Practical Histology. Cardiovascular System. Dr Narmeen S. Ahmad

Transcription

1 Practical Histology Cardiovascular System Dr Narmeen S. Ahmad

2 The Cardiovascular System A closed system of the heart and blood vessels Functions of cardiovascular system: Transport nutrients, hormones Remove waste products Gaseous exchange Immunity

3 The Cardiovascular System A- Heart: Highly modified, muscular blood vessel specialized for pumping the blood composed of two atria and two ventricles. B- Closed circuit of vessels: The vessels are listed below in the order that blood would follow as it leaves the heart. 1. Elastic arteries (e.g., aorta and pulmonary arteries). 2. Muscular arteries (medium arteries). 3. Small arteries and arterioles. 4. Capillaries. 5. Venules and small veins. 6. Medium veins 7. Large veins (e.g., venue cavae return blood to the heart).

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5 Basic Structural Organization: The walls of the entire cardiovascular system, consists of three concentric layers or tunics that are continuous between both the heart and vessels. The constituents and thickness of these layers vary depending on the mechanical and metabolic functions of the vessel. 1. Tunica interna or intima 2. Tunica media 3. Tunica externa or adventitia

6 Inner tunic In the heart, this layer is called the endocardium; in vessels it is termed the tunica intima. Composition: I. Simple squamous epithelium (endothelium). II. Varying amounts and types of connective tissue. III. In the largest vessels, smooth muscle may be present in the connective tissue layer.

7 Middle tunic In the heart this layer is composed of cardiac muscle and is called the myocardium. In vessels this layer is composed of circularly oriented smooth muscle plus connective tissue and is called the tunica media.

8 Outer tunic In the heart, this layer consists of a serous membrane, called the epicardium (visceral pericardium) composed of connective tissue covered with a simple squamous epithelium (mesothelium). In vessels, this layer is called the tunica adventitia (externa) and is composed of connective tissue; variable amount of longitudinally arranged smooth muscle is present in this layer in the largest veins.

9 The Heart: Chambers Right and left side act as separate pumps Four chambers Atria Receiving chambers Right atrium Left atrium Ventricles Discharging chambers Right ventricle Left ventricle

10 Innermost layer of heart: Endocardium Consists of an endothelium (simple squamous epithelium) plus underlying connective tissue. Cardiac valves: Folds of the endocardium. Semilunar valves at the base of the aortic and pulmonary trunks prevent backflow of blood into the heart. Atrioventricular valves (bicuspid and tricuspid) prevent backflow of blood from the ventricles into the atria. Bicuspid valve

11 Middle layer of heart: Myocardium Composed of cardiac muscle. Thickest layer of the heart. Variation in thickness depends on the function of each chamber; thicker in ventricles than atria and thicker in left ventricle than right ventricle. Exernal layer of heart: Epicardium (visceral pericardium): Serous membrane on the surface of the myocardium. Consists of a simple squamous epithelium and a loose connective tissue, with adipocytes, adjacent to the myocardium.

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14 Arteries Carry blood away from the heart and toward capillary beds Have thicker walls and smaller lumens than veins of similar size. Tunica media is the predominate tunic. Types: 1- Elastic (large) arteries (aorta, pulmonary arteries): The tunica intima: formed of simple squamuse epithelium called the endothelium rest on basement membrane of elastic fibers Tunica media: It is thick layer formed of smooth muscle with elastic fibers distributed between it Tunica adventitia: formed of collagen fibers

15 2- Muscular (medium arteries): Tunica intima: formed of endothelium separated from the tunica media by the internal elastic layer Tunica media: It is muscular layer of smooth muscle it is thin than of the large arteries separated from the adventitia by the external elastic layer Tunica adventitia: formed of collagenous fibers

16 3- Small arteries and arterioles: Tunica intima: formed of endothelium Tunica media: formed of smooth muscle arranged into six layers Tunica adventitia: formed of collagen fibers fused with the surrounded structure.

17 Capillaries Function to exchange oxygen and carbon dioxide and nutrients and metabolic wastes between blood and cells. Lumen is approximately 8 microns in diameter, thus only large enough for RBCs to move through in a single row. Composed of the endothelium (simple squamous epithelium) and its underlying basal lamina.

18 Veins Return blood from capillary beds to the heart. Have thinner walls and larger lumens than arteries of similar size. Tunica adventitia is the predominate tunic. Larger veins possess valves that are extensions of the tunica intima that serve to prevent back-flow of blood. Types: 1- Small vein or venule: tunica intima: formed of endothelium and not contain elastic fibers tunica media: formed of tow layers of smooth muscle and it is very thin. tunica adventitia: it is formed of collagen fibers connected the vein with the surrounded structures

19 2- Medium veins: The medium veins formed by the collection of the small veins and drainage into the large veins The histological structure is similar to the small veins but the tunica media is thicker and contain elastic fibers 3- large vein It is structure similar to the medium vein but the tunica media very thick and contain collagen fibers and the internal elastic layer may present Medium vein Large vein

20 SYSTEMIC AND PULMONARY CIRCULATION Pulmonary circulation The flow of blood between the heart and lungs. Systemic circulation The flow of blood between the heart and the cells of the body.