principles of blood flow Flashcards
what is the trend of blood pressure as an individual ages?
sharp increase during early growth and subsequent rise after age 45
what are the mean pressures in the large arteries, arterioles, capillaries, venules and veins?
large arteries 95, arterioles 60, capillaries 35-15, venules 15, veins 15-3
is blood a newtonian fluid?
no
what is the main change of blood pressure in the body?
cyclic periodic beating of the heart
from what is the energy in the blood composed of?
static pressure, gravitational force and motion
how to blood vessels accommodate pressure changes?
they change shape (elastic)
describe flow through a series of tubes with different diameters? what property does this support?
constant flow throughout the tubes
conservation of mass- same amount of blood flows in as blood flows out in a given time
define blood flow (Q).
the quantity of blood passing in a particular observation point in a given time interval
describe blood flow in a parallel circuit.
volume flow is additive (Qt=Q1+Q2)
flow across any total cross sectional area is constant
what two major vessels can be compared in the vascular system as being in series and having the same blood flow?
the aorta and the pulmonary artery
describe a parallel circuit in the body and how it relates to flow in other vessels.
capillaries can be thought of as parallel circuits and their total blood flow is the same as the blood flow in the aorta
what controls the rate of blood flow to a tissue? how is this accomplished?
the tissue need
accomplished by he adjustment of resistances located prior to the capillary beds
what mainly controls cardiac output?
the sum of all local tissue flows
id the arterial pressure regulated by local blood flow or cardiac output control?
no, arterial pressure has other means of regulation
what is the main overall arrangement of vasculature? what are some exceptions?
overall arrangement is primarily a parallel circuit
splenic and mesenteric capillaries are in series with hepatic circulation and renal glomerular and tubular circulations are in series with each other
how is hypoxia avoided in tissues?
flow of oxygen in the arteries to the tissues must be equal to or greater than the rate of oxygen consumption by the tissues
what is mobilized during exercise to accomplish the necessary added profusion of tissues? Where does the added flow go?
venous reserve
the flow goes to the skin, muscles and heart while maintaining flow to the brain
what is the flow of oxygen in arteries?
flow of O2=cardiac output x arterial O2 content
define the velocity of a fluid. how is it different from flow?
the rate of displacement of a particle of fluid with respect to time. flow is the rate of displacement of a volume of fluid (distance per hour instead of volume per hour)
what is the equation for volume in a cylindrical tube. under what conditions is the flow past successive cross sections equal?
Q=A (cross sectional area) x v (velocity)
the fluid must be incompressible and the tube must be rigid
what is the equation for cross sectional area of a cylinder?
A=pi x r^2
what is the velocity of a particle?
v=change in distance/change in time
v=Q/A
if the flow of a fluid is constant and v=Q/A, then what must be true of two different cross sectional areas in the same circuit?
v1 x A1=v2 x A2
how does linear velocity relate to cross sectional area?
velocity is inversely related to cross sectional area
what is the Q of the aorta?
5L/min
what is the ratio of velocity of the aorta to the velocity in the capillaries?
510:1
what is the equation for transit time of a blood cell between two points in the system?
t=l/v (length/velocity)
t-V/Q (volume/flow)
how long does it take for a red blood cell to travel through a capillary bed?
1 second
what is the total circulation time for one bass through the systemic and pulmonary circulation?
one minute
when is the approximation for circulating blood in a steady flow of incompressible fluids in rigid, straight cylindrical tubes acceptable?
for all but the smaller vessels
what assumptions are not always true of flow when talking about blood?
that the flow is laminar with no slippage at the wall and that the viscosity is constant across the diameter of the vessel
define viscosity. when does it effect fluid flow?
how much a fluid resists shear forces
affects flow when there are changes in velocity
what is a at the vessel surfaces in contact with blood?
a boundary layer.
what is another equation for flow using pressure and resistance? where does resistance to flow come from?
Q= pressure difference/resistance
resistance comes from the walls of the vessel and the viscosity of the blood
why is pressure from the heart propagated throughout the circulatory system?
because the blood is incompressible and continuous
blood viscosity and resistance from vessel walls are what type of forces?
frictional forces
what variables of flow does Poiseuille’s law relate?
pressure difference, radius of the vessel, viscosity and length of the tube
how is resistance related to radius and area?
resistance is inversely related to the radius to the fourth power
resistance is inversely related to the square of the cross sectional area
what vessels mainly determine the resistance to the flow of the blood?
the arterioles
how does the sympathetic nervous system control blood flow?
receptors are stimulated that cause vasoconstriction of vascular smooth muscle. This increases the flow greatly
besides vessel radius, what affects resistance to flow? what variable has an inverse relationship to this variable?
viscosity
temperature is inversely related to viscosity
(colder temperatures increase blood viscosity and decrease blood flow)
what equation can help you measure pressure drop along a length of blood vessel? what conditions increase pressure drop in blood vessels?
Poiseuille’s law
decreased radius, increased viscosity and increased lenth of the vessels
where in the vasculature is blood pressure decreased more slowly and where more rapidly?
slowly: large arteries and veins
rapidly: small arterioles and capillaries
what is the total resistance for blood vessels in series?
Rt=R1+R2+R3…
what is the total resistance for blood vessels in parallel?
1/Rt=1/R1+1/R2+1/R3…
how are branches in a parallel network correlated to the total resistance? what is the implication of this for capillaries?
more branches in a parallel network decreases the total resistance
the overall resistance for a capillary bed may be very low even though the resistance in each capillary is relatively high
