test 2 key Flashcards
what are the 2 things that the force of a cardiomycote depends on with each systole
- ionotropy (contractility)
- optimal overlap between myosin and actin in diastole
what is ionotropy and what is it increased by
contractility from calcium binding troponin
increased by SNS, HR, cortisol, thyroid homrone
what is the optimal overlap between actin and myosin in diastole length? what’s it determined by?
(1.95-2.25)
Determined by preload (ventricular filling- end diastolic volume)
afterload
(pressure to overcome to eject blood into great arteries).
Tension the ventricles need to open aortic valve
what increases afterload
Increased by aortic stenosis, elevated BP
increasing afterload has what effect on stroke volume and ejection fraction
Increasing afterload decreases stroke volume and ejection fraction
if ionotropy decreases then what happens to ejection fraction and stroke volume
decreased ejection fraction lower stroke volume
chronotropy
Rate of depolarization aka heart rate
how much of ventricular filling is passive
80%
which side of heart has lower pressure
right ventricle bc left ventricle goes into systemic
Atrial pressure curve
- A Wave – Atrial contraction (atrial systole)
- C Wave – Bulging of tricuspid
- X Wave – Atrial relaxation (atrial diastole)
- V Wave – Passive filling of the atria (ventricular systole)
- Y Wave – Emptying of atria into the ventricles with the opening of AV valves (early diastole).
what is the dicrotic notch
2nd wave after aortic valve closes (elastic recoil)
s3 and s4 ok?
- S3 in healthy people unless new emergence (MI)
- S4 pathologic (non compliant ventricle)
what part of the heart has the highest pressure and is what causes our 120/80 blood pressure
aorta
what corresponds to preload
end diastolic volume
what is end diastolic volume
the volume in the ventricle at the end of diastole
what is end systolic volume
the volume in the ventricle at the end of systole
what is stroke volume
the volume ejected with each heartbeat
formula for stroke volume
SV = EDV – ESV
what is stroke volume impacted by
- Preload
- Contractility (inotropy)
- Afterload
increasing afterload does what to stroke volume and ejection fraction
decreases stroke volume and ejection fraction (higher oxygen demand in hypertension)
cardiac ouput
is the volume ejected by each systole X heart rate
cardiac output formula
CO = SV X HR
what determines oxygen and nutrient delivery to tissues
cardiac ouput
what is cardiac output increased by
catecholamine, stretching of ventricles, increased HR and contractility, increased central blood volume, increased systolic BP, increased preload and venous return
what is the SNS trope effect and how does it increase cardiac output
accumulate Ca2+ in SR as HR increases; not enough time to remove Ca2+
what decreased cardiac ouput
PNS
why does cardiac output need to be equal in the left and right ventricle
ventricle to prevent pulmonary congestion and systemic hypoperfusion
what is ejection fraction
is the proportion of EDV that is ejected each beat
what is an estimate of heart function in heart failure
ejection fraction
what is a normal ejection fraction
> 50%
ejection fraction formula
▪ EF = SV/EDV = (EDV – ESV)/EDV
preload of one ventricles depends on ____ of the other
cardiac output
SERCA (Sarcoplasmic/Endoplasmic Reticulum Calcium ATPase)
- Reuptake Ca2+ into SR after contraction
what happens if SERCA activity decreases
prolonged muscle relaxation (diastolic dysfunction), reduced Ca2+ release for contraction and weaker heartbeats (negative ionotropy)
Skeletal myocyte excitation contraction coupling
- Ach on nicotinic receptor initial depolarization
- Na+ VGC open depolarize sarcolemma (AP) open Ca2+ VGC
- L type Ca2+ VGC opens ryanodine receptor in SR (T tubules get AP deeper into myocyte)
a. Most Ca2+ that enters cytoplasm if from SR - Increased cytosolic Ca2+ binds troponin open myosin binding site on actin (move tropomyosin out of way) cross bridge formed and force generation
- Ca2+ decrease when AP stop; pump Ca2+ into ECF or SR
- When Ca2+ decrease the tropomyosin covers myosin binding sites again sarcomeres relax
what acts on nicotinic receptor to start excitation contraction coupling (in skeletal muscle)
Ach
what gets AP deeper into myocyte in skeletal muscles
t tubules
most of the Ca2+ that enters the cytoplasm is from the (in skeletal muscle)
SR
cross bridge cycle
- ADP + Pi on myosin head, allosterically inhibited by tropomyosin so cant bind actin
- Ca2+ binds troponin C so myosin can bind actin rigor state detach when ATP binds myosin head and is hydrolyzed
sarcomere
- Thick (myosin) and thin (actin) filaments overlap for contraction and cross bridge
similarities in skeletal and cardiac myocutes
- Striated, involve actin: myosin overlap
- Parabolic isometric length: tension relationship
- Peak isometric forces matches optimum passive resting length
- T-tubules exist in both (get AP deeper into muscle fibers)
- Ca2+ ATPase pumps to remove Ca2+ into SR
what is in cardiac myocytes that’s not in skeletal
no tetany in cardiac
have a syncytium
why no tetanic contraction in cardiac myocytes?
