Week 25 / Circulatory System 3

Question 1

What is refractoriness in cardiac cells?

Answer 1

Refractoriness is the inability of even a strong stimulus to elicit an action potential in cardiac cells for some time after a previously elicited action potential.

Question 2

What does refractoriness give rise to? [2]

Answer 2

It gives rise to the
absolute/effective refractory period (ARP/ERP)
and the
relative refractory period (RRP).

Question 3

Question: What is the physiological significance of refractoriness in cardiac cells? [2]

Answer 3

Answer: It protects against premature excitation and tetany.

Question 4

Question: How does the refractory period differ between fast and slow response cells?

Answer 4

Answer:

Fast response cells: Faster recovery of excitability.
Slow response cells: Slower recovery of excitability.

Question 5

Question: What is the clinical implication of variations refractoriness in cardiac cells?

Answer 5

Answer: Variations in refractory period durations can increase the risk of conduction block.

Question 6

Question: What is automaticity in cardiac cells?

Answer 6

Answer: Automaticity is the ability of some cardiac cells to initiate or fire action potentials spontaneously.

Question 6

Question: What is another term for automaticity?

Answer 6

Answer: Automaticity is also referred to as pacemaker activity.

Question 7

Question: Which cardiac cells exhibit normal automaticity? [3]

Answer 7

Answer:

Sinoatrial (SA) node
Atrioventricular (AV) node
Specialized conducting tissue, such as the His-Purkinje system

Question 8

Question: What is the difference between primary and latent pacemakers?

Answer 8

Answer:

Primary pacemakers: Dominant pacemaker cells (e.g., SA node).
Latent (subsidiary) pacemakers: Backup pacemaker cells, such as those in the AV node or His-Purkinje system.

Question 9

Question: What underlies the basis of automaticity in pacemaker cells?

Answer 9

Answer: Automaticity is based on the “funny” current (I𝑓f) and spontaneous phase 4 depolarization.

Question 10

Question: How is automaticity controlled? [2]

Answer 10

Answer: Automaticity is regulated by intrinsic factors (e.g., ion channel dynamics) and extrinsic factors (e.g., autonomic nervous system).

Question 11

Question: How does the heart beat maintain its rhythmic beating?

[how does it beat ?
how is the beat triggered?
]

Answer 11

Answer: The heart beats spontaneously and rhythmically throughout life, triggered by the spread of action potentials across muscle cell membranes.

Question 12

Question: How are action potentials initiated and conducted in the heart?
[what fires the action potentials?]

Answer 12

Answer: Action potentials are cyclically initiated and conducted in an orderly sequence by electrical or autorhythmic cells.

Question 13

Question: What is the natural sequence of excitation in the heart?

Answer 13

Answer:

SA node
Atria
AV node
Bundle of His
Purkinje fibers
Ventricles

Question 14

Question: What is the purpose of the AV conduction delay?

Answer 14

Answer: The AV conduction delay allows the ventricles to relax while the atria are contracting, ensuring efficient blood flow and filling of the ventricles.

Question 15

Question: What generates the electrical currents detected in an ECG?

Answer 15

Answer: Electrical currents are generated by cardiac muscle during depolarization and repolarization.

Question 16

Question: How are these electrical currents detected and recorded?

Answer 16

Answer: The currents are conducted through body fluids and tissues, detected on the body surface, and recorded as the Electrocardiogram (ECG or EKG).

Question 17

Question: What does the ECG represent?

Answer 17

Answer: The ECG is a summation of the overall spread of electrical activity throughout the heart during depolarization and repolarization.

Question 18

Question: What is a standard 12-lead ECG composed of?

Answer 18

Answer:
Six limb leads: I, II, III, aVR, aVL, aVF
Six chest leads: V1 to V6

Question 19

Question: What are the three distinct waveforms of a normal ECG?

Answer 19

Answer:

P wave: Represents atrial depolarization.

QRS complex: Represents ventricular depolarization.

T wave: Represents ventricular repolarization

Question 20

Question: What is the basic functional unit of the heart pump?

Answer 20

Answer: Cardiac muscle fibers are the basic functional unit of the heart pump.

Question 21

Question: How are cardiac muscle cells interconnected?
[what doe they form]

Answer 21

Answer: Individual cardiac muscle cells are interconnected to form branching fibers, with adjacent cells joined end to end at intercalated discs.

Question 22

Question: What are the two types of membrane junctions within an intercalated disc?

