1. Histology of the Circulatory System Heart - pump the blood Arteries - efferent vessels Capillaries - anastomosing thin tubules where interchange between blood and tissue takes place Veins - convergence of the capillaries into a system of larger channels to the heart Lymphatic vascular system

2. Basic structure of vessels Tunica intima Endothelial layer Subendothelial layer Internal elastic lamina (arteries) Tunica media Concentric layers of helically arranged smooth muscle cells Varying amounts of elastic fibers, reticular fibers, and proteoglycans External elastic membrane-(larger arteries) Tunica Adventitia - longitudinally oriented collagen (type I)

3. Classic muscular artery- elastic stain

4. Small muscular artery

5. Vasa Vasorum In larger vessels Small vessels branch profusely in the adventitia and outer part of the media Nourish the media

6. Vaso vasorum Media of large art.

7. Innervation Most vessels have a profuse network of sympathetic fibers Sympathetic transmitter cause vasoconstriction - epinephine Arteries in skeletal muscle also have cholinergic vasodilatior nerve supply Sensory nerve endings - baroreceptors in the carotid sinuses and arch of aorta and chemoreceptors in the carotid and aortic bodies

9. Capillaries Single layer of endothelial cells Diameter 7 to 9  m Gap junctions are present Held together by zonula occludens Pericytes - partly surround the endothelial cells- they have myosin, actin, & tropomyosin--contractile function Most endothelial cells are continuous Fenestrated - kidney, intestine, endocrine Discontinuous - liver, spleen, bone marrow

10. Capillary

12. Capillary(b) and venule(a)

13. Capillary in heart(B)

14. Capillary - pericyte

15. Fenestrated capillary (kidney)

16. Arteries -resist changes in blood pressure and regulate blood flow Arterioles - < 0.5mm in dia., endothelial cells, thin subendothelial layer, most have no internal elastic layer, 1 or 2 layers of smooth muscle, no external elastic lamina

17. Small artery & Vein (arrow) artery

18. Arteriole & venule

19. Arteriole --small artery

20. Muscular Arteries Most arteries in the body Thin intimal layer Well developed internal elastic lamina Muscle layer up to 40 layers Varying intermingled elastic fibers adventitia consists of nerves, vessels, collagen, elastic fibers, fibroblasts and adipose cells

21. Muscular artery- very thin intima, thick internal elastic lamina

22. Small muscular artery

23. Large Elastic Arteries Aorta and its large branches Thick intima (subintima) Internal elastic lamina Media concentrically perforated elastic lamina with smooth muscle and ground substance in between Poorly formed external layer

24. Elastic artery Aorta

25. Elastic artery- note thin intima and wavy elastic fibers

26. Elastic artery- elastic stain

27. Adventitia of large artery

28. Carotid Bodies Small structures near the bifurcation of the carotid artery Chemoreceptors(low 02 tension, high CO2 and low blood pressure) Composed of glomus cells surrounded by fenestrated capillaries and many afferent nerve fibers Glomus cells have numerous dense core vesicles that store dopamine, norepinephrine and seratonin

29. Carotid Sinuses Slight dilation of internal carotid artery Contain baroreceptors that detect changes in blood pressure

30. Arteriovenous anastomoses Direct communication between arterial and venous circulation Plays a role in regulation of blood pressure, flow and temperature in various areas Glomus - complex anastomoses in fingerpads, fingernail beds, and ears

31. Arteryvein

32. Veins Capacitance vessels - 70% of blood volume Venules - thin walls - only contractile pericytes Small and medium sized veins - thin intimia, thin media, valves

33. Muscular artery (a) and vein(b)

34. Muscular vein

35. Muscular vein with valve

36. Vein with valve

37. Arteriole (b) and venule (a)

38. lymphatic

39. Lymphatic with valve

40. Heart Pump Produces atrial natriuretic factor Fibrous skeleton - base for the valves and site of origin and insertion of muscle cells

41. Tunics of the Heart Endocardium Endothelial layer Subendothelial layer - veins, nerves and Purkinje cells Myocardium Cardiac muscle cells Epicardium Visceral layer of the pericardium - mesothelium Subepicardial layer of loose connective tissues - veins, nerves and ganglia

42. Layers of the heart

43. Heart - * endocardium

44. Heart - epicardium

45. Cardiac muscle

47. Cardiac muscle - intercalated disks

48. Conduction System(Purkinji fibers) Subendocardial area Cells larger, pale cytoplasm, few myofibrils, rich in glycogen but no T tubule system Junctions via desmosomes and gap junctions rather than intercalated disks

49. Sinoatrial node - pacemaker of the heart Close to the entrance of the superior vena cava into the right atrium Modified cardiac muscle cells Fewer myofibrils

50. Atrioventricular node In wall of membranous septum Atrioventricular bundle of this formed by Purkinje cells Divides into Rt and Lt bundle branches

51. AV node

52. Bundle of His Bundle

53. Innervation of the Heart Both parasympathetic and sympathetic Ganglionic nerve cells and nerves are present near both nodes