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Blood Vessels

Blood Vessels. Blood Vessels. hollow structures for carrying blood form closed system beginning & ending at heart Arteries Arterioles Venules Veins Capillaries. Vessel Structure. 3 layers- tunicas surround central space or lumen Tunica intima Tunica media Tunica adentitia.

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Blood Vessels

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  1. Blood Vessels

  2. Blood Vessels • hollow structures for carrying blood • form closed system beginning & ending at heart • Arteries • Arterioles • Venules • Veins • Capillaries

  3. Vessel Structure • 3 layers-tunicas • surround central space or lumen • Tunica intima • Tunica media • Tunica adentitia

  4. Tunica Intima or Tunica Interna • innermost layer • in contact with blood • consists of layer of simple squamous cells-endothelium • fit closely together forming slick surface • minimizes friction as blood moves through lumen

  5. Tunica Media • middle layer • usually thickest • consists of smooth muscle, collagen and in some cases elastic tissue • strengthens vessels to prevent rupture • provides vasomotion or changes in diameter of blood vessel • impulses cause muscles to contract vasoconstriction • reduction in size of lumen • impulses inhibitedmuscle fibers relaxdiameter increases-vasodilation

  6. Tunica Adventitia or Tunica Externa • outermost layer • composed of loose connective tissue • responsible for attaching vessels to surrounding tissues

  7. Arteries • carry blood away from heart • progressive diminution in diameter as recede from heart • branch, diverge, & fork

  8. Arteries • resistance vessels • relatively thick muscular walls containing elastic & contractile fibers • change diameters by expanding (elasticity) as pressure increases & by constricting under sympathetic nervous control (contractility) • vasoconstriction & vasodilation affect: afterload, peripheral blood pressure & capillary blood flow

  9. Types of Arteries • Elastic • conducting arteries • largest • transport large amounts of blood away from heart • elastin in all layers • withstand large pressure fluctuations • Muscular • distributing arteries • deliver blood to organs & skeletal muscles • named arteries • thickest media • active in vasoconstriction • Resistance arteries • arterioles • poorly defined external tunicas • diameters change in response to local conditions, sympathetic innervations & hormonal stimulation • more pressure is needed to push blood through constricted vessels • force opposing blood flow is called resistance • major site of resistance to blood flow.

  10. Capillaries • do work of cardiovascular system • walls permit exchange between blood interstitial tissues • smallest blood vessels • consist of endothelium & basement membrane • several types • Continuous • Fenestrated • Sinusoids

  11. ContinuousCapillaries • complete endothelium lining forming a continuous tube • cells joined by tight junctions • in all tissues except epithelia & cartilage • permit diffusion of water, small solutes and lipid-soluble materials into surrounding interstitial fluid

  12. Fenestrated Capillaries • haveoval pores- fenestrations • allow for rapid transport of molecules through capillary wall • found in organs that engage in rapid absorption or filtration • kidneys, exocrine glands & choroid plexus of brain

  13. Sinusoids • endothelial cells are separated by wide gaps with no basal lamina • proteins & blood cells can pass through • found only in certain organs such as liver, bone marrow, & spleen

  14. Capillaries • connect arteries to veins • do work of cardiovascular system • found in beds

  15. Capillary Beds • blood flow through beds-micro circulation • one arterioledozens of capillariesvenules • arterioles linked to capillaries via metarterioles • surrounded by band of smooth muscle-precapillary sphincter • contraction-narrows diameter of capillary entrance reducing blood flow • relaxation increases blood flow

  16. Sphincter Open • capillaries exchange materials with tissues

  17. Sphincter Closed • blood bypasses capillaries • flows through thoroughfare channel to venule

  18. Mechanisms of Movement • Diffusion • Bulk Flow • Filtration • Reabsorption • Transcytosis

  19. Diffusion • most important • net movement of ions & molecules from areas of higher to areas of lower concentration • difference between concentrations is- concentration gradient • most rapid diffusion occurs where • distances are small • concentration gradients are large • molecules are small

  20. Bulk Flow • Filtration & Reabsorption • across capillary walls • between blood & interstitial tissues • due to hydrostatic & osmotic pressures

  21. Bulk Flow • Filtration • direction of flow is out of the capillary into the interstitial fluid • at arterial end • Reabsorption • direction of flow is out of interstitial fluid into the capillary • at venous end

