Cardiovascular System - Circulation Flashcards
Functional Parts of Circulation
- arteries
- arterioles
- capillaries
- venuoles
- veins
Volume of Blood in the Heart
7%
Volume of Blood in the pulmonary system
9%
Volume of Blood in the rest of the system (other than heart and pulmonary system)
84%
Volume of Blood in the Veins
64%
Volume of blood in the arteries
13%
Volume of Blood in the Arterioles and Capillaries
7%
Time for transmission of pulse to aorta
3-5 m/sec
Time for transmission of pulse to Large Arteries
7-10 m/sec
Time for transmission of pulse to small arteries
15 - 35 m/sec
Time for transmission of pulse to arterioles and capillaries
0 m/sec - damping of pressure pulses
what is hematocrit ratio?
% by volume of whole blood that is composed of cells
40% (men)
36% (women)
Viscosity of Blood
3-4x that of water
viscosity of plasma
1-1.5 times that of water
2 factors that determine blood flow through the vessels
- Pressure Differece (delta P): tends to push blood through the vessels
- Resistance (R): resists blood flow through the vessel
Relationship: Q=(deltaP)/(R)
Laminar Flow
- streamlined flow in concentric layers
- max flow velocity is in the center
Turbulent Flow
absence of streamline flow when eddy currents are formed
tendency for turbulent flow to occur can be measured by calculating Reynolds # which represents the relationship between vessel diameter, blood viscosity, blood density and flow velocity
principal determinant of resistance to blood flow
diameter of the vessel
Poiseuille’s Law
resistance to flow is inversely proportional to the fourth power of the radius of the tube
so, small changes in radius cause large changes in resistance
so, sympathetis vasoconstrictor mechanisms in te small arteries and arterioles are the primary regulators of blood flow
how resistance is measured
in preipheral resistance units (PRU) total peripheral resistance of the systemic circulation is appx. 1 PRU
Volume of Blood Flow
product of inverse relationship of blood flow velocity and vascular cross section area
cross section of area of systemic circulation:
aorta - 2.5 cm^2
capillaries - 2500 cm^2
Vena Cava + right atrium - 8 cm^2
Critical Closing Pressure
blood vessels collapse when elastic and muscular forces in the vascular wall, coupled with the extravascular tissue pressure, exceed intravascular distending pressure
Transmural Pressure
pressure difference between the inside and outside of the vessel wall
At what presuure do the vessels usually collapse?
when distending pressure falls below appx. 20mmHg
Vascular Compliance
change in blood pressure stretches more or less blood vessel walls and causes an increase or decrease in the volume of the blood vessels.
Veins are 5x more compliant than Arteries
Capitance vessels
- distensibility of blood cells that varies with pressure
most to least compliant
- veins
- aorta
- arteries
- arterioles
