Download to read offline
Histology blood vessels thrvbgrdsdghhjjjb
- 1. HISTOLOGY OF THE CIRCULATORYSYSTEM DR O.S OYEDUN DEPT OF ANATOMY UNIVERSITY OF IBADAN
- 2. Main functions ofVascular system • Transport of oxygen, carbondioxide, nutrients, hormones, metabolic products, cells of immune defense system and many other essential products • Gaseous exchange • Temperature control
- 3. Types of BloodVessels
- 4. Structure of BloodVessels All blood vessels except capillaries have 3 basic Tunics or Coats concentrically arrranged • Tunica Intima • Tunica Media: • Tunica Adventitia :
- 5.
- 6. Arteries • Thick walledblood vessels that carry blood from heart to the capillaries. • They divide repeatedly like branch of a tree and gradually become smaller in size. • However, their luminal surface is increased many times(800 fold) compared to that of a large artery (aorta). • This causes a decrease in the rate of blood flow, facilitating an exchange of substances through capillaries.
- 7. Low Power Viewof Large Artrery Examples of Large artery: • Aorta and its branches • Brachiocephalic, Carotid carotid, Subclavian, axillary and common iliacs, pulmonary & vertebral • It conducts blood from heart. • Thickness of the wall is 1/10 the luminal diameter.
- 8. Elastic Artery(stained withorcein) Tunica Intima: • Endothelium • Basal lamina :A thin layer of glycoprotein • Subendothelial C T which contains fibrocytes, macrophages and smooth muscle like-cells called Myointimal Cells. • The collagen and elastic fibres are longitudinally arranged. • Internal Elastic Lamina forms the boundry between T Intima and T media. Consists of elastic fibres is poorly defined and is fenestrated
- 9. Elastic Artery (stainedwith orcein) Tunica Media: • Elastic tissue in the form of 40- 70 fenestrated elastic membranes • Smooth muscles and collagen fibres in matrix • Matrix rich in chondroitin sulfate. • A layer of elastic fibers external elastic lamina forms the boundary between T media and T adventitia. Tunica Adventitia: Fibroelastic C T having Vasa Vasorum and unmyelinated sympathetic fibres.
- 10. Interesting features ofElastic Artery • Fibrous elements in intima and adventitia (mainly collagen) run longitudinally that is along the length of the vessel. • Elastic fibres in the internal and external elastic lamina are often in the form of fenestrated sheets(holes in them) • Internal Elastic Lamina and External Elastic Lamina are not prominent because of the presence of large amount of elastin within the media . • In T adventitia, small blood vessels may be found, termed Vasa Vasorum. They serve to nourish the vessel.
- 11. Elastic Artery • Presenceof elastic fibres in the wall allows it to expand during contraction (systole) and recoil during relaxation (diastole). • This maintains necessary Blood Pressure and permits the blood to flow more evenly through other arterial channels
- 12. Prominent Elastic fibresin T Media of Elastic Artery
- 13. Changes due toage in Large Artery • Thickening of Tunica Intima due to migration and proliferation of smooth muscle cells from T Media. • Accumulation of lipid in the Myointimal cells and macrophages. • Formation of fibrofatty plaques by the deposition of fat and collagen in T Intima (Atheroma) • Atheroma leads to narrowing of the arterial lumen and consequently reduced blood flow. • Calcification of T Media (Arteriosclerosis) • Atherosclerosis(atheroma+arteriosclerosis) • Damage to the endothelium can cause coagulation of blood forming a thrombus which can completely obstruct the artery leading to death of the tissue it supplies • If this happens with Myocardium: Coronary thrombosis leading to Myocardial Infarction (may manifest as heart attack) • In brain: Cerebral thrombosis leading to stroke and paralysis
- 14. Aneurysm • Tunica mediamay undergo atrophy resulting in loss of elasticity of the wall. • The weakened wall may get stretched forming aneurysm. • Its rupture may cause death.
- 15. Muscular Artery Large elasticarteries branch and become medium-sized muscular arteries. Most numerous vessels in the body. Examples: Branches of External Carotid artery, radial & Ulnar arteries, femoral, popliteal etc • Distributes blood to various parts of the body. • Wall thickness=1/4 the luminal diameter. • Presence of smooth muscle in its wall helps to control flow and pressure of blood through vasoconstriction and vasodilatation.
- 16. Muscular Artery • TIntima: Endothelium Internal Elastic lamina (No subendothelial Tissue) Internal Elastic Lamina is a bright refractile membrane thrown into wavy folds due to contraction of the elastic membrane during the fixation process.
