Quiz #5 Flashcards
List the 3 main muscle types in order from lowest to highest duration of muscle twitch.
skeletal
cardiac
smooth
What similar electrical properties does cardiac muscle have to skeletal muscle?
T-tubules
Ca2+ in SR
troponin-tropomyosin regulation
What similar electrical properties does cardiac muscle have to smooth muscle?
gap junctions
extracellular Ca2+
What are the steps for electrical activity in the heart?
current spreads through gap junctions to contractile cells
action potentials travel along plasma membrane and T-tubules
Ca2+ channels open in SR and plasma membrane
Ca2+ induces Ca2+ release from SR
Ca2+ binds to troponin, exposing myosin-binding sites
cross bridge cycle
Ca2+ actively transported back to SR/ECF
tropomyosin reblocks myosin-binding sites, muscle fiber relaxes
What are the 2 main periods of the cardiac cycle?
systole - ventricular contraction
diastole - ventricular relaxation
When do the AV valves open?
when atrial pressure is greater than ventricular pressure
blood can flow high to low pressure areas
When do the semilunar valves open?
when ventricular pressure is greater than arterial pressure
blood can flow high to low pressure areas
How long is the cardiac cycle?
about 0.8 seconds
- 0.3 seconds systole
- 0.5 seconds diastole
when HR increases all phases shorten
What are the 4 phases of the cardiac cycle?
phase 1 - ventricular filling (diastole)
phase 2 - isovolumetric contraction (systole)
phase 3 - ventricular ejection (systole)
phase 4 - isovolumetric relaxation (diastole)
How does aortic pressure vary during the cardiac cycle?
lowest during diastole
- aortic valve closes as blood is still leaving the aorta, so pressure falls
highest during systole
- aortic valve opens and pressure rises rapidly with ejection
How does the aorta ensure continuous blood flow during the cardiac cycle?
can stretch out alot to store energy during systole so during diastole, can recoil and release energy to continue pumping blood
there is never no blood flowing through the aorta
What is EDV?
end diastolic volume
volume of blood in the ventricle at the end of diastole (before contraction)
What is ESV?
end systolic volume
volume of blood in the ventricle at the end of systole (after contraction)
some amount will always remain
What is SV?
stroke volume
amount of blood ejected from the ventricle each cycle
SV = EDV - ESV
What is ejection fraction?
fraction of EDV ejected during a heartbeat
EV = SV/EDV
for a healthy individual, 54% of EDV is ejected into aorta
What is cardiac output?
volume of blood pumped by each ventricle per minute
CO = SV x HR
average = 5 L/min at rest
- average HR is 70 bpm, average SV is 70 mL
How long does it take the entirety of the blood volume to circulate through the body at rest?
once per minute
What components of cardiac output are regulated by the CNS?
HR and SV
ANS nerves effect entire heart
SNS and PNS take opposite effects
Where on the heart do parasympathetic nerves innervate?
SA node and AV node
Where on the heart do sympathetic nerves innervate?
SA node and AV node and ventricular myocardium
sympathetic system can change contractile force in ventricles, parasympathetic cannot
What determines the heart rate?
firing frequency of SA node
without extrinsic control, SA node would fire at 100 bpm
under control of ANS and hormones, parasympathetic system dominates and keeps HR at 75 bpm at rest
How does the PNS act to decrease heart rate?
PNS neurons release ACh, binds to muscarinic cholinergic receptors on SA nodal cells
open K+ channels and close funny and T-type channels
slows depolarization on decreases conduction speed of impulses
What is the role of epinephrine on HR?
increases HR and conduction velocity
released from adrenal medulla to enforce SNS activity
What division of the nervous system controls stroke volume?
