Systemic Circulation and Hemodynamics Flashcards
the volume of blood contained in the arteries is called what?
stressed volume-meaning the blood volume under high pressure
which blood vessel type has the highest resistance to blood flow?
arterioles
what is a special feature of the arterioles besides them having the highest resistance to blood flow?
they are also the site where resistance can be changed by alterations in sympathetic nerve activity
what is the pressure/ volume like of veins?
low pressure; high volume
the volume of the blood contained in the veins is called what?
unstressed volume- meaning the blood volume under low pressure
where is the cross-sectional area the greatest?
in the capillaries
where is the volume of blood the greatest?
in the veins
what happens to the resistance and the flow as the diameter of the blood vessel changes?
as the diameter increases, the resistance is going to decrease and flow is going to increase; as the diameter decreases, the resistance is going to increase and flow is going to decrease
what does Poiseuille’s law calculate?
resistance through a tube
what happens to the resistance has viscosity goes down?
resistance decreases as viscosity decreases
when would viscosity decrease?
in an anemic state
what happens if there is increased hematocrit?
it will decrease the flow (because resistance is increased)
how would you find the total resistance for vascular resistances that are in a series?
you simply add the individual resistances for the total
how would you find total resistance for vascular resistance beds that are in parallel?
1/ Rtotal= the sum of the 1/R1…1/R2 etc.
what does adding resistance beds in series do to the total resistance?
it increases the total resistance
what does adding resistance beds in parallel do to the total resistance?
it decreases the total resistance
how are capillaries arrange: series or parallel?
capillaries are arranged in parallel–> low resistance
where is the site of the greatest control of blood flow and TPR?
the arterioles
what does increased sympathetic stimulation cause in the blood vessels?
vasoconstriction
what does vasoconstriction cause?
reduced flow, increased TPR or increased pressure
what does decreased sympathetic stimulation cause?
vasodilation
what does vasodilation cause?
increased flow, decreased TPR or decreased pressure
what is velocity like in arteries? In capillaries?
high in arteries and low in capillaries
what contributes to blood flow becoming turbulent?
when velocity is high, cross sectional area is large, or viscosity is low
what is reynold’s number?
an equation which takes into account the velocity, cross sectional area, and viscosity to predict when turbulence will occur
when is it considered that there is a transition from laminar to turbulent flow?
when reynold’s number is greater than 2000
what does turbulent blood flow lead to?
sound (bruits) and lesions (arteriosclerosis)
what is compliance (aka capacitance)?
the change in volume/ the change in pressure
what is compliance (aka capacitance) the reciprocal of?
elastance
where is the highest compliance?
in the veins
where is the lowest compliance found?
in the arteries
which is more elastic, arteries or veins?
arteries
blood is being pushed forward not only through the pressure gradient but also through what?
the elastic recoil of the arteries
when is the elastic recoil of the arteries prominent?
during diastole
what affect does aging and atherosclerosis have on compliance and how?
they decrease compliance by reducing the amount an artery can distend during systole and by reducing the recoil during diastole
what is the effect of smooth muscle contraction in veins?
you are contracting the blood forward; redistributing blood to the arteries
what is the pulsatile nature of the aortic end of the pressure due to?
compliance and distention of the walls during ejection and recoil during relaxation
which blood vessel sees the largest pressure drop?
arterioles
what is the driving force for blood flow?
the pressure differences that exist between the heart and the blood vessels
what is pulse pressure?
the difference between systolic and diastolic pressure
if all other factors are equal, what does the magnitude of the pulse pressure reflect?
the blood ejected from the left ventricle in a single beat AKA STROKE VOLUME
how do you calculate the mean arterial pressure?
1/3( SBP) + 2/3 (DBP) (bc you spend a lot more time in diastole than you do in systole)
what is the normal mean arterial pressure?
93.3 mm Hg
a decrease in compliance would have what effect on the pulse pressure?
a decrease in compliance would cause pulse pressure to increase
what effect does arteriosclerosis have on pressure?
it increases SBP, MAP, and pulse pressure; DBP does not generally change
what effect does aortic stenosis have on pressure?
it decreases SBP, MAP, and pulse pressure; DBP does not generally change
what is the general rule of thumb for the venous system?
low pressure, high compliance, and large volume
what effect does venoconstriction have on the venous system?
it decreases venous “compliance” with minor changes to the radius of the veins (so there is little resistance change)
what is the backflow of blood in veins prevented by?
valves
what does venous pressure in the cardiac cycle look like?
there is an A wave, a C wave, and a V wave
when does the A wave occur?
during atrial contraction (so between the mid p-wave on the ECG and R wave of the QRS complex)
when does the C wave occur?
during ventricular contraction
what is the C wave caused by?
partially by slight backflow of blood into the atria at the onset of ventricular contraction but mainly by the bulging of the AV valves backwards into the atria due to increases in pressure in the ventricles
when does the V wave occur?
at the end of the ventricular contraction
what causes the V wave?
slow flow of blood into the atria from veins while the AV valves are closed
What are the walls of the arterioles rich with?
extensive smooth muscle
what is the composition of metarterioles?
they have more limited smooth muscle along the walls
what do the capillaries have that further control flow?
precapillary sphincters
in the capillary walls, what allow for the passage of water soluble substances such as glucose or electrolytes?
clefts
where are clefts found to be very small? Where are clefts found to be very large?
