The anatomy of the heart

Question 1

what type of heart do amphibians and reptiles have?

Answer 1

3-chambered heart

Question 2

what type of heart do mammals have?

Answer 2

4-chambered heart

Question 3

describe a 4-chambered heart

Answer 3

• Completely separated ventricles
• (Patients) left side is oxygenated blood and pump blood at a much higher pressure
  
  • Means birds and mammals can have a higher metabolic rate
  • Grow to a larger size
• (Patients) right side is deoxygenated blood and pump blood at a much lower pressure (as separate)
  
  • Facilitates good gas exchange (particularly in the lungs)

Question 4

what is the role of the pericardium?

Answer 4

mechanical protection for the heart and big vessels

Question 5

what is the length of a human heart?

Answer 5

approx. 15cm/6in

Question 6

what is the average mass of a human heart?

Answer 6

approx. 300g

Question 7

what is the average stroke volume of a human heart?

Answer 7

approx. 70ml

Question 8

roughly how many beats per year does the human heart complete?

Answer 8

approx. 38 million beats/year

Question 9

what is cardiac output (CO)?

Answer 9

CO is the amount of blood pumped by each ventricle in one minute

Question 10

what is the equation for cardiac output?

Answer 10

cardiac output = heart rate X stroke volume
(ml/min) (beats/min) (ml/beat)

Question 11

what is the stroke volume?

Answer 11

the amount of blood pumped out by a ventricle with each beat

Question 12

do larger animals have faster or slower heart rates?

Answer 12

slower

Question 13

why is the left ventricle thicker than the right ventricle?

Answer 13

it forces blood out against more resistance; the systemic circulation is much longer than the pulmonary circulation

Question 14

why is the atria thin?

Answer 14

ventricular filling is done by gravity, requiring little atrial effort

Question 15

what is the epicardium?

Answer 15

• outer layer of the heart
• visceral layer of serous pericardium

Question 16

what is the myocardium?

Answer 16

• middle layer of the heart
• the muscle

Question 17

what is the endocardium?

Answer 17

• innermost layer of the heart
• lines the chambers

Question 18

how many tricuspic and bicuspic valves does the heart have?

Answer 18

tricuspic: 3
bicuspic: 1

Question 19

what muscles are heart valves connected to? why?

Answer 19

• connected to papillary muscles via tendinous strings (chordae tendinae)
• papillary muscle contracts during systole thus preventing valves from inverting

Question 20

name the 2 heart sounds. describe them.

Answer 20

• S1: the closing of AV (Mitral and Tricuspid) valves at the start of ventricular systole
• S2: the closing of the semilunar (aortic and pulmonic) valves at the end of ventricular systole

Question 21

what is the length of sarcomere?

Answer 21

1.8-2.0µm

Question 22

what is the role of Ca2+ in heart mucle contraction?

Answer 22

• At rest, the proteins troponin and tropomyosin prevent actin and myosin from interacting with each other.
• Ca2+ binding to troponin causes conformational changes in tropomyosin that allow actin-myosin interaction.

Question 23

what are the 7 steps to the cardiac cycle?

Answer 23

1. atrial contraction
2. isovolumetric contraction
3. rapid ejection
4. reduced ejection
5. isovolumetric relaxation
6. rapid filling
7. reduced filling

Question 24

describe atrial contraction

Answer 24

• valves between atria and ventricles open
• semilunar valves closed

Question 25

describe isovolumetric contraction

Answer 25

• all valves closed
• first heart sound (S1)
• ventricular pressure rises rapidly without volume change

Question 26

describe rapid ejection

Answer 26

• blood flows rapidly from ventricles into arteries
• AV valves closed
• semilunar valves open

Question 27

describe reduced ejection

Answer 27

• ventricle repolarises
• tension on ventricle reduces, therefore rate of ejection falls
• blood flow results mainly from kinetic energy of blood

Question 28

describe isovolumetric relaxation

Answer 28

• all valves closed
• ventricular pressure decreases; rate determined by rate of muscle fiber relaxation
• end-systolic volume ~50 ml in left ventricle
• stroke volume was ~70 ml

Question 29

describe rapid filling

Answer 29

• AV valves open
• semilunar valves closed
• caused by ventricle relaxation

Question 30

describe reduced filling

Answer 30

• AV valves open
• semilunar valves closed
• ventricles are already considerably relaxed
• at the end of this phase, ventricle is ~90% filled

Question 31

what stages of the cardiac cycle are systole and which are diastole?

Answer 31

systole: 1 - 4
diastole: 5 - 7

Question 32

what are dyads?

Answer 32

The dyads are like orchestra conductors: They coordinate incoming electrical signals with release of calcium in the muscle, triggering contraction.

Question 33

explain exication-contraction coupling

Answer 33

• Action potential causes the Ca2+ concentration in cytosol of cardiac myocytes to increase from 0.1 mM to about 10 mM. Activates ATPase activity of actomyosin and initiates contraction.
• About 75% of the Ca2+ comes from the sarcoplasmic reticulum and about 25% from the extracellular space (through L-type Ca2+ channels)