  22. Capillary Exchange Pressures • two main factors promote filtration • blood hydrostatic pressure (BHP) &interstitial fluid osmotic pressure (IFOP) • primary pressure promoting reabsorption-blood colloid osmotic pressure (BCOP) • in vessels hydrostatic pressure is due to pressure that water in blood exerts against vessels walls (BHP) • BHP is about 35mm of Hg at arterial end of capillary & 16mm Hg at venous end • BHP pushes fluid out of capillary into interstitial fluid. • Interstitial fluid hydrostatic pressure (IFHP) pushes fluid from interstitial spaces back into capillaries- value is close to zero • Blood colloid osmotic pressure (BCOP) isdetermined by proteins present in plasma • BCOP pulls fluid from interstitial spaces into capillaries-averages 26mm Hg • Opposing BCOP interstitial fluid osmotic pressure (IFOP) • IFOP pressure pulls fluid out of capillaries into interstitial fluids- value i0.1 – 5mm Hg • Net Filtration Pressure = (NFP) = (BHP + IFOP) – (BCOP + IFHP) • NFP is equal to pressures promoting pressure minus pressures promoting reabsorption

  23. Net Filtration Pressure • Net Parterial end = (35 mm Hg + 1) - (26mm Hg + 1) = 10mm Hg • value tells there is a net outward pressure • fluid moves out of capillaries into interstitial fluid-net filtration • Net P venous end = (16mm Hg )+ 1) + (26 mm Hg + 1) = -9 mm Hg • value tells net absorption is taking place • there is a net inward pressure forcing fluid into capillaries from interstitial fluid

  24. Veins • carry blood back to heart • join, merge, & converge • diameters small in venules • become progressively larger as approach heart

  25. Veins • thin walls • can distend • capable of holding a great deal of blood • capacitance vessels- blood reservoirs which can be drawn upon in time of need • many especially in arms & legs, have flaps or valves • composed of 2 leaflets • close if blood begins to back up in veins

  26. Distribution of Blood • blood volume unevenly distributed • heart, arteries & capillaries account for 30-35% total volume • venous system contains 64% total volume

  27. Cardiovascular Physiology • blood must circulate • heart provides force &blood vessels are conduits • blood flow is the volume of blood that flows through a tissue in a given time (ml/min) • total blood flow is CO • volume of blood that circulates through systemic or pulmonary circuits each minute • CO = SV X HR • how CO becomes distributed into circulatory routes depends on two more factors • pressure differences & resistanceto flow

  28. Pressure Differences & Resistance • pressure gradient • difference in pressure from one end of vessel to another-P • largest-from base of aorta to proximal ends of peripheral capillaries • greater P more blood flow • resistance • any force opposing movement • due mainly to friction of blood with blood vessel walls • greater resistanceslower blood flow

  29. Blood Pressure • produced by contraction of ventricles • determined by: CO, resistance & blood volume • measured by using a sphygmomanometer & brachial artery • highest in arteries during systole • lowest in arteries during diastole • expressed as mmHg

  30. Blood Pressure • systemic arterial pressure ranges from 100mm Hg-aorta to 35mm Hg-capillaries • venous end of capillaries, pressure 16 mmHg • pressure continues to drop as blood enters systemic veins • reaches zero mm Hg as blood flows into right ventricle

  31. MAP • Mean arterial pressure • value for arterial pressure representing it driving process • average blood pressure in the arteries • MAP = diastolic pressure + 1/3(systolic pressure – diastolic pressure) • If normal: MAP = 80mm Hg + 1/3(120-80mm Hg) = 93mm Hg • CO = MAP/R or MAP = CO X R • shows that if CO rises due to HR or SV then so does MAP since CO = SV x HR

  32. Blood Pressure & Blood Volume • blood pressure also depends on total volume of blood in cardiovascular system • anything that increases blood volume will increase blood pressure • kidney helps with long term regulation of blood pressure

  33. Peripheral ResistanceSystemic Vascular Resistance • resistance of entire arterial system • F = P/R • Flow = change in pressure divided by resistance • equation shows blood flow is directly proportional to pressure gradient & inversely proportional to resistance • higher PRlower rate of blood flow • pressure gradient must be greater than total peripheral resistance for blood to flow • vascular resistance is the opposition to blood flow due to friction between blood vessel walls & blood • depends on • vessel lumen • blood viscosity • total vessel length

