Circulatory system

MUSCULAR ARTERY HAS THICK MEDIA

Drains excess fuid Found in all tissues except CNS, cartilage,

the bone, bone marrow, thymus, placenta, cornea and teeth.

They can be distinguished from the venous vessels by the absence of erythrocytes and the presence of small number of lumphocytes.

Lymphatic capillaries differ from blood capillaries that they have great permeability.

Endothelial cells are extremely thin.

Basement membrane is absent There are no pericytes. Fine collagenous filaments known as

anchoring filaments link the endothelium to the surrounding supportive tissue preventing collapse.

Wall consists of three tunics:◦ Endocardium:

homologous with the intima of blood vessels; subendothelial layer

◦ Myococradium: thickest; arranged in layers that surround the heart chamber in a complex spiral and insert themselves onto the fibrous skeletal.

Epicardium: a subepicardial layer of loose connective tissue contains veins, nerves and nerve ganglia and edipose tissue; it corresponds to the visceral layer of pericardium.

Fibrous skeletal is composed of dense connective tissue. Its components are trigona fibrosa and annuli fibrosi. These structures are composed of dense connective tissue with thick collagen fibers. They also contain nodules of fibrous cartilage.

Two nodes located in the atrium are SA node, AV node and the AV bundle.

The cells of the impulseconducting system arefunctionally integratedby gap junctions.

The SA node is a mass of modified cardiac musclecells that is fusiform smaller than the atrial musclecells and has fewer myofibrils.

The cells of AV node are similar to that of the SA node but their cytoplasmic projections branch in various directions to form a network.

The AV bundle is formed by similar cells of the AV node but they are larger than ordinary cardiac muscle cells and acquire a special apperance so called purkinje cells.

They have one or two central nucleis. Mitochondria and glycogen rich cytolplasm. Few myofibrils which are restricted to the

periphery of the cytoplasm. After travelling the subendocardial layer,

they penetrate the ventricle and become intramyocardiac. This arrangement allows the stimulus to get into the inner most layer of the ventricular muscles.