Unit 5 - Cardiovascular System I
Define the absolute refractory and relative refractory periods of myocardial action potentials and when they occur.
Absolute Refractory: period during an action potential when a new action potential cannot be stimulated under any circumstances. This takes place from the beginning of the action potential until midway through repolarization (membrane potential reaches approximately -50 mV) and lasts about 250 msec. Relative Refractory: period during an action potential when a new action can be stimulated under specific conditions. This can takes place midway through repolarization until the end of repolarization (-50 mV to -90 mV) and just before relaxation phase.
Describe how the potassium channels are influenced by the parasympathetic nervous system.
Acetylcholine attaches to plasma membrane proteins, activating G-proteins and opening K+ channels.
Indicate the major driving forces of blood throughout the body.
1. Contraction of ventricles 2. Venous return 3. Elasticity of arteries - absorbs pressure from ejection phase and gradually returns it to arterial system to help maintain blood flow
Relate volume and pressure changes over the cardiac cycle and indicate: isovolumetric contraction, isovolumetric relaxation, ejection, rapid filling, atrial contraction.
1. Isovolumetric Contraction: ↑ to maximum volume ↑↑ Pressure 2. Ejection ↓ in volume ↑ followed by↓ in Pressure 3. Isovolumetric Relaxation ↓ to lowest volume low Pressure (no change) 4. Rapid Filling ↑ in volume low Pressure 5. Atrial Contraction ↑ in volume ↑ Pressure
State the proportion of blood flow to the ventricles that is due to atria and venous circulation.
25% due to the contraction of atria 75% due to venous return
Identify major vessels of the heart including: aorta, pulmonary trunk, pulmonary arteries, pulmonary veins, superior vena cava and inferior vena cava.
Aorta: large, elastic artery that originates from the left ventricle and distributes blood to smaller arteries throughout the body. Pulmonary trunk: carries blood from the right ventricle to the pulmonary arteries. Pulmonary arteries: the right and left pulmonary artery receives blood from the pulmonary trunk and distributes it to the right and left lung, respectively. Pulmonary veins: the right and left pulmonary vein will carry freshly oxygenated blood back the left atrium. Superior vena cava and inferior vena cava: two large veins that collect and return venous blood to the heart's right atrium. The superior vena cava receives blood from the upper half of the body, whereas, the inferior vena cava receives blood from the lower half of the body.
Discuss the importance of ECGs.
ECG is an important non-invasive procedure to assess cardiac function and identify possible cardiac pathologies.
Describe the path of an action potential through the conduction system.
Electrical activity is transmitted through the heart via specialized myocardial cells starting from the atria and moving through the ventricles. 1. action potential is spontaneously generated by the SA node 2. travels rapidly to the Bachmann's bundle causing contraction of the atrium 3. Transmitted to the atrioventricular node (AV node), where the conduction rate will slow down. (This will cause a delay in ventricular contraction, allowing the ventricles to fill with blood before contracting). 4. The action potential then passes through the Bundle of His and is conducted rapidly to the apex of the heart via the right and left bundle branches 5. Continues to Purkinje fibers within the ventricular wall. The action potential spreads from the inside of the heart towards the outside, causing ventricles to contract at the same time.
Define: end-diastolic volume, stroke volume, end-systolic volume, ejection fraction, isovolumetric contraction, isovolumetric relaxation.
End Diastolic Volume: volume of blood in the ventricles at the end of diastole (refilling). (after atrial contraction, before ventricular contraction) Stroke Volume: volume of blood pumped by one ventricle per heartbeat End-Systolic Volume: volume of blood that remain in the ventricles following ventricular contraction Ejection Fraction: volume of blood that is ejected by the left and right ventricle per heartbeat Isovolumetric Contraction: Period between contraction of the atria and beginning of ventricular contraction (when the ventricles are filled with blood) Isovolumetric Relaxation: Period where atria and ventricles are both relaxed prior to venous return (after ventricular contraction)
Describe the HCN channels and how they are influenced by the sympathetic nervous system.
HCN channels, or hyperpolarization activated cyclic nucleotide-gated channels, are opened by the presence of cAMP. Cathecholamines, released by the sympathethic nervous system, will cause the production of cAMP in the pacemaker cells by stimulating β1-adrenergic receptors, thus opening more HCN channels.
Describe the functional syncytium of the heart and indicate its importance in cardiac physiology.
Myocardial cells are electrically interconnected by gap junctions Allows rapid, coordinated contractions so the heart contracts as one unit
Describe the myocardial resting membrane potential, depolarization and repolarization.
