The Circulatory System Flashcards
why do we have a circulatory system?
an evolutionary consequence of increased size and complexity
to create a steep conc gradients to deliver nutrients/remove waste from centrally located cells
primary function of circulatory system
deliver gases and other molecules for nutrition, growth and repair
secondary function of circulatory system
fast chemical signalling (hormones), dissapation of heat, mediates inflammatory and host defense responses to invading microbes
organisation of circulatory system - human
3 parts:
heart = pump (dual)
blood = fluid
blood vessels = containers
left side of circulatory system
systemic circualtion
parallel pathways left to right
usually lows through single extensive capillary bed
can have capillary beds in series e.g. kidney
or in parallel and series e.g. spell, intestines, liver
right side of circulatory system
pulmonary circulation
single pathways from right to left side of heart
vasculature
arteries - away from heart - distribution system
veins - into heart - collection system (reservoir)
microcirculation - diffusion and filtration system
arterioles —– capillaries —– venules
variations of branching in vasculature
vessel radius dec with branching
combined cross sectional area of daughter vessels is greater than parent vessels
sharpest increase occurs in microcirculation, but total volume of flow = same so velocity = low
structure of vascular walls
endothelial cells
elastic fibres
collagen fibres
smooth muscle cells
endthelial cells
line blood vessels, single continuous layer lining all vasculature, junctionla complexes keeping cells together in arteries
elastic fibres
privides stretch for vessels due to weave and loose attachment to other elements
collagen fibres
less extensible, maintain integrity, prevent bursting
smooth muscle cells
different arrangements in vascular arteries or muscular arteries etc - determines diameter of vessels
3 layers of blood vessel walls
intima - tunica interna
media - tunica media
adventitia - tunica externa
capillaries - only intimal layer resting on basement membrane
tunica interna
endothelial cells rest on basement mem, seen in all types if vessels
tunica media
smooth muscle and elastic fibres, have elastin core surrounded by microfibrils
tunica externa
collagen fibres, elastic fibres and blood supply to vessel itself, supplied by vaser vasorum, also nerves to regulate and control
variation in structure of vessels
aorta = highest pressure so most elastic fibres
smooth muscle - higher in capillary sphincter to close off capillary
increase in smooth muscle - smaller vessel is
decrease in elastic fibres - smaller vessel is
elastic arteries
largest artery
hgihly compliant, stretch easy without tearing in response to pressure increase
enables vessels to cope with peak ejection pressure
recoil of elsatic fibres forces blood to move even when ventricles are relaxed
muscular arteries
smooth muscle cells arranged circumferentially
capable of greater vasoconstriction and vasodilation to adjust rate of blood flow
vascular tone = state if partial contraction, maintains vessel pressure and efficient flow
arterioles
smooth muscle enabling regulation of blood flow into capillary networks
terminal regions of arterioles = metarterioles, pre capillary sphincters monitor blood flow into capillary (mesenteric / cerebral circulation)
venules
post capillary venules are porous - act as exchange sites for nutrients and waste, muscualr venules have thin smooth muscle cell layer (less muscular than arterioles)
(arterioles more spherical than venues)
thin walls allow expansion = excellent reservoirs for blood, allow expansion without sacrificing integrity
veins
less musclular and elastic but distensible enough to adapt to variations in volume and pressure
can ‘store’ blood
large veins
mroe muscular than other veins, have valves to prevent back flow, defective, leaky valves can lead to varicose veins
capillary exchange
function of CVS to maintain suitable environment for tissues principle of exchange sites: gases, water, nutrients, waste most tissue capillaries serve nutritional needs, in addition: glomerular filtrate, skin temperature regulation, hormone and platelet delivery
capillaries
only endothelial cells on basement membrane
exchange of substances between blood and intersitial fluid, 3 groups based on degree of leakiness
types of capillaries
continuous
fenestrated
sinusoidal
continuous capillaries
intercellular junctions, apart from blood brain barrier where they have tight junctions
fenestrated capillaries
found where extensive molecular exchange occurs e.g. small intestines
fenestrae allow much larger molecules to pass through = ‘leakier’
sinusoidal capillaries
discontinuous
found in liver and bone marrow
gaps allows some blood cells through = ‘leakiest’
fluid transfer in capillaries
starlings forces
driven by sum of hydrostatic and osmotic pressures
oncotic pressure due to serum proteins
Kf haydraulic conductance - water permeability of capillary wall - variety with tissue
starlings forces equation
remove +/- signs from values when calculating
Jv = fluid movement
Kf = hydraulic conductance
Pc/Pi = hydrostatic pressure of capillary / interstitial
pi = oncotic pressure
Pc changes across capillary wall …
Pc declines along length of capillary through fluid filtration
net filtration becomes net absorption
arteriole filtration exceeds venular absorption
2-4L fluid/day in interstitium
lymphatic system
drains excess interstitial fluid
formed in lymph capillary
have 1 way valves
blockage leads to oedema
maintenance of blood volume
lympathic system returns lymphatic fluid to CVS via subclavian veins
