heart author" faq
Structure of blood vessel


Arteries consist of three layers of different types of cells:

1. the innermost, intima,

2. the media,

3. the outermost, adventitia.

A. The intima is comprised of a single layer of endothelial cells embedded in an extracellular matrix.

B. The media is separated from the intima by the internal elastic lamina,and consists of smooth muscle cells,elastic laminae,bundles of collagen fibers and elastic fibrils,all embedded in an extracellular matrix.

C. The adventitia is the most variable layer, containing dense fibroelastic tissue, nutrient vessels, and nerves.


The actual composition of each of these layers varies with the type of blood vessel.

Large conduit arteries are referred to as elastic ones,because of their high ratio of elastic laminae to smooth muscle cells.

Muscular arteries are smaller and have a prevalence of smooth muscle cells

Arterioles consist of only one or two layers of smooth muscle cells.

The smallest vessels are the capillaries,made up of a single layer of endothelial cells, that are occasionally apposed to pericytes-smooth muscle-cells that serve a contractile function.

The venous system has a similar architecture to that of the arterial system above,the main difference being the orientation of the smooth muscle cells within the wall.

The two most important cell types in the vascular system are the endothelial cell and the vascular smooth muscle cell.

The endothelial cell is generally oriented with the direction of blood flow parallel to the main axis of the vessel. Endothelial cells are held together by junctional complexes that regulate permeability and control cell-to-cell communication.

The smooth cell is a spindle-shaped cell, whose orientation varies with the artery,but is generally helical in large, elastic arteries and concentric in muscular arteries.