Structure of blood vessels
The blood vessels show a vast range of structural modifications. However a few basic patterns can be studied. A blood vessel consists of a wall and a lumen or cavity. The wall of the blood vessels is made up of 3 distinct layers or tunica. They are the tunica intima, tunica media and tunica externa or tunica adventitia. The tunica intima is formed of an endothelium, a delicate connective tissue and elastic fibres. The tunica media contains smooth muscle cells. It causes vasoconstriction and vasodilation. The tunica externa is composed of connective tissue. The composition and thickness of layers varies with the diameter of the blood vessels and the type.
Types of blood vessels :
1. Large elastic arteries :
The walls of these arteries contain elastic fibres. The smooth wall measures about 1micron in thickness. It gets stretchedunder the effect of pulse and recoils elastically
2. Muscular arteries :
There are larger and smaller muscular arteries. The larger muscular arteries are inelastic and they have thick walls. The wall has 30-40microns in diameter in the layers of smooth muscles. Since they regulate blood supply, they are called distributing arteries. The small muscular arteries are capable of vasodilation and vasoconstriction.
3. Arterioles :
They conduct blood from the arteries to the capillary bed. These are small vessels capable of vasodilation and vasoconstriction.
4. Capillaries :
These are fine vessels found between arterioles and venules. They measure 5-8micron in diameter.
5. Venules :
These are tubes of flat, oval or polygonal endothelial cells. Each venule is formed by the convergence of two or more capillaries. Its diameter ranges upto 30micron.
6. Veins :
Veins seen in anatomy are medium veins. They run in between venules and large veins. Large veins transport blood to the heart. Veins with diameter above 2 mm have valves. They are of semilunar type. They allow movement of blood towards the heart. There are several valves in the medium veins.
Branching of blood vessels :
When an artery divides into two equal branches, the original artery ceases to exist. Hence the branches are called terminal branches. The smaller branching vessels formed on the sides are called the collateral branches. When arteries are joined to each other it is named as anastomosis.
Blood supply to blood vessels :
As any other region, the cells and tissue on the wall of the blood vessel require nourishment. Some amount can diffuse from blood in the lumen. For vessels having diameter greater than 1 mm, diffusion of nutrients may not be possible. Such vessels have very minute vessels called vasa vasorum spread over them. They penetrate into the wall of the blood vessels.
Innervation of blood vessels :
The walls of the blood vessels are innervated by sympathetic nerve fibres. They regulate the contraction of the musculature. They effect vasoconstriction.
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| Blood Vessels |
The blood vessels show a vast range of structural modifications. However a few basic patterns can be studied. A blood vessel consists of a wall and a lumen or cavity. The wall of the blood vessels is made up of 3 distinct layers or tunica. They are the tunica intima, tunica media and tunica externa or tunica adventitia. The tunica intima is formed of an endothelium, a delicate connective tissue and elastic fibres. The tunica media contains smooth muscle cells. It causes vasoconstriction and vasodilation. The tunica externa is composed of connective tissue. The composition and thickness of layers varies with the diameter of the blood vessels and the type.
Types of blood vessels :
1. Large elastic arteries :
The walls of these arteries contain elastic fibres. The smooth wall measures about 1micron in thickness. It gets stretchedunder the effect of pulse and recoils elastically
2. Muscular arteries :
There are larger and smaller muscular arteries. The larger muscular arteries are inelastic and they have thick walls. The wall has 30-40microns in diameter in the layers of smooth muscles. Since they regulate blood supply, they are called distributing arteries. The small muscular arteries are capable of vasodilation and vasoconstriction.
3. Arterioles :
They conduct blood from the arteries to the capillary bed. These are small vessels capable of vasodilation and vasoconstriction.
4. Capillaries :
These are fine vessels found between arterioles and venules. They measure 5-8micron in diameter.
5. Venules :
These are tubes of flat, oval or polygonal endothelial cells. Each venule is formed by the convergence of two or more capillaries. Its diameter ranges upto 30micron.
6. Veins :
Veins seen in anatomy are medium veins. They run in between venules and large veins. Large veins transport blood to the heart. Veins with diameter above 2 mm have valves. They are of semilunar type. They allow movement of blood towards the heart. There are several valves in the medium veins.
Branching of blood vessels :
When an artery divides into two equal branches, the original artery ceases to exist. Hence the branches are called terminal branches. The smaller branching vessels formed on the sides are called the collateral branches. When arteries are joined to each other it is named as anastomosis.
Blood supply to blood vessels :
As any other region, the cells and tissue on the wall of the blood vessel require nourishment. Some amount can diffuse from blood in the lumen. For vessels having diameter greater than 1 mm, diffusion of nutrients may not be possible. Such vessels have very minute vessels called vasa vasorum spread over them. They penetrate into the wall of the blood vessels.
Innervation of blood vessels :
The walls of the blood vessels are innervated by sympathetic nerve fibres. They regulate the contraction of the musculature. They effect vasoconstriction.
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