Chapter 20 THE HEART Flashcards
heart factoids
size of fist, less than a pound, beats an av of 100,000 times a day
Pulmonary Circuit pump
pumps sCo2 rich blood and O2 deficient, to the lungs. Blood is pumped through the lungs by the heart to reverse these gasses in the blood
Systemic circuit pump
blood returns to heart from lungs rich in O2 and low in Co2 and is pumped to rest of the body
Arteries
efferent vessels that carry blood away from the heart
Veins
Afferent, carry blood to the heart
Capillaries
Connect arteries and veins, referred to as exchange vessels
Cavity where the heart is located
mediastinum, between plural cavities
Apex
tip of the heart lies just above the diaphragm, left of the midline
Base
wide and directed towart the right shoulder
base is on top
Pericardium
double walled fibrous sac the encloses the heart
fibrous pericardium
loosely fitting, superficial part of sac anchoring
parietal pericardium
lines internal surface of the fibrous pericardium
Visceral Pericardium (epicardium)
upon the heart…layer covers surface of heart
serous fluid
fluid between parietal, visceral layers, prevents friction
myocardium
cardiac muscle layer, contracting part of the heart
Myocardium characteristics
pg. 3
intercalated discs
membranes of adjacent cells are held together by desmosomes and linked by gap junctions; this propagates action potentials
endocardium
inner most layer. most internal layer, made of simple squamous epithelium, provides a smooth surface to prevent clotting
Chambers of the heart
pg. 3, fig 20-6
Flow of blood, ex. cr.
pg. 4-6
Coronary vessels
blood supply to the myocardium
coronary arteries
first branches of the ascending aorta supplying nutrient/oxygen rich blood to myocardium
arterial anastomomosis
joining up of vessels to maintain good blood supply despite fluctuation in pressure
coronary veins
arteries merge with veins that will return blood to the right atrium
Cardiac conduction pathway
beating of the heart is regulated by electrical activity of the myocardium cardiac muscle cells contract spontaneously; the heart generates its own heartbeat called automaticity
conducting system cells
control/coordinate heartbeat through action potential
contractile cell
produce contractions that propel blood
The entire heart contracts in what series
1st the atria, then the ventricles; there is lag time between the beginning of the electrical impulse and the contraction (calcium entering sarcoplasm)
Impulse route
pg. 7 fig 20-12
electrocardiogram
electrical events in the cardiac cycle can be recorded (EKG or ECG)
P wave
depolarizing of atria
QRS complex
ventricles depolarize contraction of ventricles. happens shortly after that
T wave
ventricles repolarizing
P-R interval
from the start of atrial depolarization to the start of the QRS complex
Q-T interval
from the time the ventricles depolarize to the time that they repolarize
Action Potential of cardiac muscle
1.Rapid depolarization
cause: Na+ entry
duration: 3-5 msec
ends with: closure of voltage-gated fast sodium channels
Action Potential of cardiac muscle
2. The Plateau
cause: Ca2+ entry
Duration: 175 msec
ends with: closure of slow calcium channels
Action Potential of cardiac muscle
3. Repolarization
cause: K+ loss
Duration: 75 msec
Ends with: closure of slow potassium channels
Energy for cardiac contractions
aerobic reactions occur when mitochondria break down fatty acids and glucose and in the presence of O2 convert them to ATP, O2 is stored in myogloblin for normal circulation
Cardiac Cycle
sequences of events in one heart beat= simultaneous contraction of the two atria followed by the simultaneous contraction of the ventricles, followed by a rest period
Systole
contraction
diastole
relaxation
cardia cycle, Atrial systole
3:
- blood flows passively to rgt. atrium & ventricle during atrial & ventricular diastole
- pressure builds as more blood enters rgt. atrium & it contracts, filling ventricles to capacity
- atrial diastole occurs
Ventricular systole
ventricles enter_____ at the same time the atria enter _____
systole
diastole
Ventricular systole (phase #1)
forces the L and R AV valves closed but there is not enough pressure to eject blood into arteries…pressure continues to rise until it exceeds pressure in the arterial trunks
Ventricular systole (phase #2, called ventricular ejection)
ventricle contract strong enough to send blood into aortic and pulmonary trunks
stroke volume of heart
amount of blood pumped by ventricle per beat, 60-80 mL of blood
Ejection fraction
the percent of blood in a ventricle that is pumped during ventricle systole = pumps out 60% of the blood
End systolic volume
amount of blood remaining in the ventricle when semilunar valves closed
what gives the heart a rest for every beat?
ventricular diastole paired with atrial diastole
S1- the lubb-loudest and longest
ventricular systole CLOSING the AV valves
S2-dupp-ventricular diastole
closure of the aortic and pulmonary semilunar valves
S3-blood flowing into the?
ventricles
S4
atrial contraction
Pulse=heart rate, a healthy adult has a resting heart rate of
60-80 beats per min, which is also the rate of depolarization of the SA node
child pulse
100 beats per min
Infant pulse
120 beats per min
athletes pulse
35-50 beats per min
Cardiac output
amount of blood pumped by a ventricle in one min. determined by stroke volume x heart rate
average cardiac output
5-6 liters per min.
starling’s law of the heart
the more the cardiac muscle fibers are stretched the more forcefully they contract
venous return
the amount of blood returning to the heart through veins; if the amount increases the atrial walls stretch causing a more rapid depolarization
Factors affecting heart rate, autonomic innervation
parasympathetic and sympathetic divisions innervate the heart innnervating both the SA and AV nodes, the atrial muscles fibers and ventricular muscle cells
