| Organ or system | Percent of blood flow |
|---|---|
| digestive system | 21% |
| liver | 6% |
| kidneys | 20% |
| skin | 9% |
| brain | 13% |
| heart | 3% |
| skeletal muscle | 15% |
| bone | 5% |
homeostatic blood flow
necessitated blood flow
arteries
rapid-transit passageways
pressure reservoirs
elastic recoil and arterial pressure fluctuation
pulse pressure
mean arterial pressure as driving force
Part = dbp + 1/3 pp
arterioles
major resistance vessels
pressure drop from 93 mm Hg to 37 mm Hg
provides the DP
damps out the pulsatile pressure swings
vasoconstriction
increased O2
decreased CO2 and metabolites
sympathetic stimulation
epinephrine
vasopressin (ADH)
angiotensin II
vasodilatation
vascular tone
local control determines distribution of cardiac output
reactive hyperemia and vasodilatation
extrinsic control regulates arterial blood pressure
sympathetic tone
local control to override vasoconstriction
particularly skeletal muscle and skin
generally no parasympathetic innervation
exceptions: penis and clitoris
cardiovascular control center
hormones
capillaries
10–40×109
sites of exchange
walls thin: 1 µm
small diameter: 7 µm
extensive branching: no cell is more than 100 µm away
surface area of about 600 m2, only 250 mL of blood
slow velocity of flow
calculate the cross-sectional area
diffusion across capillary wall for solute exchange
there are no carrier-mediated transport systems
bulk flow across capillary wall and ECF distribution
ultrafiltration
reabsorption
driving forces
| Type of pressure | Pressure value |
|---|---|
| capillary blood pressure | 37 mm Hg ® 17 mm Hg |
| blood colloid osmotic pressure (oncotic pressure) | 25 mm Hg |
| interstitial-fluid hydrostatic pressure | 1 mm Hg |
| interstitial-fluid: colloid osmotic pressure | ~ 0 mm Hg |
lymphatic system and interstitial fluid return
structure of lymphatic capillaries
muscle contractions and valves
functions
return of excess filtered fluid
defense against disease
transport of absorbed fat
return of filtered protein
edema
reduced concentration of plasma proteins
urine loss
decreased synthesis
protein deficiency
massive skin loss
increased permeability of capillary walls
inflammation, blisters, hives
increased venous pressure
blockage of lymph vessels
elephantiasis
veins
capacitance vessels: >60% in systemic veins
venous return
sympathetic activity
contrast results of arteriolar constriction
skeletal-muscle pump
gravity
venous pressure
fainting
venous valves
respiratory pump
cardiac suction
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