Cardiac muscle

Elastic artery

Muscular artery

Large vein

The Cardiovascular system: Histology of heart & blood vessels

Learning objectives Describe the histology (microscopic anatomy) of heart (cardiac muscle). Describe the histology (microscopic anatomy) of arteries (large, medium sized & small). Explain the histology (microscopic anatomy) of veins (small, medium, sized & large).

Cardiovascular system Heart Arteries Veins Capillaries

Cardiac muscle Form of striated muscle, found only in the heart. Structurally similar to skeletal, but some differences. Cells are smaller having specialized communication structures. Contraction is an inherent property, no direct neural stimulation needed. No neuro muscular junction.

Heart- right atrium and ventricle Epicardium (Visceral layer of serous pericardium) Myocardium (cardiac muscle) Endocardium (Endothelial cells)

Cardiac muscle Desmosomes Gap junctions Cardiac muscle fibre is 15 m wide X 100 m long, shows cross striations. Uninucleated and oval nucleus in the centre of the cell. Branched. Presence of Intercalated discs. Desmosomes Gap junctions

Cardiac muscle • Unique structure, the intercalated disc. • Striations are present. • Unique structure, the intercalated disc.

Intercalated disc structure for communication & adhesion. Special structure for communication & adhesion. Includes adhering junctions & gap Junctions.

Cardiac muscle -Regeneration & repair Cardiac muscle cells can’t divide. Injury causes some loss of material, part or all of a myofiber. Scarring “fills in” the space with non-contractile collagen. A scanty reserve of myoblasts exists in skeletal muscle not in smooth or cardiac. Limited regeneration in skeletal muscle – but not in cardiac muscle.

OSPE Uninucleated,oval nucleus in the centre. Presence of branches and intercalated disc.

Histology of blood vessels

General structure of the blood vessels Blood vessels are composed of 3 layers or tunics. 1.Tunica Intima: - Consists of a layer of endothelial cells lining interior surface which rest on a basal lamina. Endothelial cells are specialized mesenchymal cells and not an epithelial tissue. Endothelium normally provides a non-thrombogenic surface because it contains heparan sulfate. - Beneath the endothelium is the sub endothelial layer, consisting of loose connective tissue and smooth muscle cells, arranged longitudinally.

General structure of the blood vessels 2.Tunica Media - Consists chiefly of concentric layers of helically arranged smooth muscle cells. Interposed among the smooth muscle cells are variable amounts of elastic and reticular fibers, type I collagen, and proteoglycans. - In arteries, the intima separated from the media by internal elastic lamina , composed of elastin, has gaps that allows substances to diffuse to and nourish cells. - In arteries, a thinner external elastic lamina is found separating the media from the outer layer.

General structure of the blood vessels 3.Tunica adventitia: Made up of loose connective tissue,consists of longitudinally oriented collagen and elastic fibres. Contains vasa vasorum (vessels of the vessel)-In large vessels, vasa vasorum branch profusely in the adventitia and the outer part of the media. - Vaso vasorum supply blood to the tunica media and the tunica adventitia.

General structure of the blood vessels

Arteries - Types Elastic Arteries: e.g., aorta, brachiocephalic artery, carotid artery. Muscular Arteries: (medium-sized, distributing) e.g., superior mesenteric artery, radial artery, Small Arteries: the last of the distributing arteries. Arterioles: tunica media consisting of 1 or 2 layers of smooth muscle cells.

Histology of Arteries

Elastic artery - Aorta Tunica intima: Thicker than in the muscular arteries. Endothelial cells line the lumen.Sub endothelial layer is thick. Internal elastic lamina is similar to the elastic lamina of the next layer. Hence not seen clearly. Tunica media: Consists of concentrically arranged perforated elastic laminae. Between the elastic laminae are smooth muscle cells, reticular fibers. External elastic lamina not seen clearly. Tunica adventitia: relatively undeveloped, contains elastic and collagen fibers. Vasa vasorum are seen.

Elastic artery - Aorta Tunica Intima Tunica media Tunica adventitia

Elastic artery Elastic laminae and smooth muscle (arrowheads) of Tunica media. Vasa vasora (venule and arteriole) in tunica adventitia.

Muscular artery- Medium sized artery Tunica intima: endothelial cells & subendothelial layer - thicker than in the arterioles, few smooth muscle cells present. Internal elastic lamina prominent. Tunica media: contain up to 40 layers of smooth muscle cells, intermingled with elastic lamellae. External elastic lamina seen clearly. Tunica adventitia: consists of collagen and elastic fibers, few fibroblasts, and adipose cells.

Muscular artery- Medium sized artery Elastic fibers in tunica media form the internal elastic lamina. Tunica intima Tunica media Tunica adventitia

Muscular artery- Medium sized artery Tunica intima Internal elastic lamina External elastic lamina Tunica media Tunica adventitia

Muscular artery - Medium sized artery

Internal elastic lamina Small artery Tunica adventitia Internal elastic lamina Tunica media Endothelium

Small artery and vein Artery Capillary Vein

Arteriole Arteriole

Arteriole within subcutaneous connective tissue Capillary

Capillary Blood from capillary bed passes into thin walled venules. Are simple endothelial tubes. Connecting arterial & venous sides. Interchange of oxygen, nutrients waste products with extracellular fluid occurs. Blood from capillary bed passes into thin walled venules. Two types – fenestrated & continuous.

Histopathology of arteries Degenerative changes in elastic and muscular arteries are strongly influenced by both genetics & life style. Changes are present in the aorta and its branches in most individuals after 50 years. However, these can often be found as early as the late teens and early 20’s. These degenerative changes are collectively designated as arteriosclerosis. Degenerative changes do not occur in small arteries.

Arteriosclerotic changes in a medium-sized artery External Elastic membrane Internal Elastic membrane: fragmented Loss of elastic fibers apparent Lumen T. media T. intima T. adventitia

Coronary artery arteriosclerosis & thrombosis T. Adventitia T. media T. intima thickened Thrombus Narrowed lumen of artery

Histology of veins Small veins and venules. Medium-sized veins. Large veins.

Companion arteriole & venule

Medium-sized vein Example : Basilic, cephalic & saphenous veins. Tunica intima has a thin sub endothelial layer. Tunica media consists of small bundles of smooth muscle cells intermixed with reticular and elastic fibers. Tunica adventitia rich in collagen, well-developed.

Medium-sized vein (spermatic cord) Tunica intima Tunica media Tunica adventitia

Medium-sized vein of leg Tunica adventitia Tunica media Tunica intima

Medium-sized vein

Large vein Tunica intima: Consists of endothelial cells and subendothelial layer made up of connective tissue. Tunica media: Much thinner, with few layers of smooth muscle cells and abundant connective tissue. Tunica adventitia: Thickest and best developed, contains longitudinal bundles of smooth muscle, present in the connective tissue.

Large vein (inferior vena cava) Tunica intima Tunica media Tunica adventitia

Large vein (inferior vena cava) Tunica media Tunica adventitia

Comparison (A) artery and (B) vein

To sum up

Cardiac muscle

Elastic artery

Muscular artery

Large vein

Any questions ?

Thank you