Anatomy of the heart Flashcards
Role of the heart
The heart pumps blood through the circulatory system, delivering oxygen and nutrients to tissues and removing waste products
Whats the gross structure of the heart?
Structure: A four-chambered organ (2 atria, 2 ventricles).
Location: Located in the thoracic cavity, between the lungs, slightly left of the midline.
Whats the location and role of the heart valves?
Valves:
Atrioventricular (AV) valves:
Tricuspid (right) and mitral (left) valves.
Prevent backflow from ventricles to atria during systole.
Semilunar valves:
Pulmonary and aortic valves.
Prevent backflow from arteries to ventricles during diastole.
cellular structure of cardiac muscle
Structure:
Striated, branched cells.
Single nucleus per cell.
Contains sarcomeres for contraction.
Abundant mitochondria for energy.
How are individual heart cells are coupled
Mechanical coupling:
Intercalated discs contain desmosomes that anchor cells together during contraction.
Electrical coupling:
Gap junctions in intercalated discs allow ions to pass, enabling synchronized contraction.
What ionic gradients are across the heart cell membrane?
Key Ions: Na⁺ (high extracellular), K⁺ (high intracellular), Ca²⁺ (high extracellular).
Resting Potential: Maintained by Na⁺/K⁺ ATPase and selective membrane permeability, with K⁺ contributing most to the resting membrane potential (~ -90 mV in ventricular cells).
What are the main classes of ion channels in the heart?
-Voltage-Gated Channels:
Na⁺ channels: Rapid depolarization.
-Ca²⁺ channels (L-type): Plateau phase and contraction.
-K⁺ channels: Repolarization and resting potential maintenance.
-Pacemaker Channels (If): Allow slow depolarization in SA node cells.
-Ligand-Gated Channels: Modulated by neurotransmitters.
What creates the initiation of the cardiac action potential?
Site: SA node (primary pacemaker).
Mechanism:
Pacemaker potential: Slow depolarization via If (Na⁺/K⁺ influx).
Threshold: Activation of Ca²⁺ channels (L-type) for rapid depolarization.
Repolarization: K⁺ efflux through voltage-gated K⁺ channels.
What is the ionic basis of the action potential in SA node and ventricular muscle
SA Node:
Phase 4: Pacemaker potential (If channels, T-type Ca²⁺ channels).
Phase 0: L-type Ca²⁺ channel activation.
Phase 3: K⁺ efflux for repolarization.
Ventricular Muscle:
Phase 0: Rapid Na⁺ influx.
Phase 1: Transient K⁺ efflux.
Phase 2: Ca²⁺ influx (plateau phase).
Phase 3: K⁺ efflux for repolarization.
Phase 4: Resting potential (K⁺ channels).
Describe the configuration of action potential as it spreads through the heart muscle
SA Node to Atria: Gradual depolarization; slower upstroke.
AV Node: Delayed conduction for ventricular filling.
Purkinje Fibers: Rapid conduction, ensuring synchronized ventricular contraction.
Ventricles: Strong, sustained action potential with prominent plateau phase for efficient contraction.
Describe the implications of the absolute refractory period
Definition: Period during which no new action potential can be initiated.
Importance:
Prevents tetany in cardiac muscle.
Ensures unidirectional propagation of the action potential.
Allows time for ventricular filling before the next contraction.
Whats the role of heart?
Role: The heart pumps blood through the circulatory system, delivering oxygen and nutrients to tissues and removing waste products.
Describe the gross structure of the heart
Structure: A four-chambered organ (2 atria, 2 ventricles).
Location: Located in the thoracic cavity, between the lungs, slightly left of the midline.
Describe the location and role of the heart valves
Valves:
Atrioventricular (AV) valves:
Tricuspid (right) and mitral (left) valves.
Prevent backflow from ventricles to atria during systole.
Semilunar valves:
Pulmonary and aortic valves.
Prevent backflow from arteries to ventricles during diastole.
Cellular structure of cardiac muscle
Structure:
Striated, branched cells.
Single nucleus per cell.
Contains sarcomeres for contraction.
Abundant mitochondria for energy.
How are individual heart cells are coupled?
Mechanical coupling:
Intercalated discs contain desmosomes that anchor cells together during contraction.
