Blood vessels.2.


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  • supported by a thin layer of loose CT (basement membrane)
  • Blood pumped out of the heart is at a very high pressure, so the structure of the arteries must be adapted to this. They can withstand high pressure by having very thick walls made up of elastic fibres and smooth muscle. The elastic fibres increase its elastic strength. The smooth muscle can change the diameter of the lumen, especially in the smaller arteries. (higher students The smaller arteries and arterioles are more muscular and can contract ( vasoconstriction ) to close off the capillary beds to which they lead; or relax ( vasodilation ) to open up the capillary bed. ) . Lumen is relatively narrow. The tunica media layer is thicker in arteries than in veins tunica intima In arteries this layer is composed of an elastic membrane lining and smooth endothelium that is covered by elastic tissues.
  • carry blood from every tissue in the body to the heart.
  • A blood vessel is a tube with a space in the centre, called the lumen.
  • So blood leaves the heart through arteries, which in turn give way to arterioles and then capilliaries where the oxygen is delivered and exchanged for carbon dioxide. The capillaries then become larger venules and then veins which then deliver the blood back to the heart.
  • Now lets have a look at the structure of these vessels There are three layers of tissue in both arteries and veins 1 - tunica intima 2 - tunica media 3 - tunica externa (or adventitia) The capillaries are made of a single layer of endothelial cells.
  • Capillaries are where the transported substances actually enter and leave the blood No exchange of materials takes place in the arteries and veins, whose walls are too thick and impermeable. Capillaries are very narrow and thin-walled, but there are a vast number of them (10 8 m in one adult!), so they have a huge surface area : volume ratio, helping rapid diffusion of substances between blood and cells. Capillaries are arranged in networks called capillary beds feeding a group of cells, and no cell in the body is more than 2 cells away from a capillary.
  • Capillary diameter is very small. A typical small artery or vein may be 5mm (in diameter in a human) But a capillaries are approx 10 micrometer about the size of a red blood cell (erythrocyte)
  • A realistic representation of the major blood vessels of the systemic circuit shows how the systemic arteries and veins are arranged in the body.
  • Blood vessels.2.

    1. 1. Blood Vessels SMS 1053 Dr. Mohanad R. Alwan
    2. 2. Blood vessels <ul><li>Learning Objectives: </li></ul><ul><li>Compare and contrast the structure and function of </li></ul><ul><ul><li>Arteries </li></ul></ul><ul><ul><li>Veins </li></ul></ul><ul><ul><li>Capillaries </li></ul></ul>
    3. 3. Blood Vessels <ul><li>Closed circulatory system </li></ul><ul><li>Arteries </li></ul><ul><li>Arterioles </li></ul><ul><li>Capillaries </li></ul><ul><li>Venules </li></ul><ul><li>Veins </li></ul><ul><li>3 tunics </li></ul><ul><li>Lumen </li></ul>
    4. 4. The Vessels <ul><li>Functions: </li></ul><ul><li>Distribution of blood </li></ul><ul><li>Exchange of materials with tissues </li></ul><ul><li>Return of blood to the heart </li></ul><ul><li>Structure: </li></ul><ul><li>Most have the same basic structure: </li></ul><ul><li>– 3 layers surrounding a hollow lumen </li></ul>
    5. 5. General Structure of Blood Vessels <ul><li>Arteries and veins are composed of three tunics: </li></ul><ul><li>tunica interna </li></ul><ul><li>tunica media </li></ul><ul><li>tunica externa </li></ul><ul><li>Capillaries are composed of endothelium. </li></ul>
    6. 6. Generalized Structure of Blood Vessels <ul><li>Arteries and veins are composed of three tunics – tunica interna, tunica media, and tunica externa </li></ul><ul><li>Lumen – central blood-containing space surrounded by tunics </li></ul><ul><li>Capillaries are composed of endothelium with sparse basal lamina </li></ul>
