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The Heart

The Heart: Study Stack for Test

Arteries bring blood away from the heart (rich in blood)
Veins bring the blood towards the heart (not rich with blood)
Left side of heart: fully oxygenated blood arrives from lungs via pulmonary veins. blood sent to all organs of the body via aorta.
Right side of heart: lesser oxygenated blood arrives from inferior and superior vena cava. blood sent to lungs via pulmonary trunk.
The heart: located in the mediastinum, between lungs
Base of the heart (top): wide, superior portion of the heart, blood vessels attach here.
Apex of the heart (bottom): inferior end, tilts to the left, tapers to point.
Heart: protected by the sternum.
Pericardium: Double-walled sac that encloses the heart. Allows heart to beat without friction, provides room to expand, yet resists excessive expansion. Anchored to diaphragm inferiorly and sternum anteriorly.
Parietal pericardium: Outer wall of sac. Includes superficial fibrous layer of connective tissue, and a deep thin serous layer.
Visceral pericardium (epicardium): Heart covering. Serous lining of sac turns inward at base of heart to cover the heart surface.
Pericardial cavity Space inside the pericardial sac filled with 5-30 mL of pericardial fluid.
Pericardial fluid lubricates the membranes & allows the heart to beat without painful friction.
Pericarditis: Inflammation of the membranes. There is painful friction rub with each heartbeat.
Epicardium (visceral pericardium): serous membrane covering heart, adipose in thick layer in some places, coronary blood vessels travel through this layer
Coronary Blood Vessels: supplies oxygen to the heart as an organ.
Endocardium: smooth inner lining of heart and blood vessels, covers the valve surfaces and continuous with endothelium of blood vessels.
Myocardium: layer of cardiac muscle proportional to work load...muscle spirals around heart which produces wringing motion.
Fibrous skeleton of the heart: framework of collagenous and elastic fibers which provieds structural support and attachment for cardiac muscle and anchor fro valve tissue, electrical insulation between atria and ventricles important in timing and coordination of contractile activity.
Heart Chambers (four chambers): right & left atria, right & left ventricle
Right and Left Atria: two superior chambers, receive blood returning to heart, auricles enlarge chamber.
Right and left Ventricle: (more muscular) two inferior chambers, pump blood into arteries.
Atrioventricular sulcus: separates atria and ventricles.
Interventricular sulcus: overlies the interventricular septum that divides the right ventricle from the left.
Sulci: contain coronary arteries.
Heart Chambers (Internal): Interatrial septum, pectinate muscles, interventricular septum, trabeculae carnae.
Interatrial septum: wall that separates atria
pectinate muscles: internal ridges of myocardium in right atrium and both auricles
interventricular septum: muscular wall that separates ventricles
trabeculae carnae: internal ridges in both ventricles
Heart Valves: valves ensure a one-way flow of blood through the heart.
Atrioventricular (AV) Valves: controls blood flow between atria and ventricles
Right AV valve has 3 cusps (tricuspid valve)
Left AV valve has 2 cusps (mitral or bicuspid valve)
Chordae Tendineae: cords connect AV valves to papillary muscles on floor of ventricles. prevent AV valves from flipping inside out or bulging into the atria when the ventricles contract.
Semilunar Valves: control flow into great arteries- open and close because of blood flow and pressure.
Pulmonary semilunar valve: in opening between right ventricle and pulmonary trunk.
Aortic semilunar valve: in opening between left ventricle and aorta.
Function of Heart Valves: to prevent the back flow of blood.
AV valve mechanics: ventricles relax and contract
Ventricles relax: pressure drops inside the ventricles, semilunar valves close as blood attempts to back up into the ventricles from the vessels, AV valves open, blood flows from atria to ventricles.
Ventricles contract: AV valves close as blood attempts to back up into the atria, pressure rises inside of the ventricles, semilunar valves open and blood flows into great vessels.
Coronary Circulation: 5% of blood pumped by the heart is pumped to the heart itself through coronary circulation to sustain its strenuous workload (250 ml of blood per minute, needs abundant O2 and nutrients)
Left Coronary Artery (LCA): branch off the ascending aorta.
Anterior interventricular branch: supplies both blood ventricles and anterior two-thirds of the interventricular septum.
Circumflex branch: passes around left side of heart in coronary sulcus, gives off left marginal branch and then ends on the posterior side of the heart, & supplies left atrium and posterior wall of left ventricle.
Right Coronary Artery (RCA): branch off the ascending aorta.