Myocytes: RMP: -90mV Depolarization: -15mV i. opens Na+ Gated Channels, opening more Na+ channels, increasing potential to -15mV ii. Na+ channels quickly close, maintaining membrane potential at 200-300ms iii. K+ and Ca2+ channels open at the same time, causing simultaneous diffusion of K+ and Ca2+ INTO cell Repolarization: -90mV i. closure of Ca2+ channels ii. Opening of voltage-gated K+ channels ii. K+ out of cell
Describe the steps in a full cardiac cycle.
Systole 1. Isovolumetric contraction - Ventricles at full of blood, closing AV valve - Semilunar valves not quite pushed open 2. Ejection - Contraction of ventricles - Opening of semilunar valves DIASTOLE 3. Isovolumetric relaxation - Pressure transferred to the arteries - Ventricular pressure drops - Semilunar valves close 4. Rapid filling - Venous blood fills the atria - AV valve pushed open - Passive refilling 5. Atrial contraction - Contraction of Atria by SA Node - Pushed final vol of blood into ventricles
Describe the pacemaker of the mammalian heart.
The SA node, is located near the superior vena cava in the right atrium. The SA node will spontaneously generate and action potential once every 0.8 seconds.
Discuss how the autonomic nervous system can alter pacemaker potentials of the SA node.
The autonomic nervous system release epinephrine and norepinephrine; this increases the rate of depolarization by stimulating β1-adrenergic receptors and production of cAMP within the cells. This causes opening HCN channels open and influx of Na+ and allows the cell to reach threshold faster; this ultimately causes an increase in heart rate. Alternatively, the release of acetylcholine causes opening of K+ channels, increasing the amount of K+ leaving the pacemaker cell. This slows down depolarization since it takes longer for the cell to reach threshold; this ultimately causes a decrease in heart rate.
Discuss what produces the heart sounds and when over the cardiac cycle.
The lub-dub sounds that you hear with a stethoscope correspond to the closing of heart valves during one cardiac cycle. 'Lub': closing of AV valves (isovolumetric contraction) 'Dub': closing of semilunar valve (isovolumetric relaxation)
Describe how relaxation occurs after contraction in cardiomyocytes.
Relaxation of cardiomyocytes is achieved by removing calcium from the cytoplasm following contraction. This is achieved by 2 methods: 1) Ca2+ is transported to the extracellular fluid by Na+/Ca2+ exchange pumps 2) Ca2+ is transported back to sarcoplasmic reticulum via Ca2+/ATPase
Indicate RMP and threshold potentials of the sinoatrial node.
Resting Membrane Potential of SA node: -60 mV Threshold Potential of SA node: -40 mV
Describe the intrinsic rate of the sinoatrial (SA) and atrioventricular (AV) nodes and factors which can increase and decrease the rate.
SA Node: spontaneously generates AP every 0.8sec (60-100 bpm) AV Node: generates an AP also, but slower than SA node (40-50 bpm) Stimulation of sympathetic nervous system would increase the rate of AP generation; parasympathetic system decreases the rate
Identify tissues that are capable of automaticity in the heart.
SA node AV node Purkinje fibers
Identify anatomically: SA node, Bachmann's bundles, AV node, bundle of His, bundle branches, Purkinje fibers.
SA node: located in the upper quadrant of the right atrium, near the superior vena cava. Bachmann's bundles: conductive tissue that passes action potentials from the right to the left atria. AV node: located on the inferior portion of the interatrial septum. Bundle of His: conductive tissue located at the top of the interventricular septum. It then splits into right and left bundle branches that run down the interventricular septum. Bundle branches: fibers that run along the interventricular septum to the apex of the heart. Purkinje fibers: fibers within walls of ventricles. They continue from the right and left bundle branches and run through the right and left ventricle, respectively.
Describe the blood flow through the left and right side of the heart and associated vessels.
Vena Cava → R AV valve (tricuspid) → R ventricle → pulmonary valve (semi-lunar) → pulmonary trunk & arteries → lungs → pulmonary veins → L atrium → L AV valve (bicuspid/mitral) → L ventricle → aortic valve
Define: venous return, diastole, systole, end diastolic volume, end systolic volume.
Venous return: volume of blood returning to the heart Diastole: phase of relaxation Systole: phase of contraction End Diastolic Volume: volume of blood in the ventricles at the end of diastole (refilling). This is during the period following atrial contraction but prior to ventricular contraction. End Systolic Volume: volume of blood that remain in the ventricles following ventricular contraction
Discuss the role of the sarcoplasmic reticulum in myocardial excitation-contraction coupling.
90-98% of the Ca2+ needed for myocardial contraction originates from the sarcoplasmic reticulum. Used for calcium-induced-calcium-release
Discuss the functional significance of the gap junctions in myocardial cells.
Allows action potentials to rapidly spread across the entire heart; allowing synchronized contractions
Define ectopic pacemaker.
An ectopic pacemaker is a group of cells, other than the SA node, that is capable of spontaneously generating an action potential and act as a pacemaker. AV node and Purkinje fibers are ectopic pacemakers.
