated blood returning from the systemic circulation enters the right side of the four-chambered heart, whence it is pumped into the pulmonary circulation that it may be oxygenated in the lungs. The newly oxygenated blood flows through the pulmonary vein into the left side of the heart, where it is pumped to the body.
 * Transports nutrients and oxygen to tissues;
 * Carries waste away from tissues;
 * Acts as a vehicle for the immune system;
 * Transport hormones from the endocrine glands ( ductless glands ) to the target organs.
 * Produce human milk, the most precious infant food to the growing child .--Shkumara (discuss • contribs) 15:04, 8 January 2014 (UTC)

the sound that is often heard when you put your ear to somebody's chest i.e the sound lub-dub lub-dub......is nothing but the opening and closing of valves in the heart.

PARTS:
 * Heart; located inside the chest behind the sternum. It is not located in the exact center of the chest; it lies slightly more to the left of the sternum than to the right.
 * Blood vessels
 * Blood

The heart, when beating @ 65 beats/minute, with 2-3 oz. of blood being pumped with each beat, it could fill a 2,000 gallon tanker in one day.

Basic Structure of the circulatory system
Blood - The blood is composed of oxygen-carrying erythrocytes (red blood cells, or RBCs), immunological white blood cells (of varying types), puncture clogging platelets, and plasma, a straw-coloured liquid containing many dissolved substances, such as glucose, hormones, and carbon dioxide.

Heart - The heart is a four-chambered muscular pump. On examination, the left side of the heart is larger than the right side of the heart, and this illustrates an important division of labour in the heart. The right heart receives blood from the systemic (body) circulation, and pumps it through the lungs, the blood doesn't have to travel very far, so there isn't much resistance to flow, resulting in a relatively weak muscle. The left heart receives blood from the pulmonary circulation and pumps it to the systemic circulation, it has to supply the entire body, from head to toe, with fresh, oxygenated blood, the resistance to flow is much greater, which causes a relative hypertrophy of the left side (imagine using a 15kg weight with one arm and a 5kg weight with the other, and the difference in the arm muscles that would result.

Arteries

Arterioles

Capillaries

Venules

Veins