Local regulation of blood flow - supply and demand Flashcards
haemodynamics
physical study of flowing blood and all the solid structures through which it flows
in poiseuille formula Q( flow) is proportional to what
change in pressure x vessel radius to the power of 4 divided by /////
blood viscosity x vessel length
lood flows from higher pressure system largest being arotia down to lower pressure in capillaries and then to lowest point in the vena cava.
what are the 4 physical determinants of blood flow through the vascular system
pressure change
vessel radius
blood viscosity
vessel length
As fluid becomes thicker (viscosity increases), flow decreases in proportion
What conditions may result in increased blood viscosity
Polycythemia Hypercholesterolaemia Diabetes Smoking, alcoholism, severe dehydration, diuretics (Anaemia can reduce blood viscosity)
Q=1/n
Flow is inversely proportional to the viscosity of the fluid
Moderate anaemia can actually increase tissue oxygen delivery by lowering blood viscosity and increasing flow through the vascular bed
Transfusions of cold, concentrated red blood cells run slowly
which factor is most important in the regulation of blood flow?
vessel radius
this causes the resistance
What property of the vasculature determines vessel radius?
Vascular smooth muscle tone (vasoconstriction/dilatation)
A change in vascular tone of which vessel type is the most influential in regulating blood flow to tissues/organs?
Arterioles are the main sites of resistance to blood flow within the vascular system
Arterioles have a thick layer of smooth muscle (tunica media) in their walls, highly innervated by what
by sympathetic nerve fibres
what arterioles vasoconstriction what happens to resistance and blood flow to the capillaries
resistance goes up and blood flow to the capillaries decreases
in the regulation of blood flow what two mechanisms controls whole body circulation
neurological - autonomic NS
Humoral via angiotensine II , vasopressin , adrenaline, atrial natriuretic peptide
in the regulation of blood flow what mechanism controls regional/ organ blood flow
Local(metabolic and myogenic)
what type of receptor does adrenaline have a greater affinity for creating what effect
Beta-2 so vasodilation
What type of receptor does nor-adrenaline have a greater affinity for creating what effect
Alpha-1 so vasoconstriction - there are no alpha-1 receptors however in cerebral arteriolar smooth muscle
A high dose of adrenaline is used in clinical settings to do what?
increase blood pressure through vasoconstriction
how is the increase of blood pressure achieved
Through binding to both α1 and β2 adrenergic receptors on vascular smooth muscle
Adrenaline has higher affinity for β2 receptors but there are more α1 receptors overall across the vascular bed, so a high dose of adrenaline leads to overall vasoconstriction and an increase in arterial blood pressure. Physiological levels of adrenaline cause vasodilatation through binding to β2 receptors within skeletal muscle vascular beds, decreasing blood pressure.
obviously cell respiration and metabolic demand goes up so Lowered partial pressure of oxygen
this triggers release of NO what does this do
vasodilator - relax underlying smooth muscle
what is active hyperaemia
caused by increased of blood flow to organs - blood vessels widen to increase supply of blood. - local intrinsic mechanism of increasing blood flow to tissues to meet metabolic demand
what does NO do
Local chemical and physical changes due to increased metabolic demand
Increased shear stress on endothelium
what does endothelin do
and what stimulates and inhibits it
A potent vasoconstrictor
Stimulated by angiotensin II, vasopressin
Inhibited by NO
what do vascular endothelia growth macros do
promote angiogenesis - Long-term adaptation to decreased blood flow to a tissue
the intrinsic myogenic response is called what
auto-regulation - important in kidneys
vascular tone is controlled by 3 influences yes or no
Neurogenic (sympathetic NS)
Humoral (vasoactive substances)
Local (intrinsic) mechanisms
Local/intrinsic control of blood flow includes what
Active hyperaemia – responds to changes in demand
Autoregulation – responds to changes in supply
when is local control of blood flow most important
local control of blood flow is the most important mechanism in cerebral, coronary, renal, pulmonary & exercising skeletal muscle vascular beds
functions of cardiovascular system
Delivery of oxygen and nutrients to tissues and removal of waste products
Distributes hormones fluids , electrolytes
Immune function
Thermoregulation
Consists of pump ( heart) pipes ( blood vessels) and a carrier ( blood)
what circulatory system exists at lower pressure
pulmonary - 25/10mmHg
lower resistance to
what is the mean arterial blood pressure - MABP - approximate to diastolic +1/3 of the difference between systolic and diastolic pressure ( pulse pressure)
AROUND 87
diastolic normally twice as long
elastic ompianc allows them to take blood
veins share the largest amount of blood
total peripheral resistance TPR or systemic vascular resistance SVR is controlled how
by constricting or dilating muscular arteries and arterioles
the autonomic nervous system provides short term regulation and influences what
CO and vascular resistance
the humeral response through hormones and molecules provides short and long term regulation and influences what
vascular resistance and blood volume
where are baroreceptors found
aortic arch and carotid sinus
mechnaorecptors are detected where
aortic wall
what nerves reduce HR or BP
glossopharyngeal from carotid
vagus from aortic arch
increase para of heart and at same time bak though vagus increase para to SNS to decrease activity by B1
