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Chapter 15: Blood Flow and the Control of Blood Pressure (part 1) (Blood…
Chapter 15: Blood Flow and the Control of Blood Pressure (part 1)
Blood Vessels
arterioles create a high-resistance outlet for arterial blood flow (selectively constrict and dilate and direct distribution of blood flow)
total blood flow through any level of circulation is equal to cardiac output
endothelium makes up the inner lining of all blood vessels
vascular smooth muscle makes up the smooth muscle of blood vessels, which is arranged in either circular or spiral layers
muscle tone: state of partial contraction maintained at all times
precapillary sphincters: muscle rings which direct blood into capillary beds
metarterioles act as bypass channels to capillary beds
veins have valves which ensure one-way passage of blood
angiogenesis: process by which new blood vessels develop
coronary heart disease: blood flow to the myocardium is decreased by fatty deposits that narrow the lumen of the coronary arteries
Blood Pressure
flow is directly proportional to the pressure gradient between any two points and inversely proportional to the resistance of the vessels to flow
highest in the arteries and decreases as blood flows through the circulatory system
rapid pressure increase in the aorta is felt as a pulse
pulse pressure: a measure of the strength and pressure wave (systolic pressure-diastolic pressure)
mean arterial pressure (MAP) represents driving pressure and is estimated as diastolic pressure plus 1/3 of pulse pressure
measured using a sphygmomanometer (blood pressure cuff)
korotkoff sound is heard with each pressure wave
peripheral resistance: resistance to flow offered by the arterioles
factors that affect blood pressure: increased peripheral resistance without changes in cardiac output, distribution of blood in the systemic circulation and the total blood volume
the kidney is primarily responsible for adjustments for increased blood volume
Resistance in the Arterioles
Poiseuille's law: resistance to blood flow is directly proportional to the length of the tubing through which the fluid flows and to the viscosity of the fluid, and inversely proportional to the fourth power of the tubing radius
myogenic autoregulation: ability to regulate its own state of contraction
active hyperemia: process in which an increase in blood flow accompanies and increase in metabolic activity
reactive hyperemia: increase in tissue blood flow following a period of low blood flow
in response to low tissue oxygen, myocardial cells release adenosine which dilates coronary arterioles in an attempt to bring additional blood flow into the muscle
smooth muscle contraction in arterioles is regulated by neural and hormonal signals in addition to locally produced paracrines
blood vessels with ß2 receptors respond to epinephrine by vasodilating
pressure to drive blood flow is created by the pumping heart and captured by the arterial pressure reservoir, as reflected by the mean arterial pressure
Distribution of Blood to the Tissues
distribution of systemic blood varies according to the metabolic needs of individual organs
more than 2/3 of the cardiac output is routed to the digestive tract, liver, muscles and kidneys
blood is diverted from high-resistance arterioles to lower-resistance ones