    7. 7. The Anatomy Of Blood Vessels <ul><li>Layers: </li></ul><ul><li>Tunica interna (intima): </li></ul><ul><ul><li>Endothelial layer that lines the lumen of all vessels. </li></ul></ul><ul><ul><li>In vessels larger than 1 mm, a subendothelial connective tissue basement membrane is present </li></ul></ul><ul><li>2. Tunica media: </li></ul><ul><ul><li>Smooth muscle and elastic fiber layer, regulated by sympathetic nervous system </li></ul></ul><ul><ul><li>Controls vasoconstriction/vasodilation of vessels </li></ul></ul><ul><li>3. Tunica externa (adventitia): </li></ul><ul><ul><li>Collagen fibers that protect and reinforce vessels </li></ul></ul><ul><ul><li>Larger vessels contain vasa vasorum </li></ul></ul>
    8. 8. General Structure
    9. 9. The Vessels <ul><li>1. Tunica Intima </li></ul><ul><li>Innermost smooth layer </li></ul><ul><li>Simple squamous epithelium </li></ul><ul><li>Continuous with the endocardium </li></ul><ul><li>Present in all vessels </li></ul>
    10. 10. The Vessels <ul><li>2. Tunica Media </li></ul><ul><li>layer of smooth muscle - circular arrangement – contains elastin </li></ul><ul><li>Supplied by sympathetic division of the ANS </li></ul><ul><li>Depending on body’s needs – lumen is narrowed (vasoconstriction) or widened (vasodilation) </li></ul>
    11. 11. The Vessels <ul><li>3. Tunica Externa (Adventitia) </li></ul><ul><li>Thin layer of CT </li></ul><ul><li>Elastic & collagen fibres </li></ul>
    12. 12. The Vessels <ul><li>Types of Vessels: </li></ul><ul><li>Arteries – carry blood away from the heart </li></ul><ul><li>Veins – carry blood towards the heart </li></ul><ul><li>Capillaries – the most important part of the vascular system; site of exchange of materials </li></ul>
    13. 13. The Blood Vessels and the Cardiovascular System <ul><li>Arteries: blood from heart </li></ul><ul><ul><li>Strong & Elastic </li></ul></ul><ul><ul><li>Conduct blood to capillaries </li></ul></ul><ul><ul><li>Sphincters </li></ul></ul><ul><li>Capillaries: exchange with cells </li></ul><ul><li>Veins </li></ul><ul><ul><li>Return blood to heart </li></ul></ul><ul><ul><li>Valves </li></ul></ul>
    14. 14. Histological Structure of Blood Vessels
    15. 15. Make Up of Blood Vessels: Arteries and Arterioles <ul><li>Endothelium </li></ul><ul><li>Elastic tissues </li></ul><ul><ul><li>Rebounds </li></ul></ul><ul><ul><li>Evens flow </li></ul></ul><ul><li>Smooth muscles </li></ul><ul><li>Fibrous tissue </li></ul><ul><ul><li>Tough </li></ul></ul><ul><ul><li>Resists stretch </li></ul></ul>Figure 15-2: Blood vessels
    16. 16. Artery with thick wall Connective tissue Muscle layer Endothelium
    17. 17. 1 2 3 ELASTIC ARTERY (AORTA)      Stained with orsein 1 - tunica intima 2 - tunica media 3 - tunica externa
    18. 18.
    19. 19. Types of Blood vessels: Arteries <ul><li>Elastic Arteries: </li></ul><ul><li>Thick-walled arteries near the heart; the aorta and its major branches . </li></ul><ul><li>Large lumen allows low-resistance conduction of blood. </li></ul><ul><li>Contain lots of elastin in all three tunics. </li></ul><ul><li>walls stretch and recoil to propel blood </li></ul><ul><li>Withstand and regulate large blood pressure fluctuations . </li></ul><ul><ul><li>Allow blood to flow fairly continuously through the body </li></ul></ul>
    20. 20. Muscular (Distributing) Arteries and Arterioles <ul><li>Muscular arteries – distal to elastic arteries; deliver blood to body organs </li></ul><ul><ul><li>Have thick tunica media with more smooth muscle and less elastic tissue </li></ul></ul><ul><ul><li>Active in vasoconstriction </li></ul></ul><ul><li>Arterioles – smallest arteries; lead to capillary beds </li></ul><ul><ul><li>Control flow into capillary beds via vasodilation and constriction </li></ul></ul>
    21. 21. Types of Blood vessels: Arteries <ul><li>Muscular (distributing) arteries </li></ul><ul><li> medium sized vessels </li></ul><ul><li> tunica media more smooth muscle; less elastin </li></ul><ul><li> major area of vaso-constriction & dilation to regulate blood flow </li></ul>
