Factors affecting blood flow Flashcards
how does blood flow vary
from one organ to another
what does blood flow between organs depend on
the metabolic demands of each organ system
what does blood flow to the lungs align with
cardiac output
why does blood flow to the lungs align with the cardiac output
because all blood must pass through the lungs for oxygenation and removal of carbon dioxide
which organ system requires blood flow similar to cardiac output
the lungs
what increases and decreases the blood flow to specific organs
metabolic requirements of the tissues
why does blood flow to skeletal muscle increase during exercise
greater demand for oxygen
why does blood flow to the GI system increase following a meal
there is greater demand for oxygen following ingestion of food
why are there interorgan blood flow differences
as a result of alterations in vascular resistance
how can the mechanisms of blood flow regulation be categorised
local and hormonal
describe local control of blood flow
matches blood flow to metabolic requirements of the tissue systems
direct action on the metabolites on arteriolar resistance
describe the neural/hormonal control of blood flow
action of sympathetic nervous system on vascular smooth muscle
action of vasoactive substances
what are some vasoactive substances involved in hormonal control of blood flow
- histamine
- bradykinin
- prostoglandins
what are the specific needs for blood flow
- delivery of oxygen to tissues and nutrients
- removal of carbon dioxide and hydrogen ions
- maintenance of ion concentrations in tissues
- transport of hormones
what are the nutrients that blood delivers to tissues
glucose
amino acids
fatty acids
what are the mechanisms by which intrinsic control of blood flow can occur
autoregulation
reactive hyperemia
active hyperemia
describe autoregulation
maintenance of constant blood flow while arterial pressure changes
example of autoregulation
if the coronary arterial pressure decreases, there is immediate compensatory vasodilation of coronary arterioles to decrease the coronary vasculature resistance
describe active hyperemia
blood flow to tissues is proportional to its metabolic activity
increased blood flow when metabolic activity increases
increased arteriolar dilation
when would there be an increase in blood flow due to metabolic activity
exercising skeletal muscle tissue which increases oxygen consumption
describe reactive hyperemia
increase in blood flow in response to a prior period of decreased blood flow
example of reactive hyperemia
following a period of arterial occlusion, oxygen debt accumulates. the longer the arterial occlusion, the greater the oxygen debt and the greater the increase of blood flow above the pre occlusion levels. this continues occurs the oxygen debt is reversed
what are the factors that determine resistance to blood flow
vessel diameter
vessel length
viscosity of blood
how does vessel diameter change
with vasoconstriction and vasodilation as a result of contraction and relaxation of vascular smooth muscle
what is the vascular smooth muscle
the tunica media
how does a small change in vessel diameter affect resistance
there are large changes as a result of even just small changes
does viscosity of blood ever really change
no it usually remains within a narrow range
what is the exception to the concept that blood viscosity changes
haemocrit
what can happen to the blood vessels to lead to changes in resistance
change in their diameter
what can cause an increase in blood viscosity
dehydration and immobility
what can reduce the risk of increases blood viscosity
hydration
movement
compression socks
why does movement decreases changes in normal blood viscosity
it encourages venous return
what can a change in blood viscosity lead to
risk of deep vein thrombosis
what is vessel resistance directly proportional to (an increase in one will increase the other)
length of the vessel and viscosity of the blood
what is vessel resistance inversely proportional to
radius to the fourth power of the vessel
describe the equation for the relationship between flow, pressure and resistance
flow = change in pressure over resistance
what is poiseuilles equation
Q = r^4 times change in pressure over viscosity times length of the vessel
what does poiseuilles equation describe
how flow is related to perfusion pressure, radius, length, and viscosity
what does the poiseuilles equation assume
- flow is through a uniform straight pipe
- flow is non pulsatile
- flow is laminar
what does it mean to say that flow is laminar
it is smooth
when can velocity of flow be considered the same across the tube
when the flow has negligible resistance
what happens to the velocity of flow as viscosity increases
it increases to a maximum at the centre of the tube
do veins have a large or small cross sectional area
large
how are venous valves orientated
toward the heart
why are venous valves orientated toward the heart
to maintain blood flow in one direction
what is venous return to the heart aided by
the action of working skeletal muscles intermittently contracting to compress the veins
what happens to intrathoracic pressure during exercise
it becomes more negative because there are more frequent respirations that increase the pressure gradient between abdominal and thoracic veins
what is in control of the sympathetic activation of venous return
noradrenaline
how does noradrenaline play a role in venous return
sympathetic activation which constricts the veins and increases venous return to the heart
what is preload
venous return to the right ventricle
what happens when there is an increase in preload
the heart will have to work harder to pump the blood out and this can be a problem in coronary artery disease and heart failure
what is angina
coronary artery disease
what is coronary circulation
this is circulation that facilitates the perfusion of the myocardium
maintains high basal rate of oxygen supply to cardiac muscle
what is skeletal muscle adapted for
meeting the metabolic demands of skeletal muscle during exercise
what is the function of cerebral circulation
regulation to maintain cerebral perfusion
what name is given to the blood vessels that supply the heart
coronary arteries
how much of resting cardiac output is provided to the heart through coronary circulation
5%
what is blood supply to the myocardium derived from
right and left coronary arteries
where do the coronary arteries originate on the heart
at the root of the aorta behind the cusps of the aortic valve
what supplies the right ventricle and atrium
the right coronary arteries
what supplies the left ventricle and atrium
the left coronary arteries
what are the branches of the left coronary artery
left circumflex artery
anterior descending artery
what does the left circumflex artery supply
the left atrium and ventricle
what does the anterior descending artery supply
