Blood vessels

• Blood vessels are highly branched tubes through which blood circulates from the heart to all parts of the body.

Types of Blood vessels

• There are three types of blood vessels -:

  1. Arteries

     • An artery is a vessel which distribute oxygenated blood (except pulmonary artery) to various body parts from the heart.
       OR,
     • Vessels that carry blood away from the heart are called arteries.
     • They are distributary in function.
     • Characters –
       • Thick muscular walls
       • Narrow lumen
       • Valves are absent as there is no danger of backward flow of blood
     • Structure of Artery
       • The wall of artery is made up of three layers of tissue
         1. Tunica Externa – It is outermost coat made up of connective tissue.
         2. Tunica Media – Middle very thick coat, made up of smooth walled muscles.
         3. Tunica Interna or Endothelium – Innermost coat made up of flattened cells called endothelium which is an elastic layer.

  2. Veins

     • A vein is a vessel which collects deoxygenated blood from body parts (except pulmonary vein) to the heart.
       OR,
     • Vessels that carry blood towards the heart are called veins.
     • They are collecting in function.
     • Characters –
       • Thin muscular walls
       • Wider lumen
       • Contain valves at regular intervals which prevents the backward flow of blood

         

  3. Capillaries

     • Capillaries are very thin – walled mainly single – celled in thickness narrow vessels.
     • They are present at the junction of an artery and a vein.
     • Functions of Capillaries –
       • Thin wall of capillaries helps in exchanging of various materials between the blood and tissues through the wall of capillaries -:
         1. Oxygen diffuses from the blood to body tissues.
         2. Carbon dioxide diffuses from the tissues to blood.
         3. Nutrients diffuse from blood to the body tissues.
         4. Metabolic wastes diffuses from tissues to blood for elimination.
         5. Leucocytes (WBCs) squeeze through the wall of capillaries by means of amoeboid movement.
       • Capillaries are capable of vasodilation and vasoconstriction.