Chapter 20 Lecture 4

Question 1

Conduction System of Heart

Answer 1

Coordinates contraction of heart muscle.

Question 2

Autorhythmic Cells

Answer 2

Cells fire spontaneously, act as pacemaker and form conduction system for the heart

Question 3

SA node

Answer 3

cluster of cells in wall of Rt. Atria
begins heart activity that spreads to both atria
excitation spreads to AV node

Question 4

AV node

Answer 4

in atrial septum, transmits signal to bundle of His

Question 5

AV bundle of His

Answer 5

the connection between atria and ventricles

divides into bundle branches & purkinje fibers, large diameter fibers that conduct signals quickly

Question 6

Timing of Atrial & Ventricular Excitation

Answer 6

SA node setting pace since is the fastest
In 50 msec excitation spreads through both atria and down to AV node
100 msec delay at AV node due to smaller diameter fibers- allows atria to fully contract filling ventricles before ventricles contract
In 50 msec excitation spreads through both ventricles simultaneously

Question 7

Physiology of Contraction

Answer 7

Depolarization, plateau, repolarization

Question 8

Depolarization

Answer 8

Cardiac cell resting membrane potential is -90mv
excitation spreads through gap junctions
fast Na+ channels open for rapid depolarization

Question 9

Plateau Phase:

Answer 9

250 msec (only 1msec in neuron) 
slow Ca+2 channels open, let Ca +2 enter from outside cell and from storage in sarcoplasmic reticulum, while K+ channels close
Ca +2 binds to troponin to allow for actin-myosin cross-bridge formation & tension development

Question 10

Repolarization:

Answer 10

Ca+2 channels close and K+ channels open & -90mv is restored as potassium leaves the cell

Question 11

Refractory period:

Answer 11

very long so heart can fill

Question 12

action potential in cardiac muscle:

Answer 12

changes in cell membrane permeability

Question 13

EKG (Electrocardiogram)

Answer 13

Action potentials of all active cells can be detected and recorded

Question 14

P wave

Answer 14

atrial depolarization

Question 15

P to Q interval:

Answer 15

conduction time from atrial to ventricular excitation

Question 16

T wave

Answer 16

ventricular repolarization

Question 17

Cardiac Cycle:

At 75 beats/min, one cycle requires 0.8 sec

Answer 17

systole (contraction) and diastole (relaxation) of both atria, plus the systole and diastole of both ventricles

Question 18

End diastolic volume (EDV)

Answer 18

volume in ventricle at end of diastole, about 130ml

Question 19

End systolic volume (ESV)

Answer 19

volume in ventricle at end of systole, about 60ml

Question 20

Stroke volume (SV)

Answer 20

the volume ejected per beat from each ventricle, about 70ml

SV = EDV - ESV

Question 21

Phases of Cardiac Cycle:

Answer 21

Isovolumetric relaxation
Ventricular filling
Ventricular systole

Question 22

Isovolumetric:

Answer 22

brief period when volume in ventricles does not change– ventricles relax, pressure drops and AV valves open

Question 23

Ventricular filling

Answer 23

as blood flows from full atria
diastasis: as blood flows from atria in smaller volume
atrial systole pushes final 20-25 ml blood into ventricle

Question 24

Ventricular systole

Answer 24

isovolumetric contraction

ventricular ejection: as SL valves open and blood is ejected

Question 25

Fibrillation

Answer 25

erratic heartbeat, uncoordinated contractions.

Question 26

Atrial (AF, A-fib) =

Answer 26

interference with AV node  erratic, incomplete atrial contractions. Often secondary to other heart problem, and rarely life-threatening.

• Treatment: drug/electro-cardioconversion; anti-coagulants
• Symptoms: none, palpitations, fainting, nausea, chest pain; can lead to stroke and congestive heart failure.

Question 27

Ventricular fibrillation (VF, V-fib) =

Answer 27

erratic, incomplete ventricular contractions. Immediately life-threatening due to lack of somatic, pulmonary, and cardiac circulation; often secondary to other heart disease.

• Symptoms: sudden collapse; death often first “symptom.”
• Treatment: electric cardioconversion, then treat underlying issue

Question 28

Tachycardia:

Answer 28

rapid (especially ventricular) heartbeat.

• Symptoms: range from faintness, short-of-breath to sudden death, depending location and cause.
• Treatment: drug or electric cardioconversion, then treat underlying issue

Question 29

bradycardia:

Answer 29

slow heartbeat

Question 30

Blood pressure in aorta

Answer 30

is 120mm Hg

Question 31

Blood pressure in pulmonary trunk is

Answer 31

30mm Hg

Question 32

The volume of blood ejected from each ventricle is

Answer 32

70ml (stroke volume)

Question 33

To increase:

More blood/beat

Answer 33

Upper limit = size of ventricle and time allowed to fill.

Question 34

To increase:More beats/min

Answer 34

Upper limit = need to reinitiate beat (refractory period)

Question 35

1. Nervous System -Sensors:

Answer 35

: limbic system, baroreceptors, chemoreceptors, proprioreceptors. Feed into medulla’s cardiovascular center (medulla). Control through ANS.

Question 36

1. Nervous System - Sympathetic NS:

Answer 36

nerves connect with SA & AV nodes and myocardium. increases rate of autorhythmic SA firing and uptake of Ca++ ( contractility) by all muscle cells.

Question 37

1. Nervous System - Parasympathetic NS:

Answer 37

nerves that connect with SA & AV nodes and myocardium of atria. Decreases rate of autorhythmic firing with ACh.

Question 38

2. Endocrine System Control:

Answer 38

Adrenal medulla (responding to hypothalamus) releases epinephrine and norepinephrine = increase of autorhythmic rate and contractility.

Question 39

3. Cation Control:

Answer 39

Why is KCl included in lethal injection cocktails?
Increased K+ prevents action potential
Increased Na+ blocks Ca++ entry
Increased Ca++ boost contractility, rate

Question 40

4. Metabolic Control

Answer 40

Increased H+ (acidosis) or OH– decrease heart rate