the interventricular spetum and a portion of the right and left ventricles
which branch of the left coronary arteries descends to the apex
the anterior descending artery
what do coronary arteries branch into
segments dividing into capillary networks that facilitate oxygen diffusion into cardiac myocytes that have a high ATP requirement
what are the epicardial veins
venules that the blood drains into following coronary circulation
what do the epicardial veins collect into
coronary sinus
what does the coronary sinus do
collect the blood from the epicardial veins to empty blood into the right atrium
what is another name for the epicardial veins
the coronary veins
what are thebesian veins
vascular channels on the heart that drain deoxygenated blood from the capillary network in the ventricular wall directly into the cardiac chambers
what is the coronary blood flow at rest
70-80 ml/min/100g
when does perfusion of the myocardium from the coronary arteries occur
during early diastole
do relaxed ventricles compress the arteries
no
what constricts the blood vessels
contraction of the myocardium
what proportion of left coronary blood flow occurs during diastole
80%
what is coronary blood flow during exercise
300-400ml/min/100g
what can increase the number of arterioles and capillaries
exercise training
why does ventricular mass increase with exercise training
to meet the physiological demands of prolonged exercise training
what is meant by athletic heart
this is a physiological adaptation of structural and functional remodelling in response to exercise training
what is the difference between exercise induced hypertrophy and pathological hypertrophy
the cellular mechanisms
what are some pathological causes of cardiac hypertrophy
valve heart disease
cardiac myopathy
how does muscle circulation change during exercises and what is the reason for this
it increases to increase oxygen and glucose delivery to match the increase in work
how can the relationship between blood flow and exercise intensity be described
coupled
what is the vascular resistance of skeletal muscle a major influence of
total peripheral resistance
what regulates blood flow at rest
sympathetic innervation
what regulates blood flow during exercise
local control mechanisms
what are the local vasodilators that work to increase blood flow to skeletal muscle during exercise
lactact
adenosine
potassium ions
what is the muscle capillary density adapted for
muscle function
what does alpha one adrenoreceptor activation cause
vasoconstriction
which form of vasoconstriction is the most usual in the body
alpha one induced
how does vasoconstriction work
it decreases resistance to increase blood flow
what does beta two adrenoreceptor activation lead to
vasodilation
how does vasodilation work
decreased resistance, increased blood flow
which hormone causes vasodilation during stress or exercise
adrenaline released from the adrenal gland
during exercise, do all capillaries vasodilate
no, there is tonic sympathetic vasoconstriction that continues to feed the arteries and proximal resistance vessels, which prevents excessive decrease in the total peripheral resistance
what couples blood flow to exercise intensity
the metabolic vasodilation
what accounts for half of vascular resistance
cerebral arteries
which arteries enter the cranial cavity to supply the brain
the basilar and internal carotid arteries
what forms the circle of willis
the anastomosation of the basilar and internal carotid arteries once they enter the cranial cavity
describe cerebral autoregulation
- cerebral resistance vessels dilate to maintain perfusion when arterial blood pressure falls.
- the cerebral blood flow will steeply decline at a blood pressure lower than 60mmHg
what happens if the there is hypotension to the brain
mental confusion and syncope
what is syncope
loss of consciousness
what are the cerebral resistance vessels sensitive to
local hypoxia and arterial carbon dioxide
what is hypercapnia
too much carbon dioxide
what does hypercapnia cause
cerebral vasodilation, which is mediated by endothelial nitric oxide
what does hypocapnia cause
cerebral vasoconstriction, leading to hyperventiculation, reducing cerebral perfusion
what is the symptom of cerebral perfusion
dizziness
what does local hypoxia lead to
cerebral vasodilation
what does systemic hypoxia stimulate
ventilation
what are some circulations in the body with specialised local control
- pulmonary circulation
- skin circulation
- renal circulation
describe the arrangements of blood components in a capillary following centrifugation
- red blood cells are at the bottom
- buffy coat containing leukocytes
- plasma at the top
what does local control of blood flow allow
matching of flow to metabolic demands
what does autoregulation allow
maintenance to constant blood flow to tissue systems despite changes in arterial pressure
why does reactive hyperaemia occur
due to occlusion of the vessel lumen which leads to greater blood flow due to accumulation of blood
what can cause occlusion of the blood vessel lumen
atherosclerotic plaque
why is blood flow not smooth
there are different factors that can make blood flow turbulent
where in the blood vessels is blood flow fastest and why
in the centre as there is resistance against the blood flow in the vessel wall
describe the importance of venous valves
there is no pulsatile pushing or compliance to push the blood flow, so there can be tendency of blood to backflow if there were not these valves to maintain the blood flow in the one direction
what aids preload
skeletal muscle contraction
what constricts the veins to help push blood back toward the heart
sympathetic activation
what is starlings mechanism
greater preload stretches the myocardial cells leading to increased contractility
how do coronary arteries profuse cardiomyocytes
they branch to become arterioles and capillaries
how many mils of blood per minute are involved in coronary circulation
70-80
what is angiogenesis
formation of new capillaries from existing blood vessels
what is an angioplasty
a procedure used to widen the coronary arteries that are blocked or narrowed
what is an angiogram
an x ray photograph of blood or lymph vessels to check for blockages to reduce risk of infarction
can the myocardium be profused during systole
no
why is capillary density adapted to muscle function
to increase or decrease the metabolic demands of the muscle groups engaged in activity
what does tonic vasoconstriction mean
it is a slow and graded physiological response
what is the specialised circulation of skin related to
temperature regulation
why was the level of haematocrit in the blood samples of the lab lower than the suggested range
there is species variation in the haematocrit layers
what must be maintained to maintian the profusion of vital systems
cardiac output
