Physiology 3

Question 1

What mechanism allows cardiac muscle shortening?

Answer 1

Sliding filament mechanism

Actin filaments slide along adjacent myosin filaments by cycling of cross-bridges with myosin

Question 2

What occurs to the Z lines during muscle contraction?

Answer 2

Z lines come closer together

Question 3

What is the role of Ca2+ ions in muscle contraction?

Answer 3

Ca2+ ions enable actin-myosin interaction

Question 4

What happens during excitation-contraction coupling?

Answer 4

Cells depolarize and L-type Ca channels open

Question 5

What percentage of Ca2+ ions that enter the cell directly causes contraction?

Answer 5

25%

Question 6

What is the process called that triggers the release of Ca2+ from the sarcoplasmic reticulum?

Answer 6

Calcium-induced calcium release (CICR)

Question 7

What is the function of troponin C in muscle contraction?

Answer 7

Binds to Ca2+ ions

Question 8

How does tropomyosin change during muscle contraction?

Answer 8

Moves to allow actin-myosin interaction

Question 9

What are the three mechanisms employed to reduce intracellular Ca2+ after contraction?

Answer 9

• SR ATP-dependent Ca pump (SERCA)
• Sodium-calcium (Na+-Ca2+) exchange pump
• Cell membrane ATP-dependent Ca pump

Question 10

What regulates the activity of the SR ATP-dependent Ca pump (SERCA)?

Answer 10

Phospholamban (PLN)

Question 11

What is the role of the Na+-Ca2+ exchange pump?

Answer 11

Extrudes Ca2+ out of the cell powered by the Na+ gradient

Question 12

What is Starling’s Law of the heart?

Answer 12

The heart increases stroke volume in response to increased end-diastolic volume (EDV)

Question 13

What effect does sympathetic stimulation have on cardiac muscle?

Answer 13

• Increases active tension
• Increases rate of tension development
• Increases rate of relaxation

Question 14

What is the positive inotropic effect?

Answer 14

Increased contractility of the heart

Question 15

What agents have a positive inotropic effect?

Answer 15

• Noradrenaline
• Adrenaline
• Digoxin

Question 16

What agents have a negative inotropic effect?

Answer 16

• Hypoxia
• Sepsis
• Calcium channel blockers
• Beta-adrenergic blockers

Question 17

What is the consequence of an overly dilated heart?

Answer 17

Reduced ability to produce active tension

Question 18

What does an increase in contractility shift on the Starling curve?

Answer 18

Shifts to a higher Starling curve

Question 19

What happens to cardiac output during acute cardiac failure?

Answer 19

Decreased cardiac output, increased end-diastolic volume

Question 20

What compensatory mechanism is activated in acute cardiac failure?

Answer 20

Activation of the renin-angiotensin-aldosterone system

Question 21

What is the role of the ryanodine receptor (RyR)?

Answer 21

Facilitates Ca2+ release from the sarcoplasmic reticulum

Question 22

What is the lusitropic effect?

Answer 22

Phosphorylation of PLN promotes the rate of relaxation

Question 23

What does increased intracellular Ca2+ concentration cause?

Answer 23

Increased force of contraction

Question 24

What does the sliding filament mechanism involve?

Answer 24

Cross-bridges cycling between actin and myosin

Question 25

What regulates SERCA activity?

Answer 25

Phospholamban (PLN) inhibits Ca2+ uptake by the SR when in its dephosphorylated state ## Footnote PLN is a regulatory protein that plays a crucial role in calcium handling in cardiac muscle cells.

Question 26

What are the main mechanisms for cardiac muscle relaxation?

Answer 26

The majority of cytoplasmic Ca2+ is pumped back into the SR by SERCA, extruded through the Na+-Ca2+ exchanger, and a small amount is pumped out by the Ca2+ pump (Ca-ATPase) ## Footnote These mechanisms are essential for returning the heart to a relaxed state after contraction.

Question 27

What effect does sympathetic nervous system (SNS) stimulation have on cardiac muscle?

Answer 27

Increases active tension, rate of tension development, and rate of relaxation ## Footnote This is crucial for enhancing cardiac performance during increased physiological demands.

Question 28

What is the role of beta-adrenergic stimulation in cardiac contraction?

Answer 28

It increases cAMP concentration, activates protein kinase A (PKA), phosphorylates calcium channels, and enhances Ca2+ entry during depolarization ## Footnote This leads to a positive inotropic effect, increasing the force of contraction.

Question 29

What is the lusitropic effect in relation to cardiac muscle relaxation?

Answer 29

Phosphorylation of PLN promotes the rate of relaxation by reducing PLN's inhibition of SERCA2 ## Footnote This enhances calcium uptake into the SR, facilitating quicker relaxation.

Question 30

What does Starling's Law of the heart state?

Answer 30

The heart's stroke volume increases in response to increased left ventricular end-diastolic volume (LVEDV) ## Footnote This law describes the relationship between ventricular filling and stroke volume.

Question 31

What happens when cardiac muscle is overstretched?

Answer 31

Its ability to produce active tension is reduced ## Footnote An overly dilated heart is less effective as a pump.

Question 32

What defines positive inotropic agents?

Answer 32

Agents that increase contractility, such as noradrenaline, adrenaline, and digoxin ## Footnote These agents enhance calcium influx and uptake by the SR.

Question 33

What are negative inotropic agents?

Answer 33

Hypoxia, sepsis, calcium channel blockers, and beta-adrenergic blockers ## Footnote These agents decrease contractility and can impair cardiac function.

Question 34

What occurs in acute cardiac failure following myocardial infarction?

Answer 34

Cardiac output decreases, end-diastolic volume increases, and right atrial pressure rises ## Footnote This condition is characterized by a significant reduction in heart function.

Question 35

What compensatory mechanism can restore cardiac output in acute cardiac failure?

Answer 35

Activation of the renin-angiotensin-aldosterone system increases plasma volume ## Footnote This helps to increase right atrial pressure and cardiac output back to normal.

Question 36

What is the relationship between myocardial ischemia and cardiac function?

Answer 36

Decreased contractile mass, decreased left ventricular function, and decreased mean arterial pressure (MAP) ## Footnote This creates a vicious cycle that can lead to severe outcomes, including death.

Question 37

Fill in the blank: The ability of cardiac muscle to increase its contractile force with a slight increase in length is known as _______.

Answer 37

Starling's Law

Question 38

True or False: Increased contractility shifts the Starling curve higher, resulting in a higher stroke volume for the same end-diastolic volume.

Answer 38

True ## Footnote This reflects the heart's improved ability to pump more effectively.

Question 39

What is the consequence of decreased contractility on the Starling curve?

Answer 39

It shifts to a lower Starling curve ## Footnote This indicates a reduced stroke volume for any given end-diastolic volume.

Question 40

What are the six key concepts related to cardiac contraction mentioned?

Answer 40

* Sliding filaments - crossbridges * Calcium - CICR – SERCA * Sympathetic effects * Contractility - inotropy - “a better pump” * Length - tension Starling’s Law * Adaptability / compensation