Answer 22

Answer:

Desmosomes: Cell-to-cell anchoring junctions.
Gap junctions: Cell-to-cell communication junctions.

Question 23

Question: What is the functional significance of cardiac muscle fibers forming a syncytium?

Answer 23

Answer: The muscle mass forms a functional syncytium, allowing all cells to become excited and contract as a single unit.

Question 23

Question: What are intercalated discs in cardiac muscle?

Answer 23

Answer: Intercalated discs are specialized structures where adjacent cardiac muscle cells are joined, enabling both mechanical and electrical connections.

Question 24

Question: What two key types of membrane junctions are present within intercalated discs?

Answer 24

Answer: Desmosomes: Provide mechanical anchoring between cells. Gap junctions: Facilitate electrical communication by allowing ion flow between cells.

Question 25

Question: What other structural components are found in cardiac muscle cells? [4]

Answer 25

Answer: Sarcolemma: The cell membrane of cardiac muscle cells. Mitochondria: Provide energy for contraction. Sarcoplasmic reticulum: Stores and releases calcium for muscle contraction. Nucleus: Controls cellular activities.

Question 26

Question: How do intercalated discs contribute to cardiac function?

Answer 26

Answer: They enable the heart to function as a coordinated syncytium, ensuring efficient contraction and pumping action.

Question 27

What are the steps to Excitation Contraction Coupling?

Answer 27

1 Action potential enters from adjacent cell. 2 Voltage-gated Ca?+ channels open. Ca?+ enters cell. 3 Ca?+ induces Ca?+ release through ryanodine receptor-channels (RyR). Local release causes Ca2+ spark. 5 Summed Ca?+ sparks create a Ca?+ signal. 6 Ca?+ ions bind to troponin to initiate contraction. Relaxation occurs when Ca?+ unbinds from troponin. 8 Ca?+ is pumped back into the sarcoplasmic reticulum for storage. 9 Ca?+ is exchanged with Na* 40 Na* gradient is maintained by the Na*-K+-ATPase.

Question 28

Question: What triggers the rhythmic pumping action of the heart?

Answer 28

Answer: The rhythmic pumping action of the heart is triggered by the spread of excitation through the heart.

Question 29

Question: What are the two sub-phases of systole?

Answer 29

Answer: Isovolumetric contraction: Ventricles contract but no blood is ejected yet. Ejection period: Blood is ejected from the ventricles.

Question 29

Question: What are the two alternate phases of the cardiac cycle?

Answer 29

Answer: Systole: The phase of ventricular contraction and emptying. Diastole: The phase of ventricular relaxation and filling.

Question 30

Question: What are the two sub-phases of diastole?

Answer 30

Answer: Isovolumetric relaxation: Ventricles relax but no blood enters yet. Filling period: Blood enters the ventricles, completing the cycle.

Question 31

Question: What happens during isovolumetric ventricular contraction? [ventricles , is blood ejected, aortic valves, pulmonary valves, AV valves ]

Answer 31

Answer: The ventricles contract, but no blood is ejected yet. The AV valves and aortic/pulmonary valves are closed.

Question 32

Question: What occurs during ventricular ejection? [where does the blood flow , aortic valves, pulmonary valves, av valves ]

Answer 32

Answer: Blood flows out of the ventricles into the aorta and pulmonary artery. The aortic and pulmonary valves open while the AV valves remain closed.

Question 33

Question: What is the state of the atria , ventricles , AV , aortic and pulmonary valves during systole?

Answer 33

Answer: The atria are relaxed, the ventricles are contracting, the AV valves are closed, and the aortic and pulmonary valves are open during the ejection phase.

Question 34

Question: What happens during isovolumetric ventricular relaxation? [ventricles , aortic valves, pulmonary valves, AV valves ]

Answer 34

Answer: The ventricles relax, but no blood enters yet. Both the AV valves and aortic/pulmonary valves are closed.

Question 35

Question: What occurs during ventricular filling?

Answer 35

Answer: Blood flows into the ventricles as the atria contract. The AV valves open, while the aortic and pulmonary valves remain closed.

Question 36

Question: What is the state of atria , ventricles , AV , aortic and pulmonary valves during diastole?

Answer 36

Answer: Atria relaxed during isovolumetric relaxation. Atria contract during ventricular filling to assist in pushing blood into the ventricles. AV valves are open during ventricular filling, while the aortic and pulmonary valves are closed.