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Part A: Normal Physiology of the Heart
I. Molecular Level
A) Role of ions, hormones, and second messengers in cardiac signaling
1) Ion Signals (1)
(a) Na+, K+, Ca2+
2) Hormones (2)
(a) ANP
(b) BNP
(c) Epinephrine/norepinephrine
(d) Acetylcholine
3) Second Messengers (2)
(a) cGMP
(b) cAMP
II. Cellular Level
A) Cardiomyocyte (3)
1) Largely responsible for contraction of the heart
2) Centrally located nucleus (uninucleate)
3) Have abundance of ion channels above average sarcoplasmic reticulum.
(a) Allows for constant muscle contraction.
B) Excitation-contraction coupling (4)
1) Electrical excitation leads to contractual forces
C) Cardiac Pacemaker cells (5, 6)
1) Cardiac pacemaker cells, subset of cardiomyocytes.
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(a) Form intrinsic conduction system
(i) Allows propagation of action potentials throughout heart tissue.
2) Cells are autorhythmic
(a) Spontaneously depolarization, even in the absence of hormonal and
neural stimuli.
D) Gap junctions (5)
1) Cardiomyocytes connected via gap junctions.
(a) Formed from the proteins Connexin.
(i) transmembrane protein.
(b) Allows efficient and timely electrical communication between cells.
III. Tissue Level
A) Cardiac muscle tissue (3)
1) Mononucleated, striated, branched, muscle tissue under autonomic
control.
B) Calcium Handling (6)
1) Calcium plays a critical role in the contraction of cardiac muscle.
(a) Release of calcium from the sarcoplasmic reticulum
(i) Induces coordinated sarcomere contraction.
(b) Sarcomere contraction utilizes ATP
(i) Requires extensive oxygenation to meet energy demands.
1. Myocardium is oxygenated by the coronary arteries.
C) Conduction system (7)
1) A conduction system of pacemaker cells within the heart
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(a) Allows autonomic contraction of heart muscle.
(b) Origin at Sinoatrial (SA) node (located in the right atrium) to
atrioventricular (AV) node to separate sides of the heart via bundle of
HIS and Purkinje fibers.
(i) Causes ventricular depolarization and contraction.
2) SA node pacing rate innately around 100bpm.
(a) Susceptible to neural and hormonal changes which maintain
homeostasis.
IV. Organ System Level
A) General structure and blood flow throughout the heart (7):
1) Composed of four compartments:
(a) left and right atria and left and right ventricles.
2) Valves regulate the directionality of blood flow.
(a) Tricuspid valve, pulmonary valve, mitral (bicuspid) valve, aortic valve.
3) Pathway of blood flow
(a) Right atrium
(i) Tricuspid valve
(b) Right ventricle
(i) Pulmonary valve
(c) Left atrium
(i) Mitral valve
(d) Left ventricle
(i) Aortic valve
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B) Phases of contraction (8)
1) Heart undergoes phases of contraction
(a) systole (contraction)
(b) diastole (relaxation).
2) In systole, action potential propagated through cardiomyocytes causes
depolarization leading to heart contraction.
(a) Decreases the volume of the atria which increases the pressure within
the atria.
(b) Increased atrial pressure supersedes the pressure of the ventricles,
and the blood follows its pressure gradient through the open tricuspid
or mitral valves.
3) Same mechanism occurs for ventricular contraction.
C) Regulating cardiac output (2,7,9)
1) Constantly regulated as the body’s oxygen needs are in continual flux.
2) Regulation of this requires complex neural and endocrine control.
(a) Sympathetic
(b) Parasympathetic
V. Organism Level (5, 7, 8)
A) The heart is the pump generating force for blood flow throughout the body.
1) Blood flows through a network of pipes
(a) Arteries, capillaries, veins
2) Blood flow allows the transport of things throughout the body
(a) Mainly oxygen
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(b) Hormones
(c) Proteins, Fats, carbohydrates, etc.
References
(1) Grant AO. Cardiac Ion Channels.CCirc Arrhythm ElectrophysiolC2: 185–194, 2009.
https://doi.org/10.1161/circep.108.789081.
(2) Lugnier C,CMeyer A,CCharloux A,CAndrès E,CGény B,CTalha S. The Endocrine
Function of the Heart: Physiology and Involvements of Natriuretic Peptides and Cyclic
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Nucleotide Phosphodiesterases in Heart Failure.CJ Clin Med 8, 2019.
https://doi.org/10.3390/jcm8101746.
(3) Keepers B,CLiu J,CQian L. What’s in a cardiomyocyte – And how do we make one
through reprogramming?CBiochim Biophys Acta - Mol Cel ResC1867, 2019.
https://doi.org/10.1016/j.bbamcr.2019.03.011.
(4) Calderón JC,CBolaños P,CCaputo C. The Excitation–contraction Coupling
Mechanism in Skeletal Muscle.CBiophys RevC6: 133–160, 2014.
https://doi.org/10.1007/s12551-013-0135-x.
(5) Burkhard S,Cvan Eif V,CGarric L,CChristoffels V,CBakkers J. On the Evolution of
the Cardiac Pacemaker.CJ Cardiovasc Dev DisC4: 4, 2017.
https://doi.org/10.3390/jcdd4020004.
(6) Patel DM,CGreen KJ. Desmosomes in the Heart: A Review of Clinical and
Mechanistic Analyses.CCell Commun AdhesC21: 109–128, 2014.
https://doi.org/10.3109/15419061.2014.906533.
(7) Gordan R,CGwathmey JK,CXie L-H. Autonomic and endocrine control of
cardiovascular function.CWorld Journ CardiolC7: 204, 2015.
https://doi.org/10.4330/wjc.v7.i4.204.
(9) Buckberg G,CNanda N,CNguyen C,CKocica M. What Is the Heart? Anatomy,
Function, Pathophysiology, and Misconceptions.CJ Cardiovasc Dev DisC 5: 33, 2018.
https://doi.org/10.3390/jcdd5020033.
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