Identify chambers and areas of the heart including: atria, ventricles, auricles, anterior interventricular sulcus, interventricular septum, interatrial septum.
Atria: chambers that receive blood returning from venous circulation Ventricles: chambers that pumps blood to the arterial circulation Interventricular Septum: muscular wall that separates the left and right ventricle Interatrial septum: wall of muscle tissue that separates the left and right atrium
Define: automaticity, conductivity, rhythmicity, excitability, contractility.
Automaticity: self-generated or automatic Conductivity: ability to transmit electrical signal Rhythmicity: ability to spontaneously depolarize/repolarize in repetitive and stable method Excitability: ability to be excited when stimulated Contractility: ability to contract
Identify the channel and movement of ions which result in a pacemaker POTENTIAL of the SA node.
Channel: HCN ('funny channel') Ion Movement: diffusion of Na+ into cell; K+ out of cell (more diffusion of Na+ into cell because the electrogradient is greater)
Identify the channel(s) and movement of ions which results in the plateau phase of the myocardial action potential.
Channel: slow voltage gated Ca2+ channel (L-type); voltage gated K+ channels Ion Movement: slow diffusion of Ca2+ into cell; K+ out of cell
Identify the channel(s) and movement of ions which results in repolarization of the myocardial action potential.
Channel: voltage gated K+ channel Ion Movement: diffusion of K+ out of cell
Identify the channel and movement of ions which results in repolarization of the SA node.
Channel: voltage-gated K+ channels Ion Movement: diffusion of K+ ions out of cell
Identify the channel(s) and movement of ions which result in myocardial depolarization.
Channel: voltage-gated Na+ channel (fast Na+ channel) Ion Movement: fast diffusion of Na+ into cell
Identify the channel and movement of ions which results in DEPOLARIZATION of SA node.
Channel: voltage-gates Ca2+ channels (L-type) Ion Movement: diffusion of Ca2+ ions into cell
Describe myocardial excitation-contraction coupling.
Involves Ca2+ stimulated Ca2+ release "Puff" of Calcium from voltage-gated channels will stimulate calcium released from the sarcoplasmic reticulum will bind to troponin on the sarcomere fiber, triggering contraction of the cardiac muscle.
Identify the significance of the plateau phase of the myocardial action potential.
It allows a more sustained contraction of the atria, allowing for full expulsion of blood from heart chambers Prevents tetany
Identify major valves and valve components including: mitral, left and right atrioventricular, bicuspid, tricuspid, aortic valve, pulmonary valve, chordae tendineae, papillary muscle.
Left atrioventricular valve (mitral/dicuspid): prevents the backflow of blood from the left ventricle back to the left atrium. Right atrioventricular valve (tricuspid): prevents the backflow of blood from the right ventricle back to the right atrium. Aortic valve: one-way valve located in the opening of the aorta. The pressure from contraction of the left ventricle will force the aortic valve open. Following contraction, when the pressure is in the arteries, the valve will snap shut, preventing backflow of blood into the left ventricle. Pulmonary valve: one-way valve located in the opening of the pulmonary artery. The pressure from contraction of the right ventricle will force the pulmonary valve open. Following contraction, when the pressure is in the pulmonary arteries, the valve will snap shut, preventing backflow of blood into the right ventricle. Chordae tendineae: tendinous cords that attach AV valves to papillary muscles. Papillary muscle: muscles found within ventricles. These muscles are connected to the AV valves via chordae tendineae. Together, they ensure the AV valves remain closed during ventricular contraction to prevent backflow of blood into the atrium.
Correlate the P, QRS, and T wave to phases of the cardiac cycle.
P wave: depolarization/contraction of atria QRS wave: - Depolarization/contraction of ventricles. - Atrial repolarization takes place in the QRS wave. (We do not see a separate wave since it is masked by the contraction of ventricles. T wave: repolarization of ventricles
Identify the morphology of the P, QRS, and T waves.
P wave: small positive wave QRS wave: sharp upward wave, followed by a sharp downward wave T wave: small positive wave
Identify the PR and ST interval and indicate their significance to the cardiac cycle.
PR interval: represents the time it takes for the action potential to pass through the AV node (i.e. delay in ventricular contraction) ST interval: represents the time between ventricular depolarization and repolarization when the heart is in its relaxed state.
Describe the pulmonary and systemic circuits of the mammalian cardiovascular system.
Pulmonary Circulatory System: circuit that delivers deoxygenated blood to the lungs for gas exchange and returns oxygenated blood back to heart. Systemic Circulatory System: circuit that delivers oxygenated blood to all organ systems and body tissues for cellular respirations and returns deoxygenated blood to the heart.
Describe what makes the waveforms on an ECG.
The electrical impulse of the heart (NOT action potentials) Plotted against time to produce the waves on an ECG
