Cardiac Conduction System

Study Notes

Cardiac muscle cells contract spontaneously and are coordinated by the sinoatrial (SA) node.
The SA node is composed of nodal tissue with characteristics of both muscle and nervous tissue and is located in the upper wall of the right atrium.
When the SA node contracts, it generates nerve impulses that travel throughout the heart wall, causing the atria to contract.
The atrioventricular (AV) node delays the impulses for some seconds, allowing the atria to contract and empty their content of blood.
The impulses are then sent down the atrioventricular bundle, which branches off into two bundles, and carried down to the center of the heart and then to the left and right ventricles.
At the base of the heart, the atrioventricular bundles start to divide further into Purkinje fibers, triggering the muscle fibers in the ventricles to contract.

There are three main types of blood vessels: arteries, veins, and capillaries.
All blood vessels have three layers: tunica intima, tunica media, and tunica adventitia.
The endothelium, a thin layer of simple squamous epithelium, lines the blood vessels, keeping blood cells inside and preventing clots from forming.

Capillaries are very small, with thin walls, and often appear to have only a tunica intima.
Arteries have the thickest muscular layers to pump blood around the body.
Veins have very little muscle in their walls and tend to have the largest lumens.

Lines the blood vessel and is exposed to blood
Composed of endothelium - simple squamous epithelium overlying a basement membrane and a sparse layer of loose connective tissue.