due to long electrical refractory period (extracellular calcium triggers intracellular calcium release)
syncytium in cardiac myocytes
cardiac myocytes are interconnected via branches and intercalated disks (gap junctions and desmosomes)
t tubules in cardiac myocytes
T tubules play a less important to the excitation- contraction coupling of cardiac cells; they are larger but fewer
cardiac cells; how many nuclei and mitochondria ? what form of metabolism?
cells have 1 single nucleus and LOTS of mitochondria
Oxidative metabolism (use fats), little glycogen stores
4 APs in the heart
myocyte:
1. atrial
2. ventricular
- purkinje
- automatic cell
4 phases of myocyte APs
- Phase 4= resting membrane potential (RMP)
- Phase 0= rapid depolarization (upstroke)
- Phase 1 and 2= prolonged depolarization/plateau
- Phase 3= repolarization
what’s shorter; atrial or ventricular APs?
- Atrial APs shorter than ventricular, allowing for faster contraction cycles
purkinje fibers have an unstable phase _
unstable phase 4; can spontaneously generate APs in abnormal conditions
automatic cells are :
pacemaker cells (SA and AV nodes)
automatic cells have an unstable phase _ and depolarize via __________
unstable phase 4 to spontaneously depolarize via funny currents (If)
which node sets the HR
SA node
where is SA node located
SA nodes in right atrium close to entrance of superior vena cava
phase 4; what is open? memebrane potential?
resting membrane potential
o (leaky K+ channels are open)
o Nernst= -84mV
phase 0; what opens?
rapid depolarization
o open VGC Na+; Na+ influx
phase 1
initial rapid repolarization
o close Na+ VGC
o open fast K+ VGC allowing K+ efflux
o membrane potential close to 0
phase 2
plateau
o open L-type Ca2+ channels that allow Ca2+ to influx
o No summation is possible due to the prolonged depolarization of the myocyte, no further action potential can be delivered to the cardiac myocyte
o Plateau bc Ca2+ channels (in) and slow K+ channels (out) cancel each other out
phase 3
: slow repolarization
o Close Ca2+ channels
o open slow K+ VGCs
calcium spark
1 Ca2+ VGC opens and elicits small amount of Ca2+ release from neighbouring ryanodine receptor on SR summation of these to increase cytosolic Ca2+
how to get ca2+ into SR? regulated by?
- SERCA get Ca2+ into SR
Regulated by phospholamban (phosphorylate to increase activity)
how is calcium removed from cytoplasm
Calcium sequestered by sarcolemma calcium ATPase (ca2+ out) and sodium-calcium exchanger (3 Na in, 1 Ca out; depolarize)
activation of SNS has what effect on contractility
- Active SNS (Beta 1 receptors) increase cAMP phosphorylate phospholamban and troponin and l-type Ca2+ VGC
SNS
- Increases cytosolic calcium release with each AP greater force of contraction
- Increase relaxation after reduced troponin affinity and increased SERCA activity
- Net: quick, forceful contraction and quicker relaxation
atria vs ventricular myocyte AP
- Atria don’t need to generate as much force
- RMP (phase 4) is slightly more depolarized (reduced K+)
- Lower plateau (phase 2) (lack of Ca2+ channels)
what are the pacemakers
- SA node, AV node, Purkinje fibers: generate APs spontaneously (no external stimuli)
primary pacemaker? bpm? backup?
