Cardio & Respiratory Wk 12 - Lesson 88

What are cardiomyocytes?

specialized muscle cells that form the myocardium of the heart

What is the cardiac conduction system?

group of specialized cardiac muscle cells that initiate and propagate electrical impulses to coordinate heartbeats

What is the sinoatrial node?

cluster of pacemaker cells located in the right atrium that initiates the electrical impulse for the heartbeat

What is the atrioventricular node?

cluster of cells located at the junction between the atria and the ventricles that delays the electrical impulse briefly before passing it on to the ventricles

What is the bundle of His?

specialized fibers that conduct the electrical impulse from the AV node to the ventricles

What are the perkinje fibers?

specialized conducting fibers that distribute the electrical impulse to the myocardium of the ventricles

What are pacemaker cells?

specialized cardiac cells with automaticity that generate electrical impulses at regular intervals to initiate heartbeats

What is syncytium?

coordinated contraction of cardiac muscle cells due to the propagation of electrical impulses through gap junctions

What do intercalated discs contain?

desmosomes and gap junctions

What is dromotropism?

rate of conduction of electrical impulses affects the timing and coordination of heartbeats

What is chronotropism?

heart rate or the speed at which the heart beats affects the frequency of cardiac contractions

What is inotropism?

force or strength of cardiac muscle contraction

What does positive inotropism mean?

increases contraction strength

What is bathmotropism?

excitability threshold of cardiac tissue

What does lower bathmotropism mean?

cells are more excitable and easier to depolarize

What is electromechanical coupling?

process by which an electrical stimulus leads to mechanical contraction of cardiomyocytes

Where is the sinoatrial node?

right atrium

3 multiple choice options

What is group I purkinje fibers?

partial penetration in primate and carnivores

What is group II purkinje fibers?

full penetration in pigs and other mammals

What is the function of the heart?

pump blood through the circulatory system

Which cell represent 99% of cardiomyocytes?

contractile phenotype

3 multiple choice options

What cell represents 1% of cardiomyocytes?

autorhythmic phenotype

3 multiple choice options

What is required during diastole that gap junctions help with?

synchronized relaxation of the heart

What is the structural unit of cardiomyocytes?

sarcomeres

What makes up the striations in the cardiac muscle?

light (I) band and dark (A) bands

How do autorhythmic cells differ from contractile structurally?

have few myofibrils or filaments needed for contraction

What regulates the function of the autorhythmic phenotype cells?

autonomic nervous system motor neuron fibers

What are the phases of the contractile phenotype?

phase 0-4

What is phase 0 of contractile?

rapid depolarization (Na influx)

What is phase 1 of contractile?

partial repolarization (slight efflux of K)

What is phase 2 of contractile?

plateau phase (influx Ca and efflux K; balance)

What is phase 3 of contractile?

repolarization (K efflux)

What is phase 4 of contractile?

resting membrane potential (K leak channels maintain)

What is important about the refractory period?

contractile phenotype has longer period than the skeletal muscle fibers

What are the phases of the autorhythmic phenotype?

phase 4, 0, 3

What is phase 4 of the autorhythmic phenotype?

unstable membrane potential, prepotentials (non-specifc Na and K channels open then transient Ca voltage channels open to reach the threshold)

What are the names for the non-specific Na and K channels?

hyperpolarization, unusual, or "funny"

What is phase 0 of autorhythmic phenotype?

depolarization (long lasting Ca voltage channels open and Ca influx)

What is phase 3 of autorhythmic phenotype?

repolarization (open K voltage channels for K efflux)

What acts as a calcium intracellular reservoir?

sarcoplasmic reticulum

What element does the heart require more of for contraction than skeletal muscle?

calcium

3 multiple choice options

Who found out that the heart requires more calcium?

Sidney Ringer in 1882

What is calcium-induced calcium release?

voltage-gated L-type calcium channel letting in small amounts of calcium and triggers release of Ca from the SR

How do the cardiomyocytes relax?

Calcium reaccumulates in the ST by the SERCA and Calcium is extruded by the Na and Ca antiporter and a sarcolemmal Ca pump

How does parasympathetic affect chronotropism?

lower heart rate and shows shallow pacemaker potential slope

How does sympathetic affect chronotropism?

higher heart rate and shows steeper pacemaker potential slope

What does the long action potential of the cardiomyocyte help prevent?

tetany

What is the second messenger of sympathetic inotropism?

cAMP

What breaks down cAMP?

phosphodiesterase (PDE3)

How does isoproterenol affect inotropism?

increases intracellular Ca and consequently a more forceful contraction

How does pimobendan affect inotropism?

higher inotropic effect

What does stretching of the heart do?

increases the force of contraction

What is the frank-starling law?

ability of the heart to increase its force of contraction when stretched, which happens with increased venous return, until it reaches its limit

What is the metabolism of cardiomyocytes?

uses energy in ATP and ATP is replenished by aerobic metabolism, including the oxidation of fats and carbohydrates

What humoral components control heart activity?

hormones, electrolytes, drugs

What filament uses ATP?

myosin

Where does the parasympathetic nerve stem from?

medulla oblongata

Where does the parasympathetic nerve innervate?

left and right atrium, SA and AV node

Where does the sympathetic nerve innervate?

left and right atrium, SA and AV node, left and right ventricle

How does the sympathetic nervous system affect the heart?

increase HR, speed of conduction, excitability, force of contraction

How does the parasympathetic nervous system affect the heart?

decrease HR, speed of conduction, excitability; limited affect on the contractility of the ventricle

Why does norepinephrine cause a steeper depolarization?

increases Na and Ca influx; decreases K efflux

Why does acetylcholine cause a flatter depolarization?

increases K efflux; decreases Ca influx

What causes larger stroke volume?

increased contractility

What causes a smaller stroke volume?

decreased contractility

What drug increases contractility?

pimobendan, isoproterenol

What drug decreases contractility?

propofol, propranolol

What does decreased contractility and smaller stroke volume result in?

heart failure: cardiac hypoxia, myocarditis, valve defects, toxic reactions, electrolye imbalance