1. Cardiovascular System

2. Overview of the cardiovascular system The cardiovascular system is a transport system. The cardiovascular system is a transport system. The cardiovascular system includes the heart, blood vessels, and lymphatic vessels. The cardiovascular system includes the heart, blood vessels, and lymphatic vessels.

3. General features of arteries and veins The walls of arteries and veins are composed of three layers, from the lumen outward, which are tunica intima, tunica media and tunica adventitia. The walls of arteries and veins are composed of three layers, from the lumen outward, which are tunica intima, tunica media and tunica adventitia.

4. Tunica intima It consists of three components: endothelium, basal lamina, subendothelial layer( loose connective tissue) and internal elastic membrane. It consists of three components: endothelium, basal lamina, subendothelial layer( loose connective tissue) and internal elastic membrane.

5. Internal elastic membrane Structure: A sheet-like layer or lamella of fenestrated elastic material. Structure: A sheet-like layer or lamella of fenestrated elastic material. Function: Fenestrations enable substances to diffuse readily through the layer and reach cells deep within the wall of the vessel. Function: Fenestrations enable substances to diffuse readily through the layer and reach cells deep within the wall of the vessel.

6. Tunica media This layer consists primarily of layers of elastic tissue or of smooth muscle. This layer consists primarily of layers of elastic tissue or of smooth muscle. Some connective tissue is usually present. Some connective tissue is usually present. Variable amounts of elastin, reticular fibers, and proteoglycans are interposed between the smooth muscle cells of the tunica media. All of the extracellular components of the tunica media are produced by the smooth muscle cells. Variable amounts of elastin, reticular fibers, and proteoglycans are interposed between the smooth muscle cells of the tunica media. All of the extracellular components of the tunica media are produced by the smooth muscle cells.

8. Tunica adventitia It is composed primarily of longitudinally arranged collagenous tissue and a few elastic fibers. It is composed primarily of longitudinally arranged collagenous tissue and a few elastic fibers. In addition, the tunica adventitia of large arteries and veins contains a system of vessels, called vasa vasorum, that supply blood to the vascular walls themselves, as well as a network of autonomic nerves, called nervi vascularis, that contral contraction of the smooth muscle in the vessel wall. In addition, the tunica adventitia of large arteries and veins contains a system of vessels, called vasa vasorum, that supply blood to the vascular walls themselves, as well as a network of autonomic nerves, called nervi vascularis, that contral contraction of the smooth muscle in the vessel wall.

9. Contraction and relaxation of smooth muscle cells in the tunica media influence blood flow and pressure. Contraction and relaxation of smooth muscle cells in the tunica media influence blood flow and pressure. Contraction of smooth muscle in the tunica media reduces the luminal diameter of vessels, increasing the vascular resistance. Leading to an increase in the blood pressure. Contraction of smooth muscle in the tunica media reduces the luminal diameter of vessels, increasing the vascular resistance. Leading to an increase in the blood pressure. Relaxation of smooth muscle cells increases the luminal diameter of the vessels, decreasing vascular resistance and blood pressure. Relaxation of smooth muscle cells increases the luminal diameter of the vessels, decreasing vascular resistance and blood pressure.

10. Arteries Arteries are classified into three types on the basis of size and the characteristics of the tunica media: Arteries are classified into three types on the basis of size and the characteristics of the tunica media: Large or elastic arteries Large or elastic arteries Medium or muscular arteries Medium or muscular arteries Small arteries and arterioles Small arteries and arterioles

11. Elastic arteries Elastic arteries have multiple sheets of elastic lamellae in their walls. Elastic arteries have multiple sheets of elastic lamellae in their walls. Function: elastic arteries serve pimarily as conduction tubes, however, they also facilitate the continuous and uniform movement of blood along the tube. Function: elastic arteries serve pimarily as conduction tubes, however, they also facilitate the continuous and uniform movement of blood along the tube.

12. Elastic arteries-tunica intima The tunica intima consists of endothelium, basal lamina, subendothelial connective tissue, and an inconspicuous internal elastic membrane. The tunica intima consists of endothelium, basal lamina, subendothelial connective tissue, and an inconspicuous internal elastic membrane.

13. Elastic arteries-tunica intima Endothelial cells possess rod-like inclusions, called Weibel-Palade bodies, which are present in the cytoplasm. Endothelial cells possess rod-like inclusions, called Weibel-Palade bodies, which are present in the cytoplasm.

