Heart Physiology 2

Question 1

Define syncytium

Answer 1

One cellular mass formed by the fusion of smaller cells or nuclei division

Question 2

Structures attaching adjacent cardiac myocytes

Answer 2

Intercalated Discs

Question 3

Name the 2 types of membrane junctions found in intercalated discs

Answer 3

1) Desmosomes

2) Gap Junctions

Question 4

Where are action potentials in the heart initiated?

Answer 4

at the SA node (in right atrium by superior vena cava)

Question 5

Action potentials in the heart open intramembrane protein channels, allowing which ion to enter the myoplasm and trigger muscle contraction?

Answer 5

Calcium

Question 6

What is the approximate duration of a ventricular cardiac action potential?

Answer 6

~.25-.30 sec

(250-300 msec)

Question 7

What is the amplitude of a typical ventricular muscle cell action potential? What is the resting potential? What is the peak?

Answer 7

1) Amplitude ~110-120

2) Resting potential ~ -90mV

3) Peak Potential ~+20-30mV

Question 8

Label the following ventricular action potential diagram.

Answer 8

Question 9

Label this Wiggers Diagram; Draw your own

Answer 9

Question 10

What is typical left atrial pressure?

Answer 10

10-15 mmHg

Question 11

The P wave indicates what event?

Answer 11

Atrial Contraction

Question 12

What is peak left ventricular pressure during systole?

Answer 12

120 mmHg

Question 13

What is the nadir of left ventricular pressure during diastole?

Answer 13

0 mmHg

Question 14

What is peak aortic pressure during systole?

Answer 14

120 mmHg

Question 15

What is the nadir of aortic diastolic pressure?

Answer 15

80 mmHg

Question 16

When might you hear a split heart sound?

Answer 16

When 2 AV valves close at different times. Or when 2 semilunar valves close at different times.

Question 17

What is end-diastolic volume of the left ventricle?

Answer 17

~135mL

Question 18

What is end-systolic volume of the left ventricle?

Answer 18

~65 mL

Question 19

What is the source of heart sound 1?

Answer 19

Closing of Mitral and Tricuspid (AV) valves

Question 20

What is the source of heart sound 2?

Answer 20

Closing of aortic and pulmonary (semilunar) valves.

Question 21

Describe what an EKG is really measuring.

Answer 21

Measures extracellular electric potential AT BODY SURFACE induced by cardiac action potential that travels through body fluid and reaches the electrodes. Amplitude of actual EKG is only 1-2 mV while heart cell amplitude is ~120mV

Question 22

The T wave indicates what event?

Answer 22

Ventricular Repolarization

Question 23

The space between the P wave and Q wave indicates what process?

Answer 23

AV nodal delay

Question 24

The space between the S and T wave indicates what process?

Answer 24

Uniform depolarization accross ventricle - Ventricular Action Potential Plateau

Question 25

Describe systolic events.

Answer 25

**Systole begins with QRS action potential leading to contraction of ventricles. Mitral valve closes because of increased left ventricular pressure and isovolumetric contraction occurs until aortic valve opens and blood is ejected from the ventricle. Systole ends when the aortic valve opens.**

Question 26

Describe diastolic events.

Answer 26

**Diastole begins when aortic valve closes and isovlumetric relaxation occurs until mitral valve opens. The ventricles then fill because of a pressure differential and the contraction of the atria. Diastole ends when the mitral valve closes after a ventricular contraction begins. **

Question 27

What is the pacemaker of the heart?

Answer 27

**Sinoatrial node**

Question 28

What is the purpose of the Sodium/Calcium Exchange protein?

Answer 28

**Creates very large calcium concentration differential between inside and outside of cell**

Question 29

What is the resting potential of cardiac myocytes bothe in atria and ventricles?

Answer 29

**~-90mV**

Question 30

What are fast response action potentials?

Answer 30

**Ventricular/atrial/Purkinje fiber action potentials**

Question 31

What are slow-response action potentials?

Answer 31

**SA and AV node action potentials**

Question 32

What is the name of the abnormal bypass tract connecting the atria and ventricles parallel to the AV node?

Answer 32

**Bundle of Kent**

Question 33

Label this diagram

Answer 33

Question 34

Label this

Answer 34

Question 35

What are some causes of heart arrhythmia?

Answer 35

**1) SA node is too slow and pacemaker activity of AV node or Purkinje fibers occurs** **2) Presence of bypass tracts paralell with AV node** **3) Conduction block that re-routes action potential pathway** **4) Reentrant loop - self-sustaining electrical current in part of heart**