- 17. Muscular Artery • TMedia: 40 layers of smooth muscle cells arranged circularly, hence the name muscular artery. • Contains few collagen and elastic fibres intermixed with smooth muscle cells
- 18. Muscular Artery T Adventitia: •Elastic and collagen fibres running longitudinally • Contains vasa vasorum and unmyelinated sympathetic nerve fibres.
- 19. Low Power Viewof Medium Sized Artery
- 20.
- 21.
- 22. Cross section ofMuscular artery(100X) stained specifically for elastin
- 23. Difference between Elastic& Muscular artery Elastic Artery • T Intima: is much thicker, sometimes 20% of the total wall thickness. • Subendothelial C T has more elastic fibres • IEL is not distinct (as it has the same structure as the elastic membranes of the media) • T Media:Elastic fibres ++ Muscular Artery • T Intima: IEL is well demarcated. • T Media: Smooth M + • EEL is also very prominent. • T adventitia: Thickness is more and sometimes may be equal to the thickness of the media.
- 24. Elastic and Muscularartery
- 25. Arteriole • Smallest branchesof the arterial system. • Deliver blood to the smallest blood vessels, the capillaries. • Diameter - less than 100 Micron m • Larger Arterioles: Dia 100-50 Micron m • Terminal Arterioles: Dia less than 50 Micron m • Wall is relatively thicker than the lumen. • Serve as a transition vessel between muscular arteries and capillaries. Three coats are present T Intima: Endothelium + no subendothelial layer thin or absent IEL. T Media: 1-5 layers of circularly arranged smooth muscle cells. T Adventitia: thin and poorly developed. Made up of a thin network of collagen fibers.
- 26.
- 27. Capillaries • Arterioles breakup into small blood vessels, the capillaries. • Often referred to as Exchange vessels as they are involved in the exchange of gases, nutrients and metabolities between blood and tissue. • Tissues with high metabolic rate have abundant capillary network. Example: kidney, liver and cardiac muscle.
- 28. Capillary • Diameter –8 micron m,(7-9 micron m)equal to the size of an erythrocyte. • Wall has only one layer-the Intima-Consists of 1-3 circimferentially arranged endothelial cells • Underlying basal lamina • Few randomly scattered Pericytes, branching perivascular cells. • Lacks T Media and therefore no smooth muscle cells • Pericytes or Adventitial cells contain contractile filaments in the cytoplasm and can transform into other cells
- 29. Types of Capillaries Continuousor Somatic • Commonest type • Present in connective tissue, muscle, brain, lung etc • Endothelial cells form the continuous lining of the capillary. • Tight junctions, desmosomes and gap junctions are seen. • Fenestrated or visceral • Tiny pores(openings , fenestrations) are present in the cytoplasm of endothelial cells. • Pores are often closed by a thin diaphragm(thinner than the cell membranes) • Pores are so designed for rapid exchange of molecules between blood and tissue(greater permeability) • Examples: Kidney glomeruli intestinal villi, choroid plexus, endocrine glands etc
- 30. Sinusoidal capillary • Alsocalled Discontinuous capillaries because basal lamina is not continuous(Lumen is lined by discontinuous endothelium) • Thin walled, irregular and tortuous • Have much wider irregular lumen (30-40 micron m) which slow down the flow of blood. • Wide gaps are present between the individual endothelial cells • These two facts permit passage of blood cells and macromolecules. • Found in liver and haemopoietic organs like red bone marrow and spleen. • Phagocytic cells may be seen in its wall(e.g. kuffer cells in liver)
- 31. Capillaries with RBCs(Longitudinal Plane)
- 32. Functions of CapillaryEndothelium • Permeability: • Allows exchange of water, CO2 and metabolites between blood and tissue • .Allows migration of leucocytes from blood to tissue (diapedesis) which is increased during inflammation. • Forms Blood brain Barrier-the tight junctions between the endothelial cells • Metabolic function: Activates- angiotensin I to angiotensin II Inactivates bradikinin,serotonin.prostaglandin.norepinephrin and thrombin into inert compounds Breaks down lipoproteins into triglycerides and cholesterol. • Nonthrombogenic Function: • Platelets normally do not adhere to an intact endothelium because Prostacyclin is released by endothelium which is a powerful inhibitor of platelet aggregation and thus prevents clot formation
- 33. Summary of Histologicalfeatures of Capillary and Arteries
- 34. High Power ofSmall Artery and arteriole
- 35. Venous System • Veinsare thin walled • Carry blood from capillaries to heart • Large veins are formed by the union of smaller vein like tributary of a river. • Often provided with valves • Valves serve to prevent reflux of blood.
