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