Cardiovascular System

• The cardiovascular system (CVS) is composed of: Heart Blood vessels

Arteries Capillaries Veins

Heart• It is formed of three

layers: Endocardium Myocrdium Epicardium

Endocardium

Composed of:• Endothelium (simple

squamous epithelium)• Subendothelial layer of

fibroelastic connective tissue

Myocardium

• Forms the main bulk of the wall of the heart

• Composed of cardiac muscle fibers, arranged in spirals around the orifices of the chambers

Epicardium

• Outermost layer• Also called the visceral

layer of pericardium• Composed of simple

squamous epithelium• The subepicardial layer

of loose connective tissue contains the coronary vessels, nerves, ganglia and fat

Histologically blood vessels can be divided as: Large (Conduction, Elastic) arteries Medium size (Muscular) arteries Arterioles Capillaries Venules & small veins Medium veins Large veins

General Structure of Blood Vessels

• Formed of three concentric layers: Tunica intima

(interna) Tunica media Tunica adventitia

(externa)

Tunica Intima• Is the innermost layer

• Composed of: Single layer of flattened

endothelial cells (resting on the basal lamina) lining the lumen of the vessel

Subendothelial layer made up of loose connective tissue.

Beneath the subendothelial layer is an internal elastic lamina, composed of elastin (fenestrated sheet), separating the tunica intima from the tunica media

Tunica Media• Intermediate layer• Is the thickest layer• Composed of smooth

muscles, some elastic fibers, and collagen Large muscular arteries have external elastic lamina, separating the tunica media from the tunica adventitia

• Capillaries do not have a tunica media.

Tunica Adventitia

• Outermost layer• Composed of

connective tissue containing type I collagen, fibroblasts and elastic fibers

• The tunica media and adventitia of large vessels (especially veins) are nourished by the vasa vasorum, which are small arteries that enter the vessel wall and branch to supply both tunicae

M

A

VV

Elastic Arteries• Intima characterized by the

presence of subendothelial lamina of elastic fibers in addition to the internal elastic lamina

• Media consists of many fenestrated elastic membranes (lamellae) alternating with few smooth muscle fibers.

• They also have an external elastic lamina.

• Tunica adventitia is thin and has vasa vasorum

• Examples: aorta.

Muscular Arteries• Most of the rateries arising

from aorta are muscular arteries

• Internal elastic lamina is very prominent

• Media is formed mainly of smooth muscle fibers

• External elastic lmina is prominent in large muscular arteries

Capillaries• Very small vessels• Consist of a single layer

of endothelial cells surrounded by a basal lamina & occasional pericytes

• Are responsible for the exchange of gas, metabolites and other substances between the blood and the tissues of the body

Veins

• Generally they have: Larger lumina Thinner walls Fewer layers of smooth muscle fibers than their

companion arteries Prominent connective tissue components than

their companion arteries Valves in the lumen

Medium-sized Veins• Intima is thin, formed of

endothelium, basal lamina and few elastic fibers

• No internal elastic lamina• Media is thin containing few

smooth muscle intervowen with collagen fibers and fibroblasts

• Adventitia is the thickest layer, composed of longitudinally arranged collagen & elastic fibers and few smooth muscle cells

• They have valves formed of thin fold of intima

Comparison of Artery & Vein

Neurovascular Bundle

Practical Slides

Elastic Artery

Medium-sized (Muscular ) Artery

Medium-sized Vein