Regulation of arteriolar resistance Flashcards
what is poiseuilles law
a statement in physics
describe poiseuilles law
the velocity of steady flow of a fluid through a narrow tube varies directly as the pressure and the fourth power of the radius of the tube and inversely as the length of the tube and the coefficient of viscosity
what is active hyperaemia
it is the increase in organ blood flow that is associated with increased metabolic activity of an organ or tissue
give an example of active hyperaemia
the increase in blood flow that accompanies muscle contraction, which is also called exercise or functional hyperaemia in skeletal muscle
what is pressure auto regulation defined as
the intrinsic ability of an organ to maintain a constant blood flow despite changes in perfusion pressure,
as resistance decreases, blood flow increases despite the presence of reduced perfusion pressure
describe reactive hyperaemia
it is the transient increase in organ blood flow that occurs following a brief period os ischameia
what does vascular tone refer to
the degree of constriction experienced by a blood vessel relative to its maximally dilated state
what do all arterial and venous vessels under basal conditions exhibit
some degree of smooth muscle contraction that determines the diameter of the vessel
what is meant my haemodynamics
literal meaning - blood movement
it is the study of blood flow or the circulations of blood, it is the dynamics of blood flow
what is active hyperaemia
it is the increase in organ blood flow
what is active hyperaemia associated with
increased metabolic activity of an organ or tissue
give an example of active hyperaemia
increased blood flow that accompanies muscle contraction
what is the result when blood flow falls?
arterial resistance falls as the resistance vessels dilate
what is reactive hyperaemia
it is the transient increase in organ blood flow that occurs following a brief period of ischaemia
basically describe reactive hyperaemia
it is an increase in organ blood flow when there is an inadequate blood supply to an organ
what is marcy’s law
it is an equation that describe the flow of a fluid through a porous medium
what is blood flow equal to
the change in pressure over the resistance
what pressure equal to
blood flow multiplied by the resistance
what is varying the radius of arterioles used to control
flow through individual vascular beds
what does varying the radius of arterioles affect
the change in pressure
what does the total peripheral resistance affect
the mean arterial pressure
what is cerebral circulation
it is the movement of blood through the network of cerebral arteries and veins supplying the brain
what is the rate of the cerebral blood flow in a typical adult
750ml per minute
what percentage of cardiac output does cerebral blood flow represent
15%
describe the extrinsic neural control of arteriolar resistance
sympathetic nerves cause arteriolar constriction, increasing total peripheral resistance
parasympathetic nerves usually don’t have an effect on arteriolar resistance
describe how sympathetic nerves control arteriolar resistance
sympathetic nerves release norepinephrine
this binds to alpha 1 receptors
this causes arteriolar constriction
this decreases flow through that tissue
this increases total peripheral resistance
describe how parasympathetic nerves control arteriolar resistance
usually have no effect on arteriolar resistance
where is the hormone epinephrine/adrenaline released from
the adrenal medulla
describe how the hormone epinephrine/adrenaline controls arteriolar resistance
this hormones binds to alpha 1 receptors
causing arteriolar constriction
decreasing flow through that tissue
increasing the total peripheral resistance
in skeletal and cardiac muscle what is the result of epinephrine/adrenaline activating beta 2 receptors
causes arteriolar dilation
increasing flow through that tissue
decreasing total peripheral resistance
describe how the hormone angiotensin II controls arteriolar resistance
causes arteriolar constriction
increases blood pressure
stimulates the release of aldosterone
increases the total peripheral resistance
what is arteriolar resistance (vascular resistance)
it is the resistance that must be overcome to push blood through the circulatory system and create flow
what is arteriolar resistance used in calculations of
blood pressure, blood flow and cardiac output
what is systemic vascular resistance also known as
total peripheral resistance
what is pulmonary vascular resistance
it is the resistance offered by the pulmonary circulation
describe how the hormone vasopressin controls arteriolar resistance
it increases blood pressure promotes water retention released in response to low blood volume causes arteriolar constriction increases the total peripheral resistance
describe how the atrial natriuretic peptide hormone controls arteriolar resistance
released in response to high blood volume
increases renal sodium excretion
reduces an expanded extracellular fluid volume
causes arteriolar dilation
decreases total peripheral resistance
describe how the brain natriuretic peptide hormone controls arteriolar resistance
released in response to high blood volume
secreted in response to stretching caused by increased ventricular blood volume
causes arteriolar dilation
decreases total peripheral resistance
in terms of local (intrinsic) control of arteriolar resistance describe how active hyperaemia controls arteriolar resistance
increased organ blood flow associated with increased metabolic activity of an organ increased metabolic activity increased concentration of metabolites triggers release of EDRFs causing arteriolar dilation smooth muscle relaxation increasing flow to wash out metabolites
what is the mean arterial pressure
the average pressure in a patient’s arteries during one cardiac cycle
describe how pressure auto regulation controls arteriolar resistance
decrease in mean arterial pressure causes decrease in flow metabolites accumulate triggering the release of EDRFs causing arteriolar dilations causing flow to be restored to normal
describe how the injury response controls arteriolar resistance
arteriolar dilation
increased blood flow
increased permeability
