Cardiac cycle Flashcards
Describe the mechanisms of excitation- contraction coupling
Trigger: Action potential opens L-type Ca²⁺ channels in the sarcolemma.
Calcium-Induced Calcium Release: Ca²⁺ enters and triggers release from sarcoplasmic reticulum via ryanodine receptors.
Contraction: Ca²⁺ binds troponin, enabling actin-myosin cross-bridge cycling.
Relaxation: Ca²⁺ reuptake by SERCA and extrusion via Na⁺/Ca²⁺ exchanger.
Describe the architecture and micro-artitecture of cardiac muscle
Architecture: Branched, striated fibers with intercalated discs for mechanical and electrical coupling.
Micro-architecture: Sarcomeres composed of myofilaments (actin and myosin) arranged in repeating units.
What is the myofilament structure? describe the individual structure of both parts?
Thin Filaments: Actin, troponin (T, I, C subunits), and tropomyosin.
Thick Filaments: Myosin with globular heads for ATP hydrolysis and actin binding.
What actin-myosin interactions and the role of troponin?
Troponin C: Binds Ca²⁺, causing conformational change.
Troponin I: Inhibits actin-myosin binding in the absence of Ca²⁺.
Troponin T: Anchors troponin complex to tropomyosin.
Interaction: Ca²⁺ binding exposes actin binding sites for myosin heads.
What is cross bridge cycle?
Attachment: Myosin head binds actin (cross-bridge forms).
Power Stroke: ADP + Pi released; myosin pulls actin.
Detachment: ATP binds myosin, releasing it from actin.
Reactivation: ATP hydrolysis repositions myosin head.
Define cardiac output
Definition: Volume of blood pumped by each ventricle per minute.
Formula: Cardiac Output = Heart Rate × Stroke Volume.
What factors are affecting cardiac output?
Heart Rate: Influenced by autonomic input and hormones.
Stroke Volume: Dependent on preload, afterload, and contractility.
What does it mean when we talk about the autonomic innervation of the heart?
Sympathetic: Increases heart rate (SA node) and contractility (ventricles).
Parasympathetic: Decreases heart rate via vagus nerve (SA and AV nodes).
Describe the mechanisms of excitation-contraction coupling
Trigger: Action potential opens L-type Ca²⁺ channels in the sarcolemma.
Calcium-Induced Calcium Release: Ca²⁺ enters and triggers release from sarcoplasmic reticulum via ryanodine receptors.
Contraction: Ca²⁺ binds troponin, enabling actin-myosin cross-bridge cycling.
Relaxation: Ca²⁺ reuptake by SERCA and extrusion via Na⁺/Ca²⁺ exchanger.
What is the architecture and micro-architecture of cardiac muscle?
Architecture: Branched, striated fibers with intercalated discs for mechanical and electrical coupling.
Micro-architecture: Sarcomeres composed of myofilaments (actin and myosin) arranged in repeating units.
What is the myofilament structure?
Thin Filaments: Actin, troponin (T, I, C subunits), and tropomyosin.
Thick Filaments: Myosin with globular heads for ATP hydrolysis and actin binding.
What are the actin-myosin interactions and role of troponin?
Troponin C: Binds Ca²⁺, causing conformational change.
Troponin I: Inhibits actin-myosin binding in the absence of Ca²⁺.
Troponin T: Anchors troponin complex to tropomyosin.
Interaction: Ca²⁺ binding exposes actin binding sites for myosin heads
Describe the cross bridge cycle
Attachment: Myosin head binds actin (cross-bridge forms).
Power Stroke: ADP + Pi released; myosin pulls actin.
Detachment: ATP binds myosin, releasing it from actin.
Reactivation: ATP hydrolysis repositions myosin head.
Define cardiac output
Definition: Volume of blood pumped by each ventricle per minute.
Formula: Cardiac Output = Heart Rate × Stroke Volume.
What factors affect cardiac output?
Heart Rate: Influenced by autonomic input and hormones.
Stroke Volume: Dependent on preload, afterload, and contractility
What is the autonomic innervation of the heart?
Sympathetic: Increases heart rate (SA node) and contractility (ventricles).
Parasympathetic: Decreases heart rate via vagus nerve (SA and AV nodes).
What is the effects of sympathetic and parasympathetic stimulation?
Sympathetic: ↑ Heart rate, ↑ force of contraction, ↓ AV nodal delay.
Parasympathetic: ↓ Heart rate, ↓ conduction velocity, ↑ AV nodal delay.
Define valve operation, blood volume and blood pressure
Valve Operation: Opens/closes due to pressure differences between chambers.
Blood Volume: End-diastolic and end-systolic volumes affect stroke volume.
Blood Pressure: Maintained by cardiac output and systemic vascular resistance.
what are the main events within the ecg? (pqrst wave)
P Wave: Atrial depolarization; precedes atrial contraction.
QRS Complex: Ventricular depolarization; triggers ventricular contraction.
T Wave: Ventricular repolarization; precedes ventricular relaxation.
Valve Timing:
AV valves close: Start of QRS (ventricular systole).
Semilunar valves open: During ventricular ejection.
What are the events of the cardiac cycle?
Atrial Systole: Atria contract to fill ventricles.
Ventricular Systole: Ventricles contract; blood ejected into aorta/pulmonary artery.
Diastole: Chambers relax and fill with blood.
What is the valve operation within the heart?
Atrioventricular (AV) Valves: Open during diastole; close during ventricular systole.
Semilunar Valves: Open during systole; close during diastole.
What is the blood volume and pressure changes in the cardiac cycle?
Peaks during systole; lowest during diastole.
End-diastolic volume (EDV) and end-systolic volume (ESV) define stroke volume.
what is the ecg correlation?
P Wave: Atrial depolarisation (atrial systole).
QRS Complex: Ventricular depolarisation (ventricular systole).
T Wave: Ventricular repolarisation (diastole).
