The Heart

Flashcards covering key vocabulary terms and concepts related to the anatomy and physiology of the heart.

Cardiac Output (CO)

The volume of blood pumped by the left ventricle in one minute; calculated as CO = HR \times SV (Heart Rate × Stroke Volume).

Stroke Volume (SV)

The amount of blood ejected by each ventricle during contraction; calculated as SV = EDV - ESV (End-Diastolic Volume - End-Systolic Volume).

End-Diastolic Volume (EDV)

The amount of blood in each ventricle at the end of ventricular diastole (relaxation), before contraction.

End-Systolic Volume (ESV)

The amount of blood remaining in each ventricle at the end of ventricular systole (contraction), after ejection.

Heart Location

The heart is located in the mediastinum, slightly to the left of the midline, between the lungs and posterior to the sternum.

Pericardium

The membrane surrounding the heart, composed of an outer fibrous layer and an inner serous layer.

Layers of the Heart Wall

1. Epicardium: Outermost layer, continuous with the visceral layer of the serous pericardium.
2. Myocardium: Middle layer, composed of cardiac muscle tissue, responsible for pumping action.
3. Endocardium: Innermost layer, lining the chambers and valves, continuous with the endothelium of blood vessels.

Chambers of the Heart

The four main chambers: right atrium, right ventricle, left atrium, and left ventricle.

Heart Valves

Structures that ensure unidirectional blood flow:

• Atrioventricular (AV) valves: Tricuspid (right) and Mitral/Bicuspid (left), between atria and ventricles.
• Semilunar (SL) valves: Pulmonary (right) and Aortic (left), between ventricles and great arteries.

Coronary Circulation

The circulation of blood to and from the tissues of the heart muscle itself, via coronary arteries and cardiac veins.

Blood Flow Pathway

The route blood takes through the heart and body, including:

• Pulmonary Circuit: Blood from the right side of the heart to the lungs and back to the left atrium.
• Systemic Circuit: Blood from the left side of the heart to the body and back to the right atrium.

Conducting System of the Heart

A network of specialized cardiac muscle cells that initiate and distribute electrical impulses; includes:

1. Sinoatrial (SA) Node: Primary pacemaker.
2. Atrioventricular (AV) Node: Delays impulse to allow ventricular filling.
3. AV Bundle (Bundle of His):
4. Bundle Branches (left and right):
5. Purkinje Fibers: Distribute impulse to ventricular myocardium.

Pacemaker Cells

Specialized cardiac muscle cells in the sinoatrial (SA) node that generate their own action potentials (autorhythmicity) and control the heart rate.

Impulse Conduction Pathway

1. SA node depolarizes.
2. Electrical activity spreads through the atria to the AV node.
3. AV node delays the impulse.
4. AV bundle and bundle branches conduct the impulse to the apex.
5. Purkinje fibers spread the impulse throughout the ventricular myocardium, leading to contraction.

Electrocardiogram (ECG or EKG)

A graphic record of the electrical activity of the heart over time. Key waves include:

• P wave: Atrial depolarization.
• QRS complex: Ventricular depolarization (and hidden atrial repolarization).
• T wave: Ventricular repolarization.

Cardiac Contractile Cells

Cells that make up the bulk of the myocardial muscle, responsible for the actual pumping of blood. They contract in response to electrical impulses generated by pacemaker cells.

Action Potential of Contractile Cells

Distinct phases leading to muscle contraction:

1. Rapid Depolarization: Na+ influx.
2. Plateau Phase: Ca2+ influx (prolongs contraction and prevents tetany).
3. Repolarization: K+ efflux.

Action Potential of Pacemaker Cells

Characterized by an unstable resting potential (pacemaker potential) due to slow Na+ influx, followed by depolarization (Ca2+ influx) and repolarization (K+ efflux).

Role of Calcium Ions (Ca^{2+}) in Cardiac Contraction

Ca^{2+} influx during the plateau phase of the contractile cell action potential triggers the release of more Ca^{2+} from the sarcoplasmic reticulum, leading to cross-bridge cycling and muscle contraction (excitation-contraction coupling).

Refractory Period

The time during which cardiac contractile cells cannot respond to a new stimulus, which is prolonged by the Ca^{2+} plateau phase. This prevents tetanic contractions in the heart.

Cardiac Cycle

The sequence of events during one complete heartbeat, including periods of contraction (systole) and relaxation (diastole) for both atria and ventricles, resulting in blood flow.

Autonomic Intervention of the Heart

The autonomic nervous system regulates heart rate and contractility:

• Sympathetic nervous system: Increases heart rate and contractility (via norepinephrine/epinephrine).
• Parasympathetic nervous system: Decreases heart rate (via acetylcholine).