  34. Blood Viscosity thickness of blood greater viscositymore friction greater resistance anemia & polycythemia will change hematocrit changes viscosity changes resistance under normal conditions negligible

  35. Vessel Length • longer vesselsgreater resistance • length increases friction • two vessels-equal diameters • if one is twice length of other-longer vessel has twice resistance of shorter vessel • factor is usually constant

  36. Vessel Diameter • most important factor contributing to resistance • significant effects • smaller vesselsgreater friction • more fluid in contact with vessel wallmore frictionmore resistance • friction in larger vessels is low because blood comes into contact with vessel wall less oftenless less friction less resistance

  37. Vessel Diameter • two vessels-equal lengths • One- twice diameter of other • using formula: R-  1/r4 • vessel with twice diameter of other has 1/16 as much resistance as smaller diameter vessel • or-smaller vessel has 16X as much resistance

  38. Blood Velocity • depends on flow rate & cross sectional area • flow rate • volume of blood passing one point in system/unit time • given as Liters/minute or ml/min • Velocity • distance fixed volume of blood travels in given time period • measured in cm/sec • inversely related to cross sectional area • slowest where total cross sectional area is greatest • fastest where cross sectional area is leas • cross sectional area of aorta-3 – 5cm2 • average velocity - 40cm/sec • Capillaries-total cross sectional area-4500 – 6000cm2 - velocity is less than 0.1 cm/sec • slows down for capillary exchange

  39. Control of Blood Pressure & Flow • Nervous System • Hormones • Autoregulation

  40. Neural Mechanisms • CV center regulates HR & SV • controls blood vessels via ANS • exert sympathetic & parasympathetic control over blood vessels throughout body • Sympathetic input reaches heart via cardiac accelerator nerves • increase in sympathetic stimulation increases HR & contractility. • decrease in sympathetic stimulation decreases HR & contractility • Parasympathetic stimulation is conveyed along vagus nerve • results in decreased HR

  41. Nervous System Control • cardiovascular center integrates nerve impulses from cerebral cortex, limbic system & hypothalamus • Proprioceptors • monitor joint movements • Barorecepetors • monitor pressure changes • Chemoreceptors • monitor chemical changes in blood • regulates via negative feedback loops & 2 major reflexes • Baroreflexes • Chemoreflexes

  42. Baroreflex • autonomic negative feedback response to change in blood pressure • detected by baroreceptors • located in carotid arteries & aorta • monitor stretch in walls due to pressure of blood flowing to brain • two types-carotid sinus reflex & aortic reflex • carotid reflex • regulates bp in brain • aortic reflex regulates systemic bp • blood pressure rises walls stretch increases rate of baroreceptors signals over glossopharygeal nervesinhibits sympathetic neurons & increases parasympathetic firing reduces HR & force of contraction which decreases CO • blood pressure drops back to normal • slows rate sympathetic stimulation is sent to vasomotor nerves that cause vasoconstriction results in vasodilation • SVR, lowers CO & lowers blood pressure

  43. Baroreflex • Baroreceptors in walls of ascending aorta &aortic arch begin aortic reflex • Once stimulated send impulses over vagus nerve to CV center. • blood pressure decreases baroreceptors stretch lesssend impulses at slower rate to CV center decreases parasympathetic stimulation & increases sympathetic stimulation via cardiac accelerator nerves • Sympathetic nervous stimulation increases secretion of epinephrine & norepinephrine from adrenal medulla • causes the heart to beat faster & more forcefully increases SVR, CO & blood pressure

  44. Baroreflexes • important in short term regulation of blood pressure • keep BP stable when moving from reclining to standing position • quickly adapt to prolonged or chronic episodes of high or low blood pressure • kidneys come in to restore & maintain BP by regulating blood volume • major determinant of CO through influences on venous pressure, venous return, EDV & SV

  45. Chemoreflex • autonomic response to changes in blood chemistry • especially pH,O2& CO2 • Chemoreceptors-aotic &carotid bodies • negative feedback • abnormal conditions cardiovascular centers noticerespond in ways to counteract abnormal condition homeostasis restored • low O2 (hypoxia), high CO2(hypercapnia) & low pH (acidosis) stimulate chemoreceptors CV centerwidespread vasoconstriction  increases BP • also sends impulses to the respiratory center • primary response is to adjust respiration

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