Heart Anatomy PART 2 Cardiac functions Study Guide

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1

Conduction system

>MADE UP OF AUTORHYTHMIC CELLS: SPECIALIZED CARDIAC CELL THAT INITIATE AND DISTRIBUTE INPULSES

>ENSURES THAT THE HEART DEPOLARIZES IN AN ORDERLY FASHION.

>IMPULSES PASS THROUGH CARDIAC CELLS IN THE FOLLOWING ORDER: SINOATRIAL NODE -->ATRIOVENTRICULAR NODE, -->ATRIOVENTRICULAR BUNDLE, --> RIGHT AND LEFT BUNDLE BRANCHES, --> AND PURKINJE FIBERS

2

SINOATRIAL (SA) NODE

>MODIFIED MUSCLE FIBERS THAT ORIGINATE THE RHYTHMIC BEATING OF THE HEART
>LIES IN THE RIGHT ATRIUM NEAR THE ENTRY OF THE SUPERIOR VENA CAVA
>SPONTANEOUSLY DEPOLARIZES FROM 60-100 TIMES/MIN
>SENDS SIGNALS TO DEPOLARIZE THE RIGHT AND LEFT ATRIA --> CAUSES CONTRACTION OF THE ATRIA (DIASTOLE)->FILLS THE RIGHT AND LEFT VENTRICLES
>SUPPLIED BY RIGHT CORONORY ARTERY 50% OF TIME AND CIRCUMFLEX ARTERY OTHER 50% OF TIME

3

ATRIOVENTRICULAR (AV) NODE

> RECEIVES IMPULSES FROM THE ATRIA
> SENDS IMPULSES ALONG SPECIALIZED CONDUCTIONG MUSCLE FIBERS CALLED PURKINJE FIBERS
>DEPOLARIZE THE REGULAR MUSCLE CELLS OF THE VENTRICLES, LEADING TO VENTRICULAR CONTRACTION (SYSTOLE)
> DELAY AT THE AV NODE HELPS ENSURE THAT THERE IS ENOUGH TIME FOR VENTRICLES TO FILL
> RAPID CONDUCTION THROUGH PURKINJE FIBERS ENABLES VENTRICLES TO CONTRACT SIMULTANOUSLY
>RIGHT CORONARY ARTERY SUPPLIES AV NODE 90% OF TIME

4

PACE MAKER POTENTIAL

>CELLS HAVE AN UNSTABLE RESTING POTENTIAL THAT CONTINUOUSLY DEPOLARIZES.
>SA NODE IS THE NORMAL PACEMAKER
*IT DEPOLARIZES AT A FASTER RATE THAN REST OF THE CONDUCTION SYSTEM (60-100 BEATS/MIN)
>AV NODE IS THE PACEMAKER IN ABSENCE OF SA NODE
*SPONTANEOUSLY DEPOLARIZES AT A RATE 40-60 BEATS/MIN.
>VENTRICULES ARE PACEMAKER IN TOTAL ABSENCE OF CONDUCTION SYSTEM STIMULATION
*SPONTANEOUSLY DISCHARGES AT ABOUT 20-40 BEATS/MIN.
>SPONTANEOUS DISCHARGE OF THE AV NODE AND VENTRICULAR MUSCLES DOES NOT OCCUR BECAUSE OF CAPTURE OF THE RHYTHM BY THE SA NODE
>BACKUP MECHANISMS HELP ENSURE THE VENTRICLES WILL CONTINUE BEATING IN PRESENCE OF DEFECTS OF SA AND/OR AV NODAL DISCHARGES.

5

AUTONOMIC NERVOUS SYSTEM MODIFIES THE HEARTBEAT:

>SYMPATHETIC CENTER INCREASES RATE AND DEPTH OF THE HEARTBEAT
>PARASYMPATHETIC CENTER SLOWS THE HEARTBEAT

6

ELECTROCARDIOGRAPH

card image

MONITORS AND AMPLIFIES THE ELECTRICAL SIGNALS OF THE HEART AND RECORDS IT AS AN ELECTROCARDIOGRAM (ECG).