Contractility

The intrinsic strength of the heart muscle contraction, independent of preload and afterload. Influenced by:

• Positive inotropic agents: Increase contractility (Ca^{2+}, sympathetic stimulation).
• Negative inotropic agents: Decrease contractility (acidosis, some drugs).

Cardiac Skeleton

A structure of dense connective tissue that supports the heart valves and great vessels, anchors cardiac muscle, and acts as an electrical insulator between the atria and ventricles.

Cardiac Output (CO)

The volume of blood pumped by the left ventricle in one minute; calculated as CO = HR \times SV (Heart Rate × Stroke Volume).

Stroke Volume (SV)

The amount of blood ejected by each ventricle during contraction; calculated as SV = EDV - ESV (End-Diastolic Volume - End-Systolic Volume).

End-Diastolic Volume (EDV)

The amount of blood in each ventricle at the end of ventricular diastole (relaxation), before contraction.

End-Systolic Volume (ESV)

The amount of blood remaining in each ventricle at the end of ventricular systole (contraction), after ejection.

Heart Location

The heart is located in the mediastinum, slightly to the left of the midline, between the lungs and posterior to the sternum.

Pericardium

The membrane surrounding the heart, composed of an outer fibrous layer and an inner serous layer.

Layers of the Heart Wall

1. Epicardium: Outermost layer, continuous with the visceral layer of the serous pericardium.
2. Myocardium: Middle layer, composed of cardiac muscle tissue, responsible for pumping action.
3. Endocardium: Innermost layer, lining the chambers and valves, continuous with the endothelium of blood vessels.

Chambers of the Heart

The four main chambers: right atrium, right ventricle, left atrium, and left ventricle.

Heart Valves

Structures that ensure unidirectional blood flow:

• Atrioventricular (AV) valves: Tricuspid (right) and Mitral/Bicuspid (left), between atria and ventricles.
• Semilunar (SL) valves: Pulmonary (right) and Aortic (left), between ventricles and great arteries.

Coronary Circulation

The circulation of blood to and from the tissues of the heart muscle itself, via coronary arteries and cardiac veins.

Left Coronary Artery (LCA)

Arises from the aorta and branches into the anterior interventricular artery (LAD) and circumflex artery, supplying the left atrium, left ventricle, and interventricular septum.

Right Coronary Artery (RCA)

Arises from the aorta and supplies the right atrium, right ventricle, and parts of the interventricular septum, inferior left ventricle, and often the SA and AV nodes.

Coronary Sinus

A large vein on the posterior surface of the heart that collects deoxygenated blood from the great, middle, and small cardiac veins and empties into the right atrium.

Interventricular Septum

The muscular wall separating the right and left ventricles, crucial for maintaining separate systemic and pulmonary circulations.

Papillary Muscles and Chordae Tendineae

Structures within the ventricles; papillary muscles contract to pull on the chordae tendineae, preventing the AV valve cusps from everting into the atria during ventricular contraction.

Trabeculae Carneae

Irregular muscular ridges and folds on the internal surfaces of the ventricles, contributing to the turbulence of blood flow and potentially preventing suction effects.

Intercalated Discs

Specialized cell junctions unique to cardiac muscle, containing desmosomes (for strong adhesion) and gap junctions (for electrical coupling, allowing rapid ion flow and synchronized contraction).

Blood Flow Pathway

The route blood takes through the heart and body, including:

• Pulmonary Circuit: Blood from the right side of the heart to the lungs and back to the left atrium.
• Systemic Circuit: Blood from the left side of the heart to the body and back to the right atrium.

Conducting System of the Heart

A network of specialized cardiac muscle cells that initiate and distribute electrical impulses; includes:

1. Sinoatrial (SA) Node: Primary pacemaker.
2. Atrioventricular (AV) Node: Delays impulse to allow ventricular filling.
3. AV Bundle (Bundle of His):
4. Bundle Branches (left and right):
5. Purkinje Fibers: Distribute impulse to ventricular myocardium.

Pacemaker Cells

Specialized cardiac muscle cells in the sinoatrial (SA) node that generate their own action potentials (autorhythmicity) and control the heart rate.

Impulse Conduction Pathway

1. SA node depolarizes.
2. Electrical activity spreads through the atria to the AV node.
3. AV node delays the impulse.
4. AV bundle and bundle branches conduct the impulse to the apex.
5. Purkinje fibers spread the impulse throughout the ventricular myocardium, leading to contraction.

Electrocardiogram (ECG or EKG)

A graphic record of the electrical activity of the heart over time. Key waves include:

• P wave: Atrial depolarization.
• QRS complex: Ventricular depolarization (and hidden atrial repolarization).
• T wave: Ventricular repolarization.