- 36. Features of venoussystem to distinguish them from arteries • The ratio of wall thickness to lumen diameter is less • Media is thin and poorly developed (Intima and adventitia are more prominent) • Internal and external elastic lamina are difficult to distinguish • An artery will always have a larger wall- thickness-to-lumen ratio than a vein of corresponding size.
- 37. Types of Veins •Large sized Veins • Medium sized veins • Venules • A clear distinction between T intima, media and adventitia cannot be made outin small veins as all the layers consist predominantly of fibrous tissue • Same 3 layered organisation as arterial system. • T intima • T media • T adventitia
- 38. Histological features ofLarge vein Examples: SVC and IVC • T intima: well developed, endothelium and subendothelial C T + • T media: thin or – • T adventitia: well developed, thickest coat, many longitudinal bundles of smooth muscle fibers are embedded in C T. • Longitudinal bundles facilitate shortening and elongation of the vena cava with respiration.
- 39. Low Power Viewof Large Vein
- 40. High Power Viewof Large Vein
- 41. Medium sized Vein •T intima: endothelium & thin layer of subendothelium • T media: Few circularly arranged smooth muscle fibers embedded in C T having predominantly collagen fibers, less elastic fibers. • T adventitia:loose fibroelastic C T with vasa vasorum and nerve fibres.
- 42. High Power Viewof Medium Vein
- 43. Differences between Mediumsized Vein and a medium sized artery Medium sized vein • A collapsed larger lumen • Thin wall • No IEL • T media has large quantity of collagen (few smooth muscles and less elastic fibers) that is the reason veins are easily compressed. • T adventitia is thicker than T media in large veins • Presence of valves to prevent back flow Medium sized artery • Thick wall • Arteries retain their patency • Internal Elastic Lamina is present only in arteries • T media is thicker than adventitia
- 44.
- 45. Venules • Receive bloodfrom capillaries • Have a larger diameter than arterioles(0.5-1 mm) • Small venules(post capillary venules) take part in exchange of metabolites between blood and tissue • Also permit leucocytes migration as do capillaries. • Venules are sensitive to inflammatory agents resulting in leakage of fluids and defensive cells. • The post capillary venules in mucosa associated lymphoid tissue(MALT) are lined by tall cuboidal endothelial cells and are called high endothelial venules(HEV)
- 46. Three layers ofVenules • Wall is thin • Large collapsed lumen • T intima: endothelium • T media: 1-2 layers of smooth muscle fibers. • T adventitia: thick and composed of connective tissue rich in collagen fibres.
- 47. Cross section ofa venule and arteriole(200X)
- 48. Arterioles, venules andcapillaries within adipose tissue(200X)
- 49. Cross section ofa vein and an artery(200X)
- 50. Cross section ofartery and vein
- 51. Summary of Histologyof Veins
- 53. High Power Viewof Medium Sized Vein and valve • Valves + in most Veins • For unidirectional flow of blood • Made of 2 semilunar cusps • Each cusp is afold of endothelium with elasitic fibre rich connective tissue in them.
- 54. Medium Vein andValve
- 55. MCQ 1 A largeartery is characterized by the presence of a) A Well Developed Internal Elastic Lamina b)Elastic Fibres In Tunica Media c) Smooth Muscle Fibres In Tunica Adventitia d)Mesothelial lining
- 56.
- 57. MCQ 2 Atherosclerosis inan artery is due to a) Thickening of T intima b) accumulation of lipid in myointimal cells c) Calcification of T media d) All of the above
- 59. MCQ Medium-sized artery ischaracterized by the presence of a) a well developed Internal elastic lamina b) a well developed subendothelial connective tissue c)elastic fibres in tunica media. d)smooth muscle fibres in tunica adventitia
- 60.
- 61. MCQ Pericytes are a) Modifiedendothelial cells b) Phagocytic cells c) Pluripotent cells found in association with capillaries d) Found in tunica media of arterioles
- 62. MCQ Capillary endothelial cellsare involved in a) Conversion of angiotensin I to angiotensin II b)Exchange of metabolites c)Diapedesis d) All of the above
- 63.
- 64. MCQ Capillaries in endocrineglands are lined with a) Continuous endothelium b) Discontinuous endothelium c) Fenestrated endothelium d) Sinusoidal endothelium
- 65. That’s it • Seeyou next lecture