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Chpt 18Bu;a

Cardiovascular system

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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