The Heart Flashcards
heart
four-chambered muscular organ composed of myocardium
striated muscle with high capillary density, numerous mitochondria, and a single nucleus
right atrium and ventricle
receive blood returning from throughout body
pumps blood to lungs for aeration through pulmonary circulation
left atrium and ventricle
receive oxygenated blood from lungs
pump blood through aorta for distribution throughout systemic circulation
coronary circulation
provides oxygen and nutrient supply to the heart
myocardium extracts about 70-80% of the oxygen from the blood in coronary vessels
during exercise the only way to increase myocardial oxygen supply is to increase blood flow
myocardial tissue
has a threefold higher oxidative capacity than skeletal muscle and has the greatest mitochondrial concentration of all tissues
similar patterns of myocardial metabolism exist in trained and untrained
an endurance-trained person has greater myocardial reliance on fat catabolism in submaximal exercise
SA node
a 3 mm cluster of cells in the right atrium that generates electrical impulses for contraction of the heart
gap junctions
electrical linkages which spread signals in a patterned way from cardiac cell to cardiac cell
action potentials are responsible for cardiac contraction
caused by time-dependent changes in the permeability of the plasma membrane to K+, Na+, and Ca2+ ions
action potential arises spontaneously at the sinoatrial node and electrical signal spreads through the right and left atrium via gap junctions
atrial contraction (ejection of blood) and ventricle relaxation (filling)
the signal arises at the AV node, delays 0.1 second, and then conducts through the Bundle of His (AV bundle) and Purkinje system which spreads action potential through right and left ventricle
ventricle contraction (ejection of blood) and atrial relaxation (filling)
intercalated discs
complex structural junctions that couple mechanically one cardiac muscle cell to another allowing for a quick continuous rhythmic contraction
normal resting heart rate
would be 100 BPM if left to inherent spontaneous depolarization and repolarization of the myocardium
autonomic nervous system
component of the peripheral nervous system that regulates involuntary physiologic processes
the SNS and PNS motor pathways consist of a two-neuron series
a preganglionic neuron with a cell body in the CNS and a postganglionic neuron with a cell body in the periphery that innervates target tissues
postsynaptic sympathetic neurons
produce norepinephrine/epinephrine as their effector transmitter
postsynaptic parasympathetic neurons
use acetylcholine as their effector transmitter
sympathetic influence
neurons innervate the atria and ventricles
release catecholamines epinephrine and norepinephrine
increase SA node depolarization
tachycardia
increase cardiac contractility
exercise: progressive stimulation with more intense exercise by reflex activity
parasympathetic influence
neurons innervate the atria
release acetylcholine
decrease SA node depolarization
no effect on cardiac contractility
exercise: central command inhibits parasympathetic stimulation at onset and during low-to-moderate intensity exercise
central command
provides the greatest control over exercise heart rate
anticipation of exercise
causes a neural outflow from the central command
decreases parasympathetic inhibitory input with exercise
neural outflow is greater with anaerobic exercise than aerobic
mechanoreceptors
specialized neurons that transmit mechanical information from the left ventricle, right atrium, and veins into electrical signals
input modifies parasympathetic and sympathetic outflow to initiate appropriate responses to intensity of exercise
baroreceptors
pressure-sensitive neurons located in the aortic arch and carotid arteries
too great of stretch will activate baroreceptors to slow heart rate and dilate peripheral vasculature
local factors of extrinsic regulation of the heart
byproducts of energy metabolism