    22. 22. The Vessels <ul><li>Arterioles (diameter of 0.3 mm or less) </li></ul><ul><li>smallest arteries; lead to capillary beds. </li></ul><ul><li>close to capillaries - single layer of muscle spiralling around the endothelial lining </li></ul><ul><li>regulates blood flow to capillary </li></ul>
    23. 23. General Structure
    24. 24. Venous System: Venules <ul><li>Are formed when capillary beds unite </li></ul><ul><ul><li>Allow fluids and WBCs to pass from the bloodstream to tissues </li></ul></ul><ul><li>Postcapillary venules – smallest venules, composed of endothelium and a few pericytes </li></ul><ul><li>Large venules have one or two layers of smooth muscle (tunica media) </li></ul>
    25. 25. Venous System: Veins <ul><li>Veins are: </li></ul><ul><ul><li>Formed when venules converge </li></ul></ul><ul><ul><li>Composed of three tunics, with a thin tunica media and a thick tunica externa consisting of collagen fibers and elastic networks </li></ul></ul><ul><ul><li>Capacitance vessels (blood reservoirs) that contain 65% of the blood supply </li></ul></ul>
    26. 26. Venous System: Veins <ul><li>Veins have much lower blood pressure and thinner walls than arteries </li></ul><ul><li>To return blood to the heart, veins have special adaptations </li></ul><ul><ul><li>Large-diameter lumens, which offer little resistance to flow </li></ul></ul><ul><ul><li>Valves (resembling semilunar heart valves), which prevent backflow of blood </li></ul></ul><ul><li>Venous sinuses – specialized, flattened veins with extremely thin walls (e.g., coronary sinus of the heart and dural sinuses of the brain) </li></ul>
    27. 27.
    28. 28. Make Up of Blood Vessels: Veins and Venules (Contrasted to Arteries) <ul><li>Thinner walls </li></ul><ul><li>Larger diameter </li></ul><ul><li>Closer to skin </li></ul><ul><li>Less muscle </li></ul><ul><li>Less elastic </li></ul>Figure 15-3: Metarterioles
    29. 29. Anatomy of Vessels
    30. 30. Comparison of Veins and Arteries Arteries: Veins:
    31. 31.
    32. 32.
    33. 33.
    34. 34.                                               
    35. 35.                                                              
    36. 36. <ul><li>They also have semi-lunar valves to stop the blood flowing backwards </li></ul>
    37. 37. <ul><li>This is a medium sized vein, recognizable as such by its scanty wall and the presence of a valve inside it. </li></ul><ul><li>The valve flaps are marked by arrows. </li></ul>
    38. 38. Artery and a vein
    39. 39. Vascular Anastomoses <ul><li>Merging blood vessels, more common in veins than arteries </li></ul><ul><li>Arterial anastomoses provide alternate pathways (collateral channels) for blood to reach a given body region </li></ul><ul><ul><li>If one branch is blocked, the collateral channel can supply the area with adequate blood supply </li></ul></ul><ul><li>Thoroughfare channels are examples of arteriovenous anastomoses </li></ul>
    40. 40. <ul><li>A capillary wall is very thin and composed of (endothelium only) </li></ul><ul><li>single layer of cells as it does not have to withstand high internal pressure. </li></ul><ul><li>A capillary wall is often highly permeable, partly because its very thin and partly because of holes in and between cells in some capillaries (particularly those with high demand of exchange e.g endocrine glands) </li></ul>Capi ll aries
    41. 41. Capillaries <ul><li>Capillaries are the smallest blood vessels </li></ul><ul><ul><li>Walls consisting of a thin tunica interna, one cell thick </li></ul></ul><ul><ul><li>Allow only a single RBC to pass at a time </li></ul></ul><ul><ul><li>Pericytes on the outer surface stabilize their walls </li></ul></ul><ul><li>There are three structural types of capillaries: continuous, fenestrated, and sinusoids </li></ul>
    42. 42.
    43. 43.
    44. 44.
    45. 45.
    46. 46. A capillary bed
    47. 47.
