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24 Cards in this Set

  • Front
  • Back
Distribution of blood volume by %:
Systemic circ: 84%- 64% in veins and 13 % in arteries and 7% in arterioles and capillaries.

Heart and lungs: 16%- 7% in heart and 9% in lungs
The velocity of blood flow is inversely proportional to vascular cross- sectional area:
v=F/A
Velocity of blood flow, aorta VS. capillaries:
Aorta: 33 cm/sec
Capillaries: 0.3 mm/sec
How long due blood stay in the capillaries:
Only 1-3 sec, because of their short length. Diffusion must happen during this time
Pressures in circulation:
Aorta: Sys: 120, Dia 80, mean: 100
Arteriolar ends: 35 mmHg
Venous end: 10 mmHg
Mean capillary bed pressure: 17 mmHg
Pulmonary aa.: Sys: 25, Dia: 8, mean: 16
Mean pulmonary pressure: 7 mmHg
Small, large veins and v. cava: 0 mmHg
Basic principle of circulatory function:
1. The rate of blood flow to each tissue of the body is almost precisely controlled in relation to tissue needs
2. The cardiac output is controlled mainly by the sum of all the local tissue flows
3. Arterial pressure regulation is generally independent of either local blood flow control or cardiac output control
Blood flow:
Pressure difference (in and out) of a vessel/ Vascular resistance
Ohm`s law:
F= ΔP/R
ΔP= FxR
R= ΔP/F
CO:
5000ml/ min
Three types of flow through blood vessels:
1. Laminar: Smooth flow at steady rate
2. Parabolic velocity profile of laminar flow: Fastest flow in the middle and slowest near the vessel wall due to adherents to the wall
3. Turbulent: Eddy currents with great resistence
Calculation of resistance:
Cardiac output / ΔP (systemic a.- systemic v.)
Peripheral resistance unit: 100ml/sec/ 100mmHg= 1 PRU
Changes in total peripheral resistance:
From 0.2 PRU in very dilated vessels to 4.0 PRU in very constricted vessels
Total pulmonary vascular resistance:
ΔP (16mmHg in pulmonary aa. - 2mmHg in left atrium= 14mmHg)/ 100 ml/ sec= 0.14PRU
Conductance:
A measure of the blood flow through a vessel for a given pressure difference.
=1/ Resistance
Increase of conductance with increase in diameter:
The conductance of a vessel increase to the fourth power of the diameter
Why is there increased rate of flow with increased diameter?
Because of parabolic velocity profile during laminar flow. In small vessels all the blood are close to the vessel wall, and thus flow slowly. But in large vessels each ring closer to the vessel flow faster due to less adherents to the vessel wall and "rolling" on the previous ring
Where is there most resistance in the systemic circulation:
2/3 of the resistance is within in arterioles. Arterioles have diameter ranging from 4 micrometers to 25 micrometers and can increase its diameter a fourfold---> increasing blood flow 256- fold (due to 4th power law)
Parallel branching and its influence on total resistance to blood flow:
Parallel branching greatly reduces total resistance, thus total resistance is much lower then resistance in each vessel.
Viscosity of blood:
About three times the viscosity of water
Hematocrit:
The proportion of blood that is red blood cells
(Male 42, female 38)
A reason for increased viscosity:
Polycythemia (increased hematocrit)
Blood flow autoregulation:
The ability of each tissue to adjust its vascular resistance and to maintain blood flow during changes in arterial pressure between 70 mmH and 175 mmHg
Hormonal vasoconstrictors:
Norepinephrine
Angiotensin II
Vasopressin
Endothelin
The effect of BP on blood flow may be greater then predicted by Poiseuille`s law because:
Increased arterial pressure not only increase the force that push blood through the vessel but it also distends elastic vessels actually decreasing vascular resistance.