Vascular and Lymphatic System Pathology

1. Vascular and Lymphatic System Pathology

2. Blood Flow Systemic blood flow is a circuit : Heart →Arteries→ Arterioles→ Capillaries→ Venules→ Veins→ Heart Artery – any vessels that carries blood away from the heart. Vein – any vessels that carries blood toward the heart

4. Structure of blood vessels Tunica intima Endothelium and connective tissue Tunica media Smooth muscle and elastic tissue Tunica externa or tunica adventitia Connective and elastic tissue

7. Arteries Large arteries are elastic (conducting) arteries – pressure reservoirs Medium arteries are muscular (distributing) arteries – more smooth muscle Contraction or relaxation of muscle changes the size of the lumen, and so controls the blood pressure in the vessel.

9. Capillaries Only a single layer of endothelium and a basement membrane Connect arterioles and venules Functional part of system True capillaries begin at a precapillary sphincter which controls blood flow through the capillary

11. Veins Relatively thin; less elastic Larger in diameter than arteries Have valves to prevent backflow of blood Flow to heart is assisted by contraction of skeletal muscles

15. Control of systemic circulation Nervous control – innervated by sympathetic nervous system ONLY Cardiac control center (primarily in medulla oblongata) Heart has both Sympathetic and Parasympathetic innervations.

16. Baroreceptors and chemoreceptors: Monitor pressure Monitor blood levels of O2, CO2 and H+ Send information to cardiovascular center, which responds

17. Compliance The increase in volume a vessel can accommodate for a given increase in pressure. Depends on the ratio of elastic fibers to muscle fibers in the vessel wall. Elastic arteries more compliant than muscular arteries Veins more compliant than either artery (blood reservoirs) Decreased compliance suggests an increased stiffness of vessel wall. Determines the vessel’s response to changes in pressure.

18. Blood pressure Mean arterial pressure is the average in pressure in the arteries throughout the cardiac cycle. Depends on the compliance of the arteries and the amount of blood in the arterial system.

19. Blood pressure BP = Cardiac Output * Total Peripheral Resistance

20. Lymphatic System A vascular system that runs “parallel” to the blood vascular system Flow does not circulate – begins in tissue Returns to venous system at subclavian veins Fluid in vessels is lymph – mostly water and proteins Interstitial fluid→ lymphatic capillaries→ lymphatic vessels→ lymphatic trunks→ lymphatic ducts

23. Lymph nodes Lie along lymphatic vessels Contain lymphocytes that filter lymph and eliminate microbes/damaged cells/ toxins Biological filtration

25. Diseases of Arteries and Veins Thrombus- “clotting” in an unbroken vessel Maintains a point of attachment Organized differently than a clot usually due to damage to endothelium and exposure of collagen in the basement membrane

26. Arterial thrombus Forms where blood is moving rapidly – see alternating lines of platelets and red cells trapped in fibrin Lines of Zahn

27. Venous thrombus Forms differently due to decreased blood flow Mixed region at site of attachment More blood clotting forms a downstream red cap

28. Factors that predispose to thrombosis Endothelial damage Bacterial damage Damage to the myocardium Wear and tear – hemodynamic stress Hypertension increases this Arteriosclerosis Inflammation Tumors and irritation by their products

29. Factors that predispose to thrombosis Flow abnormalities Increases platelet contact with endothelium Reduction in flow: Arterial: Cardiac damage and decreased pumping action Increased blood viscosity Venous: Physical inactivity Varicose veins

30. Turbulence: Damaged heart valves Congenital heart defects Compression of the vessel Weakened arterial wall - aneurysm

31. Other Causes Aging Immobilization Injury to vessel endothelium Increased clotting response Effects: Decreased venous emptying Increased venous pressures Edema Pain

32. Sequelae of Thrombosis 1 Resolution – Anticoagulation system Fibrolytic system Moderate exercise increases thrombus resolution

33. 2 Organization The thrombus is digested by phagocytes and replaced by connective tissue – incorporating the thrombus into the vessel wall. May recanalize – small channels open up and restore blood flow

34. Recanalization

35. 3 Propagation – Thrombus extends further down the vessel, usually a vein. Initial thrombus acts as a site for further platelet adherence.

36. Propagation

37. 4 Infarction – an infarct is an area of necrosis caused by ischemia and hypoxia. More common in arteries than veins due to blood flow patterns Collateral circulation and anastomosis prevent infarction

39. Embolism – obstruction of vessel by matter circulating in blood stream Matter could be fat, air, infant’s cells, in addition to pieces of clot – thromboemboli Thromboemoboli from the venous system tend to end up in the: lungs and liver

41. Treatment Anticoagulants Fibrinolytics – t-Pas Prophylactic aspirin therapy

43. Arterial Occlusions Arteriosclerosis – abnormal thickening and hardening of the arterial walls Smooth muscle cells and collagen fibers migrate into the tunica intima, causing stiffening and thickening, narrowing the lumen Can exacerbate high blood pressure, and cause weakening and outpouching of vessel walls

45. Atherosclerosis A form of arteriosclerosis where soft deposits of intra-arterial fat and fibrin harden over time – atheroma May see build up in skin – Xanthoma or arcus in cornea. In general, patients suffer few symptoms unless > 60 % of blood supply is blocked

46. Progressive over years Starts with some injury to endothelium Smoking, hypertension, hyperlipidemia, diabetes, autoimmune disease, and infection Inflammation, release of enzymes by macrophages causes oxidation of LDL, which is then consumed by macrophages – foam cells – accumulate to form fatty streaks Fatty streaks of lipid material appear first as yellow streaks and spots Smooth muscle cells proliferate, and migrate over the streak forming a fibrous plaque

47. Fibrous plaque results in necrosis of underlying tissue and narrowing of lumen Inflammation can result in ulceration and rupture of the plaque, resulting in platelet adherence to the lesion = complicated lesion Can result in rapid thrombus formation with complete vessel occlusion → tissue ischemia and infarction

50. Clinical manifestations Signs and symptoms of inadequate perfusion – TIAs, often associated with exercise or stress When lesion becomes complicated, can result in tissue infarction Coronary artery disease – myocardial ischemia In brain – major cause of stroke