14. Elastic arteries-tunica intima Weibel-Palade bodies are electron- dense structures and contain von Willebrand factor (also called coagulating factor Ⅷ ). Weibel-Palade bodies are electron- dense structures and contain von Willebrand factor (also called coagulating factor Ⅷ ). von Willebrand factor can combine with collagen fibers and platelets simultaneously, when vessels broken, platelets adhere to collagen fibers to form thrombus through von Willebrand factor. von Willebrand factor can combine with collagen fibers and platelets simultaneously, when vessels broken, platelets adhere to collagen fibers to form thrombus through von Willebrand factor.

15. Subendothelial layer is connective tissue.The main cell type is the smooth muscle cell. Subendothelial layer is connective tissue.The main cell type is the smooth muscle cell. The internal elastic membrane is usually identified only because it is the innermost elastic layer of the arterial wall. The internal elastic membrane is usually identified only because it is the innermost elastic layer of the arterial wall. Elastic arteries-tunica intima

16. Elastic arteries-tunica media The tunica media consists of multiple layers of smooth muscle cells separated by elastic lamellae. The tunica media consists of multiple layers of smooth muscle cells separated by elastic lamellae. Elastin in the form of fenenstrated sheets or lamellae between the muscle cell layers. They are arranged in concentric layers. Elastin in the form of fenenstrated sheets or lamellae between the muscle cell layers. They are arranged in concentric layers.

17. Elastic arteries-tunica media Smooth muscles arranged in layers. Fibroblast are not present in the tunica media. Smooth muscles arranged in layers. Fibroblast are not present in the tunica media. Collagen fibers and ground substance are synthesized and secreted by the smooth muscle cells. Collagen fibers and ground substance are synthesized and secreted by the smooth muscle cells.

18. Elastic arteries-tunica adventitia The tunica adventitia is a relatively thin connective tissue layer. It is usually less than half the thickness of the tunica media. The tunica adventitia is a relatively thin connective tissue layer. It is usually less than half the thickness of the tunica media. Collagen and elastic fibers are in the form of a loose network. Collagen and elastic fibers are in the form of a loose network.

19. Elastic arteries-tunica adventitia Fibroblast and macrophages are the principal cells of the tunica adventitia. Fibroblast and macrophages are the principal cells of the tunica adventitia. It consists of blood vessels and nerves. It consists of blood vessels and nerves.

20. Muscular arteries Muscular arteries have more smooth muscle and less elastin in the tunica media than do elastic arteries. Muscular arteries have more smooth muscle and less elastin in the tunica media than do elastic arteries.

21. Muscular arteries- tunica intima The tunica intima is thinner and contains a prominent internal elastic membrane. The tunica intima is thinner and contains a prominent internal elastic membrane. Subendothelial layer is sparse. Subendothelial layer is sparse. In histologic sections, the internal elastic membrane usually appears as a well- defined, wavy structure. In histologic sections, the internal elastic membrane usually appears as a well- defined, wavy structure.

22. Muscular arteries- tunica media The tunica media is composed almost entirely of smooth muscle amid collagen fibers, with little elastic material. The tunica media is composed almost entirely of smooth muscle amid collagen fibers, with little elastic material. The smooth muscle cells are arranged in a spiral fashion. The smooth muscle cells are arranged in a spiral fashion. There are no fibroblasts in this layer. There are no fibroblasts in this layer.

23. Muscular arteries- tunica adventitia The tunica adventitia is relatively thick and is often separated from the tunica media by a recognizable external elastic membrane. The tunica adventitia is relatively thick and is often separated from the tunica media by a recognizable external elastic membrane.

24. Muscular arteries- tunica adventitia It consists of fibroblasts, collagen fibers, elastic fibers, and scattered adipose cells. It consists of fibroblasts, collagen fibers, elastic fibers, and scattered adipose cells. It is about the same thickness as the tunica media. It is about the same thickness as the tunica media. Nerves and small vessels travel in it. Nerves and small vessels travel in it.

25. Small arteries and arterioles They are distinguished from one another by the number of smooth muscle cell layers in the tunica media. They are distinguished from one another by the number of smooth muscle cell layers in the tunica media. Arterioles have only one or two layers of smooth muscle in their tunica media; a small artery may have up to about eight layers. Arterioles have only one or two layers of smooth muscle in their tunica media; a small artery may have up to about eight layers.

