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PHYSIOLOGY OF
VASCULAR SYSTEM
,
,Concise medical physiology Vascular
Circulation
+
(1) Systemic (general) circulation
+
(2) Pulmonary circulation
Carries oxygenated blood to a// parts of the body Carries deoxygenated blood to the lungs
From Lt. ventricle 9 aorta From Rt. ventricle 9 pulmonary artery
9 arteries 9 arterioles 9 arterioles 9 pu lmonary capil laries
9 capillaries(for exchange with ISF ) (gas exchange with alveoli)
9 venules 9 veins 9 SVC & IVC 9 Rt. atrium 9 4 pulmonary veins 9 Lt. atrium
Blood carrytng carbon dtOJCide 1n vetns
~ Head
Functional parts of the circulation:
Functions
~--
1- Transport blood under high pr. to tissues
1 _ Aorta & large Elastic (rich in elastic
arteries fibers) & contain 2- Distend during systole & recoil during diastole
smooth muscles 3- Maintain blood flow&prevent marked drop of pr.
2- Small arteries 1- Act as control vessels to bl. flow into capillaries
& arterioles Strong muscular wall 2- Responsible for the peripheral resistance
3- The Flat endothelium with Exchange fluids , nutrients & electrolytes
precapillary sphincter between blood & ISF
Major reservoir of blood (collect blood from
Thin venous wall
capillaries to larger veins then to the heart)
Flat endothelium Accessory route for the fluid flow from
with pores the ISF spaces to blood.
Volumes of blood in different parts of the circulation
S stemic circulation (84%) Heart & P.Uimonary vessels (16'Yo)
Veins (64%) , arteries (13%), heart (7%) & pu lmonary vessels (9%)
arterioles & cap illaries (7%)
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Pressures in different parts of the circulation
Aorta Systolic (120 mmHg) diastolic (80 mmHg) mean pr. (90 mmHg)
Pulmonary artery Systolic (25 mmHg) diastolic (8 mmHg) mean pr. (16 mmHg)
At arteriolar end (35 mmHg) At venous end (1 0 mmHg)
Systemic capillaries
Functional capillary pressure (25 mmHg)
Pulmonary capillaries The mean pulmonary capillary pr. (1 0 mmHg)
Enough for gas exchange & low to prevent filtration of f luid into alveoli
Biophysical considerations
Mechanical forces acting on blood vessel wall:
1- Pressure: (compression stress)
~ The force per un it area app lied perpendicular to the surface of vessel wa ll.
~ The physical unit is the kilo Pasca/(kPa)"Pascal is Newton/m " but commonly measured in mmHg
2
2-Tension:
)> Tens ile force (measured in Newton) acting parallel to the surface of the vessel & tends to
stretch it.
3-Shear stress:
)> The tangential drag force produced by moving blood across endothelial su rface .
2
)> Normally it is about 20- 40 dyne I cm in large arteries. -=..,-----------------,-..
The endothelial ce lls & extracellular matrix tra nsm it pressure, tensi le
& shear stress to vascular smooth ms cells to regulate their fu nction.
Basic principles of pressure, flow & resistance:
F (Flow) a l:l P (Pressure gradient) R a L (Length) t'] (Viscosity)
R (Resistance) r 4 (radiust
4 4
F a l:l P r F -- 1t l:l p r P otseUI
. "11e- Hagen ,ormu
& Ia
t1 L 8t']L
( 1t & 8 are constants)
~~----~EE}>======~
ve~s~
~~~,c=====~~
Pol se ullle "s L a w Same ~
pressure
gradient
( Vessel2
R ea d ius In vess el 2 =
2 times that of
vessel1
Q flo w
.- rodh,..l$ o~ v essel R esis tance in v essel 2= 1/16 that of
OP o r-ess u re qradien l vessel 1
..., v l s co s l l y
L v es s e l l e ng t h flow in vess el2 =16 times that of
vessel1
Reslsta nce cx1/r4
Flow cx:r ..
- 126
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