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Blood Vessel Physiology (Terms (Tunica intima - deepest layer of vessels…

- - - - thickest tunica media of all vessels
        
        largely assist in vasoconstriction and vasodilation
    - - Arterioles
        
        arteries that connect muscular arteries to capillary beds
        
        smallest type of artery and only contains tunica intima and muscle fibers; other tunica levels are not present
    - - largest diameter of all arteries and contain the more elastin than any other blood vessel
        
        expand and recoil as blood enters to...
        
        keep blood flow continuous and prevent blood from staying stationary
        
        decrease pressure against arteriole walls to protect them from rupturing
      - Thick walled artery near the heart
- - - - thin walls that only contain tunica intima in some venules
        
        allows fluid and leukocytes to easily travel through walls
        
        most WBC's reach inflamed tissue by passing through these
  - - - large lumen increases blood flow but decreases blood pressure
    - - these valves are similar to SL valves of the heart
      - this prevents gravity from trapping blood
      - veins are aided with blood flow by contraction of skeletal muscles
- - - - most common capillary type
        
        endothelial cells joined by tight junction to provide solid lining
        
        provide basic exchange of nutrients and waste where higher permeability is not requiers
        
        these junctions normally leave gaps called intercellular clefts to increase permeability
      - found where the other two capillaries are not
    - - contains all of the characteristics of continuous capillaries with the addition of small oval openings called fenestrations
        
        allow easier passage of small solutes and fluids
      - found in small intestine and endocrine organs to aid in absorption, and the kidney to aid in filtration
    - - leaky capillaries found only in certain organs
        
        large oddly shaped lumen with less tight junctions and larger fenestrations
        
        slow down blood flow to modify it, which normally involves moving large solutes and even blood cells across the sinusoid wall
      - found in red marrow, liver, and spleen
- - - - forms a slick surface to minimize friction as blood travels through the lumen
  - - - provides regulation of blood pressure and blood flow
        
        while contracted blood pressure increases and blood flow decreases
        
        while relaxed causes blood pressure to decrease and blood flow to increase
  - - - Collagen fibers protect the vessel wall and anchor the vessel to nearby structures
      - Elastic fibers allow flexibility in the vessel wall to change shape with changing blood pressure
- - - - Hydrostatic pressure (HP) - force exerted by fluid pressing against the capillary wall
        
        forces fluid through capillary walls to promote filtration
        
        always higher at the arteriole end due to blood pressure decreasing as the blood flows through the capillary bed
        
        this pressure measurement is the same as that of the blood pressure itself
      - Colloid osmotic presure a.k.a. Oncotic pressure (OP) - pressure against the walls from the interstitial fluid outside of the capillary
        
        cause by large nondiffusible molecules such as albumin
        
        This pressure does not change much from either end of the capillary, but is normally higher than the HP at the venous end
        
        encourages osmosis of fluid into capillary
    - - When the OP is higher than the HP, fluid enter s the capillary bed
  - - - the capillary has a vascular shunt, which is the middle vessel that connects directly from the arteriole end to the venous end
        
        there are anywhere between 10-100 true capillaries that branch off of the vascular shunt
        
        these true capillaries deliver the blood to the tissue surrounding the capillary bed
        
        the blood then travels to the postcapillary venule where it is returned to the heart
        
        on the root of each true capillary there is a precapillary sphincter. This is made of smooth muscle and controls blood flow to the true capillaries
        
        When open blood is delivered to the surrounding tissue
        
        when closed blood passes along the vascular shunt only and does not go to the true capillaries
        
        this is done when blood is more needed at another part of the body