Heart Anatomy and Circulation - Flashcards

Location and Orientation

• The heart is located in the thoracic cavity, medial to the lungs, within the mediastinum.
• Surrounded by the pericardium (pericardial sac) and sits in the pericardial cavity.
• Dorsal surface lies near vertebral bodies; anterior surface sits deep to sternum and costal cartilages.
• The base (superior surface) is where the great veins (superior vena cava, inferior vena cava) and great arteries (aorta, pulmonary trunk) attach; located at the level of the third costal cartilage.
• The apex (inferior tip) lies just to the left of the sternum, between the junction of the fourth and fifth ribs near their costal articulation.
• Right side deflected anteriorly; left side deflected posteriorly.
• Cardiac orientation matters for auscultation and midsagittal imaging; apex shift to the left creates a cardiac notch in the left lung.
• Size and weight: typical adult heart is about the size of a fist; roughly 12
  m \,cm ext{ (length)} imes 8
  m \,cm ext{ (width)} imes 6
  m \,cm ext{ (thickness)}
• Sex-related size differences: female heart ~ 250 ext{–}300
  m \,g; male heart ~ 300 ext{–}350
  m \,g; well-trained athletes can have larger hearts due to hypertrophy (growth in cell size, not cell number).
• Exercise-induced hypertrophy increases pumping efficiency at lower heart rates; other enlargements can result from disease (e.g., hypertrophic cardiomyopathy).

Anatomy and Circulation Overview

• Four chambers: right atrium (RA), left atrium (LA) (receiving chambers); right ventricle (RV), left ventricle (LV) (pumping chambers).
• Dual circulation:
  • Pulmonary circuit: deoxygenated blood to lungs for gas exchange; oxygenated blood returns to the heart.
  • Systemic circuit: oxygenated blood delivered to body tissues; deoxygenated blood returns to the heart.
• Blood flow sequence (oxygenation context):
  • Blood from body returns to the RA via the superior vena cava, inferior vena cava, and coronary sinus.
  • RA → RV through tricuspid valve (RP semilunar valves not involved yet).
  • RV ejects blood into the pulmonary trunk → left/right pulmonary arteries → pulmonary capillaries (gas exchange: CO₂ out, O₂ in).
  • Oxygenated blood returns via pulmonary veins → LA → LV through mitral valve.
  • LV ejects into the aorta → systemic arteries → systemic capillaries (O₂ delivered, CO₂ collected).
  • Systemic venous blood returns to the RA to repeat the cycle.
• Coronary circulation supplies the heart muscle itself; without it, myocardial tissue would suffer ischemia and dysfunction.
• A note on flow: the left ventricle generates higher pressure to overcome systemic resistance; the right ventricle operates at lower pressure for the shorter, lower-resistance pulmonary circuit.
• Normal total cardiac output is maintained by matching output of right and left sides, notwithstanding different wall thicknesses.

Membranes, Surface Features, and Layers

• Pericardium: surrounds the heart and roots of major vessels; consists of two sublayers:
  • Fibrous pericardium: tough dense connective tissue; protects and stabilizes the heart.
  • Serous pericardium: two layers – parietal pericardium (fused to fibrous pericardium) and visceral pericardium (epicardium) fused to the heart.
• Pericardial cavity: space between parietal and visceral layers; filled with lubricating serous fluid to reduce friction during heart contractions.
• Epicardium: visceral layer of serous pericardium; macroscopic layer made of simple squamous epithelium (mesothelium) and loose connective tissue; secretes serous fluid.
• Heart wall layers (superficial to deep):
  • Epicardium (visceral pericardium)
  • Myocardium: thick, muscular layer; cardiac muscle cells with a collagenous framework; responsible for contraction.
  • Endocardium: inner lining; covers heart chambers and valves; made of simple squamous epithelium (endothelium) continuous with blood vessel endothelium.
• Cardiac skeleton: dense connective tissue rings around openings of atrioventricular and semilunar valves; anchors valves; important boundary for electrical conduction.
• Cardiac tamponade (disorder): accumulation of excess pericardial fluid (often blood) that restricts ventricular filling; can be rapidly life-threatening; treated with pericardial drainage; slow accumulation (e.g., hypothyroidism) may permit some expansion of the cavity.

