location: thoracic cavity, in mediastinum, between lungs, behind sternum, ribs 2 - 5
position: tilted to the left, so 2/3 rds of the heart is to the left of the median plane
describe the external anatomy of the heart:
pericardial sac: tough, fibrous layer of dense irregular connective tissue, and a deep serous layer. dense connective tissue anchors heart to- diaphram, sternum, mediastinum, secrets serous fluid to lubricate/reduce friction
heart wall: epicardium, myocardium - cardiac muscle, thickest layer, left ventricle 3x thicker than the R ventricle, endocardium
great vessels: major vessels entering/leaving the heart, vena cava, plumonary trunk, pulmonary veins, aorta
coronary vessels: fills grooves between chambers
arteries: blood flow away from the heart
veins: blood flow towards the heart
describe the internal anatomy of the heart:
4 chambers: two superior are R and L atria- receving chambers for blood returing to the heart, two inferior chambers R and L ventricles- pumps that eject blood to arteries
valves
R atrioventricular (AV, tricuspid),
L atrioventricular (AV, bicuspid, mitral valve)
plumonary valve: opening from R ventricle into pulmonary trunk, (semilunar)
aortic valve: opening from L ventricle into aorta (semilunar)
chordea tendineae: connects the AV valves to papillary muscles (prevents AV valves from flipping inside out)
describe the structure of the pericardium:
pericardium: encloses heart in a double-walled sac
pericardial sac: tough, fibrous layer of dense irregular connective tissue, and a thin deep serous layer
pericardial sac is anchored: to diaphram, sternum, mediastinum
epicardium: serous membrane of the external heart surface
myocardium: under edpicardium, thickest layer, cardiac muscle, L ventricle is 3x thicker than R ventricle
endocardium: lines interior of the heart chambers, covers valve surfaces, continuous with endothelium of the blood vessels
describe the location, structure, and fxn of the heart vavles:
location: Atrioventricular (AV) valves regulate the openings between the atria and ventricles, Semilunar valves regulate the flow of blood from the ventricles into the great artieries
structure:
fxn: ensure one way blood flow, open/close due to pressure not muscle contraction,
distinguish between the pulmonary and systemic circuits:
pulmonary circuits: carries blood to the lungs for gas exchange and returns it to the heart, right side of the heart, lower pressure pump, thicker walls
systemic circuit: supplies blood to every organ of the body, including parts of the lungs, and part of the heart itself, left side of heart, higher pressure pump, thinner walls
pulmonary circulation flow
pulmonary trunk - low O2
lungs - load O2, unload CO2
aorta- high O2
body - unload O2, load CO2
vena cava- low O2
pulmmonary trunk > lungs > pulmonary veins > L atrium > L AV valve > L ventricle > aortic valve > aorta > body > vena cava > R atrium > R AV valve > R ventricle > pulmonary valve > pulmonary trunk > over again
* distribution of blood: pulmonary 18%, heart 12%, 2/3 systemic - arteries 11%, capillaries 5%, veins 54% (70% systemic)
describe and identify the major vessels that carry blood into and out of the heart:
blood enters the R atrium from the superior and inferior venae cavaeblood in the R atrium flows through R AV valve into the R ventricle
contraction of the R ventricle forces the pulmonary valve to open
blood flows thru pulmonary valve into pulmonary trunkblood is distribued by R and L pulmonary arteries to the lungs where it unloads CO2 and loads O2
blood returns from lungs via pulmonary veins to L atrium
blood in the L atrium flows through left AV valve to left atrium
blood in L atrium flows thru L AV valve into L ventricle
contraction of L ventricle (simultaneous with step 3) forces aortic valve open
blood flows through the arotic valve into ascending aortablood in arota is distribued to every organ in the body, where it unloads O2 and loads CO2
blood returns to the heart via venae cavae
Put the following structures of the heart in the correct order from deep to superficial:
epicardium
myocardium
pericardium
endocardium
endocardium
myocardium
epicardium
pericardium
The________ valve separates the right ventricle and pulmonary trunk, whereas the _______ valve separates the
left atrium and left ventricle.
atrioventricular; semilunar
right AV; left AV
aortic; right AV
pulmonary; left AV
right AV; pulmonary
pulmonary; left AV
Blood returning to the heart from the lungs enters which chamber of the heart?
left atrium
right ventricle
left ventricle
right atrium
left atrium
Which of the following is NOT characteristic of cardiocytes (cardiac muscle cells)?