a. SA node= primary pacemaker (60-100bpm)
i. AV node as backup
ii. Purkinje in pathologic states
heart rate is determined by
which cell depolarizes most frequently - SA node
phase 4 RMP in automatic cells
not stable; funny current from gNa+ and gK+ open during hyperpolarization and closed in depolarization
which phases are missing in automatic cells
phase 1 and 2
which phases are in automatic cell APs
phase 4, 0, 3
phase 0 and phase 3 in automatic cells
- Depolarization in phase 0 if from L type Ca2+ channels NOT Na+ VGC (closed)
- Phase 3: Ca2+ VGC close, K+ open (efflux = more negative)
PNS impacts on automatic cell AP
- Increase K+ = hyperpolarize
- Decrease Ca2+ influx= slow depolarization
- Increased atrial refractory period= decrease HR and decrease cardiac output
negative and positive ionotropy
- Positive ionotropy (contractility) = SNS increases rate of depolarization, RMP more +
- Negative ionotropy= PNS decrease rate of depolarization, RMP more –
where in the conduction system is there a delay
- Delay at AV node: time for atria to eject blood into ventricle prior to ventricular contraction
what carries the AP along the septum of the heart
- Bundle of His (AV bundles)
where do purkinje fibers carry AP to
to apex and base of heart ventricles contract
fibrous skeleton of heart purpose
isolates atria and ventricles and prevents direct conduction (so that only communication is via AV node)
Bachman’s bundle
allows for rapid conduction from right to left atrium = simultaneous atrial contraction
ECGs measure what
electrical differences across the heart
baseline in an ECG
= whole heart is either repolarized or depolarized
wave in an ECG
different electrical state in 2 separate areas of the heart
little box in an ECG
0.1mV high x 0.04 seconds wide
(big box= 0.5 mV x 0.2 seconds)
P wave
atrial depolarization (via SA node)
PR interval
time it takes for impulse to travel from SA node through atria and AV node to ventricles
QRS complex
ventricular depolarization (conduction pathway via Bundle of His and Purkinje fibers)
ST segment
when ventricles are fully depolarized, before they repolarize
T wave
ventricular repolarization
QRS interval
time it takes for AP to travel from end of AV node and throughout ventricles
QT interval
ventricular depolarization and repolarization
heart failure
- Contractility is significantly impaired resulting in reduced ejection fraction (how much is pumped out versus how much remains in the ventricle)
cardiac arrest
- Heart suddenly and unexpectedly stops pumping, often caused by ventricular arrhythmia’s, such as ventricular fibrillation or ventricular tachycardia
angina
- Pain brought on by ischemia, that doesn’t result in permanent heart damage
tachyarrhythmia
Abnormal heart rhythm (arrhythmia) with a heartbeat of >100 beats per minute (tachycardia)
3 layers of walls of veins and arteries (in to out)
tunica intima
tunica media
tunica externa/adventitia
what’s in the tunica intima
a. Simple squamous endothelium, subendothelial CT, internal elastic lamina
what’s in the tunica media
a. Thickest layer in arteries
b. Smooth muscle cells and fibroelastric CT, external elastic lamina
what’s in the tunica advnetitia/externa
a. Outermost layer
b. Thickest layer in veins
c. Dense irregular CT
d. Houses vasa vasorum (blood vessels to supply tunica adventitia and media)
which layer is thickest in veins? in arteries?
