Normal heart beat triggered by SA node at 70-80 beats per minute. 60-100 though is not unusual
11. What is ectopic focus? What can cause it?
Any spontaneous firing of the ventricles ( spontaneous heart beats ) other than from the sinoattrial node.
Stimuli such as hypoxia, electrolyte imbalance, caffeine, and nicotine can cause this.
12. What is nodel rhythm?
When ectopic focus takes over for controlling heart rhythm when SA or AV node is damaged.
Slow 40-50 BPM.
13. When is a pacemaker needed?
When SA and AV nodes are damaged and BPM drops to 20-40. This doesn't provide enough flow to the brain hence this is needed.
14. What is arrhytmeia?
Abnormal cardiac rhythm caused by a heart block ( failure of any part of the cardiac conduction system to transmit signals )
15. What causes heart blocks?
Disease and degeneration of conduction system fibers.
Bundle branch block - damage to bundle of his branches.
Total heart block - damage to AV node where ventricles don't receive signals.
16. What is the membrane potential of SA Node? What is this called?
The membrane potential is at -60 MV and drifts upwards at depolarization.
This is known as pacemaker potential
17. When does voltedgated calcium channels open and starts flowing in from extracellular fluid?
When membrane potential reaches -40 mV thus producing the rising phase of action potential until it slightly passes 0.
18. When does potassium channels open and start flowing out from the cell?
When membrane potential reaches 0 mV and starts repolization of the cell.
What's the steps of pacemaker potential?
1. At -60 mV, Na+ slowly flows into the cell. ( Rising slowly and depolarizing )
2. At -40 mV, pacemaker potential reaches its threshold. Voltage gated channels of calcium open and Ca2 flows in from extracellular fluid. Depolarization is occuring.
3. Depolarization occurs until peaking at 0 mV. K+ channels open and K+ leaves the cell starting repolization bringing it back down to 60 mV.
In the action potential of CARDIOCYTES, what is theri stavble resting potential? Why are they different from the cells of SA nodes?
Cardiocyte resting potential = -90 mV
Theyre different from SA nodes because they only deplarize when stimulated.
Describe the action potentials of cardiocytes.
1. From resting ( - 90 mV ) It is stimulated and action potential occurs. Voltage-gated sodium channels allows sodium to flow in thus depolarizing the cells. As it depolarizes, it opens more voltage-gated sodium channels.
2. As the cell depolarizes and peaks at +30 mV, the channels close quickly
3. At +30 mV slow calcium channels open allowing Ca2+ to come in the cell.
4. As Ca2+ flows into the cell depolarization is prolonged ( plateau ) and falls slightly because of K+ leakage.
5. At hhe end of pleateu, Calcium Channel close and Ca2+ is transported out of the cell. Potassium channels open and rapid Potassium outflow retruns the membrane down to -90 mV.
When is the P wave produced? What happens during the PQ segment?
When a a signal from the SA node spreads through DEPOLARIZING the atria.
As the atrium depolarizes, atrial systole begins known as the PQ segment.
What happens at the QRS complex? Why does it happen?
Q = A downward dip
R = A tall sharp peak
S= Final downward deflection.
Producerd when Signals from the AV node its the myocardium of ventricle and depolarizes the muscles.
What happens at the ST segment?
1. Ventricular systole begins.
2. Represents thetime durign whcih the ventricles contract and eject blood.
When does Atrial repolarization and diaostole occur?
Occurs during the QRS complex.
What happens at the T wave?
Repolarization of ventriclles before diastole.
What causes the lubb-dupp?
Lupp: Closing of the AV valve within the heart.
Dupp: Shutting of the aortic and pulmonary valve semilunar valves.
Why is it bad for people older than 30 to have a three rhythm heart beat?
Indicates an enlarged failing heart.
What are the phases of the cardiac cycle?
1. Ventricular Filling
2. Isovulumetric Contraction
3. Ventricular Ejection
4. Isovulumetrix Relxation
What happens at ventricular filling?
