the circulatory system Flashcards
circulatory system functions
-unicellular organisms- meet metabolic needs using simple diffusion and convection
-evolution increases size and complexity of CVS
-maintains step IC:EC concentration gradient to deliver nutrients and remove waste from centrally located cells
-fast convection system circulating fluids between surfaces
-primary function is the distribution of gases and molecules for nutrition growth and repair
-secondary functions are fast chemical signalling (hormones ), dissipation of heat and mediates inflammation and host defence responses to invading microbes
what are the 3 functional parts of the CVS and how are they used
-heart, blood and blood vessels
-heart: pump (pressure)
-blood : fluid
-blood vessels: set of containers- arteries, veins, capillaries
-blood visits heart 2x during circulation
what kind of demand changes require regulation
-sleep/awake
-body position/ intrathoracic pressure
-rest/exercise, acceleration/ deceleration
-digestion
-emotional stress, thermal stress
how does the heart being a dual-pump work
-heart pumps blood in two serial circuits
-left heart; systemic circulation:
=parallel pathways from left to right
=usually flows through a single capillary bed (extensive)
=two capillary beds in series e.g. kidneys
=capillary beds in parallel and series e.g. spleen
-right heart; pulmonary circulation
=single pathway from right to left side of heart
what’s vasculature
-arteries- the distribution system, under higher pressure (major arteries to minor arteries to arterioles)
-microcirculation- diffusion and filtration system
-veins- collection system, returns heart under low pressure venules to minor veins to major veins
what are the 4 building blocks in vascular wall
-endothelial cells (internal)
-elastic fibres
-collagen fibres
-smooth-muscle cells
what are the 3 layers of blood vessel cells walls
-intima (tunica interna)
-media (tunica media)
-adventitia (tunuca externa)
why is it important that in capillaries only the intimal layer is resting on a basement membrane
-pressure in veins is low which causes back flow
variation in structure of blood vessels
-veins have a large capacity of blood but can’t upstanding a large amount of pressure
-lots of elastic fibres in aorta which is important for the pulsatile blood from the heart
what do elastic arteries have
-high compliance as walls can stretch easily without tearing
-recoil of elastic fibres forced blood to move even when there ventricles are relaxed
what do muscular arteries consist of
-vascular smooth muscle cells arranged circumferentially
-capable of greater vasoconstriction/ vasodilation to adjust blood flow rate
-vascular tone- partial contraction maintains vessel pressure and efficient flow
what are arterioles
-smooth muscle enables blood flow regulation to capillary network
-intermittent flow through capillary bed due to periodic contraction of VSMC
-terminal regions- met arterioles (shortcuts)
-precapillary sphincters monitor blood flow to capillary (mesenteric/cerebrak circulation- not innervated but sensitive to local tissue conditions)
what does venules consist of
-post capillary venules are porous - act as exchange sites for nutrients and waste
-muscular venules have thin smooth muscle cell layer (less muscular than arterioles)- can expand and contract which is excellent reservoirs for blood
-thin walls allows expansion
what leads to varicose veins
-defective and leaky valves which allows back flow
what do capillaries consist of
-endothelial cells and basement membrane
-very gappy so many substances can pass through