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Parts of Circulatory System

types of circulatory systems - open/closed 

  • open circulatory system - found in mollusks, arthropods
    • no difference between circulating/extracellular fluid
    • hemolymph - collective name for the fluid
  • closed circulatory system - circulating fluid (blood) always in vessels
    • found in all vertebrates

circulatory system functions - transportation, regulation, protection 

  • interstitial fluid - plasma fluid that leaks out of capillaries
    • some return to capillaries, some enter lymph vessels
  • transportation - substances needed for cellular metabolism carried by circulatory system
    • erythrocytes carry the hemoglobin which carry oxygen for respiration
    • absorbed nutrients sent to cells throughout body
    • metabolic wastes carried out of body
  • regulation - hormones carried in blood to distant organs
    • endotherms - warm-blooded vertebrates
    • cold temperature >> vessels constrict >> warm blood goes to deeper vessels
    • warm temperature >> vessels dilate >> warmth of blood lost through radiation
    • countercurrent heat exchange - vessel w/ warm blood passes by vessel w/ cold blood
  • protection - prevents injury from foreign microbes/toxins
    • blood clotting >> prevents blood loss when vessels get damaged
    • leukocytes (white blood cells) provide immunity against certain microbes

blood - made up of fluid plasma, different types of blood cells 

  • plasma - extracellular matrix w/ solutes
    • contains metabolites (used by cells), ions (mainly Na, Cl), proteins (mostly albumin)
    • globulins - carry lipids, steroid hormones
    • fibrinogen - needed for blood clotting
    • serum - plasma w/o fibrinogen
  • erythrocytes (red blood cells) - carry oxygen through hemoglobin
    • hematocrit - fraction of blood volume occupied by red blood cells (45% in humans)
    • develops from stem cells (unspecialized cells)
    • in mammals only, nuclei disappear
  • leukocytes (white blood cells) - 1% of blood cells
    • able to go outside of capillaries into interstitial fluid
    • defends body against microbes
  • platelets - help blood clot
    • formed from cytoplasm of megakaryocytes
    • reinforced w/ fibrin when blood vessel breaks

blood vessels - high pressure in arteries >> low pressure in veins 

  • arteries - carry blood away from the heart
    • arterioles - smallest branches of arteries
    • aorta - largest artery coming from heart
  • veins - returns blood to the heart
    • venules - smallest branches of veins
    • venous pump - skeletal muscles around veins contract >> squeezes veins
    • venous valves - makes sure blood only moves in 1 direction
  • capillaries - thinnest/most numerous blood vessels, connects arterioles w/ venules
    • lack elastin fibers, smooth muscle layers, and connective tissue layers found in arteries/veins
    • blood can filter in/out
    • every cell within 100 micrometers of capillary
  • vasoconstriction >> increases resistance, decreases flow
  • vasodilation >> decreases resistance, increases flow
  • precapillary sphincters - rings of smooth muscle around arterioles, regulates blood flow through capillaries
  • lymphatic system - interstitial fluid brings oxygen/nutrients to tissue cells
    • blood pressure >> filter out of capillaries near arterioles
    • oncotic pressure (osmosis due to plasma proteins) >> filter in to capillaries near venules
    • lymph - fluid in the system
    • returns excess blood in open circulatory system to closed
    • drains into veins on sides of neck
    • germinal centers - found in lymph nodes/organs, lymphocytes (type of white blood cell) created/activated
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