26. Small arteries and arterioles Typically, the tunica intima of a small artery has an internal elastic membrane, whereas this layer may or may not be present in the arteriole. Typically, the tunica intima of a small artery has an internal elastic membrane, whereas this layer may or may not be present in the arteriole. Both the tunica adventitia is a thin, ill-defined sheath of connective tissue. Both the tunica adventitia is a thin, ill-defined sheath of connective tissue.

28. Veins-characteristics: Veins are divided into three types on the basis of size: Veins are divided into three types on the basis of size: Small veins or venules ( postcapillary Small veins or venules ( postcapillary and muscular venules) and muscular venules) Medium veins Medium veins Large veins Large veins

29. Veins-characteristics: Veins have thinner walls than their accompanying arteries, and the lumen of the vein is larger than that of the artery. Veins have thinner walls than their accompanying arteries, and the lumen of the vein is larger than that of the artery. The tunica media contains a much larger quantity of collagen than in arteries. The amount of elastic tissue or of muscle is much less. The tunica media contains a much larger quantity of collagen than in arteries. The amount of elastic tissue or of muscle is much less.

30. Veins-characteristics: The wall of a vein is easily compressed. The wall of a vein is easily compressed. In arteries the tunica media is usually thicker than the adventitia. In contrast the adventitia of veins is thicker than the media. In arteries the tunica media is usually thicker than the adventitia. In contrast the adventitia of veins is thicker than the media. The tunics of veins are not as distinct or well defined as the tunics of arteries. The tunics of veins are not as distinct or well defined as the tunics of arteries.

31. Veins-characteristics: Many veins, especially those that convey blood against gravity, contain valves that allow blood to flow in only one direction, back toward the heart. The valves are semilunar flaps consisting of a thin connective tissue core covered by endothelial cells. Many veins, especially those that convey blood against gravity, contain valves that allow blood to flow in only one direction, back toward the heart. The valves are semilunar flaps consisting of a thin connective tissue core covered by endothelial cells.

32. Summary Understand the general features of arteries and veins. Understand the general features of arteries and veins. Emphasis: understand the structure of arteries (elastic, muscular, small arteries and arterioles). Emphasis: understand the structure of arteries (elastic, muscular, small arteries and arterioles). Know the characteristics of veins. Know the characteristics of veins.

33. Homework Review the structure of arteries and veins. Review the structure of arteries and veins. Prepare for the next lesson-the structure of capillaries, microcirculation, and the heart. Prepare for the next lesson-the structure of capillaries, microcirculation, and the heart. Wish you have a good time!

34. Capillaries-general structure Capillaries are the smallest diameter blood vessels. Capillaries are the smallest diameter blood vessels. Capillaries form blood vascular network that allow fluids containing gases, metabolites, and waste products to move through their thin walls. Capillaries form blood vascular network that allow fluids containing gases, metabolites, and waste products to move through their thin walls.

35. Capillaries-general structure The wall of a capillary is formed essentially by endothelial cells which are lined on the outside by a basal lamina. Overlying the basal lamina there may be isolated branching perivascular cells (pericytes), and a delicated network of reticular fibers and cells. The wall of a capillary is formed essentially by endothelial cells which are lined on the outside by a basal lamina. Overlying the basal lamina there may be isolated branching perivascular cells (pericytes), and a delicated network of reticular fibers and cells.

36. Capillaries- pericytes Pericyte with branching cytoplasmic processes, is enclosed by a basal lamina that is continuous with that of the endothelium. Pericyte with branching cytoplasmic processes, is enclosed by a basal lamina that is continuous with that of the endothelium. It displays features of a unspecialized cell with a large nucleus. It displays features of a unspecialized cell with a large nucleus. It can give rise to endothelial cells and smooth muscle cells during vessel growth. It can give rise to endothelial cells and smooth muscle cells during vessel growth.

37. Capillaries-classification Based on their morphology, three types of capillaries are described: continuous capillaries, fenestrated capillaries, and discontinuous capillaries. Based on their morphology, three types of capillaries are described: continuous capillaries, fenestrated capillaries, and discontinuous capillaries.

38. Continuous capillaries Seen in the skin, connective tissue, muscle lungs and brain. Seen in the skin, connective tissue, muscle lungs and brain. The edges of endothelial cells fuse completely with those of adjoining cells to form a continuous wall. The edges of endothelial cells fuse completely with those of adjoining cells to form a continuous wall.