PR Interval

The duration from the beginning of atrial depolarization (P wave) to the beginning of ventricular depolarization (QRS complex), representing conduction time through the atria and AV node.

QT Interval

The duration from the beginning of ventricular depolarization (QRS complex) to the end of ventricular repolarization (T wave), indicating the total time required for ventricular electrical activity.

ST Segment

The isoelectric period between the end of the S wave and the beginning of the T wave, representing the time when the entire ventricular myocardium is depolarized.

Cardiac Contractile Cells

Cells that make up the bulk of the myocardial muscle, responsible for the actual pumping of blood. They contract in response to electrical impulses generated by pacemaker cells.

Action Potential of Contractile Cells

Distinct phases leading to muscle contraction:

1. Rapid Depolarization: Na+ influx.
2. Plateau Phase: Ca2+ influx (prolongs contraction and prevents tetany).
3. Repolarization: K+ efflux.

Action Potential of Pacemaker Cells

Characterized by an unstable resting potential (pacemaker potential) due to slow Na+ influx, followed by depolarization (Ca2+ influx) and repolarization (K+ efflux).

Role of Calcium Ions (Ca^{2+}) in Cardiac Contraction

Ca^{2+} influx during the plateau phase of the contractile cell action potential triggers the release of more Ca^{2+} from the sarcoplasmic reticulum, leading to cross-bridge cycling and muscle contraction (excitation-contraction coupling).

Refractory Period

The time during which cardiac contractile cells cannot respond to a new stimulus, which is prolonged by the Ca^{2+} plateau phase. This prevents tetanic contractions in the heart.

Cardiac Cycle

The sequence of events during one complete heartbeat, including periods of contraction (systole) and relaxation (diastole) for both atria and ventricles, resulting in blood flow.

Ventricular Systole

The period of ventricular contraction, encompassing isovolumetric contraction (pressure buildup with closed valves) and ventricular ejection (blood forced into arteries through open semilunar valves).

Ventricular Diastole

The period of ventricular relaxation and filling, including isovolumetric relaxation (ventricles relax with closed valves) and ventricular filling (blood flows from atria to ventricles through open AV valves).

Autonomic Intervention of the Heart

The autonomic nervous system regulates heart rate and contractility:

• Sympathetic nervous system: Increases heart rate and contractility (via norepinephrine/epinephrine).
• Parasympathetic nervous system: Decreases heart rate (via acetylcholine).

Contractility

The intrinsic strength of the heart muscle contraction, independent of preload and afterload. Influenced by:

• Positive inotropic agents: Increase contractility (Ca^{2+}, sympathetic stimulation).
• Negative inotropic agents: Decrease contractility (acidosis, some drugs).

Cardiac Skeleton

A structure of dense connective tissue that supports the heart valves and great vessels, anchors cardiac muscle, and acts as an electrical insulator between the atria and ventricles.

Coronary Artery Disease (CAD)

A condition characterized by the narrowing or blockage of the coronary arteries, typically by atherosclerosis, leading to myocardial ischemia.

Angina Pectoris

Chest pain or discomfort occurring when the heart muscle doesn't get enough oxygen-rich blood, often a symptom of CAD.

Myocardial Infarction (MI)

Commonly known as a heart attack, it is the irreversible death of heart muscle tissue due to prolonged lack of oxygen supply, usually from a complete blockage of a coronary artery.

Modifiable Risk Factors for CVD

Lifestyle factors that can be changed to reduce heart disease risk, including high blood pressure, high cholesterol, smoking, diabetes, obesity, and physical inactivity.

Non-modifiable Risk Factors for CVD

Risk factors that cannot be changed, such as increasing age, male gender, and a family history of early heart disease.

Percutaneous Coronary Intervention (PCI) / Angioplasty with Stent

A minimally invasive procedure to open narrowed or blocked coronary arteries using a balloon catheter, often followed by the placement of a stent to keep the artery open.

Coronary Artery Bypass Graft (CABG)

A surgical procedure where a healthy blood vessel (from the leg, arm, or chest) is grafted to create a new path for blood to flow around a blocked or narrowed coronary artery, restoring blood flow to the heart muscle.

Heart Valve Surgery

Surgical repair or replacement of diseased or damaged heart valves (e.g., aortic, mitral), performed to restore proper blood flow through the heart.

Common Medications for CVD

Pharmacological agents used to manage cardiovascular disease, including statins (for cholesterol), beta-blockers (for heart rate/blood pressure), ACE inhibitors (for blood pressure), and antiplatelet drugs (to prevent clots).