Arteries, Veins, PVR Flashcards
what is PVR
peripheral vascular resistance
what are arterioles
smaller arteries
what does the vascular role play an active role in
regulation of blood pressure and distribution of blood flow to tissues
what are the blood vessels of the body
- arteries
- arterioles
- capillaries
- venules
- veins
how is the mean arterial pressure calculated
diastolic blood pressure plus one third of the pulse pressure
which factors can impact the mean arterial pressure
the cardiac output and the total peripheral resistance
what does the pulse pressure represent
the force the heart generates with each contraction to overcome the arterial resistance
what is the afterload
the force against which the heart must contract to eject blood into the arteries
what are the parameters that can influence pulse pressure
stroke volume
ejection velocity of stroke volume
arterial compliance
what can increase pulse pressure
increase in stroke volume
increase in ejection velocity
less complacency in the arteries
describe the walls of the arteries
thick and muscular with large quantities of elastic tissue
what do arteries act as a reservoir for
pressure, maintaining blood flow through tissues during diastole
what are the major branches of the aorta
subclavian
common carotid
iliac
describe the blood content of arteries
low volume, high pressure
what are the muscular arteries
coronary and renal arteries
diameters of small arteries
less than 2mm
diameter of arterioles
20-100 micrometers
where are arterioles found
within organs and tissues
why is there variable resistance in the arterioles
to distribute the blood and dissipate most of the aterial blood pressure
how large is the cross sectional area of the aorta
small
how large is the cross sectional area of the capillaries
large
why do capillaries get described as having a large surface area
they form large networks within tissues and have a large overall cross sectional area
what is the lumen diameter of the capillaries
5-10 micrometers
how does the size of the lumen of capillaries compare to the diameter of erythrocytes
the same size roughly
what does flow of capillaries depend on
the flow from arterioles
how do red blood cells flow in smaller capillaries
single file
how thick are the capillary cell walls
one cell thick
how thick are capillary walls
20 micro meters
function of capillary walls
allow optimal exchange between blood and tissues via fenestrations
what diffuses from the capillaries to the tissues
gases and glucose
what do the capillary walls lack
tunica media and tunica adventitia
how do veins compare to arteries
larger lumen and diameter, thinner vessel walls, work at low pressure
how much of total blood volume is within the veins
70%
what is the purpose of venous valves
they prevent the backward flow of blood
what can happen to the venous walls or valves if there is loss of elasticity
they can become weakened, causing turbulent blood flow within the vessel
what can cause varicose veins
distension of vessel walls caused by a weakening in the elasticity of the venous walls and valves
how many layers are there to the vessel wall structure (all apart from capillaries)
three
what are the three layers found in the blood vessels apart from the capillaries
- tunica intima
- tunica media
- tunica adventita
what is the tunica intima
- endothelial cells attached to a basement membrane
- has an underlying layer of extracellular matrix
- separated from the media by the internal elastic lamina
what is the tunica media
- layers of elastin fibres and smooth muscle cells, in which the proportion is dependent on whether it is an elastic or a muscular artery
- high elastin content, enabling vessel wall expansion during systole and recoil during diastole
what is the tunica adventitia
- external layer of vessel wall
- separated from the media by external elastic lamina
- thick connective tissue, elastic and collagen fibres
- contains a network of nerve fibres, lymphatics and smaller arterioles which perfuse from the outer media
what are vasa vesorum
the small arterioles that perfuse from the outer media - vessels of vessels
when is there vaso vasorum in the tunica adventita of vessels
only in the larger arteries is this found
what is meant by the compliance of blood vessels
the ability of the blood vessel wall to passively expand and recoil in response to changes in pressure
what is compliance in relation to volume and pressure
change in volume over change in pressure
what does compliance reflect about a vessel
its buffering function
describe arterial compliance
this is when the arterial wall expands to accommodate the ventricular stroke volume, allowing it to act as a pressure reservoir
what happens to the compliance of arteries during diastole
the wall will recoil to help drive the flow of blood within the artery
what does arterial compliance decline with
age
what can a decline in arterial compliance do to pulse pressure
increase
what is anteriosclerosis