39. Continuous capillaries The pericyte surrounds the capillary with branching cytoplasmic processes. The pericyte surrounds the capillary with branching cytoplasmic processes. Numerous pinocytotic vesicles underlie both the luminal and basal plasma membrane surfaces. Numerous pinocytotic vesicles underlie both the luminal and basal plasma membrane surfaces.

40. Fenestrated capillaries Found in endocrine glands and sites of fluid and metabolite absorption, such as the gallbladder and intestinal tract. Found in endocrine glands and sites of fluid and metabolite absorption, such as the gallbladder and intestinal tract. Fenestrations provide channels across the capillary wall. Fenestrations provide channels across the capillary wall.

41. Fenestrated capillaries They also have pinocytotic vesicles, basal lamina and pericytes. They also have pinocytotic vesicles, basal lamina and pericytes. A fenestration may have a thin, nonmembrano us diaphragm across its opening. A fenestration may have a thin, nonmembrano us diaphragm across its opening.

42. Discontinuous capillaries (sinusoids) Found in the liver, spleen, and bone marrow. Found in the liver, spleen, and bone marrow. They are larger in diameter and more irregularly shaped than other capillaries. They are larger in diameter and more irregularly shaped than other capillaries. The wall consists only of endothelium supported by a thin layer of connective tissue. The wall may be incomplete at places. The wall consists only of endothelium supported by a thin layer of connective tissue. The wall may be incomplete at places.

43. Capillaries –functional aspects Two important points: blood flow and richness of the capillary network. Two important points: blood flow and richness of the capillary network. Blood flow is controlled through local and systemic signals. Blood flow is controlled through local and systemic signals. The richness of the capillary network is related to the metabolic activity of the tissue. The richness of the capillary network is related to the metabolic activity of the tissue.

44. Microcirculation-arteriovenous shunts Direct routes between the arterioles and venules that divert blood from the capillaries. Direct routes between the arterioles and venules that divert blood from the capillaries. Commonly found in the skin of the fingertips, nose and lips. Commonly found in the skin of the fingertips, nose and lips. arteriolevenule metarteriole Precapillary sphincters capillaries venule

45. Microcirculation-arteriovenous shunts Contraction of the arteriole smooth muscle of the AV shunt sends blood to a capillary bed; Contraction of the arteriole smooth muscle of the AV shunt sends blood to a capillary bed; relaxation of the smooth muscle sends blood to a venule, bypassing the capillary bed. relaxation of the smooth muscle sends blood to a venule, bypassing the capillary bed. AV shunts serve in thermoregulation. AV shunts serve in thermoregulation. arteriolevenule metarteriole Precapillary sphincters capillaries venule

46. Microcirculation-Thoroughfare channel Its proximal segment is called a metarteriole, also allow some blood to pass more directly from arteriole to venule. Its proximal segment is called a metarteriole, also allow some blood to pass more directly from arteriole to venule. Capillaries arise from both arterioles and metarterioles. Capillaries arise from both arterioles and metarterioles. arteriolevenule metarteriole Precapillary sphincters capillaries venule

47. Thoroughfare channel A sphincter of smooth muscle, called the precapillary sphincter, is located at capillaries’origin from either an arteriole or a metarteriole. A sphincter of smooth muscle, called the precapillary sphincter, is located at capillaries’origin from either an arteriole or a metarteriole. These sphincters control the amount of blood passing through the capillary bed. These sphincters control the amount of blood passing through the capillary bed. arteriolevenule metarteriole Precapillary sphincters capillaries venule

48. Heart The wall of the heart is composed of three layers. From the outside to the inside they are epicardium, myocardium, and endocardium. The wall of the heart is composed of three layers. From the outside to the inside they are epicardium, myocardium, and endocardium. myocardium epicardium endocardium

49. Epicardium Consisting of a layer of mesothelial cells and its underlying connective tissue. The blood vessels and nerves that supply the heart lie in the epicardium. Consisting of a layer of mesothelial cells and its underlying connective tissue. The blood vessels and nerves that supply the heart lie in the epicardium. Adipose tissue Mesothelium Fibroelastic tissue

50. Myocardium Consist of cardiac muscle, the principle component of the heart. Consist of cardiac muscle, the principle component of the heart. myocardium epicardium endocardium

51. Endocardium Consist of an inner layer of endothelium and subendothelial connective tissue, a middle layer of connective tissue and smooth muscle cells, and a deeper layer of connective tissue, also called the subendocardial layer. The impulse- conducting system of the heart is located in the subendocardial layer. Consist of an inner layer of endothelium and subendothelial connective tissue, a middle layer of connective tissue and smooth muscle cells, and a deeper layer of connective tissue, also called the subendocardial layer. The impulse- conducting system of the heart is located in the subendocardial layer.

