Final: Circulation 5

Question 1

how does depolarization travel through the heart (2)

Answer 1

• specialized conducting pathways
• directly between cardiomyocytes

Question 2

specialized conducting pathways (3)

Answer 2

• modified cardiomyocytes can spread action potential rapidly throughout the myocardium
• these cells are elongated, lack contractile proteins, and are pale
• they can undergo rhythmic depolarizations

Question 3

depolarization directly between cardiomyocytes (2)

Answer 3

• cardiomyocytes are electrically connected via gap junctions
• allows electrical signals to pass directly from cell to cell

Question 4

excitation-contraction coupling

Answer 4

• the coupling of the action potential and the cardiomyocyte contraction

Question 5

excitation-contraction coupling steps (8)

Answer 5

1. action potential enters from adjacent cell
2. voltage-gated Ca2+ channels open and Ca2+ enters the cell
3. entry of Ca2+ triggers release of LOTS of Ca2+ from sarcoplasmic reticulum
4. Ca2+ bind to troponin to initiate contraction
5. relaxation occurs when Ca2+ unbinds from troponin
6. Ca2+ is pumped back into sarcoplasmic reticulum for storage
7. Ca2+ is exchanged with Na+
8. Na+ gradient is maintained by Na+-K+-ATPase

Question 6

conducting pathway in mammalian heart (4)

Answer 6

1. SA node depolarizes, which spreads rapidly via the internodal pathway
2. AV node delays the signals, while the depolarization spreads through atria via gap junctions and causes atria to contract
3. depolarization spreads rapidly through bundles of His and Purkinje fibers
4. depolarization spreads upward through ventricle, causes ventricle to contract

Question 7

sequence of conduction pathway in mammalian heart (5)

Answer 7

1. SA node
2. internodal pathway
3. AV node
4. Bundle of His
5. purkinje fibers

Question 8

how do action potentials in cardiomyocytes differ from those in skeletal muscles

Answer 8

• cardiomyocyte APs are extended, containing a plateau phase during repolarization

Question 9

what is the purpose of the plateau phase (2)

Answer 9

• to prevent tetanus by removing possibility for sustained contraction during rapid APs
• allow the heart to refill with blood and relax

Question 10

cardiomyocyte AP plateau phase (2)

Answer 10

• extended repolarization that lasts as long as ventricular contraction
• caused by Ca2+ entry via L-shaped channel and temporary reduced K+ permeability

Question 11

electrocardiogram (ECG/EKG) (3)

Answer 11

• composite recording of action potentials in cardiac muscle
• contains the P wave, QRS complex, and T wave
• used for clinical diagnosis of issues with conducting system

Question 12

ECG: P wave

Answer 12

• atrial depolarization

Question 13

ECG: QRS complex

Answer 13

• ventricular depolarization

Question 14

ECG: T wave

Answer 14

• ventricular repolarization

Question 15

why is the T wave positive in the ECG if it represents a repolarization event

Answer 15

• it is negative; ECG tracks change in membrane potential, not direction of change

Question 16

heart sounds

Answer 16

• opening and closing of heart valves

Question 17

electrical and mechanical events in cardiac cycle

Answer 17

• electrical events initiate contractile (mechanical) events

Question 18

electrical and mechanical events in left heart cardiac cycle: P-wave (2)

Answer 18

• pressure is increasing in atrium and ventricle before P-wave
• P-wave initiates atrial contraction and atrial BP peaks

Question 19

electrical and mechanical events in left heart cardiac cycle: QRS-complex (3)

Answer 19

• QRS-complex initiates ventricular contraction and ventricular BP peaks
• ventricular BP first exceeds atrial BP and then aortic diastolic BP
• atrial relaxation occurs at same time

Question 20

electrical and mechanical events in left heart cardiac cycle: T-wave (2)

Answer 20

• T-wave initiates ventricular realization and ventricular BP falls below aortic BP, then below atrial BP
• energy stored in aorta is slowly released

Question 21

end-systolic volume (ESV)

Answer 21

• volume after contraction

Question 22

end-diastolic volume (EDV)

Answer 22

• volume before contraction

Question 23

cardiac stroke volume (SV) (2)

Answer 23

SV = EDV - ESV
- volume of blood pumped with each beat

Question 24

does a heartbeat fully empty the human ventricle

Answer 24

• no, but more can be expelled during exercise/more intense contraction

Question 25

why does aortic blood pressure decrease during diastole

Answer 25

- falls when heart is relaxed as blood is being transported away to the extremeties

Question 26

cardiac output (CO) (2)

Answer 26

- volume of blood pumped per unit time - CO = HR x SV

Question 27

heart rate (HR)

Answer 27

- rate of contraction (beats per minute)

Question 28

how can cardiac output be modified (2)

Answer 28

- regulating heart rate - regulating stroke volume

Question 29

cardiac output modulation: heart rate (2)

Answer 29

- modulated by autonomic nerves and adrenal medulla - activations of the parasympathetic (decreased HR) or the sympathetic system (increased HR)

Question 30

decreased HR

Answer 30

- bradycardia

Question 31

increased HR

Answer 31

- tachycardia

Question 32

cardiac output modulation: stroke volume (2)

Answer 32

- modulated by various nervous, hormonal, and physical factors - nervous and endocrine system an cause heart to contract more forcefully, pumping more blood each beat

Question 33

control of stroke volume: pathway (8)

Answer 33

1. binding of norepinephrine or epinephrine changes shape of beta1 adrenergic receptor, activating G protein 2. G protein activates adenylate cyclase 3. adenylate cyclase catalyzes ATP --> cAMP 4. cAMP activates protein kinase A 5. protein kinase phosphorylates L-type Ca2+, allowing Ca2+ to enter cell, stimulating contraction 6. protein kinase phosphorylates Ca2+ channel on sarcoplasmic reticulum, allowing Ca2+ to move to cytoplasm, which stimulates contraction 7. protein kinase phosphorylates myosin, stimulating contraction 8. protein kinase phosphorylates sarcoplasmic Ca2+ ATPase speeding the removal of Ca2+ from cytoplasm during relaxation, decreasing relaxation time

Question 34

how is stroke volume increased by the sympathetic nervous sytem

Answer 34

- more Ca2+ in cytoplasm increases contractile magnitude, promoting muscle contraction

Question 35

Frank-Starling effect (2)

Answer 35

- increased end-diastole volume results in more forceful contraction and increased SV - heart automatically compensates for increases in volume of blood returning to the heart (autoregulation) due to length-tension relationship for muscle

Question 36

control of stroke volume: sympathetic activity levels and the Frank-Starling effect

Answer 36

- levels of sympathetic activity shifts positions of cardiac muscle length-tension relationship

Question 37

Frank-Starling effect: increased sympathetic activity

Answer 37

- intensifies Frank-Starling effect, increasing the possible range of the stroke volume

Question 38

Frank-Starling effect: decreased sympathetic activity

Answer 38

- reduces Frank-Starling effect, reducing the possible range of the stroke volume

Question 39

what potentials are generated in the heart (5)

Answer 39

- SA node - atrium - AV node - bundle of His - ventricular cardiomyocyte

Question 40

what potentials display a plateau phase in the heart (3)

Answer 40

- atrium - bundle of His - ventricular cardiomyocyte

Question 41

what potentials don't have a plateau phase in the heart (2)

Answer 41

- SA node - AV node