Cardiovascular system

Department of Histology and Embryology Medical college in Three Gorges University

• The circulatory system comprises both the cardiovascular and lymphatic system.

The cardiovascular system:

heart

blood vessels: capillaries

arteries

viens

• There are three layers in the wall of the heart :

• (1)Endocardium:epithelium

subepithelial layer

subendocardial layer

• (2)Myocardium: cardiac muscle

• (3)Epicardium: connective tissue

mesothelium

Histology of the heart

Endocardium 心内膜

It provide smoothing lining for the chambers of the heart

endocardium

subepithelial layer

Purkinje fibers

Endocarditis: inflammation which most caused by bacteria

Myocardium 心肌膜 myocarditis

Pumping action, involuntary like SM

Epicardium: the visceral layer of the serous pericardium

Epicardium:connective tissue and mesothelium

• Arteries: Arteries are blood vessels that carry blood

away from the heart.

1. Classification of arteries:arteries are of three types:

elastic arteries (conduction arteries)

muscular arteries( distributing arteries)

arterioles

• 2. Basic structure of arteries:

The wall of an arteries is made up of three layers:

(1) tunica intima 内膜 : inner layer

(a) endothelial lining

(b) subendothelial connective tissue

(c) internal elastic lamina: a membrane formed by elastic fibers.

• 2. Tunica media 中膜 : or middle

layer,which is outside the tunical intima.

The media may consist predominantly of

elastic tissue or of smooth muscle.Some

connective tissue is usually present. On the

outside the media is limited by a membrane

formed by elastic fibers.This is the external

elastic lamina.

• 3. Tunica adventitia 外膜 : the outmost

layer of arteries. This coat consist of

connective tissue in which collagen fibers

are prominent. This layer presents undue

stretching or distension of the artery.

• Elastic Arteries:

• The feature of elastic arteries is the media

which have predominently elastic

membrane known as fenestrated membrane,

or occupy much of the tunica media.

Between the elastic membranes there is

some loose connective tissue. Some smooth

muscle cells may be present.

• Muscular arteries:

Muscular arteries are characterized by a thick

tunica media that is composed mostly of smooth

muscle cells. The musles is arranged circulary

made up mainly of smooth muscle.This muscle is

arranged circulary. Between groups of muscle

fibers, come connective tissue is present. This may

contain some elastic fibers.

Vasa vasorum

Arterioles

• When traced distally, muscular arteries

progressively decrease in calibre till they

have a diameter of about 100 um.They then

become continuous with arterioles. The

larger or muscular arterioles are 100 to 50

um in diameter.

• Arterioles less than 50 um in diameter are

called terminal arterioles. Muscular

arterioles can be distinguished from true

arteries:

(1) by their small diameter

(2) by the fact that they do not have an

internal elastic lamina.

• Veins:

• The basic structure of veins is similar to that of arteries.The tunica intima, media and adventitia can be disinguished specially in large veins.the structure of veins differs from that of arteries in the following respects:

• (1) The wall of a vein is distinctly thinner than that of an artery having the same sized lumen.

• (2) the tunica media contains a much larger quantity of collagen than in arteries. Elastic tissue

• (3) Vein is easily compressed, usually collapsed

• (4) In arteries the tunic media is usually thicker than the adventita.In contrast the adventitia of veins is thicker than the media.

• Capillaries:

• Arising from the terminal ends of the

arterioles are capillaries ,which form, by

branching and anastomosing,a capillary bed

(network ) between the artrioles and the

venules. The richness of the capillary

network is related to the metabolic activity

of the tissue.

• General structure of capillaries:

Capillaries composed of a single layer of endothelial cells, are the smallest blood vessels.

The average diameter of a capillary is 8 um. The wall of a capillary is formed essentially by endothelial cells which are lined on the outside by a basal lamina secreted by the endothelial cells.

• Overlying the basal lamina there may be

isolated branching perivascular cell

(pericytes) and a delicate network of

reticular fibers and cells.

• Classification of capillaries:

(1)Continuous capillaries:

The endothelial cell is continuous, no pores or fenestrated in their walls.

The basement membrane is completedly.

Distribution: connective tissue ,muscle, nervous tissue

• (2) Fenestrated capillaries: fenestrated capillaries possess pores (fenestrate) in their walls that are covered by pore diaphrgms.

• The pores are 60-80 nm in diameter, ridged by an ultra thin diaphragm. diffusion of substances takes place through the numerous fenestrate in the capillaries wall.

• Distribution: kindney, small intestine

• (3) Sinusoidal capillaries:

• Sinusoidal capillaries or sinusoids may

discontinuous endothelial cells and basal

lamina and contain many large fenestrate

without diaphragms,enhancing exchange

between blood and tissue.

• Distribution: liver and spleen