52. A fibrous skeleton At the junction of the atria and ventricles, and around the openings of aorta and pulmonary trunk there are rings of dense connective tissue. Similar dense connective tissue is also present in the membranous part of the interventricular and interartrial septum. At the junction of the atria and ventricles, and around the openings of aorta and pulmonary trunk there are rings of dense connective tissue. Similar dense connective tissue is also present in the membranous part of the interventricular and interartrial septum. These masses of dense connective tissue constitute the skeleton of the heart. They give attachment to fasciculi of heart muscle. They also act as an electrical insulator by preventing the free flow of electrical impulses between atria and ventricles. These masses of dense connective tissue constitute the skeleton of the heart. They give attachment to fasciculi of heart muscle. They also act as an electrical insulator by preventing the free flow of electrical impulses between atria and ventricles.

53. Heart valves The valves of the heart are folds of endocardium that enclose a plate like layer of dense connective tissue. The valves of the heart are folds of endocardium that enclose a plate like layer of dense connective tissue. myocardium epicardium endocardium Heart valve

54. Impulse-conducting system The pace of the beating action in the heart is initiated at the sinuatrial (S-A) node, a group of specialized cardiac muscle cells located near the junction of the superior vena cava and the right atrium. The pace of the beating action in the heart is initiated at the sinuatrial (S-A) node, a group of specialized cardiac muscle cells located near the junction of the superior vena cava and the right atrium.

55. Impulse-conducting system The S-A node initiates an impulse that spreads along the cardiac muscle fibers of the atria and along internodal tracts composed of modified cardiac muscle fibers. The S-A node initiates an impulse that spreads along the cardiac muscle fibers of the atria and along internodal tracts composed of modified cardiac muscle fibers.

56. Impulse-conducting system The impulse is then picked up at the atrioventricular (A-V) node and conducted across the fibrous skeleton to the ventricles by the atrioventricular (A-V) bundle. The impulse is then picked up at the atrioventricular (A-V) node and conducted across the fibrous skeleton to the ventricles by the atrioventricular (A-V) bundle.

57. Impulse-conducting system The bundle divides into smaller right and left bundle branches and then into subendothelial branches commonly called Purkinje fibers. The bundle divides into smaller right and left bundle branches and then into subendothelial branches commonly called Purkinje fibers.

58. Purkinje fibers They are chains of cells, united by desmosomes, and intercalated discs are absent. These cells have a larger diameter, and are shorter, than typical cardiac myocytes. Purkinje fiber has a central nucleus surrounded by clear cytoplasm. They are chains of cells, united by desmosomes, and intercalated discs are absent. These cells have a larger diameter, and are shorter, than typical cardiac myocytes. Purkinje fiber has a central nucleus surrounded by clear cytoplasm. N N N N

59. Nodal myocytes Nodal myocytes (present in the A- V node and the S-A node) are narrow, rounded, or cylindrical cells with single nuclei. They are responsible for pace-maker functions. Nodal myocytes (present in the A- V node and the S-A node) are narrow, rounded, or cylindrical cells with single nuclei. They are responsible for pace-maker functions.

60. Transitional myocytes They are present in the A-V node and the S-A node, and in the stem and main branches of the A-V bundle.They are similar to cardiac myocytes except that they are narrower. Conduction through them is slow. They are present in the A-V node and the S-A node, and in the stem and main branches of the A-V bundle.They are similar to cardiac myocytes except that they are narrower. Conduction through them is slow.

61. Summary Understand the structure of three kinds of capillaries. Understand the structure of three kinds of capillaries. Know the structure and function of every segment of microcirculatory vessel. Know the structure and function of every segment of microcirculatory vessel. Understand the structure of Purkinje fibers, Nodal myocytes, and Transitional myocytes Understand the structure of Purkinje fibers, Nodal myocytes, and Transitional myocytes

62. Homework Review three structure of capillaries, Purkinje fibers, Nodal myocytes, and Transitional myocytes. Review three structure of capillaries, Purkinje fibers, Nodal myocytes, and Transitional myocytes. Prepare for the next lesson- lymphatic system. Prepare for the next lesson- lymphatic system. Wish you have a good time!