Electrical coupling:
Gap junctions in intercalated discs allow ions to pass, enabling synchronized contraction.
What are the ionic gradients across the heart cell membrane?
Key Ions: Na⁺ (high extracellular), K⁺ (high intracellular), Ca²⁺ (high extracellular).
Resting Potential: Maintained by Na⁺/K⁺ ATPase and selective membrane permeability, with K⁺ contributing most to the resting membrane potential (~ -90 mV in ventricular cells).
What are the main classes of ion channels in the heart?
Voltage-Gated Channels:
Na⁺ channels: Rapid depolarization.
Ca²⁺ channels (L-type): Plateau phase and contraction.
K⁺ channels: Repolarization and resting potential maintenance.
Pacemaker Channels (If): Allow slow depolarization in SA node cells.
Ligand-Gated Channels: Modulated by neurotransmitters.
Describe the initiation of the cardiac action potential
Site: SA node (primary pacemaker).
Mechanism:
Pacemaker potential: Slow depolarization via If (Na⁺/K⁺ influx).
Threshold: Activation of Ca²⁺ channels (L-type) for rapid depolarization.
Repolarization: K⁺ efflux through voltage-gated K⁺ channels.
What is the ionic basis of the action potential in as node and ventricular muscle?
SA Node:
Phase 4: Pacemaker potential (If channels, T-type Ca²⁺ channels).
Phase 0: L-type Ca²⁺ channel activation.
Phase 3: K⁺ efflux for repolarization.
Ventricular Muscle:
Phase 0: Rapid Na⁺ influx.
Phase 1: Transient K⁺ efflux.
Phase 2: Ca²⁺ influx (plateau phase).
Phase 3: K⁺ efflux for repolarization.
Phase 4: Resting potential (K⁺ channels).
describe the configuration of the action potential as it spreads through the heart muscle
SA Node to Atria: Gradual depolarization; slower upstroke.
AV Node: Delayed conduction for ventricular filling.
Purkinje Fibers: Rapid conduction, ensuring synchronized ventricular contraction.
Ventricles: Strong, sustained action potential with prominent plateau phase for efficient contraction.
the definiton and implications of the absolute refractory period
Definition: Period during which no new action potential can be initiated.
Importance:
Prevents tetany in cardiac muscle.
Ensures unidirectional propagation of the action potential.
Allows time for ventricular filling before the next contraction.
definition of dysrhythmias
Dysrhythmias: Abnormal heart rhythms caused by disturbances in electrical activity of the heart, affecting rate, rhythm, or conduction.
Types of dysrhythmias
Bradycardia: Slow heart rate (<60 bpm).
Causes: SA node dysfunction, AV block.
Tachycardia: Fast heart rate (>100 bpm).
Causes: Increased sympathetic tone, ectopic pacemaker activity.
Fibrillation: Disorganized electrical activity.
Atrial fibrillation (AF): Rapid, irregular atrial activity.
Ventricular fibrillation (VF): Life-threatening; uncoordinated ventricular contractions.
Heart Block: Impaired conduction between atria and ventricles.
First-degree: Prolonged PR interval.
Second-degree: Intermittent conduction failure.
Third-degree: Complete block; atria and ventricles beat independently.
What are the mechanisms of dysrhymias?
Abnormal automaticity: Ectopic pacemaker activity (e.g., ischemia, hypoxia).
Triggered activity: Afterdepolarizations due to ion channel dysfunction (early or delayed).
Reentry circuits: Circular propagation of impulses (e.g., AV nodal reentrant tachycardia).
What are the risk factors of dysrhythmias
Structural heart disease (e.g., myocardial infarction, cardiomyopathy).
Electrolyte imbalances (e.g., K⁺, Mg²⁺).
Drugs (e.g., antiarrhythmics, stimulants).
Systemic conditions (e.g., thyroid disorders, fever)
What is treatment for dysrhythmias ?
Lifestyle modifications: Reduce triggers (e.g., caffeine, stress).
Pharmacological:
Beta-blockers (rate control).
Antiarrhythmics (e.g., amiodarone, flecainide).
Non-Pharmacological:
Electrical cardioversion.
Pacemaker or defibrillator implantation.
Catheter ablation (for reentry circuits).
