How Is Cardiac Function Controlled?

Question 1

Define pulmonary circulation.

Answer 1

• heart -> lungs -> heart.
• short loop.
• low pressure, low resistance.
• re-oxygenates the blood.

Question 2

Define systemic circulation.

Answer 2

• heart -> all other organs -> heart.
• long loop.
• high pressure, high resistance.
• provides oxygenated blood to body.

Question 3

What does the mediastinum contain?

Answer 3

• heart.
• trachea.
• esophagus.
• thymus.
• blood vessels and nerves.

Question 4

What are the coverings of the heart?

Answer 4

• fibrous pericardium.

- serous pericardium.

Question 5

What is the function of fibrous pericardium?

Answer 5

For anchorage and protection.

Question 6

What are the types of serous pericardium?

Answer 6

• parietal layer (adheres to fibrous pericardium).
• visceral layer (outer layer of heart).
• pericardial cavity (between layers).

Question 7

What are the wall layers of the heart?

Answer 7

• epicardium (visceral): smooth outer surface of heart.
• myocardium (cardiac muscle): muscle contraction.
• endocardium (lines chambers, cover valves): simple squamous cells-extends into blood vessels.

Question 8

Explain the steps of heart depolarisation.

Answer 8

SA nose -> atrial muscle -> AV node (delay) -> atrioventricular bundle -> R and L bundle branches -> purkinje fibres -> ventricular muscle.

Question 9

Define cardiac output.

Answer 9

• The volume of blood ejected per ventricle per minute.
• a measure of heart performance.
• CO= HR x SV
• altered by factors which change HR and SV.

Question 10

What is cardiac reserve.

Answer 10

• The difference between CO at rest and the maximum CO a person can achieve.
• the higher the CO reserve the greater the capacity for undertaking aerobic exercise.

Question 11

What are the 3 factors that affect stroke volume.

Answer 11

1. Preload (intrinsic).
2. Contractility (extrinsic).
3. Afterload.

Question 12

Anything that affects HR will also affect CO- but doesn’t change…

Answer 12

-SV.

Question 13

Define preload.

Answer 13

• the ‘force’ or ‘load’ on ventricular muscle just prior to contraction.
• determined by the end diastolic volume (EDV).

Question 14

What is stirlings law of the heart.

Answer 14

The greater the filling of the ventricles the greater is the emptying.

• as EDV increases so does SV.
• if EDV is decreased, so is SV.
• this is intrinsic control of SV.

Question 15

What are the factors affecting venous return.

Answer 15

• blood volume.
• central venous pressure/right atrial pressure.
• venous tone and the capacity of veins to hold blood.
• skeletal muscle pump.
• respiratory pump.

Question 16

What does contractility refer to?

Answer 16

Inotropic state.

Question 17

What influence does calcium have on contractility.

Answer 17

• increased calcium increases contractility.
• decreased calcium decreases contractility.
• this is extrinsic control of SV.

Question 18

What is afterload.

Answer 18

• The force against which the ventricles eject blood.
• each ventricle must develop enough force or wall tension to exceed this pressure in order to eject blood into these arteries.

Question 19

What electrical and mechanical event happens during the P wave, and what happens to the valves.

Answer 19

• electrical event: atrial depolarisation.
• mechanical event: atrial systole.
• AV valves: open.
• SV valves: closed.

Question 20

What electrical and mechanical event happens during the P-Q interval, and what happens to the valves.

Answer 20

• electrical event: completes atrial depolarisation.
• mechanical event: atrial systole (completed).
• AV valves: open.
• SL valves: closed.

Question 21

What electrical and mechanical event happens during the QRS complex, and what happens to the valves.

Answer 21

• electrical event: start ventricular depolarisation.
• mechanical event: start ventricular systole (ISOVOLUMETRIC VENTRICULAR CONTRACTION).
• AV valves: closed.
• SL valves: closed.

Question 22

What electrical and mechanical event happens during the S-T interval, and what happens to the valves.

Answer 22

• electrical event: completes ventricular depolarisation.
• mechanical event: ventricular systole (completion); ventricular ejection.
• AV valves: closed.
• SL valves: open.

Question 23

What electrical and mechanical event happens during the T wave, and what happens to the valves.

Answer 23

• electrical event: ventricular repolarisation.
• mechanical event: start ventricular diastole (ISOVOLUMETRIC VENTRICULAR RELAXATION).
• AV valves: closed.
• SL valves: closed.

Question 24

What electrical and mechanical event happens during the T wave- P wave, and what happens to the valves.

Answer 24

• electrical event: no events.
• mechanical event: atrial and ventricular diastole.
• AV valves: open.
• SL valves: closed.