The Heart Flashcards
external anatomy of the heart
2 membrane coverings (paricardium) -fibrous -serous (2 layers) heart wall (3 layers) vessels entering/exiting coronary arteries
marginal artery supplies…
apex
similarities between cardiac and skeletal mechanism of contraction
striated
-myosin/actin mechanism
t-tubule mechanism
-acting on sarcoplasmic reticulum
differences between cardiac and skeletal mechanism of contraction
t-tubule mechanism - direct diffusion of Ca++
-tubules store larger amounts of Ca++
action potential
-cardiac muscle “plateau”
-plateau results in much longer time of contraction than skeletal muscle
strength of contraction
-dependent on extracellular Ca++
ability of cardiac muscle to depolarize and contract is…
intrinsic
heart’s intrinsic conduction system components
sinus node = sinoatrial/S-A node internodal pathways A-V node A-V bundle left and right bundle branches of Purkinje fibers
features of SA node
smaller diameter muscle fibers
almost no contractile muscle fibers
connect directly with atrial muscle (mm) fibers
cell membranes naturally “leaky” to Na+ and Ca++ ions
-results in less negative resting membrane potential than other cardiac muscle cells
self-excitation
how does EKG work (very broad)
electrical impulses passing through the heart also spread into adjacent tissues and some to the surface of the body
can be captured at surface of the body using electrodes
what is the cardiac cycle
-what events are of note
events that occur from the beginning of one heartbeat to the beginning of the next
events
-chamber and vessel blood volume changes
-chamber and vessel blood pressures changes
-electrical activity noted
-heart sounds occur
-valves open and close
cardiac cycle consists of what periods?
diastole
-period or relaxation; heart filling with blood
systole
-contraction period; heart ejects blood
EDV and ESV values
EDV
-110-120 mL at rest
ESV
-40-50 mL
what is isovolumic relaxation
ventricle is relaxing and the SL valve has closed, but the AV valve has not yet opened so blood cannot rush in
what is isovolumic contraction
ventricle is contracting, but AV and SL valves are closed, so pressure is building without a change in volume
relationship of cardiac cycle to ECG
- P
- QRS
- T
P: spread of depolarization through atrial tissue followed by contraction
-increases atrial pressure
QRS complex: spread of depolarization through ventricular tissue followed by contraction
-increases ventricular pressure
T wave: repolarization of the ventricles which represents ventricular relaxation
atria function as “pumps”
atrial contraction usually causes an additional 20% ventricle filling; “primer pump”
atrial function “unnecessary” except during vigorous exercise
atrial pressure changes
a wave -during atrial contraction c wave -onset of ventricular contraction v wave -end of ventricular contraction
preload
end-diastolic pressure when the ventricle is filled
-amount of tension on the muscle when it begins to contract
afterload
pressure in the artery leading from the ventricle
load against which the muscle exerts its contractile force
energy requirements for cardiac contraction
almost exclusive reliance on O2 for metabolism
70-90% from metabolism of fatty acids
10-30% from lactate, glucose
can use lactic acid generated by skeletal muscle activity
heart pumps ____ of blood/minute
4-6 liters
blood volume pump regulated by
intrinsic cardiac regulation of pumping in response to changes in volume of blood flowing into the heart
control of heart rate and strength of heart pumping by the autonomic nervous system
Frank-Starling Mechanism
heart automatically pumps incoming blood
as cardiac muscle is stretched with returning blood volume, approach optimal length of actin and myosin fibers for contraction
extrinsic regulation of the cardiac pump
-SNS
norepinephrine released by sympathetic nerve fibers in response to stressors such as fright, anxiety, or exercise; threshold reached more quickly
- increase CO
- -pacemaker fires more rapidly
- -enhanced muscle contractility
extrinsic regulation of the cardiac pump
-PSNS
reduces HR when stressors removed
acetylcholine hyperpolarizes membranes of cells
-opens K+ channels
-PNS fibers in vagus nerves to heart can decrease CO
–primarily affects HR rather than contractility