arteries- tunica media
veins- tunica externa/adventitia
elastic arteries
have most elastic membranes (for high pressure blood flow from heart)
a. Aorta, pulmonary arteries, common carotid arteries, subclavian arteries, common iliac arteries
muscular arteries
have more smooth muscle (in tunica media) for regulating blood flow
a. Radial artery, femoral artery, brachial artery, coronary arteries, popliteal artery
arterioles
control flow into capillary beds and regulate BP through constriction or dilation
metarterioles
are transitional vessels between arterioles and capillaries (via precapillary sphincters to regulate blood flow)
what regulated blood flow to capillaries
pre capillary sphincter
3 types of capillaries
continuous
fenestrated
sinusoidal
what type of capillary is the majority
continuous capillaries
which capillary is the least permeable
continous capillarie
which capillary is the most permeabel
sinusoidal capillaries
continuous capillaries
- Least permeable, majority of capillaries
- Intercellular junction for flow of water-soluble substances
fenestrated capillaires
- Moderately permeable (filtration and absorption organs i.e. kidneys, endocrine glands)
kidneys, endocrine, pancreas, intestines are which type of capillary
fenestrated
sinusoidal capillaries
- Highly permeable to large particles (i.e proteins), in specialized organs (liver, spleen, etc)
- Discontinuous basal lamina, big gap junctionsw
what type of capillaries are CT, muscle, neural, brain
continuous capillaries
what type of capillaries are bone marrow, spleen, lymph
sinusoidal capillaries
large veins
- i.e. vena cava, pulmonary veins, portal vein
- tunica intima has prominent subendothelial layer
- tunica media is thin with few muscle cells
- tunica adventitia is thickest layer with dense CT, collagen, elastic fibers, vasa vasorum
function of large veins
return deoxygenated blood to heart from systemic
medium veins
- i.e. femoral vein, renal vein, brachial vein
- tunica intima is think subendothelial layer
- tunica media is thin and scattered smooth muscle cells
- tunica adventitia is thickest layer with collagen and elastic fibers
what do medium veins have to prevent back flow
- valves in limbs to prevent backflow of blood due to low pressure
function of medium veins
drain blood from organs and limbs using valves to direct blood flow towards heart
small veins (venules)
i.e. postcapillary venules, collecting venules
- tunica intima: thin basal lamina
- tunica media: few layers of smooth muscle or absent
- tunica adventitia: thin layer of CT
function of small veins (venules)
collect blood from capillaries and begin process of returning it to larger veins
how are valves made in medium and large veins
via reflections in tunica intima (esp lower extremities)
how much of the body blood volume is in systemic veins and why
- lumen of veins is larger (and don’t constrict much) than arteries; 2/3 of body’s blood volume is in systemic veins
a. can restrict via catecholamines
poiseuilles law for blood Flow through a tube
effect of radius, length, viscosity
a. smaller radius= higher resistance and decreased flow
b. increased length and viscosity= higher resistance (i.e. dehydration)
c. only applicable in laminar flow (not turbulent)
turbulent flow is increased by
turbulent flow at high velocities or area with bifurcations and atherosclerotic plaques (sharp changes in vessel diameter)
a. use Reynolds number for turbulent flow
b. pathologies increasing turbulent flow: atherosclerosis, stenosis, hypertension, aneurysm, valvular heart disease
Bernoulli principle
pressure is constant in a system, regardless of velocity
two types of circulation
series and parallel
series circulation
one vessel to another; less common (ie. heart to aorta)
a. total resistance= sum of resistances of each individual vessel= higher overall resistance and less efficient blood flow
what is the more common arrangement of circulation in body; series or parallel
parallel
parallel circulation
blood flow through multiple vessels simultaneous; majority arrangement in body (i.e. capillary beds)
a. total resistance is less, each additional pathway provides alternative rout for blood flow; more efficient
b. capillaries have higher resistance due to small radius but in parallel it decreases it
total blood volume in body? when is it?
- total =5 L
a. 80% systemic circulation 60% systemic veins and 20% small arteries and capillaries
veins are ____ and easily distend to hold lots of blood
floppy
compliance
- How much pressure is required to change the diameter (volume) of blood vessel
high compliance
small amount of pressure large change in volume
what is more compliant; veins or arteries
- Veins more compliant than arteries (less muscle, more floppy) “blood reservoir”
a. Arteries stiffer, esp. atherosclerosis, calcify
low compliance in
in arteries; don’t stretch easily bc of muscle and elastic fibers to help maintain high BP and efficient flow of blood
a. Compliant, yet elastic arteries decrease cardiac work
central blood volume (25%). (most is systemic
- Vena cavae, heart, pulmonary circulation
- Determines preload
upright posture; how to get blood back to heart
- Valves in leg veins of lower body
- Skeletal muscles contract when standing and surround leg veins
- Inhale decreases intrathoracic pressure and draws blood up