Lecture 16

Question 2

What is the cardiac cycle?

Answer 2

Period from atrial contraction to ventricular relaxation. Includes systole (contraction) and diastole (relaxation).

Question 3

Define systole.

Answer 3

Period of heart contraction pumping blood into circulation.

Question 4

Define diastole.

Answer 4

Period of relaxation where chambers fill with blood.

Question 5

What does the P wave represent?

Answer 5

Atrial depolarization; atria begin contracting ~25 ms after it begins.

Question 6

What does the QRS complex represent?

Answer 6

Ventricular depolarization; ventricles begin to contract at the peak of the R wave.

Question 7

What does the T wave represent?

Answer 7

Ventricular repolarization; atrial repolarization is masked by QRS.

Question 8

What is the PR interval?

Answer 8

Time from start of atrial depolarization to start of QRS complex.

Question 9

What can lengthen the QT interval?

Answer 9

Myocardial damage, ischemia, conduction impairments.

Question 10

List the 5 mechanical events of the cardiac cycle.

Answer 10

1. Late diastole: chambers relaxed, passive filling. 2. Atrial systole: atrial contraction adds final blood. 3. Isovolumic contraction: AV valves close, no ejection. 4. Ventricular ejection: semilunar valves open. 5. Isovolumic relaxation: semilunar valves close.

Question 11

What drives blood movement during diastole?

Answer 11

Blood flows from higher to lower pressure; veins → atria → ventricles.

Question 12

How much ventricular filling occurs before atrial contraction?

Answer 12

70–80%. Atrial systole adds remaining 20–30%.

Question 13

What happens during isovolumetric contraction?

Answer 13

Ventricle pressure rises, AV valves close, semilunar valves still closed.

Question 14

What happens during ventricular ejection?

Answer 14

Ventricular pressure exceeds aortic/pulmonary pressure, semilunar valves open, blood ejected.

Question 15

Define EDV.

Answer 15

End-diastolic volume: ~130 mL in a resting adult.

Question 16

Define ESV.

Answer 16

End-systolic volume: ~50–60 mL.

Question 17

Define stroke volume.

Answer 17

SV = EDV – ESV; normally 70–80 mL.

Question 18

What is S1?

Answer 18

Sound of AV valves closing (“lub”).

Question 19

What is S2?

Answer 19

Sound of semilunar valves closing (“dub”).

Question 20

Systolic BP during auscultation corresponds to what?

Answer 20

Onset of tapping sounds.

Question 21

Diastolic BP during auscultation corresponds to what?

Answer 21

Disappearance of sounds.

Question 22

What is cardiac output?

Answer 22

CO = SV × HR; blood ejected per minute.

Question 23

Three major factors affecting stroke volume?

Answer 23

Preload, contractility, afterload.

Question 24

Define preload.

Answer 24

Degree of ventricular stretch before contraction (related to EDV).

Question 25

Frank-Starling Law?

Answer 25

Greater stretch → stronger contraction → increased SV.

Question 26

Define contractility.

Answer 26

Forcefulness of ventricular contraction unrelated to fiber length.

Question 27

Define afterload.

Answer 27

Pressure that must be overcome to eject blood (≈80 mmHg aorta; 20 mmHg pulmonary trunk).

Question 28

Two major regulators of heart rate?

Answer 28

Autonomic nervous system and endocrine system.

Question 29

Parasympathetic effect on HR?

Answer 29

ACh decreases HR by lengthening repolarization.

Question 30

Sympathetic effect on HR?

Answer 30

NE increases HR by shortening repolarization.

Question 31

Hormonal influences on HR?

Answer 31

Epinephrine and thyroid hormones increase HR; high K+ decreases HR.

Question 32

How does NE/Epi increase contractility?

Answer 32

Via β1 receptors → increased Ca2+ entry, faster Ca2+ removal → stronger, shorter contractions.

Question 33

What increases venous return?

Answer 33

Skeletal muscle pump, respiratory pump, venous constriction.

Question 34

How does exercise affect HR?

Answer 34

HR increases linearly with intensity until max (≈220-age).

Question 35

How does exercise affect SV?

Answer 35

Initially increases from Frank-Starling; plateaus at moderate intensity; may decrease at high HR.

Question 36

How does exercise affect CO?

Answer 36

CO increases with intensity; at high intensities mainly HR-driven.