arterial stiffness due to calcificaion of elastin, collagen and extracellular matrix in the vessel walls
what forms the inner lining of the entire blood vessel system and the heart
the endothelial cells
what is the inner lining of the blood vessel
the tunica intima
how are endothelial cells arranged in the blood vessels
along the axis of the blood vessel to minimise shear stress and provide a friction free surface for blood flow
how do endothelial cells regulate the permeability of blood vessels
they form a selective barrier between blood and tissues
what are endothelial cells
highly specialised cells that play a key role in cardiovascular function
list the functions of endothelial cells
- form the tunica intima
- inner lining of the heart
- provide a friction free surface for blood flow
- regulate the permeability of blood vessels
- regulate platelet function and fibrinolysis
- promote angiogenesis and vessel remodelling
what is angiogenesis
the process of new capillaries forming out of preexisting blood vessels in the body
where is the vascular smooth muscle found in the vessel walls
in the tunica media
function of vascular smooth muscle
- control total peripheral resistance
- contral arterial and venous tone
- control distribution of blood flow
- provide elasticity
- determine the vessel radius by contraction and relaxation
describe the shape of smooth muscle cells
single nuclei, spindle shaped, non striated
what does vascular smooth muscle secrete to give vessels their elastic properties
extracellular matrix
how is vascular tone altered
through the contraction or relaxation of the vascular smooth muscle cells
what is vasoconstriction
contraction of the vascular smooth muscle to narrow the vessel lumen and reduce the radius
what is vasodilation
relaxation of vascular smooth muscle to widen the vessel lumen and increase the radius
what is local control of blood pressure
this refers to the mechanism of altering small artery and arteriole resistance in organs and tissues, and is done through self regulation of blood flow and also include regulation by autocrine and paracrine substances
which hormones are involved in the local control of blood pressure
adrenaline
atrial natriouretic peptide
angiotensin 2
how does adrenaline locally control blood pressure through vasodilation
circulates in the blood and binds to beta two adrenoreceptors, leading to vasodilation
this occurs via an increase in cAMP and reduced calcium sensitivity, meaning there is relaxation of the smooth muscle cells
how does adrenaline locally control blood pressure through vascoconstriction
when at high concentrations, the adrenaline binds to alpha one adrenoreceptors
this causes contraction
how does atrial natriuretic peptide function in local control of blood pressure
vasodilator by regulating sodium balance and blood volume. released when the atria of the heart are stretched or stimulated by other factors, and causes the kidneys to excrete more sodium and water, lowering the blood volume and blood pressure.
how does angiotensin 2 regulate blood pressure on a local level
constricts the arterioles, important part of RAAS
what does RAAS stand for
renin angiotensin aldosterone system
what is RAAS
a key regulatory pathway in hormonal control of blood pressure and intravascular volume
describe the process of RAAS
- reduced blood flow to the kidney is sensed by receptors in the juxta glomerular apparatus in the kidney
- release of renin from the juxta glomerular cells
- renine acts on circulating angiotensinogen to convert it to angiotensin 1
- angiotensin 1 is converted by antiotensin converting enzyme in the lungs and kidney to angiotensin II
- this is a vasoconstrictor
what produces angiotensinogen
the liver
what produces angiotensin converting enzyme
endothelial cells
what does angiotensin do
- stimulates sodium and water reabsorption
- stimulates the release of aldosterone from the adrenal cortex
- stimulate antidiuretic hormone release from the posterior pituitary gland
what does aldosterone do
acts on distal convoluted tubule and collecting duct of the kidney to increase sodium and water retention to increase intravascular volume
what does antidiuretic hormone do
released from the posterior pituitary gland, it functions to increase water via aquaporin-2 channels in the distal convoluted tubule and the collecting duct of the kidney
increases vasoconstriction of blood vessels via the V1 receptors on the vascular smooth muscle cells
which drugs lower blood pressure on the RAAS pathway
ACE inhibitors and angiotensin II receptor blockers
what are ACE inhibitor examples
captopril and enalapril
what are angiotensin II receptor blockers
losartan
what produces ACE
the surface of the lungs and renal epithelium
how do endothelial cells regulate vascular tone
by producing vasoactive substances
what are examples of vasodilators
nitric oxide and prostoglandin 12
breakdown the production and function of nitric oxide
produced by nitric oxide synthase from the L arginine in vascular endothelial cells.
