EKG (Smith) Week 4

Question 1

WHy are Gap Junctions important to Cardiac cells?

Answer 1

Gap junctions provide the ability to provide electrical connectivity between cells.

Question 2

Define Diastole/Systole

Answer 2

Systole: Heart Contraction Diastole: Part of cardiac cycle where heart refills with blood

Question 3

Describe the “Lub” & “Dub” sounds of the heart

Answer 3

“Lub” - Due to closure of AV valves (beginning of ventricular systole) “Dub” - Closing of semilunar valves (beginning of ventricular diastole)

Question 4

List the parts of the Pacemaker cell network:

Answer 4

1. SA node 2. AV node 3. Bundle of HIS 4. Bundle branches 5. Purkinje fiber This network ensures the heart beat is in rhytmic suncytium.

Question 5

List the steps of normal activation sequence of the heart

Answer 5

1. SA node (fastest conduction) 2. Atria 3. AV node (create delay) 4. His bundle 5. Bundle branches 6. Purkinje fibers (ensure simultaneous ventricular contraction) 7. Ventricles

Question 6

List the FIVE phases of the Cardiac AP

Answer 6

Phase 0: upstroke, rapid deplarization Phase 1: rapid depolarization following peak Phase 2: depolarized plateau Phase 3: rapid depolarization following the plateau Phase 4: period between max negativity -aka resting potential

Question 7

What is absolute refactory and relative refractory period?

Answer 7

Absolute: Cannot be stimulated to fire, coincides w/ systole Relative: after absolute, during which excitability recovers until it reaches normal value.

Question 8

Describe the ionic permeabilities in each phase of the cardiac AP

Answer 8

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Question 9

Excitation Contraction Coupling & Recovery

Answer 9

**Remember the strength of the cardiac muscle is DIRECTLY proportional to the intracelluar Ca+ concentration

The steps:

AP opens L-type slow Ca+ channels causing HUGE rise in the intracelluar free Ca+ (note: look at pic in lecture)

Question 10

Define Cardiac Output (CO)

Answer 10

The volume of blood pumped by the heart per unit time

CO = stroke volume x heart rate

Question 11

Define Total Peripheral Resistance

Answer 11

Sum of the total resistance in vasculature in the circulatory system

Question 12

Describe the baroreceptor & Bainbridge reflexes

Answer 12

Baroreceptor: corrects change in arterial pressue by INCREASING (HR)

Bainbridge: Responds to changes in blood volume by DECREASING the (HR)

Question 13

Define All ECG wave intervals

Answer 13

• P wave: atrial deplarization in respnse to SA node firing (precedes atrial contraction)-
• PR Interval: time foe electrical wavefron to move from atria to ventricales (slight delay from AV node)
• QRS Complex: vetricular deploraization, tirggers main pumping contractions
• ST Segment: approximate index of V AP plateu

T Wave: Ventricular Repolarization

Question 14

List order of ECG events and determine which steps ar visible on EKG

Answer 14

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Question 15

TRUE or FALSE- The SA node is the only electrical link between Atria and Ventricles

Answer 15

FALSE: The AV node is