    48. 48. Make Up of Blood Vessels: Capillaries Figure 15-16: Types of capillaries
    49. 49. Continuous Capillaries <ul><li>Continuous capillaries are abundant in the skin and muscles, and have: </li></ul><ul><ul><li>Endothelial cells that provide an uninterrupted lining </li></ul></ul><ul><ul><li>Adjacent cells that are held together with tight junctions </li></ul></ul><ul><ul><li>Intercellular clefts of unjoined membranes that allow the passage of fluids </li></ul></ul>
    50. 50. Continuous Capillaries <ul><li>Continuous capillaries of the brain: </li></ul><ul><ul><li>Have tight junctions completely around the endothelium </li></ul></ul><ul><ul><li>Constitute the blood-brain barrier </li></ul></ul>
    51. 51. Continuous Capillaries Figure 19.3a
    52. 52. Fenestrated Capillaries <ul><li>Found wherever active capillary absorption or filtrate formation occurs (e.g., small intestines, endocrine glands, and kidneys) </li></ul><ul><li>Characterized by: </li></ul><ul><ul><li>An endothelium riddled with pores (fenestrations) </li></ul></ul><ul><ul><li>Greater permeability to solutes and fluids than other capillaries </li></ul></ul>
    53. 53. Fenestrated Capillaries Figure 19.3b
    54. 54. Sinusoids <ul><li>Highly modified, leaky, fenestrated capillaries with large lumens </li></ul><ul><li>Found in the liver, bone marrow, lymphoid tissue, and in some endocrine organs </li></ul><ul><li>Allow large molecules (proteins and blood cells) to pass between the blood and surrounding tissues </li></ul><ul><li>Blood flows sluggishly, allowing for modification in various ways </li></ul>
    55. 55. Sinusoids
    56. 56. Capillary Beds <ul><li>A microcirculation of interwoven networks of capillaries, consisting of: </li></ul><ul><ul><li>Vascular shunts – metarteriole–thoroughfare channel connecting an arteriole directly with a postcapillary venule </li></ul></ul><ul><ul><li>True capillaries – 10 to 100 per capillary bed, capillaries branch off the metarteriole and return to the thoroughfare channel at the distal end of the bed </li></ul></ul>
    57. 57. Capillary Beds Figure 19.4a
    58. 58. Capillary Beds Figure 19.4b
    59. 59. Blood Flow Through Capillary Beds <ul><li>Precapillary sphincter </li></ul><ul><ul><li>Cuff of smooth muscle that surrounds each true capillary </li></ul></ul><ul><ul><li>Regulates blood flow into the capillary </li></ul></ul><ul><li>Blood flow is regulated by vasomotor nerves and local chemical conditions, so it can either bypass or flood the capillary bed </li></ul>
    60. 60.
    61. 61. Capillary Exchange Diffusion: Filtration: Reabsorption:
    62. 62. Capillary Exchange <ul><li>At the arteriole end of a capillary, water moves out of the blood due to the force of blood pressure . </li></ul><ul><li>At the venule end, water moves into the blood due to osmotic pressure of the blood. </li></ul><ul><li>Substances that leave the blood contribute to tissue fluid , the fluid between the body’s cells. </li></ul>
    63. 63. <ul><li>In the midsection of the capillary, nutrients diffuse out and wastes diffuse into the blood. </li></ul><ul><li>Since plasma proteins are too large to readily pass out of the capillary, tissue fluid tends to contain all components of plasma except it has lesser amounts of protein. </li></ul><ul><li>Excess tissue fluid is returned to the blood stream as lymph in lymphatic vessels . </li></ul>Capillary Exchange
    64. 64. Capillary exchange
    65. 65. Capillary exchange <ul><li>At the arterial end of a capillary, the blood pressure is higher than the osmotic pressure; therefore, water tends to leave the bloodstream. </li></ul><ul><li>In the midsection, oxygen and carbon dioxide follow their concentration gradients. </li></ul><ul><li>At the venous end of a capillary, the osmotic pressure is higher than the blood pressure; therefore, water tends to enter the bloodstream. </li></ul>
    66. 66. Capillary Exchang e
    67. 67. Blood Flow in Capillaries <ul><li>Blood moves slowly in capillaries because there are more capillaries than arterioles. </li></ul><ul><li>This allows time for substances to be exchanged between the blood and tissues. </li></ul>
    68. 68.
    69. 69.
    70. 70.
    71. 71.
    72. 72. Major arteries and veins of the systemic circuit
    73. 73. Finiiiiiiiiiiiiish