External Surface Features of the Heart

• Auricles (atrial appendages): small, ear-like extensions on the atria; contain pectinate muscles; more prominent in RA and left atrial appendage.
• Pectinate muscles: ridges of muscle in the right atrium and right auricle; less prominent in the left atrium except in the auricle.
• Sulci (fat-filled grooves) on the surface, housing major coronary vessels:
  • Coronary sulcus (greatest groove) between atria and ventricles.
  • Anterior interventricular sulcus between the ventricles on the anterior surface.
  • Posterior interventricular sulcus between the ventricles on the posterior surface.
• The anterior surface, posterior surface, and apex account for the heart’s external geometry.

Internal Structure: Chambers, Septa, and Valves

• Endocardium: inner lining; endothelium continuous with vascular endothelium; lines chambers and covers valves.
• Septa (walls that separate heart chambers):
  • Interatrial septum: separates the two atria; contains the fossa ovalis (oval depression) as a remnant of the fetal foramen ovale.
  • Interventricular septum: thick wall separating the two ventricles.
  • Atrioventricular septum: separation between atria and ventricles; contains four openings for blood flow between atria and ventricles; strong tissue reinforced by cardiac skeleton.
• Foramen ovale and fossa ovalis: in fetal life, blood bypasses the lungs via the foramen ovale; after birth, the foramen ovale closes; fossa ovalis is the remnant site.
• Valves (to ensure unidirectional flow):
  • Atrioventricular (AV) valves: tricuspid (right; three cusps) and mitral/bicuspid (left; two cusps).
  • Semilunar valves: aortic (left heart) and pulmonary (right heart).
• Chordae tendineae and papillary muscles: anchor AV valve leaflets and prevent regurgitation during ventricular contraction.
  • Right ventricle has three papillary muscles (anterior, posterior, septal); associated with three sections of the tricuspid valve.
  • Left ventricle has two papillary muscles (anterior, posterior) for the mitral valve.
• The moderator band: a band of cardiac muscle in the right ventricle connecting the interventricular septum to the inferior papillary muscle; contributes to conduction and maintains structure.
• Trabeculae carneae: muscular ridges on the interior walls of the ventricles; prevent sticking of blood to wall; contribute to contraction pattern.
• Ventricular wall thickness: left ventricle is thicker than right to generate higher pressure for systemic circulation; both ventricles eject equal volumes per beat.
• Valves and flow mechanics:
  • AV valves: closed during ventricular contraction; chordae tendineae keep leaflets from prolapsing into atria.
  • Semilunar valves: closed when ventricles relax; pressure from blood in aorta/pulmonary trunk fills cusps to seal.
  • Papillary muscles and chordae tendineae are not involved in the semilunar valves.
• Endocardial regulation: endothelium may actively regulate contraction through endothelins, influencing ionic balance and contractility; endothelins are potent vasoconstrictors.

