STRUCTURE OF BLOOD VESSELS The heart pumps blood

STRUCTURE OF BLOOD VESSELS The heart pumps blood into vessels that vary in structure, size and function , and there are several types: arteries, arterioles , capillaries , venules and veins. ARTERIES #. these are the bloodvessels transport blood away from the heart. #. these vary in size. #. each arterial wall consists of three layers. a. tunica adventitia b. tunica media c. tunica intima.

A. Tunica adventitia ( outer layer) Made of fibrous tissue B. Tunica media (middle layer) Made of smooth muscles and elastic tissue. C. Tunica intima(inner layer) Made of stratified epithelium.

The middle layer has more elastic than smooth muscles , hence this helps for stretching and absorb the pressure of heart during beats. #. the arteries have more thicker than the veins hence they tolerate the pressure.

ARTERIOLES The arteries further divided and redivides to form arterioles. #. the arterioles has same 3 set of layers. #. but the tunica media has only smooth muscles. #. this composition regulate the systemic pressure within arterioles hence they are called as resistant muscles. #. the arterioles further redivides to form capillaries.

CAPILLARIES #. The capillaries are branched structure of arterioles and venules #. The capillary has single layer. #. it is made up of endothelial cells (squamous epithelium). #. these endothelial cells helps for passage of some molecules and water. #. the blood cells and the large molecules such as plasma proteins cannot pass through capillary walls. #. in liver the capillaries are called as sinusoids.

VEINS AND VENULES These are the blood vessels that return impure blood at the low pressure to the heart. #. the walls of the veins are thinner than the arteries. #. the veins have three layers they are tunica adventitia - outer layer made of fibrous tissue. tunica media- middle layer made of smooth muscles or epithelial tissues. tunica intima- inner layer made of epithelial cells. #. the veins are thinner because there is less smooth muscles and less elastic tissues in the tunica media. #. the veins carry impure blood slowly therefore when veins cut, the blood circulation will stop by collapsing veins but arteries never collapse they remain open.

#. Some veins have valves which prevents the backflow of blood and ensure the flow of blood towards the heart. #. these valves are more in lower Limbs which contains equal pressure of gravity when the person is standing. #. the smallest veins are called venules. #. during bleeding the veins and venues required to prevent blood loss and also maintain blood pressure