Lecture: Heart Flashcards
Differentiate the pulmonary circuit and the systemic circuit.
the pulmonary circuit stems from the right side of heart and sends blood to the lungs for gas exchange, while the systemic circuit stems from the left side of the heart and sends blood to all the organs of the body
Differentiate the circulatory system and the cardiovascular system. What are the components of each and how do their functions vary?
Circulatory system: heart, blood vessels, blood
functions: transportation, protection, regulation
Cardiovascular system: heart and blood vessels
functions: transportation of blood
Describe the location and weight of the heart.
in the thoracic cavity, in the mediastinum
< 1 lb
Describe the structure/layers of the pericardium.
from outer to inner: parietal pericardium --fibrous layer --serous layer visceral pericardium (a.k.a. epicardium) pericardial activity filled with pericardial fluid
What are the 5 functions of the pericardium?
1) Lubrication
2) Reduce friction
3) Protection
4) Expansion of heart
5) Prevents excessive expansion
Describe the structure/layers of the heart wall.
epicardium --coronary blood vessels myocardium --cardiac muscles (left thicker than right) endocardium --covers valves --continuous with blood vessels
Describe the functions of the 2 structural components of the myocardium.
1) cardiac muscle tissue
- -arranged in spiral or circular bundles; links all parts of the heart together
2) Fibrous CT skeleton
- -provides structural support, anchors cardiac muscle fibers, limits the spread of AP’s b/c it is a nonconductor of electricity
Describe cardiac muscle tissue, and compare it to skeletal muscle. Comment on:
- -nucleus,
- -mitochondria,
- -myofibrils,
- -sarcoplasmic reticulum,
- -transverse tubules.
- -single, central nucleus
- -mitochondria are 25% volume of cell
- -myofibrils & sarcomeres similar to skeletal muscle
- -SR is less developed & contains no terminal cisternae (calcium obtained from ECF)
- -T-tubules are larger than in skeletal muscle
Describe intercalated discs and their 3 distinctive features not found in skeletal muscle.
1) interdigitating folds: p. membrane folds up to “lock on” to adjoining cells
2) mechanical junctions: fascia adherens and desmosomes
3) electrical junctions: gap junctions; form a “functional synctium”
Describe the metabolism of cardiac muscle.
aerobic metabolism
vulnerable to oxygen deficiency
not prone to fatigue
adaptable to organic fuels (fatty acids, glucose, etc.)
can change metabolic pathways (ex. can use lactic acid)
What special type of cell enables the cardiac conduction system?
autorhythmic cells
- modified cardiac muscle cells
- function independently; influences by ANS & hormones
- function as pacemakers for the conduction pathway
What is unique about the RMP of the sinoatrial (SA) node?
cells of the SA node have an unstable RMP, which starts at about -60 mV and drifts upward, showing a gradual depolarization called the pacemaker potential
What are the 5 steps of action potentials in the sinoatrial (SA) node?
1) slow Na inflow causes a pacemaker potential to reach a threshold of -40 mV
2) fast, voltage-gated calcium channels open and Ca flows in from ECF
3) AP peaks slightly above 0 mV
4) fast K channels open and K leaves the cell
5) when repolarization is complete, K channels close and pacemaker potential starts over
What are Purkinje fibers?
nervelike processes that distribute excitation through the ventricular myocardium; fastest, supply papillary muscles
What is the RMP of an individual contractile cardiac myocyte?
-90 mV
What are the 5 steps of an action potential of a ventricular myocyte?
1) voltage-gated Na channels open
2) positive-feedback cycle: more Na channels open, rapid depolarization
3) Voltage peaks around +30 mV and Na channels close
4) Ca entering through slow Ca channels prolongs depolarization, causing a plateau
5) Ca channels close and Ca is transported out of cell; K channels open, rapid K outflow restores RMP
How does the absolute refractory period of a ventricular myocyte AP compare to that of skeletal muscle?
longer
Compare right and left heart in terms of pressure and volume of blood pumped.
Right heart is 1/5 pressure of left heart, but volume of blood is the same
What are the 5 major events of the cardiac cycle?
Quiescent period Atrial systole Isovolumetric contraction Ventricular systole Isovolumetric relaxation
What happens during the quiescent period?
diastole
phases:
-rapid ventricular filling
-diastasis (reduced filling during this phase)
AV valves open
SA node depolarizes
What happens during atrial systole?
initiated by atrial depolarization atria contract, forcing blood into ventricles ventricular volume increases atria begin repolarization ventricles begin depolarization
Define: end-diastolic volume.
volume of blood contained in a ventricle at the end of ventricular filling, or diastole
What happens during isovolumetric contraction?
atria complete repolarization
ventricles complete depolarization
–QRS complex
ventricle contraction begins
pressure increases, volume remains the same
AV valves close, causing turbulence heard as the 1st heart sound (S1)
What happens during ventricular systole?
ventricular contraction continues
pressure in ventricles increases, opening SL valves
ventricles eject blood (vol. decrease & pressure drop)
ventricular repolarization begins
What happens during isovolumetric relaxation?
ventricular contraction & repolarization complete
ventricular pressure drops below arterial
–SL valves close, dicrotic notch occurs, 2nd heart sound (S2)
ventricular pressure < atrial pressure, so AV valves open
Define: end-systolic volume.
volume of blood in a ventricle at the end of contraction, or systole
Define: stroke volume (SV).
volume of blood ejected in one heart beat (avg = 70 mL)
Define: ejection fraction.
% of blood ejected by ventricle (avg = 54%)
= (EDV - ESV) / EDV
may change with exercise
altered with disease
Define: cardiac output (CO).
volume of blood ejected in one minute (avg = 5 L/min)
Define: cardiac reserve.
= maximum cardiac output - resting cardiac output
What 3 factors influence stroke volume?
1) Preload (affects EDV)
2) Contractility (affects ESV)
3) Afterload (affects ESV)
Define: Frank-Starling Mechanism.
SV is proportional to EDV
the ventricles tend to eject as much blood as they receive; within limits, the more they are stretched, the harder they contract on the next beat
What 3 factors influence preload?
1) duration of ventricular diastole
2) increased/decreased venous return
3) extremely fast heart rate