The Heart Valves: Structure, Function, and Pathology

• Valve function: ensure unidirectional blood flow; prevent backflow during chamber contractions.
• Common valve names and features:
  • Tricuspid valve (right AV valve): three leaflets; connected to papillary muscles by chordae tendineae.
  • Mitral valve (left AV valve; bicuspid): two leaflets; connected to papillary muscles by chordae tendineae.
  • Pulmonary valve (right semilunar): three cusps; no chordae or papillary muscles.
  • Aortic valve (left semilunar): three cusps; no chordae or papillary muscles.
• Valve sounds and disorders:
  • Auscultation detects abnormal heart sounds (murmurs) indicating valvular disease.
  • Prolapse: cusp(s) protrude backward due to damaged chordae tendineae or papillary muscles.
  • Regurgitation: blood leaks backward due to incomplete valve closure.
  • Stenosis: valve becomes rigid or calcified, hindering flow and increasing cardiac work.
• Common pathologies and diagnostic tools:
  • Valvular disease may be congenital or acquired (inflammation such as carditis from rheumatic fever).
  • Echocardiography (echo) is used to diagnose valve pathology.
  • Stethoscope auscultation is a key diagnostic tool to detect murmurs.
• Specific conditions (examples mentioned):
  • Patent foramen ovale: persistence of a fetal opening in the interatrial septum; may be benign or require repair; detected by heart murmur and confirmed with echo.
  • Coarctation of the aorta: narrowing of the aorta near the ligamentum arteriosum; treated with surgery or angioplasty; earlier intervention improves survival.
  • Patent ductus arteriosus: failure of the ductus arteriosus to close after birth; can cause pulmonary over-circulation; treatments include surgical closure, coils, or NSAIDs to block prostaglandin E2.
  • Tetralogy of Fallot: opening in the interventricular septum with four components (often three present): pulmonary infundibular stenosis, overriding aorta, VSD, and right ventricular hypertrophy; leading cause of cyanosis in newborns; treated with surgical repair; variable survival in early life.
• Congenital defects can lead to blue coloration (cyanosis) when oxygenated blood is limited.

Right Atrium and Right Ventricle: In-Depth Internal Details

• Right atrium (receiving chamber for systemic venous blood):
  • Receives blood via superior vena cava, inferior vena cava, and coronary sinus.
  • Superior vena cava drains regions above the diaphragm (head, neck, upper limbs, thoracic region).
  • Inferior vena cava drains regions below the diaphragm (lower limbs, abdomen/pelvis).
  • Coronary sinus drains the myocardium's blood (venous drainage of heart tissue) into the RA.
  • RA surface: pectinate muscles primarily on the anterior wall and RA; the fossa ovalis is medial.
  • RA to RV via tricuspid valve.
• Right ventricle (pumping chamber to the lungs):
  • Blood moves from RA through the tricuspid valve to RV.
  • Tricuspid valve leaflets are anchored by chordae tendineae to papillary muscles (anterior, posterior, septal).
  • During RV contraction, increased intraventricular pressure closes the tricuspid valve to prevent backflow; papillary muscles tense chordae tendineae to keep leaflets from flipping into the RA.
  • RV interior features include trabeculae carneae and the moderator band.
  • RV ejects blood into the pulmonary trunk → left and right pulmonary arteries → lungs.

Left Atrium and Left Ventricle: In-Depth Internal Details

• Left atrium (oxygenated blood from lungs):
  • Receives blood via four pulmonary veins; no pectinate muscles except in the left atrial appendage (auricle).
  • Blood flows passively into the left ventricle; atrial contraction accounts for ~20% of ventricular filling.
  • Mitral valve (left AV valve) guards the opening to the left ventricle; two leaflets connected via chordae tendineae to two papillary muscles.
• Left ventricle (main systemic pump):
  • Thickest myocardial wall to generate high pressure for systemic circulation; no moderator band.
  • Ejects into the aorta via the aortic semilunar valve; similar valve mechanics to other semilunar valves but without chordae/papillary muscle involvement.
  • Also contains trabeculae carneae and two papillary muscles (anterior and posterior).

Cardiac Valve Function, Motion, and Conduction Context

• Four-valve plane: transverse view above AV septum shows all four valves in a single plane; AV valves open while semilunar valves are closed, allowing ventricular filling, then opposite when ventricles contract.
• Atrioventricular (AV) valves vs semilunar valves:
  • AV valves (tricuspid and mitral) possess chordae tendineae and papillary muscles that stabilize leaflets during ventricular contraction.
  • Semilunar valves (pulmonary and aortic) lack chordae and papillary muscles; cusps seal passively under pressure:
  • When ventricles relax, backflow from arteries fills cusps and closes the valve.
• Cardiac cycle basics (flow and valve states summarized):
  • Ventricles relax and fill; AV valves open; semilunar valves closed.
  • Atria contract (atrial systole) to complete ventricular filling (~20% from atrial contraction).
  • Ventricles contract (isovolumetric contraction followed by ejection); AV valves close (producing first heart sounds via closure).
  • Semilunar valves open to eject blood into great vessels; ventricles relax and recoil, causing backflow closure of semilunar valves (second heart sound).
• Modulator band and conduction: moderator band helps conduction in the right ventricle and stabilizes trabeculae; the cardiac skeleton provides a boundary for electrical impulses; this ensures synchronized contraction.

