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Blood Vessels

Blood Vessels

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Blood Vessels

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  1. Blood Vessels

  2. Anatomy: 3 layers • Tunica externa (adventitia): outer layer; dense to loose connective tissue • lotsa collagen, bits of elastin, few smooth muscles (veins) • Tunica media: middle layer; concentric rings of smooth muscle within CT framework • External elastic membrane in arteries (thickest layer) • Tunica intima: inner layer; simple, squamous epithelium (endothelial lining), basement membrane, some elastic fibers • Internal elastic membrane in arteries

  3. Artery vs. Vein

  4. Arteries Contractile (thick, muscular walls) & elastic Passive changes in diameter In response to changes in BP Active changes in diameter Vosoconstrict Vasodilate Veins Few muscles & little elastic Passive blood collectors Little diameter change Larger lumen than corresponding arteries Arteries vs. Veins

  5. Elastic arteries • Large diameter, conducting arteries. • Take blood away from heart. • Ex: Aorta, pulmonary trunk, common carotid, subclavian, & common iliac arteries • Tunica media has many elastic fibers, few smooth muscle cells

  6. Muscular arteries • Medium-sized, distribution arteries • Distribute blood to skeletal muscles & internal organs • Ex: external carotid, brachial, mesenteric, femoral • Muscular (smooth) tunica media, few elastic fibers

  7. Arterioles • Small arteries, resistance vessels • 1 or 2 layers of smooth muscle; usually incomplete • Change diameter in response to sympathetic & hormonal stimulation or 02 levels. • Produce resistance to blood flow and affect BP

  8. Capillaries • Simple, squamous epithelial cells + CT layer • Blood flow regulated by precapillary sphincters. • Only vessel that allows exchange between blood & interstitial fluid

  9. Continuous capillaries • Widespread • Limited permeability • Permit diffusion of small solutes & lipid soluble material

  10. Fenestrated capillaries • Distribution limited to areas of absorption or secretion • Very permeable • Permit rapid diffusion of H20 & large solutes • Surrounding glands, intestinal tract, filtration areas • Hypothalamus, pituitary, thymus

  11. Venous return • Valves & skeletal muscle contraction return blood to the heart

  12. Blood flow • Aorta • Arteries • Arterioles • Capillaries • Venules • Veins • Vena cava

  13. Capillary exchange • About 10 billion capillaries in the body • Blood pressure • Forces fluid (but not dissolved solutes) into interstitial space • Osmosis • Fluid (lacking dissolved blood proteins) moves back into capillaries along solute concentration gradient

  14. Capillary exchange

  15. Effects of diameter & distance • F  P/R • Increased Pressure = increased Flow • Increased Resistance = decreased Flow • Cardiovascular Pressure • Blood Pressure (BP); arterial • P = 65mm Hg • Capillary hydrostatic pressure (CHP) • P = 17mm Hg • Venous pressure; P = 18mm Hg

  16. Effects of diameter & distance • F  P/R • Increased Resistance = decreased Flow • Vascular Resistance • Vessel Length • Longer vessel = more friction; more SA in contact with blood • Diameter • Smaller diameter = more friction; more blood in contact with vessel walls • Viscosity; R caused by interaction of suspended molecules & solutes • Turbulence; irregular surfaces, high flow rates, changes in diameter.

  17. BP changes with distance • From arterioles to capillaries: • BP drops quickly • P drops quickly

  18. Taking BP

  19. Local control of blood vessels • Sphincters contract or relax based on demand for: • nutrients (AA, glucose, fatty acids) • Dissolved gases (O2, CO2 load, lactic acid) • Additional capillaries grow in to area to satisfy increased energy demands

  20. Nervous Control of BP • Controlled by vasomotor center (pons & medulla oblongata, MO) • Carried out primarily by sympathetic vasoconstrictor fibers • Constitutively active = Vasomotor tone • Allows shunting of blood to/from major regions of body

  21. Regulation of Arterial Pressure • Baroreceptor reflex • Stretch receptors; autonomic control • Chemoreceptor reflex • Stimulated by change in CO2, O2 or pH; autonomic control • Hormonal control • Adrenal Medullary; Renin-Angiotensin-Aldosterone (RAA); Vasopressin; Atrial Natiuretic; autonomic control

  22. Acronyms • Heart rate (HR) • Blood Pressure (BP) • Stroke Volume (SV) • Medulla oblongata (MO) • Vasomotor Center (VaC) • Cardiovascular Center (CaC) • Vasomotor Tone (VaT)

  23. Baroreceptor • Carotid sinus & aortic arch baroreceptors • Increase stretch = increased AP frequency to MO • Increases HR, SV, VaT • Increase BR

  24. Chemoreceptor • Carotid & aortic bodies have receptors • Communicate with MO • O2 drops, or CO2 or pH increases • Increase AP frequency • CaC & VaC decrease parasympathetic stimulation & increases sympathetic stimulation of heart • Increase HR, SV, VaT • Increase BP and blood flow to lungs = MORE O2

  25. Hormonal • Adrenal Medullary • Mechanisms that increase sympathetic stimulation of heart & vessels, also stimulate adrenal medulla • Adrenal medulla releases epinephrine • Epinephrine increases HR, SV; causes vasoconstriction of blood vessels in skin & viscera; vasodilation ofblood vessels in skeletal & cardiac muscle

  26. Hormonal • RAA • BP drops • kidney secretes renin which turns on angiotensin • Angiotensin increase vasoconstriction; BP rises • Angiotensin encourages adrenal medulla to produce aldosterone. • Aldosterone increases Na+ and H20 reclamation @ kidney; BP rises

  27. Hormonal • Vasopressin (ADH) mechanism • plasma solute concentration increases or BP decreases • ADH released from pituitary • ADH stimulates vasoconstriction & water reclamation at kidney; BP rises