diffuses into the smooth muscle cells to indude relaxation via the cGMP activation of guanylate cyclase
when is nitric oxide released
in response to factors like the binding of endothelium dependent vasodilators like acetylcholine, ATP and bradykinin to receptors on the surface membrane of endothelial cells, or in response to shear stress
what is prostoglandin 12
an eicosanoid produced in endothelial cells
what is the function of prostoglandin 12
activates adenylate cyclase to increase cAMP production, and activate protein kinase A, leading to vasodilation
what are eicosanoids
fatty acid hormones found in cell membranes that act locally. their synthesis and action can be modulated by drugs
what are examples of vasoconstrictors
endothelin-1 and thromboxane A2
describe the mechanism of endothelin-1
secreted by endothelial cells in response to stimuli like pulsatile stress, shear stress, neurohormones and cytokines.
acts on the ETa receptor on vascular smooth muscle cells to initiate vasconstriction
which family does endothelin-1 belong to
the endothelin family of peptide agents
what activates thromboxane A2
tissue injury and inflammation
what is thromboxane an example of
an eicosanoid
what is the dominant effect on nitric oxide production
shear stress produced by the interaction of blood flow with endothelial cells
what does the interaction between ET-1 with the ETa receptor on vascular smooth muscle lead to
vasoconstriction
what does the interaction between ET-1 and the ETb receptors on vascular smooth muscle lead to
synthesis of nitric oxide, and hence vasodilation
what destroys nitric oxide in cells
the superoxide anion
when in the cardiac cycle is there a drop in blood pressure in systemic circulation
as blood circulates from the left ventricle to the right ventricle
when in the cardiac cycle is there a decrease in blood pressure for pulmonary circulation
as blood circulates from the right ventricle to the left ventricle
what does circulation of blood require in order to meet the metabolic demands of the body
a certain volume per minute
what is the average pressure pushing blood around the circulatory system
the mean arterial pressure
what ejects the blood into the arteries
the ventricles
what happens to the elastic wall as the blood is ejected into the arteries
it is stretched out due to the raised pressure, ie there is compliance
how does blood leave the aorta
continuously through branches > arterioles > capillaries
what offers resistance to blood flow during systemic circulation
the total vascular system downstream
when does pressure rise and fall in the arteries
during the cardiac cycle
why are blood vessels under constant mechanical load
due to blood pressure and flow
when does shear stress occur
due to blood travelling at different velocities within a blood vessel
what is shear stress
the force of flowing blood on the endothelial layer of the blood vessel
what can lead to the physiological adaptation or disease of the vessel wall
physiological and pathological factors
what are the physiological factors that alter homeostatis conditions of blood flow
exercise
pregnancy
growth
what are the pathological factors leading to alterations in homeostatic blood flow
hypertension
flow reduction
flow overload
what is the capillary system the primary location for
exchange of fluid, electrolytes, and gases
what separates the endothelial cells of the capillary wall
junctions known as intercellular clefts
what are the different classifications of capillaries
- continuous
- fenestrated
- discontinuous
describe continous capillaries
- continuous basement membrane with tight intercellular clefts
- continuous capillaries with low permeability
describe fenestrated capillaries
- perforations or fenestrations in the endothelium
- enables high permeability
describe discontinous capillaries
extremely high permeability due to large intercellular clefts and gaps int he basement membrane
where are continuous capillaries found
muscle
skin
pulmonary system
central nervous system
where are fenestrated capillaries found
exocrine glands
renal glomeruli
where are discontinuous capillaries found
in the liver
how are the capillary microcirculations of each organ arranged
so that it meets the organ’s metabolic requirements
how many times can arterioles branch when they supply blood to the capillaries
2-5 times
what are metarterioles
terminal arterioles that do not contain a continuous layer of smooth muscle, but instead contain smooth muscle fibres encircling the vessel at intermittent points along its length
is blood flow through capillaries continuous
no
describe blood flow through capillaries
intermittent due to vasomotion
what is vasomotion
spontaneous oscillation in tone of blood vessel walls, independent of heart beat, innervation or respiration
what surrounds the branching of metarterioles
pre capillary sphincters
what are pre capillary sphincters
rings of smooth muscle surrounding the branch site of capillaries from metarterioles that contract and relax in response to local metabolic factors. the contraction of these sphincters closes the entery to the capillary