Ventricles expand and pressure drops below that of atria. AV valves open and blood flows into ventricles. This marks the P wave. This is where the amount of blood in the ventricle s at its highest ( End-diastolic volume )
What happens at isovolumetric contraction?
Atria repolarizes remaining in diastole for the rest of the cardiac cycle after pushing the blood into the ventricles. At this time, the ventricles depolarize and contract but do nto eject blood yet because pressure in the ventricles is still not higher than that of the aorta.
What happens at Ventricular Ejection?
When ventricular pressure exceeds that of the aorta, semilunar valves open pushing blood out of each ventricle rapidly.
What happens at isovolumetric relaxation?
Ventricular diastole occurs when the T wave ends and ventricles begin to expand.
What is cardiac output? How do you calculate this?
The amount of blood ejected by each ventricle in 1 minute.
CO = Heart Rate x Stroke Volume.
What is the normal heart rate at rest? What is the normal stroke volume at rest?
Heart Rate: 75 bpm
Stroke Volume: 70 mL/beat
What is tachychardia?
Heart rate above 100 bpm caused by stress, anxiety, drugs, heart disease etc.
What is bradychardia?
Slow heart rate below 60 bpm.
What are the autonomous nervous sytems for the heart?
Sympathetic and parasympathetic systems
How does the sympathetic autonomus nervosu sytem affect the heart?
Increases heart rate by promoting release of noepinephrine causing a second-messenger system in the cardiocytes and nodal cells.
How does the second-messenger sytem from the sympathetic autonomous nervous system affect heart rate?
Increase it via activating enzyme that opens Ca2 channels in the plasma membrane which accelerates the depolarization of the SA node ( hence speeding up the heart contraction )
How does the Parasympthetic autonomous nervous system affect the heart rate?
It slows down heart rate by promoting acetycholine to bind with receptors in the cells thus opening Potassium Gates and removing potassium form the cells hence repolarization happens slowing down the heart rate.
What do baroreceptors do?
They sense pressure in the aorta and internaal carotid arteries. When heart rate rises and raises blood pressure, the baro receptors find sense this and send signals to the medulla to lower the heart rate.
They can also sense drop in blood pressure hence the medulla tells the sympathetic center to increase heart rate.
What do chemoreceptors do?
Mostly important in respiratory control but can also slow down the heart so that the heart does not compete with the brain for limited oxygen supply.
How does einhephrien and norepinephrine affect heart rate?
Increases heart rate.
What effect does nicotien have on heart rate?
Increases heart rate by stimulating catecholamine secretion.
How does thyrodi hormone affect heart rate
Increases heart rate.
How does caffeine, chocoalte and tea affect heart rate?
Accelerates heart beat by inhibiting cAMp break down.
How does potassium affect heart rate?
Hyperkalemia = heart rate slows down because it inhibits caridocyte repolarization.
Hypokalemia = slows down because it makes membrane potential harder to stimualte because not enough potassium means the mebmrane potential is lower than normal.
How does calcium affect heart rate?
Hypercalcemia = causes slow heart rate
Hypocalcemia = increases heart rate.
What is preload? How does it affect stroke volume?
Amount of tension in the myocardium immediate before it begins to contract.
Increased preload increases stroke volume.
What is contractility? How does it affect stroke volume?
How the myocadrium conntracts for the given preload.
Increase in contractiltiy increases Stroke Volume
What are postiive inotropic agents?
Factors that increase contractility.
Negative inotropic agents oppose this.
Whats the difference between chronotropci and inotropci agents?
Chromnotropic influences heart rate.
Inotropic influences contraction strength.
What is afterload?
The sum of all forces ventricle must overcome before it can eject blood specifically the pressure in the aorta and pulmonary trunk.
The ventricels must have higher blood pressure to eject this.
How does exercise affect cardiac out put?
Increases it because it increase the heart rate to supply muscles with enough oxygen and blood.
How does exercise affect stroke volume?
Exercise causes hypertrophy of the ventricles which increaes their stroke volume.