SNS via alpha1
hormones that cause excretion or reabsorption of sodium and water help regulate blood volume and thus blood pressure
Aldosterone released from the adrenal cortex in response to decreased blood volume increase BP what does it do
increase sodium and water reabsorption in kidney
ADH released from posterior pituitary in repose to increase blood osmolarity increase BP what does it do
increases water reabsorption from kidneys and vasoconstriction
Type A and Type B peptides ( ANP and BNP ) are released in response to high volume load ( stretch) on atria and ventricles what do they do
increase sodium and water excretion from kidneys (and vasodilation)
beta 2 receptors cause vasodilation and have a higher density in the skull muscles and cardiac muscle vessels what hormone is best tp stimulate theses
adrenaline
alpha 1 receptors cause vasoconstriction and have a high density throughout the body what hormone is more sensitive to these
Noradrenaline
hormones that mainly act through inducing vasoconstriction or vasodilation to adjust vascular resistance and thus blood pressure and blood flow ARE angiotensin II which does what
a vasoconstrictor activated by angiotensin converting enzyme ACE within blood vessels
5 main types of blood vessels
arteries - elastic ones conserve pressure, muscular ones conduit vessels and distribute the blood
arterioles - resistance vessels control the arterial pressure and local blood flow
capillaries - exchange vessels and transfer nutrients and waste products
venules
veins - capacitance vessels which return blood to the heart
three layers of blood vessels
tunica interna/intima - innermost
tunica media - middle
tunica externa/adventitia- outside
describe the tunica internal
made of endothelia cells
basement membrane
convective tissue
in contact with the blood
describe the tunica media
boundaries marked by internal and external elastic lamina
smooth muscle cells
elastin and collagen
describe the tunica external
connective tissue
nerves and blood vessels exist here
collagen and elastin
do arteries ten to have thick elastic all that resit distension and thus maintain a high pressure
yes
arterioles ahem thicker walls relative to lumen so good for constricting
veins have thin alls and large distensible lumens so are good for holding blood - capacitance
large elastic arteries such as the aorta and some main branches have many adaptations - they buffer the systolic rise in pressure and convert intermittent flow to contiouns flow and maintain blood flow and pressure during diastole. how is the artery adapted to do this
thick media containing lots of elastin fibres allowing the vessels to stretch during systole and rebound during diastole
maintain the high pressure e
wide lumen offers low resistance therefore pressure and velocity drop is low
good conductance of blood
they absorb and then propel blood through the inward elastic recoil during diastole propelling the blood forward and sustaining the high blood pressure
muscular Arteies distrubute flow, resit collapse eat joints and adjust the blood flow to tissues or organs how are they adapt to do this
thick smooth muscle media with fewer elastic fibres
smooth muscle allows some degree of vasoconstriction or dilate to adjust the flow
have a thick tunica external with loose structure and longitudinal collagen fibres too prevent retraction when cut
what vessel are the main site of resistance within the vascular system
arterioles - have a thick layer of smooth muscle with abundant amount of sympathetic nerve endings allowing extensive vasoconstriction via alpha 1 and vasodilation of b2
vasocnstriton increase upstream arterial blood pressure but reduces downstream blood flow to tissues
what is active hyperaemia
ability of arterioles to vasoconstriction/dilate rapidly and extensively allow them to adjust blood flow to tissues according to metabolic demand
where are nutrients and gases exchanged between the blood and tissue fluids
capillaries
large cross section area
endothelia cell and basement membrane
more abundant in metabolically active tissue
only abut 25% perfused arrest due to prescnece of precapillary sphincter and metarterioles
nail fold ones RBC have to deform to fit
what are the 3 types of capillaries
continuous - most common in muscle skin and fat
fenestrated- fluid exchange - renal glomerulus and synvoium of joints
discountinuous/ sinusoid - seen liver and gaps allow red cell migration in the bone marrow)
in capillaries what does velocity equal
blood flow over the cross sectional area
if large slows velocity menial gas and nutrient exchange is more effective
what determines the fluid exchange between the capillaries and surrounding tissue fluid
opposing hydrostatic and osmotic pressures
describe and explain how fluid moves out and into the capillaries
hydrostatic pressure is greater than osmotic pressure at start of capillary so net movement out
osmotic pressure is greater at the venule end so net movement in
hydrostatic pressure
flow and verse restiiacne and ia a force that pushes water out of blood vessels
osmotic pressure
aka colloid and oncotic pressure is determined by many by charges protein in the blood and pull water into blood vessels
net absorption and net filtration go to net filtration pressure
net filtration exceeds net absorption by approx 3l a day and the excess fluid is returned to circulation via the lymphatic system
veins have valves and act as capacitance vessels hat does this mean
stores and has blood volume - 65%
skeletal muscle pump and respiratory pump aid venous return from lower half of body
venoconstriction alpha 1 shunts blood from preoripjerla to central vessels to increase stroke volume like during exercise