Right coronary artery: supplies right atrium and sinoatrial node (pacemaker)
Right marginal branch: supplies lateral aspect of right atrium and ventricle.
Posterior interventricular branch: supplies posterior walls of ventricles.
Angina: chest pain from a partial obstruction of the coronary blood vessels.
Ischemia: lack of oxygen to a tissue.
Capillaries & arteries: deliver blood to the heart.
Cardiocytes: striated, short, thick, branched cells.
Intercalated discs: join cardiocytes end to end.
Interdigitating folds: increase surface area of contact.
Mechanical junctions: tightly join cardiocytes.
Fascia adherens: broad band in which the action of the thin myofilaments is anchored to the plasma membrane (each cell is linked to the next via transmembrane protein.
Desmosomes: welled-like structure/junctions prevents cardiocytes from being pulled apart.
Electrical junctions: gap junctions allow ions to flow between cells (two neighboring cells)
Fibrosis(scarring): repair of damage of cardiac muscle.
Cardiac Muscle: (has a huge mitochondria that makes up 25% of the cell) depends almost exclusively on aerobic respiration used to make ATP [myoglobin, glycogen] - glucose monomers stuck together
Adaptable to organic fuels used: more vulnerable to oxygen deficiency than lack of a specific fuel [fatty acids, glucose, ketones, lactic, amino acids]
Fatigue resistant
Cardiac Conduction System: controls the route and timing of all electrical conduction to ensure that all four chambers are coordinated.
Sinoatrial (SA) node (pacemaker): modified cardiocytes in right atrium... (1) initiates each heartbeat and determines heart rate (2) signals spread throughout atria.
Atrioventricular (AV) node: electrical gateway to the ventricles.
Atrioventricular (AV) bundle (bundle of His): pathway by which signals leave the AV node.
Purkinje fibers: nervelike processes spread throughout ventricular myocardium.
Signal pass from cell to cell through: gap junctions
Sympathetic nerves: raise heart rate
Parasympathetic: slows heart rate
Arrhythmia: any abnormal cardiac rhythm
Systole: atrial or ventricular contraction
Diastole: atrial or ventricular relaxtion
Sinus Rhythm: normal heartbeat triggered by the SA node.
General Range of Sinus Rhythm: 60-90 beats per minute (bpm) & average adult rest is 70-80 (bpm)
Ectopic focus: another part of the hear fires before SA node
AV node: most common ectopis focus (40-50) bpm
Factors that can cause Ectopic Focus: Hypoxia (lack of oxygen), Electrolyte Imbalance (low levels of potassium ions), Caffeine, and Nicotene.
SA node = modified cardiac muscles
Slow Na+ inflow: causes gradual depolarization (pacemaker potential)
At each depolarization: SA node does the heart beat
-40 (reached the threshold): Voltage gated sodium ions channel & calcium channel. (when they open, sodium and calcium go in which causes depolarization).
When depolarization occurs: contractions happen immediately.
Signal from SA node: stimulates two atria to contract almost simultaneously.
Signal slows down through: AV node
Signals travel very quickly through: AV bundle and purkinje fibers.[entire ventricular myocardium depolarizes and contracts in near unison] papillary muscles contract an instant earlier than the rest, tightening slack in chordae tendineae.
Ventricular systole: progresses up from the apex of the heart. [spiral arrangement of cardiocytes twists ventricles slightly.
The AV node: has fewer gap junctions. It allows ions in through pores.
Electrical Behavior of Myocardium: cardiocytes have a stable resting potential of -90 mV & depolarize only when stimulated.
Depolarization phase: stimulus opens voltage regulated Na+ gates, membrane depolarizes rapidly, action potential peaks at +30 mV, Na+ gates close quickly.
Plateau phase lasts 200-250 msec, sustains contraction for expulsion of blood from heart: Ca2+ channels are slow to close and SR is slow to remove Ca2+ from the cytosol.
Repolarization phase: Ca2+ channels close, K+ channels open, rpid diffusion of K+ out of cell returns it to resting potential.
Electrical Behavior of Myocardium: has a long absolute refractory period [cannot reach the threshold right away].
Wave summation: stops the heart from pumping.
Action Potential of a Cardiocyte: (1)Na+ gates open (2)Rapid depolarization (3)Na+ gates close (4)Slow Ca2+ channels open (5)Ca2+ channels close, K+ channels open (repolarization)
Electrocardiogram (ECG or EKG): composite of all action potentials of nodal and myocardial cells detected, amplified, and recorded.
P wave: SA node fires, atria depolarize and contract, atrial systole begins 100 msec after SA signal.
