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Blood Vessels 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

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anatomy 3 layers
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
arteries vs veins

Contractile (thick, muscular walls) & elastic

Passive changes in diameter

In response to changes in BP

Active changes in diameter




Few muscles & little elastic

Passive blood collectors

Little diameter change

Larger lumen than corresponding arteries

Arteries vs. Veins
elastic arteries
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
muscular arteries
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
  • 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
  • Simple, squamous epithelial cells + CT layer
  • Blood flow regulated by precapillary sphincters.
  • Only vessel that allows exchange between blood & interstitial fluid
continuous capillaries
Continuous capillaries
  • Widespread
  • Limited permeability
    • Permit diffusion of small solutes & lipid soluble material
fenestrated capillaries
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
venous return
Venous return
  • Valves & skeletal muscle contraction return blood to the heart
blood flow
Blood flow
  • Aorta
  • Arteries
  • Arterioles
  • Capillaries
  • Venules
  • Veins
  • Vena cava
capillary exchange
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
effects of diameter distance
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
effects of diameter distance18
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.
bp changes with distance
BP changes with distance
  • From arterioles to capillaries:
    • BP drops quickly
    • P drops quickly
local control of blood vessels
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
nervous control of bp
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
regulation of arterial pressure
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
  • Heart rate (HR)
  • Blood Pressure (BP)
  • Stroke Volume (SV)
  • Medulla oblongata (MO)
  • Vasomotor Center (VaC)
  • Cardiovascular Center (CaC)
  • Vasomotor Tone (VaT)
  • Carotid sinus & aortic arch baroreceptors
  • Increase stretch = increased AP frequency to MO
    • Increases HR, SV, VaT
    • Increase BR
  • 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
  • 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
  • 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
  • Vasopressin (ADH) mechanism
    • plasma solute concentration increases or BP decreases
    • ADH released from pituitary
    • ADH stimulates vasoconstriction & water reclamation at kidney; BP rises