circulatory system

Circulatory System
Is a transport system that carries blood and lymph to and from the tissue of the body.
Blood vessels :
Blood vessels are arranged so that blood delivered from the heart quickly by arteries reaches a network of narrow thin walled vessels, the blood capillaries.

General features of Arteries &Veins :
They are composed three layers called tunics they are from the lumen outward :
1-Tunica intima : The innermost layer that includes the endothelial lining (a single layer of simple squamous epithelial tissue ),resting on a basal lamina and the underlying connective tissue .
2-Tunica media : The muscular middle layer (consists primarily of circumferentially arranged layers of smooth muscle cells ).
3- Tunica adventitia : The outermost connective tissue layer.































Arteries :-Are classified into three types on the basis of size and the characteristics of the tunica media.

Artery
Vessel Inner layer
(Tunica Intima) Middle layer
(Tunica Media) Outer layer
(Tunica Adventitia)
Elastic artery Endothelium
Connective tissue
Smooth muscle Smooth muscle
Elastic lamellae Connective tissue Some elastic fibers Thinner than tunica media
Muscular artery
Large Endothelium
Connective tissue
Smooth muscle Smooth muscle
Collagen fiber
Relatively little elastic tissue Connective tissue Some elastic fibers
Thinner than tunica media
Small Endothelium
Connective tissue
Smooth muscle Prominent internal elastic membrane Smooth muscle (8-10 cell layers)
Collagen fibers Connective tissue Some elastic fibers
Thinner than tunica media
Arteriole Endothelium
Connective tissue
Smooth muscle
Internal elastic membrane Smooth muscle (1-2 cell layers) Thin , ill-defined sheath of connective tissue
Capillary Endothelium
None None



















Veins :- Generally, the tunica adventitia is the thickest layer of the wall , and are classified into three types on the basis of size and the characteristics of the tunica media :

Veins


Vessel Inner layer
(Tunica Intima) Middle layer
(Tunica Media) Outer layer
(Tunica Adventitia)
Post capillary venule Endothelium
None None


Muscular venule Endothelium
Smooth muscle
(1 or 2 layers) Connective tissue
Some elastic fibers
Thicker than tunica media
Small vein
Endothelium
Smooth muscle (2 or 3 layers) Smooth muscle
(2 or 3 layers continuous with tunica intima) Connective tissue Some elastic fibers
Thicker than tunica media
Medium vein Endothelium
Connective tissue
Smooth muscle
Internal elastic membrane in some cases Smooth muscle
Collagen fibers




Connective tissue Some elastic fibers Much thicker than tunica media

Large vein Endothelium Connective tissue
Smooth muscle
Smooth muscle (2 – 15 layers)
Cardiac muscle near heart
Collagen fibers Connective tissue Some elastic fibers Much thicker than tunica media



Capillaries :- Smallest diameter blood vessels , are consist of single layer of endothelial cells and their basal lamina .