review the special structural characteristics of cardiac muslce tissue:
short, thick brached cells
one, centrally placed nucleus
uses Ca2+ from the SR and the ECF
intercalated discs
high amouts of mitochondria
desmosomes - prevent the contracting cardiocytes from pulling apart
gap junctions - ion channel, enable each cardiocyte to electrically stimulate its neighbors
aerobic respiration to make ATP
no anaerobic fermentation - so no fatigue
describe why the heart is not dependent on the nervous system for rhythm:
each peice continues its own rhythmic pulsations, sloitary, isolated cardiac muscle cells pulsate rhymically so caridocytes are said to be autorhythmic
*
has its own pacemaker, electrical system
describe the functional characteristics of cardiac muscle tissue:
the normal heartbeat triggered by the SA nodes is called:
sinus rhythm
any region of spontaneous firing other than the SA node is called:
ectopic focus
State the normal heart rate, the heart rate from the AV node, and the heart rate from the purkinje fibers when they are acting as an ectopic focus:
normal heart rate: 70-80 BPM
AV node HR ( nodal rhythm): 40-50 BPM
purkinje fibers: 20-40 BPM
any abnormal cardia rhythm is called:
arrhythmia
a persistent, resting adult heart rate below 60 BPM is called:
bradycardia
a persistent, resting adult heart rate above 100 BPM is called:
trachycardia
irregular and chaotic action potential propagation, where the heart quivers, and blood is not being pumped, is called:
fibillation
*fatal if not corrected
*atrail fibillation vs. ventricular fibillation (only minutes to fix)
Cells of the SA node do not have a stable resting memebrane potential. their memebran potential starts at about -60 mV and drifts upward, showing a gradual depolarization called:
pacemaker potential
* results from slow inflow of Na+ w/o compensating outflow of K+
explain the flow of ions underlying each phase of a cardiac pacemaker cell action potential:
1. slow inflow of Na+
2. threshold of -40 mV
3. Ca2+ channels open, Ca2+ flows in
4. rising depolarization, peaks at 0 mV
5. K+ channels open, K+ leaves the cell
6. falling repolarization
7. pacemaker potential starts over again
* each depolarization of the SA node sets off one heartbeat
*fires every 0.8 seconds, so HR 75 bpm
explain the flow of ions underlying each phase of contractile cell action potential:
1. voltage-gated Na+ channels open
2. Na+ inflow deplarizes the membrane and triggers the opening of still more Na+ channels, creating a postitive feedback cycle and a rapidly rising membrane voltage.
3. Na+ channels close when the cell depolarizes, and the volage peaks at nearly + 30 mV
4. Ca2+ entering through slow Ca2+ channels prolongs depolarization of membrane, creating a plateau. Plateau falls slightly because of some K+ leakage, but most channels remain closed until end of plateau.
*cardiocytes contract, sustained contraction necessary for expulsion of blood
5. Ca2+ channels close and Ca2+ is transported out of cell, K+ channels open and rapid K+ outflow returns membrane to its resting potential
*absolute refractory peroid: prevents wave summation and tetnus, which would stop pumping action of the heart
describe the atrial excitation in electrical conduction of the myocardium:
signal travesl thru the atria at about 1 m/s
atrial contraction, complete
when signal reaches AV node the signal slows down to about 0.05 m/s
the delay is essential becuase it gives the ventricles time to fill with blood before they being to contract
describe the ventricular excitation in electrical conduction of the myocardium:
signal travels thru the AV bundle and prkinje fibers at a speed of 4 m/s, the fastest in the conduction system
consiquently the entire ventricular myocardium deploarizes within 200 ms after the SA node fires, causing the ventricles to contract in near unison
Explain the purpose of an electrocardiogram (ECG/EKG):
to provide a comprehensive image of the heart's electrical activity.
a composite recording of all action potentials produced by the nodal and myocardial cells- not constructed as a tracing of a single action potential
describe how the P wave segment of teh ECG corresponds to the electrical activity and contraction of the myocardium:
produced when a signla from SA node spreads thru atria and depolarizes them
*atria contract
1. atria being depolarizing
2. atria depolarization complete
describe how the QRS complex segment of teh ECG corresponds to the electrical activity and contraction of the myocardium:
(Q): small downward deflection, delay time, allow for blood flow between atria andn ventricles
(R): tall sharp peak, ventricle polarization
(S): final downward deflection, ST segment corresponds to the pateau in the myocardial action potential, thus reps. time in which ventricles contract and eject blood
describe how the T wave segment of teh ECG corresponds to the electrical activity and contraction of the myocardium:
ventricular repolarization immedialtely before diastole
*heart is ready for next cycle
describe the diagnoistic interpretation of abnormal ECGs called nodal rhythm:
missing or inverted P waves
generated by the AV node in the absences of SA node activity
describe the diagnoistic interpretation of abnormal ECGs called a heart block:
two or more P waves per cycle
some P waves are not transmitted through the AV node and thus fails to generate QRS complexes
extrasystole
describe the diagnoistic interpretation of abnormal ECGs called ventriuclar fibrillation:
enlarged Q waves
grossly irregular waves of depolarization. typically seen in a myocardial infarction
one complete contraction and relaxation of all four heart chambers is called:
cardiac cycle
Describe the operations of the AV valves in the heart in terms of gradients and flow:
when atrial pressure is greater than ventricular pressure, the AV valves opens and blood flows thru P atria > P ventricles = open
when ventricular pressure rises about the atrial pressure, the blood in the ventricles pushes the valve cusps closed P ventricles > P atria = closed
describe the operations of the semilunar valves in the heart in terms of gradients and flow:
when the pressure in the ventricles is greater that the pressure in the great arteries, the semilunar valves are forced open and blood is ejected, P ventricles > P artery = open
when ventricular pressure is lower than arterial pressure, the aterial blood holdes these valves closed, P artery > P ventricles = closed
describe the ventricular filling (1) phase of the cardiac cycle, including the timing and heart sounds:
AV valves open, blood flows into ventricles
semilunar valves closed
1st 1/3 is rapid ventricular filling
2nd 1/3 is diastasis, slower filling
last 1/3 is atrial systole
* each ventricle contains EDV of 130 ml, only 40 ml (30%) is contributed by atrial systole
*R atria contracts before L atria b/c it recvs signal from SA node 1st
diastole
describe the isovolumetric contraction (2) of the cardiac cycle, including the timing and heart sounds:
P in the ventricles rises sharply, and reverses the P gradient b/w atria and ventricles
AV valves are closed!
heart sound S1 occurs
* eventhough ventricles contract, they do not eject blood and there is no change in volume
"iso" - same - volume
systole
describe the ventricular ejection (3) phase of the cardiac cycle, including timing and heart sounds:
