Physiology

Front 1

the ---and ----also has an ERP, however, the channels that remain closed during this phase are the L-type calcium channels

Back 1

The AP of the SA node

Front 2

Briefly, when AP’s are generated in the heart, there is a period in which the tissue will not respond to excitation. This is known as

Back 2

the absolute refractory period (ARP).

Front 3

The -----includes a very short time beyond the ARP in which stimulation produces a localized depolarization that does not propagate – in other words and AP will not propagate.

Back 3

effective refractory period (ERP)

Front 4

In what? does the effective refractory period starts at the upstroke of the action potential and ends in the first half of repolarization, and during this period the sodium channels undergo several conformational changes that do not allow the passage of Na+ ions.

Back 4

the Purkinje fiber

Front 5

During what period does stimulation of the heart cells occur, but it produces a weak action potential that does not propagate as fast.

Back 5

the relative refractory (RRP)

Front 6

why does a relative refractory period occurin teh heart

Back 6

cellsThis is because some of the sodium channels have recovered from the inactivated state and they can respond again to excitation

Front 7

The refractory period of a heart cell is what?

Back 7

a function of how rapidly sodium channels recover from inactivation.

Front 8

ARP=Absolute Refractory period =

Back 8

unexcitable to stimulation

Front 9

ERP = Effective Refractory period =

Back 9

brief period beyond ARP where stimulation produces weak depolarization that does not propagate

Front 10

RRP = Relative Refractory period =

Back 10

stimulation produces a weak PA that does propagate but more slowly than usual

Front 11

P wave =

Back 11

atrial dpolarization

Front 12

QRS wave =

Back 12

ventricle depolarization

Front 13

T wave =

Back 13

ventricle repolarization

Front 14

PR interval =

Back 14

time between depolarization of atria and the spread of the impulse across the atria and through the AV node, bundle of His, bundle branches and Purkinje fibers.

Front 15

QT interval =

Back 15

time from ventricle depolarization to repolarization, and measures ventricular activity.
ST segment = measures time between end of ventricular depolarization and beginning of ventricular repolarization

Front 16

Many factors can precipitate arrhythmias: name some

Back 16

• ischemia, as a result of a myocardial infarction,
• hypoxia, acidosis or alkalosis, electrolyte disturbance, excess catecholamines,
• drug toxicity,
• overstretching of the cardiac fibers, and scarred or diseased tissue.

Front 17

Although the factors are variable for precipitating arrhythmias, all arrhythmias result from alterations in:

Back 17

• impulse formation
• impulse conduction
• both impulse formation and conduction

Front 18

where can they originate

Back 18

• specialized conduction system: SA node, AV node, His bundle, Purkinje fibers
• atrial muscle
• ventricular muscle

Front 19

beating too rapidly – can be either a ? or ? or ? or ?

Back 19

sinus or ventricular tachycardia; atrial or ventricular premature depolarization; or atrial flutter or fibrillation

Front 20

The two main mechanisms that are primarily responsible for abnormal impulse formation that lead to arrhythmias are

Back 20

1) altered automaticity (i.e pacemaker rate):
• of the sinus node, of latent pacemakers within the specialized conduction pathway,
• abnormal automaticity in atrial or ventricular myocytes

2) Afterdepolarizations – also known as triggered activity

Front 21

Under certain situations when an action potential is generated it triggers

Back 21

an additional depolarization in the ventricle heart tissue, known as afterdepolarizations

Front 22

self-sustaining depolarizations result in

Back 22

extra heart beats (ectopic beats) or rapid arrhythmias

Front 23

There are two types of self sustaining depolarization, what are they

Back 23

Early after depolarizations – beginning of Phase 2/3
Late after dpolarizations- appear after repolarization of the an action potential

Front 24

Why do self sustaining depolarization happen?

Back 24

They are believed to be the result of abnormal calcium influx during or immediately after phase 3 repolarization.

Front 25

what does digitalis toxicity do to the heart

Back 25

digitalis toxicity, causes calcium overload inside the heart tissue, which results in a type of arrhythmia known as a digitalis-induced arrhythmia (bigeminy), where an extra beat of the heart occurs

Front 26

When impulse conduction in the heart tissue is altered it can result

Back 26

in arrhythmias

Front 27

?__ is when a propagating impulse is blocked when it encounters an electrically unexcitable region of the heart. what is an example

Back 27

• Conduction block – AV block

Front 28

In 1st degree heart block the impulse is
On the EKG this can be observed by

Back 28

prolonged beyond the normal delay at the AV-node. a prolonged P-R interval

Front 29

2nd degree heart block is where there is
On the EKG this is observed as

Back 29

intermittent failure of atrioventricular conduction.
some P-waves not follwed by a QRS complex

Front 30

In 3rd degree heart block there is .
on the EKG this can be observed by

Back 30

complete failure of impulses between the atria and the ventricles. There are many P waves not followed by QRS waves. The intermittent QRS waves that develop are result of latent pacemakers in the ventricles

Front 31

? is when there is re-excitation of an area of cardiac tissue by the same impulse occurs again and again. where can this occur

Back 31

Re-entry –

Hint 31

Re-entry of an impulse can occur in a small region near the AV node, or in large sections of the atria or ventricle walls, or because of an anatomical abnormality (Wolff-Parkinson-White syndrome) that creates an additional AV connection - “bypass tract.

Front 32

In type II, most beats are conducted with a constant PR interval, but occasionally atrial depolarization is not followed by ventricular depolarization (see Figure 6). Type II is pathological and indicates disease of the conduction system where

Back 32

distal to the AV node.

Front 33

The heart’s ability to increase its CO is dependent on four main factors:

Back 33

STROKE VOLUME CONTRACTILITY, AFTERLOAD, PRELOAD, HEART RATE (AUTONOMIC NEVEROUS SYSTEM AND HORMONES)