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Cardiovascular System (Structural Differences of Blood Vessels (Venules,…

- - - - two superior atria
        
        the receiving chambers
        
        blood enters the right atrium via 3 veins
        
        Superior vena cava - returning blood from body regions superior to diaphragm
        
        Inferior Vena Cava
        
        returns blood from body areas below the diaphragm
        
        Coronary Sinus - collects blood draining from the myocardium
        
        has a smooth walled posterior part and an anterior portion which walls are ridged by bundles of muscle tissue
        
        called pectinate muscles (pectin=comb) since they look like the teeth of a comb
        
        4 Pulmonary Veins enter the left atrium
        
        these veins transport blood from the lungs back to the heart
      - two inferior ventricles
        
        the discharging chambers
        
        make up most of the volume of the heart
        
        when ventricles contract blood is propelled out of the heart into circulation
        
        Right Ventricle pumps blood into pulmonary trunk, routes blood to the lungs where gas exchange occurs
        
        Left Ventricle ejects blood into the aorta, largest artery in the body
        
        internal walls of ventricular chambers are irregular ridges of muscle - trabeculae carnae
        
        conelike papillary muscles
        
        role in valve function
    - - seperates the atria
    - - seperates the ventricles
- - - - LARGEST in diameter
      - contain MORE elastin especially the tunica media
      - are pressure reservoirs
  - - - thickest tunica media of all vessels
        
        containsMORE smooth muscle and less elastin
  - - - larger arterioles
        
        ALL 3 TUNICS
        
        tunica media is mainly smooth muscle w/ few elastic fibers
      - smaller arterioles
        
        lead into the capillary beds
  - - - thin walls = thin tunica intima
      - pericytes
        
        smooth muscle like cells
        
        stabilize the capillary wall
        
        help control capillary permeability
    - - Continuous
        
        most common
        
        abundant in skin & muscles
        
        endothelial cells - uninterrupted lining, & adjacent cells being joined laterally by tight junctions
        
        tight junctions are usually incomplete
        
        leave gaps = intercellular clefts
      - Fenestrated
        
        similar to continuous but endothelial cells are riddled with oval pores, fenestrations
        
        MORE permeable to fluids and small solutes
        
        usually covered by delicate membrane or diaphragm
        
        found wherever active capillary absorption or filtrate formation occurs
      - Sinusoids
        
        HIGHLY modified, leaky capillaries
        
        found ONLY in LIVER, BONE MARROW, SPLEEN & ADRENAL MEDULLA
        
        Large, irregularly shaped lumens & usually fenestrated
        
        endothelial lining has fewer tight functions and larger intercellular clefts
  - - - consists of endothelium
  - - - can accommodate a fairly large blood volume
      - called " capacitance vessels" or "blood reservoirs" bcs. up to 65% of body's blood supply is found in veins ANY TIME!
      - BP in veins is LOW
      - Venous valves- prevent blood from flowing backward
        
        formed from folds of tunica intima
        
        resemble the semilunar valves in the heart
        
        MOST abundant in the veins of the limbs
        
        absent in veins of thoracic and abdominal cavities
      - little smooth muscle in tunica media - poorly dvlp. and thin
      - tunica externa is the HEAVIEST wall
        
        thick longitudinal bundles of collagen fibers & elastic networks
- - - - varies directly w/ SV & HR
        
        highly vsriable & increases in response to special demand
  - - - SV= EDV - ESV
  - - - preload - is the degree in which cardiac muscle cells are stretched just before they contract.
    - - contractile strength achieved at a given muscle strength
      - an INCREASE is due to greater Ca
      - enhanced contractility results in ejection of MORE blood from the heart, lower ESV
      - INCREASED sympathetic stimulation INCREASES contractility of the heart
- - - - Action Potential Initiation by Autorhythmic Cells
        
        have an unstable resting potential that continuously depolarizes, drifts slowly toward threshold
        
        Pacemaker Potentials "spontaneously changing membrane potentials" initiate the action potentials that spread throughout the heart
        
        slow depolarization is due to both the opening of Na channels and closing of K channels
        
        at threshold, Ca channels open, allowing Ca to enter from the extracellular space
        
        In autorhythmic cells, the influx of Ca produces the rising phase of the action potential
        
        1 more item...
        
        reserves the membrane potential
  - - - (Pacemaker) generates impulses
    - - the impulses pause here
    - - connects the artia to the ventricles
    - - conduct the impulses through the interventricular septum
    - - depolarize the contractile cells of both ventricles