Blood vasculature

Arteries:

• blood vessels that carry blood away from the heart.
• it carries oxygenated blood except pulmonary and umbilical artery.
• arteries are thick walled having elastic tissues and smooth muscle.
• are under the high pressure.
• have three layers
  (1) the tunica intima, (2) the tunica media, (3) and the tunica adventitia, or tunica externa.
  
  1)tunica intima composed of Lamina propria(smooth muscle andconnective tissue) Basement  membrane and Endothelium.
  2)tunica media composed of external elastic membrane and smooth muscle.
  3)tunica adventitia is composed of connective tissues aroud the blood vessels.

Arterioles:

• transport blood from small arteries to capillaries.
• are the smallest arteries in which the three tunics can be identified.
• are the site of high resistance in the CVS that is regulated by autonomic nervous system (ANS).

Capillaries:

• composed  of single layer of endothelial cells surrounded by basal lamina.
• smallest blood vessels by diameter.
• site of exchanges of cvs.

Venules:

• are formed from merged capillaries.
• have the same structure with capillaries except for their diameter.

Veins:

• blood vessels that carry blood to the heart.
• usually have deoxygenated blood exception are pulmonary vein and umbilical vein.
• veins are thin walled and are under low pressure.
• they are major blood reservoir of systemic blood(about 70%).
• a small change in pressure can cause a large volume change in venous blood.
• veins contain valves that allow blood to flow toward the heart but not in the opposite direction.

Vesa Vasorum:

• bloos supply to walls of  large blood vessels is provided by way of small blood vessels called vasa vasorum
• penetrate from the exterior of the vessel to form a capillary network in the tunica adventitia and the tunica media.
• supply the large blood vessels.