Capillaries
The capillaries are where all of the important exchanges happen in the circulatory system. Capillaries are very thin, fragile blood vessels that receive oxygen-rich blood from arteries, exchange oxygen and carbon dioxide and then deliver the waste-rich blood to the veins. Capillaries are only one epithelial cell thick and blood can only flow through them in a single file. The red blood cells inside the capillary release their oxygen, which passes through the wall and into the surrounding tissue. The tissue releases its waste products, e.g. carbon dioxide, which pass through the wall and into the red blood cells. The exchange occurs and the waste blood is carried back to the heart and lungs through the veins.
Veins
The veins are blood vessels that carry blood towards the heart and most veins carry oxygenated blood from the tissues back to the heart. Veins differ from arteries in structure and function, e.g. arteries are more muscular than veins and veins contain valves to keep the blood flowing towards the heart while the arteries carry the blood away from the heart. The pulmonary veins are a set of veins that deliver oxygenated blood from the lungs to the heart. It is a large blood vessel that carries blood from the lungs to the left atrium of the heart. There are four pulmonary veins which extend from the left atrium to the lungs. They are the right superior, right inferior, left superior and left inferior pulmonary veins. Pulmonary Veins are the large blood vessels that bring blood to the left side of the heart from the lungs. The pulmonary veins are the only veins in the body that transport oxygenated blood. Veins carry waste-rich blood back to the lungs and heart and they carry blood at a lower pressure than the arteries, so they are not as tough as the arteries. They have three layers, which are thinner and contain less tissue than those in the arteries. The veins have valves inside them, which help ensure the blood flows in one direction through the veins and that the blood flows against the force of gravity.
References
Artery – Wikipedia, the free encyclopaedia (Last modified Sept 2011) Artery functions and the different types of arteries. [27th September]
Veins – Wikipedia, the free encyclopaedia (Last modified Sept 2011) Vein functions and the different types of veins. [27th September]
Capillaries – Wikipedia, the free encyclopaedia (Last modified Sept 2011) Capillary Structure and Functions. [27th September]
Pulmonary Vein – Wikipedia, the free encyclopaedia (Last modified August 2011) Veins in the heart and their pathways. [27th September]
Pulmonary Veins (2011) Definition of Pulmonary Veins. [27th September]
Pulmonary Veins – Function and Definition. Function and definition of the pulmonary veins. [27th September]
Capillaries (2011) Definition of Capillaries. [27th September]
Types and Structure of Arteries. Structure of the arteries and the functions of it in the circulatory system. [27th September]