SNS
sparse PNS fibers in ventricular myocardium
What is ventricular contractility?
more forceful contractions expel more blood
sympathetic control:
norepinephrine binds to beta1 adrenergic receptors, augmenting open Ca2+ channels to increase Ca2+ release from SR
What 3 factors affect stroke volume?
ventricular contractility
end-diastolic volume
afterload
How does EDV affect SV?
more blood in the heart at the end of diastole increases SV
Starlings Law
- increased EDV stretches muscle fibers closer to optimal length
- results in greater strength of contraction and therefore increased SV
What are the limits to Starlings Law?
ventricular expansion is limited by connective tissue and the pericardial sac
What is afterload?
pressure in the arterial system after contraction begins
- how resistant is the periphery to accepting blood flow
combined load of EDV and arterial resistance during ventricular contraction
increase in arterial pressure will decrease SV
What is flow?
flow = delta P/resistance
delta P = force pushing blood against various factors resisting the flow of liquid in a pipe
delta P = MAP - CVP
flow occurs from high to low pressure
What is MAP?
mean arterial pressure
pressure in aorta
2/3 DBP + 1/3 SBP
What is CVP?
central venous pressure
pressure in vena cava
What is the relationship between flow and pressure gradient?
directly proportional
Which circuit of circulation has less resistance?
pulmonary
pressure gradient is much less than in systemic circuit
What are some factors that affect the resistance of flow?
radius of vessel
length of vessel
viscosity of fluid
According to Poiseuille’s Law, what variable influences pressure the most?
change in radius
What is the relationship between resistance and flow?
inversely proportional
What are the 2 types of radius changes in arterioles?
vasoconstriction
- decreased radius = increased resistance
- typically associated with decreased metabolic activity
vasodilation
- increased radius = decreased resistance
- typically associated with increased metabolic activity
What is TPR?
total peripheral resistance
combined resistance of all blood vessels within the systemic circuit
What is the equation for cardiac output in relation to TPR and MAP?
CO = MAP/TPR
What structures make up microcirculation?
arterioles, capillaries, venules
What are the 3 layers of blood vessels?
tunica externa
- collagen fibers
tunica media
- smooth muscle and elastic fibers
- thicker in arteries
tunica intima
- endothelium
What is the vasa vasorum?
capillary network designed so large blood vessels can supply itself with blood
What is blood pressure?
force that blood exerts on the arterial wall
What are systolic and diastolic blood pressures?
systolic = peak BP during contraction
diastolic = lowest BP during relaxation
- not zero due to elastic recoil
What is pulse pressure?
SBP-DBP
strength of pressure wave
What is compliance?
a measure of how the pressure of a vessel will change with a change in volume
ex. a small increase in volume will cause a large increase in blood pressure in a small compliance vessel
What is healthy blood pressure around?
120/80 (systolic/diastolic)
How is blood pressure measured?
usually in elastic arteries, often brachial
want to inflate cuff to higher than systolic pressure to pinch off blood flow
slowly release pressure, once equal blood will start to flow through, listen for Korotkoff sounds indicative of systolic pressure (due to turbulent blood flow)
when sounds are gone, indicative of diastolic pressure
What is the role of arterioles?
where the greatest resistance occurs due to rings of smooth muscle to regulate radius
control blood flow to individual capillary beds and regulate TPR
connect arteries to capillaries
What is arteriolar tone?
contraction level (radius)
independent of extrinsic influences
What determined the regulation of blood flow to organs?
based on needs of each organ
regulated by varying resistance of vessels that supplies that organ (if a tissue doesn’t have high metabolic needs at that time resistance will be increased so decreased flow goes to that organ)
organ blood flow = MAP/organ resistance
What is active hypermia?
increased blood flow in response to increased metabolic activity
when metabolism is increased O2 is consumed faster than delivered and CO2 is produced faster than it is removed, vasodilation occurs to increase blood flow, delivering more O2 and removing more CO2
What is reactive hypermia?
increased blood flow in response to a previous reduction in blood flow (ex. an occlusion)
metabolites increase and oxygen decreases to blocked off tissues, vasodilation occurs
when blockage is released, increased blood flow due to low resistance, metabolites are removed and oxygen is delivered
What are the 2 major physiological regulators of blood flow?
blood pressure
peripheral resistance
What are the 3 major physiological regulators of blood pressure?
heart rate
stroke volume
peripheral resistance
What are some endocrine mechanisms of regulating blood flow?
