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Blood Vessels & Hemodynamics (The Physiology of Circulation (Systemic…
Blood Vessels & Hemodynamics
Capillary Exchange
all chemical and gaseous exchange between blood and interstitial fluid occurs in the capillaries, takes place across capillary walls
relies on 3 processes:
Filtration
movement of fluids through a semi-permeable membrane due to hydrostatic P
(pushes fluid against wall of its container)
Net hydrostatic pressure = CHP - IFHP
Capillary hydrostatic pressure (CHP)
capillary blood pressure creates hydrostatic pressure that promotes filtration
heart beating creates pressure --> water gets pushed out of the blood, can carry some solutes along with it
Interstitial fluid hydrostatic pressure (IFHP)
opposes CHP
Diffusion
occurs along entire length of capillary beds, most effective across short distances
nutrients can move at the same time as metabolic wastes moving in
solutes move down their concentration gradient
Osmosis
osmotic P is created in the fluid by the presence of non-diffusible solutes (plasma proteins)
plasma proteins make
blood colloid osmotic pressure/BCOP
> interstitial fluid osmotic pressure
Interstitial fluid osmotic pressure (IFOP)
opposes BCOP
oncotic pressure will draw water to that fluid compartment
~water will move to the solution with the higher osmotic pressure and solute concentration
Hydrostatic P and osmotic P interactions
factors that promote filtration (fluid movement form capillaries --> interstitium):
capillary hydrostatic pressure (CHP) and interstitial fluid osmotic pressure (IFOP)
factors that promote reabsorption (fluid movement from interstitium --> capillaries):
Interstitial fluid hydrostatic pressure (IFHP) and Blood colloid osmotic pressure (BCOP)
Starling's Equation- defines balance between these factors as
net filtration pressure (NFP)
forces that promote filtration (BHP+IFOP) - forces the promote reabsorption (BCOP + IFHP)
determines amount and direction of fluid out of the capillaries
at the aterial end of the capillaries, NFP is positive --> net movement of fluid out of the capillaries
at the venous end of the capillaries, NFP is negative --> net movement of fluid into the capillaries
Usually more fluid leaves the capillaries than returns
Edema = abnormal accumulation of interstitial fluid
The Physiology of Circulation
Definitions:
Blood pressure (BP)
= the force exerted (per unit area by the blood against the inner walls of the blood vessel
the pressure gradient (the change in P) in the CV system --> blood flow, high to low pressure
no change in P ---> no blood flow
Resistance (R)
= a force that opposes movement
most occurs in the peripheral circulation =
peripheral resistance
Important sources of peripheral resistance
blood vessel length - greater resistance to flow in a longer vessel than a shorter vessel
systemic circuit has a longer length ~ more resistance than the pulmonary circuity
blood vessel diameter - most important factor, wide diameter --> less resistance, constricted/narrow --> more resistance
resistance is inversely proportion to the 4th power of the radius, 1/r^4
blood viscosity - the more viscous, the greater the resistance
Blood flow (Q)
= the volume of blood moved through a vessel, organ, or the entire circulation per unit of time, CARDIAC OUTPUT, 5 L/min
In order for blood to flow, the change in pressure must be great enough to overcome TPR
Q ~ delta P/TPR
pressure is opposed by resistance pressure gradients keep the blood flowing
Systemic Blood Pressure
Systolic Blood Pressure (SBP)
highest pressure attained in the arteries during ventricular systole
ventricles ejecting blood into large BV
Diastolic pressures (DBP)
attained b/w heart beats
heart relaxes and atrial pressure falls, right before ventriuclar systole begins --> lowest pressure in arteries
Pulse Pressure (PP)
SBP-DBP
temporarily increases when you increase SV or HR
dissipates as blood moves to muscular arteries
Mean arterial pressure (MAP)
DBP + 1/3 PP
driving force keeping blood flowing through the vessels
expect greatest decline in arterioles where peripheral resistance is greatest
various adaptations facilitate blood flow through the veins (where pressure is low)
respiratory pump
skeletal muscle pump
structural features of the veins themselves e.g. valves, which keep blood moving in one direction to the heart and prevent backflow of blood