Very small in the brain (tight junctions) and very large in the liver and the gut
how do lipid soluble substances such as O2 and CO2 pass across the capillary walls?
through plasma membranes
how do larger molecules pass through the capillary walls?
through vesicles
Not all capillaries are open all the time; what is vasomotion?
it is the term used for the oscillating flow of blood through capillaries, which flows intermittently on and off every few seconds or minutes
how does vasomotion occur?
from the oscillating contraction of metarterioles and precapillary sphincters
what is vasomotion largely regulated by?
oxygen levels in the tissues; as oxygen consumption increases in the tissue, the frequency of vasomotion and duration the sphincters remain open increases to increase blood flow
what does the starling equation calculate?
the flow of water either out of a capillary or drawing into the capillary
what does a positive starling number indiccate?
that the flow of water is out of the capillary
what does a negative starling number indicate?
there is a drawing of water into the capillary
what represents fluid moving out of the capillary (+)?
filtration
what represents fluid moving into the capillary (-)?
absorption
what 2 forces act on the fluid exchange that is occurring in capillaries?
hydrostatic pressure and osmotic/oncotic pressure
what type of forces are the hydrostatic pressures?
pushing forces
what type of forces are the osmotic/oncotic forces?
pulling forces
what is the equation used for fluid exchange across the capillary walls?
J= [(Pcap-Pinterstial)- (Osmotic pressure cap.-osmotic pressure interstitial)} J= flow
what is the general rule about the hydrostatic pressure at the arteriole side and what effect does this have?
it is usually higher on the capillary side; so therefore, you are more likely to see filtration (+)
what is the general rule about the hydrostatic pressure at the venous side?
it is lower, so you are more likely to see absorption (-)
what is the capillary osmotic pressure caused by?
plasma proteins that tend to draw fluid from the interstitial fluid into the blood
what is the interstitial fluid pressure?
the pressure to force fluid into the capillary from the interstitial fluid
what is the interstitial osmotic pressure?
tends to pull fluid from the capillary into the interstitial fluid
how do the lymphatics re-enter venous circulation?
at the subclavian vein
what effect does elevated venous pressure have on Pc? and when might you have this?
Pc can be increased by elevated venous pressure; this can occur during right-sided heart failure
when can Pi be altered?
by restricted lymphatic flow or increased driving force out of a capillary
when can osmotic pressure of the capillary be decreased?
by reduced levels of albumin (such as in starvation or liver failure)- causes fluid to stay in the interstitial space
when might interstitial osmotic pressure be altered?
by restricted lymph flow or inflammation
what is acute control of blood flow achieved by?
rapid changes in local vasodilation or vasoconstriction of arterioles, metarterioles, and precapillary sphincters
what is autoregulation?
the maintenance of a constant blood flow to an organ in the face of changing arterial pressure
what does the vasodilator theory state?
decreased oxygen availability increases the formation of vasodilator substances
what are the vasodilator substances?
adenosine, CO2, adenosine phosphate compounds, histamine, potassium, and hydrogen ions
what does the oxygen demand theory state?
as oxygen levels rise or decrease the contraction of precapillary sphincter smooth muscle constricts or relaxes
what is active hyperemia?
the concept that blood flow to an organ is proportional to its metabolic activity
what is reactive hyperemia?
an increase in blood flow in response to or reacting to a prior period of decreased blood flow
what is the most important mechanism for coronary circulation?
local metabolic control
what is the most important mechanism for cerebral circulation?
local metabolic control
what is the most important mechanism during exercise for skeletal muscle?
local metabolic control
what is the most important mechanism during rest for skeletal muscle?
sympathetic control
what is the most important mechanism for temperature regulation of the skin?
sympathetic control
what is the most important mechanism for pulmonary circulation?
local metabolic control
what is the most important mechanism for renal circulation?
local metabolic control
what NT causes vasocontriction?
norepinephrine and epinephrine (norepinephrine greater than epinephrine)
what effect does Angiotensin II have on blood vessels?
it acts as a vasoconstrictor
what effect does vasopressin have on the blood vessels?
vasoconstrictor
what effect does serotonin have on the blood vessels?
it acts as a vasoconstrictor
what are the two main vasodilators we discussed?
bradykinin and histamine
what ions are considered vasodilators?
K+, Mg2+, H+, acetate, and citrate, and CO2
what is coronary blood flow mostly regulated by?
local control mechanisms- largely under metabolic control
what is the rate and contractility of the heart controlled by?
the sympathetic nervous system
when does coronary blood flow begin and when does it end?
begins during ventricular repolarization and lasts into diastole
when is coronary blood flow partially occluded?
during systole
what is almost entirely controlling the cerebral blood flow?
metabolic control, Pco2, and H+
injury to the head can result in what?
vasodilation and edema
what are the critical pressures that affect cerebral blood flow?
150 mmHg and 50 mmHg
what is the mean artial pressure in the pulmonary circulation?
about 15 mmHg
at rest, what is the skeletal blood flow governed by?
central and baroreceptor control
how does skeletal muscle dilate during exercise?
through the release of local factors like ATP, adenosine, NO, K+, and lactate
what effect does the central command that occurs during exercise have on the blood vessels?
it will cause an increase in the sympathetic outflow- this causes constriction of vein and constriction of the splanchnic and renal arterioles
what effect do the local responses that occur during exercise have on the blood vessels?
it causes an increase in vasodilator metabolites- so there will be a dilation of skeletal muscle arterioles and there will be a decreased in TPR
what causes constriction of the blood vessels in the skin?
constriction is induced by the alpha-1 adrenergic receptors (sympathetics)
what happens to the central sympathetics in the skin as body temperature rises?
the central sympathetic activation are inhibited to induce vasodilation of arterioles
what does trauma to the skin cause release of?
histamine
what effect does histamine have in the skin?
it produces a triple response in skin: a red line, a red flare, and a wheal (local edema)
