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Circulatory System (vertebrate system (vessels = arteries, capillaries,…

- - - - atria
        
        receives blood
      - ventricle
        
        pumps blood out
  - - - endothelium + thick layer of smooth muscle + thick layer of connective tissue
        
        connective tissue contains elastic fibers allowing vessel to stretch and recoil + collagen for strength
      - hormones and signals dilate or constrict arteries to control blood flow
    - - endothelium + basal lamina
        
        single layer of flattened epithelial cells. smooth surface that minimizes resistance to blood flow
      - very thin walls and smallest diameter
    - - endothelium + thin layer of smooth muscle + thin layer of connective tissue
      - valves maintain unidirectional blood flow
- - - - blood flowing through capillary beds loads oxygen + unloads CO2
        
        oxygen-rich blood returns to L.A via pulmonary veins
        
        oxygen rich blood flows into L.V
        
        L.V. pumps O2 blood into body via aorta
        
        coronary arteries supply blood to heart musccle, capillary beds in head, arms, abdominal organs, and legs
        
        in capillaries, net diffusion of O2 into tissues + CO2 into blood. capillaries rejoin + form venules, which carry blood to veins
        
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- - - - 2 thin-walled atria, contract first
      - 2 thick-walled ventricles, contract second
        
        left ventricle, greater force than right ventricle
    - - Atrioventricular (AV) valves
        
        between atrium and ventricle, close when ventricle contracts to prevent blood flow back into atria
      - Semilunar Valves
        
        between ventricle and 2 exits of heart
        
        pushed open by ventricle contraction pressure. Closed when ventricles relax. prevents blood flow back into ventricles
  - - - autorhythmic - contract and relax without signal from nervous system
      - produces electrical impulses that set rate and timing of contraction
      - signals from SA node (pacemaker) spread through atria
        
        signals delayed at AV node
        
        bundle branches pass signals to heart apex
        
        purkinje fibers spread signals throughout ventricles
      - regulated by physiological cues and hormones and temperature
    - - Sympathetic branch of ANS increases HR
      - parasympathetic branch decreases HR
- - - - high pressure --> low pressure
- - - - confined to vessels, distinct from interstitial fluid