QRS complex: ventricular depolarization happens (produced by the signal of the AV node...traveling through the ventricular myocardium which causes depolarization.
ST segment: ventricular systole, plateau in myocardial action potential.
T wave: ventricular repolarization and relaxation.
PQ segment: is the time required for impulses to travel from the SA node to the AV node.
Electrical Activity of Myocardium: (1)atrial depolarization begins (2) atrial depolarization complete[atria contracted] (3)ventricles begin to depolarize at apex; atria repolarize[atria relaxed] (4)ventricular depolarization complete[ventricles contracted]
Electrical Activity of Myocardium: (cont) (5)ventricles begin to repolarize at apex (6)ventricular repolarization complete[ventricles relaxed]
Cardiac Cycle: one complete contraction and relaxation of all four chambers of the heart.
Atrial Systole (contraction: oocurs while ventricles are in diastole (relaxation).
Atrial Diastole: occurs while ventricles in systole.
Quiescent period: all four chambers relaxed at the same time.
Variables that govern fluid movement: pressure and resistance
Pressure: causes fluid to flow
Resistance: opposes fluid flow
Pressure Gradient: when there is a difference in 2 points of pressure. [the greater the pressure, the faster the flow]
Function of Heart Valves: to prevent the back flow of blood.
Auscultation: listening to sounds made by the body.
First heart sound (S1): "lubb" (1)louder and longer "lubb" (2)occurs with closure of AV valves, turbulence in the bloodstream, and movements of the heart wall.
Second heart sound (S2): "dupp" (1)softer and sharper "dupp" (2) occurs with closure of semilunar valves, turbulence in the bloodstream, and movements of the heart wall.
S3: rarely heard in people over 30 years of age.
Phases of Cardiac Cycle: (1)Ventricular filling (2)Isovolumetric contraction (3)Ventricular ejection (4)Isovolumetric relaxation
Ventricular Filling - during diastole, ventricles expand: their pressure drops below that of the atria & the AV valves open and blood blows into the ventricles.
Ventricular Filling occurs in 3 phases: (1)Rapid ventricular filling (2)Diastasis (3)Atrial systole
Rapid ventricular filling: first one-thrid [blood enters very quickly]
Diastasis: second one-third [marked by slower filling & P wave occurs at the end of diastasis].
Atrial Systole: final one-third [atria contract]
*End-Diastolic Volume (EDV): amount of blood contained in each ventricle at the end of ventricular filling. [130 mL of blood].
Isovolumetric Contraction - atria reploarize and relax: remain in diastole for the rest of the cardiac cycle.
Ventricles depolarize: create the QRS complex, and begin to contract.
Av valves - close as ventricular blood surges back against the cusps.
heart sound S1 - occurs at the beginning of this phase.
'isovolumetric' because even though the ventricles contract, they do not eject blood. [the volume stays the same]
Ventricular Ejection - ejection of blood begins: when the ventricular pressure exceeds aterial pressure and forces semilunar valves open.
Rapid ejection: blood spurts out of each ventricle rapidly at first.
Reduced ejection: blood is ejected out more slowly under reduced pressure.
Ventricular ejection: last about 200-250 msec
T wave: occurs late in this phase
Stroke Volume (SV): is the amount of blood ejected from each ventricle. [of about 70 mL of blood is ejected of the 130 mL in each ventricle]. (ejection fraction of about 54%, as high as 90% in vigorous exercise)
End-systolic volume (ESV): the amount of blood left behind after ventricular ejection. [the 60 mL left behind]
Ejection Fraction: the percentage of EDV ejected.
Isovolumetric Relaxation - early ventricular diastole (EVD): when T wave ends and the ventricles begin to expand.
Elastic recoil and expansion: would cause pressure to drop rapidly and suck blood into the ventricles.
Blood from the aorta and pulmonary: briefly flows backwards, filling the semilunar valves and closing the cusps, creates a slight pressure rebound that appears as the dicrotic notch of the aortic pressure curve.
heart sound S2: occurs as blood rebounds from the closed semilunar valves and the ventricle expands.
'isovolumetric' because: semilunar valves are closed and AV valves have not yet opened [ventricles are therefore taking in no blood].
When AV valves open - ventricular filling begins
Pulmonary Circuit: (right side of heart) carries blood to lungs for gas exchange (oxygen) and back to the heart (drops off CO2)
Systemic Circuit: (left side of heart) supplies oxygenated blood to all tissues of the body and returns it to the heart.
Created by: mr209368