Cardiovascular system 


"Heart anatomy" by Patrick J. Lynch is licensed under CC BY 2.0

Cardiovascular system includes 
1- heart
2-Arteries
3-veins
4-capillaries

Heart

Heart is a pumping organ which consists of cardiac muscles. It which pumps blood through the blood vessels of the cardiovascular system which help in transport of oxygen and nutrients to all over the body. It also carry metabolic waste i.e carbon dioxide to lungs.
It consists of 4 chambers
Left atrium
Left ventricle
Right atrium
Right ventricle
the contraction of heart takes place  by SA node a peace maker which generate action potential and this action potential spread all over the heart by the help of Av bundles and purkinje fibers.

Arteries

Arteries are the type of blood vessels which carry oxygenated blood from heart to all over the body. It is a thick walled blood vessel and has a high pressure .Walls of artery consists of three layers. 
The innermost layer is called  tunica intima (knowns as tunica interna).
The middle layer is called tunica media.
The external layer is known as tunica adventitia.
Pulmonary artery carry deoxygenated blood from from right ventricle to lungs.

Veins

Veins are the type of blood vessels which carry deoxygenated blood from different parts of body back to the heart. It is a thin walled blood vessel and it has a very low pressure. It contains valves which prevents backflow of blood from body to heart. walls of vein consist of three layer which are similar to arteries but there is less smooth muscle and connective tissue which makes walls of veins thinner than arteries.

Pulmonary veins carry the oxygenated blood from lungs to left atrium of the heart.

Capillaries

They are thin blood vessels which connect arterioles to venules. they are very thin in size approximately 5 micrometer in diameter and composed of two layer of cells.
Innerlayer is called as endothelial and outerlayer is called as epithelial. Capillaries help in transport of oxygen and nutrients to different organs of body. they convey the blood between arterioles and venules.
they are site of exchange for different substances includes oxygen, carbon dioxide, water, nutrients, glucose and metabolic waste.