Week 25 / Circulatory System 3 Flashcards
What is refractoriness in cardiac cells?
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.
What does refractoriness give rise to?
It gives rise to the
absolute/effective refractory period (ARP/ERP)
and the
relative refractory period (RRP).
Question: What is the physiological significance of refractoriness in cardiac cells?
Answer: It protects against premature excitation and tetany.
Question: How does the refractory period differ between fast and slow response cells?
Answer:
Fast response cells: Faster recovery of excitability.
Slow response cells: Slower recovery of excitability.
Question: What is the clinical implication of refractoriness differences in cardiac cells?
Answer: Variations in refractory period durations can increase the risk of conduction block.
Question: What is automaticity in cardiac cells?
Answer: Automaticity is the ability of some cardiac cells to initiate or fire action potentials spontaneously.
Question: What is another term for automaticity?
Answer: Automaticity is also referred to as pacemaker activity.
Question: Which cardiac cells exhibit normal automaticity? [3]
Answer:
Sinoatrial (SA) node
Atrioventricular (AV) node
Specialized conducting tissue, such as the His-Purkinje system
Question: What is the difference between primary and latent pacemakers?
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: What underlies the basis of automaticity in pacemaker cells?
Answer: Automaticity is based on the “funny” current (I𝑓f) and spontaneous phase 4 depolarization.
Question: How is automaticity controlled? [2]
Answer: Automaticity is regulated by intrinsic factors (e.g., ion channel dynamics) and extrinsic factors (e.g., autonomic nervous system).
Question: How does the heart beat maintain its rhythmic beating?
[how does it beat ?
how is the beat triggered?
]
Answer: The heart beats spontaneously and rhythmically throughout life, triggered by the spread of action potentials across muscle cell membranes.
Question: How are action potentials initiated and conducted in the heart?
Answer: Action potentials are cyclically initiated and conducted in an orderly sequence by electrical or autorhythmic cells.
Question: What is the natural sequence of excitation in the heart?
Answer:
SA node
Atria
AV node
Bundle of His
Purkinje fibers
Ventricles
Question: What is the purpose of the AV conduction delay?
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: What generates the electrical currents detected in an ECG?
Answer: Electrical currents are generated by cardiac muscle during depolarization and repolarization.
Question: How are these electrical currents detected and recorded?
Answer: The currents are conducted through body fluids and tissues, detected on the body surface, and recorded as the Electrocardiogram (ECG or EKG).
Question: What does the ECG represent?
Answer: The ECG is a summation of the overall spread of electrical activity throughout the heart during depolarization and repolarization.
Question: What is a standard 12-lead ECG composed of?
Answer:
Six limb leads: I, II, III, aVR, aVL, aVF
Six chest leads: V1 to V6
Question: What are the three distinct waveforms of a normal ECG?
Answer:
P wave: Represents atrial depolarization.
QRS complex: Represents ventricular depolarization.
T wave: Represents ventricular repolarization
Question: What is the basic functional unit of the heart pump?
Answer: Cardiac muscle fibers are the basic functional unit of the heart pump.
Question: How are cardiac muscle cells interconnected?
[what doe they form]
Answer: Individual cardiac muscle cells are interconnected to form branching fibers, with adjacent cells joined end to end at intercalated discs.
Question: What are the two types of membrane junctions within an intercalated disc?
Answer:
Desmosomes: Cell-to-cell anchoring junctions.
Gap junctions: Cell-to-cell communication junctions.
Question: What is the functional significance of cardiac muscle fibers forming a syncytium?
Answer: The muscle mass forms a functional syncytium, allowing all cells to become excited and contract as a single unit.
Question: What are intercalated discs in cardiac muscle?
Answer: Intercalated discs are specialized structures where adjacent cardiac muscle cells are joined, enabling both mechanical and electrical connections.
Question: What two key types of membrane junctions are present within intercalated discs?
Answer:
Desmosomes: Provide mechanical anchoring between cells.
Gap junctions: Facilitate electrical communication by allowing ion flow between cells.
Question: What other structural components are found in cardiac muscle cells? [4]
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: How do intercalated discs contribute to cardiac function?
Answer: They enable the heart to function as a coordinated syncytium, ensuring efficient contraction and pumping action.
What are the steps to Excitation Contraction Coupling?
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: What triggers the rhythmic pumping action of the heart?
Answer: The rhythmic pumping action of the heart is triggered by the spread of excitation through the heart.
Question: What are the two sub-phases of systole?
Answer:
Isovolumetric contraction: Ventricles contract but no blood is ejected yet.
Ejection period: Blood is ejected from the ventricles.
Question: What are the two alternate phases of the cardiac cycle?
Answer:
Systole: The phase of ventricular contraction and emptying.
Diastole: The phase of ventricular relaxation and filling.
Question: What are the two sub-phases of diastole?
Answer:
Isovolumetric relaxation: Ventricles relax but no blood enters yet.
Filling period: Blood enters the ventricles, completing the cycle.
Question: What happens during isovolumetric ventricular contraction?
[ventricles ,
aortic valves,
pulmonary valves,
AV valves
]
Answer: The ventricles contract, but no blood is ejected yet. The AV valves and aortic/pulmonary valves are closed.
Question: What occurs during ventricular ejection?
[where does the blood flow ,
aortic valves,
pulmonary valves,
av valves
]
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: What is the state of the
atria ,
ventricles ,
AV ,
aortic and pulmonary valves
during systole?
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: What happens during isovolumetric ventricular relaxation?
[ventricles ,
aortic valves,
pulmonary valves,
AV valves
]
Answer: The ventricles relax, but no blood enters yet. Both the AV valves and aortic/pulmonary valves are closed.
Question: What occurs during ventricular filling?
Answer: Blood flows into the ventricles as the atria contract. The AV valves open, while the aortic and pulmonary valves remain closed.
Question: What is the state of
atria ,
ventricles ,
AV ,
aortic and pulmonary valves
during diastole?
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.
