Lecture 10: Overview of circulation Flashcards
Velocity of blood flow is _____ proportional to vascular cross-sectional area
Inversely
Overall blood flow of an adult at rest is
5000 mL/min = Cardiac output
Three major variables that determine resistance and which one is most important
Vessel radius (most important)
Blood viscosity
Vessel length
Prime determinant of blood viscosity is the
Hematocrit
If arterial pressure falls below 100 mm Hg, nervous reflexes:
Increase force of heart pumping
Constrict large venous reservoirs
Generally constrict most of the arterioles throughout the body (increase arterial pressure)
Kidneys may later play important role in pressure control
Eddy currents
Blood flows with greater resistance when eddy currents occur
Examples of circulations arranged in parallel
Brain Kidney Muscle GI Skin Coronary circulation
% volume of blood in arteries
13
Flow is ______ proportional to pressure difference but ______ proportional to resistance
Flow is directly proportional to pressure difference but inversely proportional to resistance
For blood vessels arranged in parallel, the total resistance to blood flow is expressed as
1/Rtotal = 1/R1 + 1/R2 +1/R3 ……
Therefore, the total resistance is far less than the resistance of any single blood vessel
Amputation of limb, removal of kidney removes a parallel circuit. What is the effect
Reduces total vascular conductance
Reduces total blood flow
Increases total peripheral vascular resistance
Laminar flow
Streamline flow Blood flows at steady rate Blood vessel is long and smooth Blood flows in streamlines (layers) Velocity of blood in center is greater than on the outer edges
Two main factors controlling blood flow
Pressure difference between the two ends of a vessel (pressure gradient)
Impediment to blood flow through the vessel (resistance)
Conductance is ______ proportional to vessel diameter
Directly
When Re rises above 2000
Turbulent flow will occur even in a straight vessel
Poiseuilles law/equation
F = (Pi*(P1-P2)*r^4) / 8nl F- rate of blood flow mL/min P-pressure r- radius of vessel l- length of vessel n- blood viscosity
Turbulent flow
Non-layered flow
Creates murmurs
Produces more resistance than laminar flow
When cardiac output is normal at 100mL/sec the total pulmonary vascular resistance is
14/100 or 0.14 PRU
Functional principles of the circulatory system
Rate of blood flow to each tissue of the body is almost always precisely controlled in relation to the tissue need
The cardiac output is controlled mainly by the sum of all the local tissue flows
Arterial pressure regulation is generally independent of either local blood flow control or cardiac output control
When vessels are greatly dilated, total peripheral resistance may
Drop to 0.2 PRU
Ohms law (Poiseuille equation)
F=(P1 - P2)/R F- flow in mL/min P1- upstream pressure P2- pressure at end of segment R- resistance b/w P1 and P2
% volume of blood in systemic arterioles and capillaries
7
% volume of blood in heart and lungs
16
Blood viscosity
The property of blood to adhere to vessel walls and to eachother
- based on the number, shape and size of RBCs
- Viscosity ensures laminar flow of blood in vessels