NE and E, antidieuretic hormone, and angiotensin II increase cardiac output and cause vasoconstriction
atrial natriuretic peptide causes vasodilation
What are some neural mechanisms of regulating blood flow?
adjusts cardiac output and peripheral resistance to maintain blood flow to tissues
SNS
- increases cardiac output and peripheral resistance (vasoconstriction)
PNS
- decreases cardiac output
- no innervation of blood vessels
How do baroreceptors function to regulate high blood pressure (hypertension)?
BP rises above normal range
baroreceptors stimulated, increase # of impulses, causes activation/inhibition of certain centres
decreases sympathetic impulses to heart to decrease HR, contractility, resistance, and cardiac output
returns BP to normal range
How do baroreceptors function to regulate low blood pressure (hypotension)?
BP falls below normal range
baroreceptors inhibited, decrease # of impulses, causes activation/inhibition of certain centres
increases sympathetic impulses to heart to increase HR, contractility, resistance, and cardiac output
bring BP back to normal range
What is the baroreflex?
stretch sensitive mechanoreceptors monitor pressure of blood flow
carotid - to brain
aortic - to body
sends info to CV control centre
What are the 2 types of capillaries?
continuous
- small gaps between endothelial cells to allow small water-soluble molecules to move through
- in muscle, lungs, adipose, brain
- most common
fenestrated
- large gaps between endothelial cells forming pores (fenestrations)
- allow proteins and in some cases blood cells to move through
- kidneys, endocrine, intestine
What are the different ways in which exchange can occur over capillary walls?
diffusion
- most common
- simply travelling over membrane, through membrane if lipophilic or through channels if lipophobic
transcytosis
- exchangeable proteins
- endocytosis on one side, exocytosis on the other
mediated transport
- ex. GLUT4 transporter in brain
What is filtration?
movement out of capillary into interstitial space
What is absorption?
movement into capillary from interstitial space
What are the Starling force that act across capillary walls?
hydrostatic pressure gradient
- force due to fluid presence
- capillary favours filtrations
osmotic pressure
- force exerted on water by non-permeating solutes
- pulls water to where there is more solute
What are the 2 types of hydrostatic pressure?
capillary hydrostatic pressure
- exerted by presence of fluid inside the capillary
- direction of force: filtration
interstitial fluid hydrostatic pressure
- exerted by pressure of fluid inside the interstitial fluid
- direction of force: absorption
What are the 2 types of osmotic pressure?
capillary osmotic pressure
- force due to presence of proteins in capillary plasma
- direction of force: absorption
interstitial fluid osmotic pressure
- force due to presence of proteins in interstitial fluid
- direction of force: filtration
What is NFP?
net filtration pressure
difference between forces for filtration and absorption
if positive - in direction of filtration
if negative - in direction of absorption
What are all the different equations to find cardiac output/flow?
SV x HR
MAP/TPR
delta P/F
Q = CO = F
What are the 2 ways in which redistribution of venous reserve is accomplished in times of need?
systemic venous constriction
- venoconstriction of medium veins shifts blood from venous system to arterial system
venomotor tone
- smooth muscle tension in veins
- increase in the tone increases CVP, decreasing venous compliance, increasing venous return
What happens to Q distribution during exercise?
most tissues decrease at the expense of skeletal muscle
heart and brain receive more but the same/lower relative amounts
Describe the ventricular filling phase of the cardiac cycle.
- blood returning to heart enters relaxed atria
- passes AV valves into ventricles
- at the end, atria contract driving more blood into ventricles
Describe the isovolumetric contraction phase of the cardiac cycle.
- once ventricular pressure exceeds atrial pressure, AV valves close (LUB), pressure continues increasing
- ventricles begin to contract
- once pressure is high enough, semilunar valves open
Describe the ventricular ejection phase of the cardiac cycle.
- ventricular volume decreases, blood ejected until semilunar valves close (DUB) to prevent back flow as ventricle now has lower pressure than aorta
Describe the isovolumetric relaxation phase of the cardiac cycle.
- heart is resting
- some blood still remains present
- pressure still present as tension takes time to decrease
- back to phase 1 when ventricular pressure allows AV valves to open and blood to enter
