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Chpt 18Bu;a
Cardiovascular system
| Question | Answer |
|---|---|
| Depolarization of the heart is rhythmic and ? | Spontaneous |
| About 1% of cardiac cells have | automaticity— (are self-excitable) |
| Gap junctions ensure the heart contracts as a | unit |
| The heart has long absolute refractory period of | (250ms) |
| During cardiac muscle contraction depolarization opens voltage-gated fast Na+ channels in the | sarrcolemma |
| Reversal of membrane potential from | from –90 mV to +30 mV |
| Depolarization wave in T tubules causes the SR to release | Ca2+ |
| Ca2+ surge prolongs the | depolarization phase |
| Ca2+ influx triggers opening of | Ca2+-sensitive channels in the SR |
| The duration of the contractile phase is much greater in cardiac muscle than | skeletal muscle |
| Repolarization results from | inactivation of Ca2+ channels and opening of voltage-gated K+ channels |
| A network of noncontractile (autorhythmic) cells that initiate and distribute impulses to coordinate the depolarization and contraction of the heart | Intrinsic cardiac conduction system |
| Have unstable resting potentials (pacemaker potentials or prepotentials) due to open slow Na+ channels At threshold, Ca2+ channels open Explosive Ca2+ influx produces the rising phase of the action potential | Autorhythmic Cells |
| In the hearts sequence of excitation the Sinoatrial (SA) node (pacemaker) Generates impulses about how many times and does what ? | 75 times/minute (sinus rhythm) and depolarizes faster than any other part of the myocardium |
| In the hearts sequence of excitation the Atrioventricular (AV) node delays impulses approximately by and does what ? | 0.1 second and Depolarizes 50 times per minute in absence of SA node input |
| What is the only electrical connection between the atria and ventricles ? | Atrioventricular (AV) bundle |
| what are the two pathways in the interventricular septum that carry the impulses toward the apex of the heart | Right and left bundle branches |
| what complete the pathway into the apex and ventricular walls AV bundle and Purkinje fibers depolarize only 30 times per minute in absence of AV node input | Purkinje fibers |
| Defective SA node may result in | Ectopic focus: abnormal pacemaker takes over If AV node takes over, there will be a junctional rhythm (40–60 bpm) |
| Defective AV node may result in | Partial or total heart block Few or no impulses from SA node reach the ventricles |
| Heartbeat is modified by the | ANS |
| Cardiac centers are located in the | Medulla oblangata |
| Cardio acceleratory center innervates SA and AV nodes, heart muscle, and coronary arteries through | sympathetic neurons |
| Cardioinhibitory center inhibits SA and AV nodes through parasympathetic fibers in the | Vagus nerve |
| P wave | depolarization of SA node |
| QRS complex | ventricular depolarization |
| T wave | ventricular repolarization |
| Two sounds of the heart (lub-dub) associated with_______of heart valves | Closing |
| First sound occurs as | AV valves close and signifies beginning of systole( tricuspid & mitral) |
| Second sound occurs when | aortic & pulmonic valves close at the beginning of ventricular diastole. |
| all events associated with blood flow through the heart during one complete heartbeat is known as | Cardiac cycle |
| Systole | contraction |
| Diastole | Relaxation |
| What takes place in mid-to-late diastole during the phases of the cardiac cycle | ventricular filling |
| AV valves are open 80% of blood passively flows into ventricles Atrial systole occurs, delivering the remaining 20% | ventricular filling |
| volume of blood in each ventricle at the end of ventricular diastole (relaxation) is known as | (End diastolic volume EDV): |
| When the Atria is relax and ventricles begin to contract Rising ventricular pressure results in closing of AV valves Isovolumetric contraction phase (all valves are closed) this is known as | Ventricular systole |
| volume of blood remaining in each ventricle is known as | End systolic volume (ESV |
| The P wave represents depolarization of the | atria |
| The PR segment = | atrial systole |
| The QRS wave represents depolarization of the | ventricles |
| The ST segment = | ventricular systole |
| The T wave represents repolarization of the | ventricles |
| what is the volume of blood pumped by each ventricle in one minute known as | cardiac output |
| CO = heart rate (HR) x | stroke volume (SV) |
| HR = | = number of beats per minute |
| SV = | volume of blood pumped out by a ventricle with each beat |
| what is the degree of stretch of cardiac muscle cells before they contract (Frank-Starling law of the heart) known as | preload |
| contractile strength at a given muscle length, independent of muscle stretch and EDV | Contractility |
| agents increase contractility Increased Ca2+ influx due to sympathetic stimulation Hormones (thyroxine, glucagon, and epinephrine) | Positive inotropic |
| agents decrease contractility Acidosis Increased extracellular K+ Calcium channel blockers | Negative inotropic |
| pressure that must be overcome for ventricles to eject blood is known as | afterload |
| Positive chronotropic factors | increase heart rate |
| Negative chronotropic factors | decrease heart rate |
| Norepinephrine causes the pacemaker to fire more | rapidly and increases contractility fight or flight |
| Acetylcholine hyperpolarizes pacemaker cells by opening | K+ channels The heart at rest exhibits vagal tone (parasympathetic) |
| from adrenal medulla enhances heart rate and contractility | Epinephrine |
| increases heart rate and enhances the effects of norepinephrine and epinephrine | Thyroxine |
| Intra- and extracellular ion concentrations (e.g., Ca2+ and K+) must be maintained for | normal heart functions |
| abnormally fast heart rate (>100 bpm) | Tachycardia |
| heart rate slower. < 60 bpm May result in grossly inadequate blood circulation | Bradycardia |
| Progressive condition where the CO is so low that blood circulation is inadequate to meet tissue needs | Congestive Heart Failure (CHF) |
Created by:
jennysevere24
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