what does hydrostatic pressure do
force fluid and dissolved substances through the capillary intercellular spaces to the interstitial spaces
what causes osmotic pressure
plasma proteins
what does osmotic pressure do
force fluid movement from the interstitial space to the blood via capillary intercellular spaces
what is net filtration pressure
the interaction of the hydrostatic and osmotic pressures that drive fluid out of the capillary
what happens if the net filtration pressure is positive
there will be net fluid filtration across the capillaries
what happens if the net filtration pressure is negative
there will be a net fluid absorption from the interstitial spaces into the capillaries
what happens to hydrostatic pressure as blood pressure drops from the arteriol to the venous systems
it will also decrease
what is hydrostatic pressure
pressure exerted by a fluid at equilibrium at any point of time due to the force of gravity
what is osmotic pressure
pressure required to stop water from diffusing through a barrier by osmosis
what happens to the osmotic pressure of the capillaries if there is a decrease in blood pressure
nothing as the proteins are too big to leave the capillary
how does the amount of fluid filtering outward from the arterial end of capillaries equate to the fluid returned to circulation by absorption
they are almost exactly equal
what does it mean if there is disequilibrium between the amount of fluid filtering outward from the arterial end compared to the fluid returned to circulation by absorption
there is excess fluid that is returned to the circulation via the lymphatic system
why is the lymphatic system important
there would be a build up of fluid in the tissues leading to oedema
what is the lymphatic system
a network of small lymph nodes and lymphatic vessels through which the lymph flows
what is lymph
fluid derived from interstitial fluid
how does lymph move through the lymphatic system
they contract to aid the movement of fluid, and is also responsible for moving absorbed fat into the circulation
what is found in lymph nodes
masses of lymphocytes and macrophages
what are the main groups of lymph nodes in the body
cervical
axillary
inguinal
mesenteric and retroperitoneal
mediastinal
what is the function of the lymphatic system
act as an overflow mechanism to return excess fluid volume from tissue spaces to the circulation
what does the lymphatic system control
concentration of proteins in interstitial fluids
volume of interstitial fluids
interstitial fluid pressure
what does increasing colloid osmotic pressure in interstitial fluid lead to
shift of the balance of forces at the membrane of blood capillaries in favour of fluid filtration
what does an increase in interstitial fluid pressure increase
the rate of lymph flow
what does the lymph flow do
carry excess interstitial fluid volume and protein that accumulates in interstital spaces away
is the hydrostatic pressure in the systemic system lower or higher than the pulmonary system
higher
is the osmotic pressure in the systemic circulation higher or lower than in pulmonary circulation
they are the same
what is pulmonary oedema
excess fluid in the lungs that collects in the alveoli
what can cause pulmonary oedema
- left side heart failure when there is an increase in hydrostatis pressure in the extremities
- right side heart failure
- high altitude exposure
- lung damage due to severe infection
- adult respiratory distress syndrome
- following major injury
pressure in the venous system
low
pressure in the arterial system
high
what are the muscular artery branches
renal and coronary
what can cause turbulent blood flow in veins
loss of elasticity in the vessels
what is the proportion of smooth muscle within the vessel wall dependent on
the function the vessel has
what are vasal vesorum
smaller arterioles within the larger arterioles
what does the contraction and relaxation of the tunica media allow
vascular flow
what does it mean to say that vessels have buffering capacity
they are able to withstand the high pressure that blood goes through when it goes through the heart
why does the aterial wall expand upon receipt of the blood
to allow for high volume and high pressure to be maintained
why is arterial recoil important
allows for the pushing of blood along the arteries to aid in travel of the blood through the vascular system
what is atherosclerosis
plaque build up in the vascular wall causing clots which leads to strokes and cardiac arrest
what is arterial sclerosis
age related stiffness caused by calcification of elastic fibres in the artery wall leading to the cardiac tissued
what is involved in the local control of blood pressure
endothelial cells and hormones
what are the two pressures involved in fluid exchange through intercellular exchanges
hydrostatic and osmotic
what derives lymph
interstitial fluid from the circulation
what is oedema
fluid accumulation in the tissues
why can oedema be observed in heart failure
the balance between the lymphatic system and blood volume is impacted. damage and difficulty to maintain respiratory function
