a-short-review-of-histology

Smooth Muscle Organisation:

Smooth muscle cells are usually organised into bundles, held together by connective tissue where the cells are close packed and lie in the same orientation
Thus, they tend to act as a group rather than as individual cells
Smooth muscle cells are typically found in the walls of muscular tubes
Within the walls of these tubes they are found as one, two or three layers
Most blood vessels, except the small capillaries, have a single layer of circularly orientated smooth muscle
When this layer of muscle contracts, the luminal diameter of the blood vessel is reduced as is the amount of blood that can flow through it
By co-ordinating the diameter of the various blood vessels in the body the flow of blood to different regions can be controlled
Where waves of alternating contraction of the circular and longitudinal layers of smooth muscle pass along a tube and in doing so move the contents of the tube along the lumen
This is the mechanism used in the intestine to move the contents from mouth to anus
In some blood vessels, there is both a circular layer and a longitudinal layer of muscle
In the cardiovascular system this organisation of muscle is found when there is a requirement for the periodic (often long periods) closure of the lumen to restrict blood flow into beds of blood vessels
Three layers of smooth muscle is not common
However, three layers are present in the wall of the stomach
The third (oblique) layer helps in churning the food to aid digestion