Ch. 13/14 Day 2

Question 1

If pressure in the heart goes high enough, the valve can prolapse. How is this prevented?

Answer 1

Papillary muscles contract w/ increasing pressure, exerts force on chordae tendineae to prevent valves from going too far.

Question 2

Chordae tendineae are connected to the?

Answer 2

Papillary Muscle

Question 3

Anatomy of the heart

Answer 3

See diagram on Ch. 13 notes (p. 28-29)

Question 4

Atrioventricular (AV) Valves

Answer 4

Between atria and ventricles

Tricuspid valve on right side

Bicuspid valve, or mitral valve, on left side

Question 5

Semilunar Valves

Answer 5

Between ventricles and arteries

Pulmonary valve

Aortic valve

Question 6

What ensures the one-way flow of blood in the heart?

Answer 6

Valves

Question 7

Ventricular Contraction

Answer 7

AV valves closed

Semilunar valves open

Question 8

Ventricular Relaxation

Answer 8

AV valves open

Semilunar valves closed

Question 9

Heart

Answer 9

Pump generating driving pressure for blood flow through the circulation.

Pumping is periodic, i.e. cardiac activity characterized by repeated cycles of active pumping (systole) followed by resting (diastole).

Heart generates pressure when it contracts (systole), pumping blood into arteries [ventricular contraction].

Arteries maintain pressure by acting as an elastic pressure reservoir between cardiac contractions (i.e. during diastole) [ventricular relaxation].

Question 10

Pressure Changes during the cardiac cycle

Answer 10

1. Ventricles begin contraction, pressure rises, and AV valves close (lub); isovolumetric contraction
   2) Pressure builds, semilunar valves open, and blood is ejected into arteries
   3) Pressure in ventricles falls; semilunar valves close (dub); isovolumetric relaxation
   4) Pressure in ventricles falls below that of atria, and AV valve opens. Ventricles fill
   5) Atria contract, sending last of blood to ventricles

Question 11

Dicrotic Notch

Answer 11

Slight inflection in aortic pressure during isovolumetric relaxation

Question 12

EDV-ESV

Answer 12

1) EDV - ESV = SV
2) Ventricle does not eject all its volume - can be altered

EDV: end diastolic volume
ESV: end systolic volume
SV: stroke volume

Question 13

Stroke Volume (SV)

Answer 13

Overall work being done by heart; increases as EDV and ESV get farther apart over time

Question 14

Cardiac Muscle: Contractile Cells

Answer 14

Striated fibers organized into sarcomeres

Question 15

Cardiac Muscle: Autorhythmic (pacemaker) Cells

Answer 15

Signal for contraction

Smaller and fewer contractile fibers

No organized sarcomeres
–so no real function to contract; instead send electrical signals

Question 16

Cardiac Muscle: Myocardial Muscle Cells

Answer 16

Branched, have single nucleus, and are attached to each other by specialized junctions known as intercalated discs

Question 17

Electrical Conduction in Myocardial Cells

Answer 17

Autorhythmic cells spontaneously fire action potentials. Depolarizations of autorhythmic cells spread rapidly to adjacent contractile cells through gap junctions.

70 bpm

Question 18

Electrical Activity of the Heart

Answer 18

Automatically

Sinoatrial node (SA node) - “pacemaker”; located in R. Atrium

AV node and Purkinje fibers - secondary pacemakers; slower rate than the “sinus rhythm”

Question 19

Conduction System of the Heart

Answer 19

Action potentials spread via intercalated discs

SA node –> AV node (atrial contraction)

AV node (base of R. Atrium) and Bundle of His conduct stimulation to ventricles.

In Interventricular Septum, Bundle of His –> R. and L. Bundle Branches

Bundle Branches –> Purkinje fibers –> ventricular contraction

Question 20

Electrical Conduction: Sinoatrial (SA) Node

Answer 20

Sets the pace of the heartbeat at 70 bpm

AV node (50 bpm) and Purkinje fibers (25-40 bpm) can act as pacemakers under some conditions

Question 21

Electrical Conduction: Atrioventricular (AV) Node

Answer 21

Routes the direction of electrical signals so heart contracts from apex to base (i.e. from bottom –> top)

AV node delay due to slower conduction through nodal cells

If SA node not working properly, AV node takes over (treatment can fix this, such as pacemaker)

Question 22

How does cardiac muscle contraction differ from skeletal muscle contraction?

Answer 22

B/c some Ca2+ coming from cytoplasmic space

Question 23

Why does Tetany NOT occur in cardiac muscle?

Answer 23

Cardiac muscle fiber refractory period lasts almost as long as the entire muscle twitch

VS

Skeletal muscle fiber refractory period compared w/ duration of contraction

Question 24

Pacemaker and Action Potentials

Answer 24

Slow, spontaneous depolarization; aka “diastolic depolarization” - between heartbeats, inward I(Na+) triggered by hyperpolarization

At -40mV, voltage-gated Ca2+ channels open, triggering action potential and contraction

Repolarization occurs w/ opening of voltage-gated K+ channels

Question 25

Electrocardiogram (ECG)

Answer 25

Represents the summed electrical activity of the heart recorded from the surface of the body

Picks up movement of ions in body tissues in response to this activity

• -does not record action potentials, but results from waves of depolarization
• -does not record contraction or relaxation, but electrical events leading to contraction and relaxation

Question 26

ECG Waves

Answer 26

P wave: atrial depolarization

P-Q interval: atrial systole

QRS wave: ventricular depolarization

S-T segment: plateau phase, ventricular systole

T wave: ventricular repolarization

Question 27

ECG: Pressures and Heart Sounds

Answer 27

“Lub” occurs after QRS wave as the AV valves close

“Dub” occurs at the beginning of the T wave as the SL valves close