Histology - Cardiovascular System Practical 2

Cardiovascular System Composition

• The cardiovascular system is composed of arteries, arterioles, veins, venules, capillaries, and the heart.

Blood Vessel Layers

• The walls of blood vessels consist of three concentric layers: tunica intima, tunica media, and tunica adventitia.
• The tunica intima is the inner layer, abutting the vessel lumen.
• The tunica media is the middle layer, sandwiched between the intima and adventitia.
• The tunica adventitia is the outer layer, abutting the perivascular soft tissue.

Artery Structure

• The tunica intima consists of endothelium, subendothelial connective tissue, and internal elastic membrane.
• The tunica media is the thickest layer, composed of abundant elastic tissue and smooth muscles.
• The tunica adventitia is composed of dense irregular connective tissue, separated from the tunica media by external elastic lamina.

Medium Arteries

• Medium or muscular arteries distribute blood to all organs, using their thick muscular walls to maintain steady blood pressure.

Small Arteries and Arterioles

• In small arteries and arterioles, the media is abundant in smooth muscle cells that vasoconstrict or vasodilate.
• Smooth muscle contraction causes dramatic changes in lumen diameter.

Vein Structure

• The walls of veins are thinner than the walls of arteries, while their diameter is larger.
• The tunica intima is very thin, with only the largest veins containing notable amounts of subendothelial connective tissue.
• Internal and external elastic laminae are absent or very thin.
• The tunica media appears thinner than the tunica adventitia, and the two layers tend to blend into each other.

Capillaries

• There are three types of capillaries: continuous, fenestrated, and sinusoid.
• Continuous capillaries consist of endothelial cells resting on a basal membrane, with pericyte and pinocytotic vesicles.
• Capillaries contain a single layer of endothelial cells and their basement membrane.
• The lumen of capillaries is so narrow that red blood cells have to pass in singly.
• Capillaries facilitate exchange of gases and small molecules between the bloodstream and surrounding tissue.

Heart Structure

• The heart is a muscular organ that pumps blood through the blood vessels of the circulatory system.
• The wall of the heart consists of three layers: endocardium, myocardium, and epicardium.
• The endocardium is composed of a continuous endothelial lining, with attendant basement membrane.
• The myocardium is a layer of cardiomyocytes that lies between the endocardium and epicardium.
• The epicardium is lined by a layer of flat mesothelial cells that lie on top of a layer of collagenous tissue.

Heart Valves

• The heart has four valves composed of connective tissue layered with endothelium on each side.
• The valves consist of three layers: spongiosa, fibrosa, and ventricularis.