The Physiology of Cardiac Function

Question 1

What is the role of ATPase in Myosin?

Answer 1

Hydrolysis of ATP is necessary to allow actin / myosin cross-bridge formation

Question 2

Describe the structure of Actin

Answer 2

A long filament of Globular actin, forming two helices. Between the two helices are rod-shaped proteins called Tropomyosin. Attatched to tropomyosin is the Troponin regulatory complex

Question 3

What three units comprise the Troponin complex?

Answer 3

TnT
TnC
TnI

Question 4

Briefly describe what occurs during Excitation-Contraction-Coupling

Answer 4

A process where an action potential triggers a myocyte to contract

Question 5

Describe the structure of a Myosin molecule

Answer 5

A myosin molecule has a rod-like tail and two heads (ATPase). Hinge region between the head and tail

Question 6

What is the functional unit of a cardiac myocyte?

Answer 6

Sarcomere

Question 7

What are the two ways in which extracellular Ca2+ can enter a Cardiac myocyte?

Answer 7

• T tubules

- L-type Ca2+ channels

Question 8

Describe “Calcium-induced-calcium-release”

Answer 8

Whereby extracellular calcium is able to activate calcium release from intracellular Ca2+ stores

Question 9

Following muscular contraction, how is Ca2+ pumped out of the cardiac myocyte for relaxation (Lusitropy)

Answer 9

• Ca ATPase (SERCA)
• Na-Ca exchanger
• Phospholamban

Question 10

Upon the arrival of an action potential, what type of Calcium ion channels open?

Answer 10

L-type Ca2+ channels

Question 11

Cardiac glycosides inhibit which pump?

Answer 11

Na-K pump

Question 12

The Na-Ca exchange transports how many Na and Ca’s?

Answer 12

3 Na in

1 Ca out

Question 13

Define “dromotropy”?

Answer 13

Ionotropy (force) + Chronotropy (rate)

Question 14

In the heart, what does the Vagus nerve ennervate?

Answer 14

AVN and SAN

Question 15

Define “chronotropy”?

Answer 15

Heart rate

Question 16

Sympathetic nerves act via which NT, which receptor, to induce what effect on the cardiomyocyte?

Answer 16

Sympathetic nerves act on Noradrenaline, which act on B1 and B2 adrenergic receptors, to INCREASE chrono/iono/dromo/lusitropy

Question 17

Define “Ionotropy”

Answer 17

Muscular contraction force

Question 18

Parasympathetic (Vagus) nerves act via which NT, which receptor, to induce what effect on the cardiomyocyte?

Answer 18

Parasympathetic nerves act on Acetylcholine, which act on M2 muscarinic receptors, to DECREASE chrono/iono/dromo/lusitropy

Question 19

Describe the 3 phases of the SAN Action Potential

Answer 19

403

Phase 4:

• Pacemaker Na2+ influx
• Ca2+ channels recover from inactivation
• Pumps restore ion gradients

Phase 0:
Ca2+ influx

Phase 3:
Ca2+ channels inactivate
K+ efflux delayed

Question 20

Describe the 5 phases of the Ventricular Action Potential

Answer 20

40123(4)

Phase 4:

• Na+ and Ca+ channels recover from inactivation
• Pumps restore ion gradients

Phase 0:
- Na+ influx

Phase 1:

• Na+ channels inactivate
• Fast K+ efflux

Phase 2:
- Ca2+ influx

Phase 3:
- Ca2+ channels inactivate
Delayed K+ efflux

Question 21

Describe the sequence for the Conductive Pathway through the Heart

Answer 21

SAN
AVN
Bundle of His
Bundle branches
Purkinje Fibres

Question 22

What is ESV?

Answer 22

End Systolic Volume, volume of blood remaining if the ventricles at the end of a contraction = 65 mL

Question 23

How long is the sub-stages for Atrial Systole, Ventricular Systole and Diastole?

Answer 23

Atrial Systole: 0.1 s
Ventricular Systole: 0.3 s
Diastole: 0.4 s

Question 24

What is EDV?

Answer 24

End Diastolic Volume, maximum amount of blood in ventricles at the end of ventricular relaxation = 135 mL

Question 25

Define “stroke volume”

Answer 25

Stroke volume (SV) is the volume of blood pumped from the left ventricle per beat

Question 26

What is the equation for Cardiac Output (CO)?

Answer 26

CO = HR x SV

HR = Heart rate
SV = Stroke Volume

Question 27

How can you calculate Stroke Volume (SV)?

Answer 27

Stroke Volume = EDV - ESV`

Question 28

What is the Frank-Starling relationship?

Answer 28

An increase in EDV causes stroke volume to increase