Coronary Circulation: Arteries and Veins

• Coronary arteries originate from the aorta just above the aortic semilunar valves:
  • Left coronary artery gives rise to:
  • Left circumflex artery (LCx): travels in the coronary sulcus toward the left.
  • Left anterior descending artery (LAD): runs in the anterior interventricular sulcus and gives off smaller branches; forms interconnections (anastomoses) with other branches.
  • Right coronary artery (RCA): runs in the coronary sulcus; supplies RA, portions of RV and LV, and the conduction system; gives rise to marginal arteries.
  • Anterior interventricular artery (LAD) and posterior interventricular artery (posterior descending) form connections that help sustain blood flow if a branch is blocked (anastomoses).
  • Note: the right posterior aortic sinus usually does not give rise to a vessel; two aortic sinuses (left posterior and anterior) contribute to coronary arteries.
• Coronary veins: drain the heart and generally parallel surface arteries; drainage point is the coronary sinus into the RA.
  • Great cardiac vein mirrors the LAD and anterior interventricular artery path; also receives posterior cardiac, middle cardiac, and small cardiac veins.
  • Posterior cardiac vein parallels the marginal artery; middle cardiac vein parallels the posterior interventricular artery; small cardiac vein parallels the RCA.
  • Anterior cardiac veins drain the anterior surface of the right ventricle directly into the RA (bypassing the coronary sinus).
• Coronary circulation significance: high metabolic demand of cardiomyocytes; atherosclerosis can cause ischemia and myocardial infarction (MI).
• Myocardial infarction (MI): often caused by occlusion of a coronary artery by atherosclerotic plaque or plaque embolus; leads to tissue death due to ischemia; STEMI vs non-STEMI classifications via ECG;
  • Common biomarkers: elevated CK-MB, elevated cardiac troponin.
  • Acute management: oxygen, aspirin, nitroglycerin; thrombolytics, heparin; coronary angioplasty with stents; bypass surgery; in severe cases, heart transplant or mechanical assist devices may be used.
• Coronary artery disease (CAD): leading cause of death worldwide; atherosclerosis narrows arteries, causes ischemia, angina, MI; risk factors include smoking, hypertension, diabetes, obesity, dyslipidemia, sedentary lifestyle, family history; treatments include lifestyle changes, medications, angioplasty, stents, and bypass.

Common Congenital and Acquired Defects (Overview)

• Patent foramen ovale: failure of the foramen ovale to close after birth; may be benign or require repair; detected via auscultation and confirmed via echocardiography.
• Coarctation of the aorta: congenital narrowing at the ligamentum arteriosum location; symptoms include dyspnea, fainting, chest pain; treated surgically or via angioplasty; earlier intervention improves survival.
• Patent ductus arteriosus: failure of the ductus arteriosus to close after birth; increases pulmonary flow and can cause respiratory issues; treatments include surgical ligation, coils, or NSAIDs to block prostaglandin E2; may lead to congestive heart failure if untreated.
• Tetralogy of Fallot: four-component defect (often three present) combining pulmonary infundibular stenosis, overriding aorta, VSD, and RV hypertrophy; leads to cyanosis; managed with surgical repair; survival rates vary with age.
• Septal defects can be congenital or disease-related and may be detected via auscultation or imaging.
• Cyanosis (blue baby) occurs when blood oxygenation is insufficient, producing a blue/purple skin tone, especially with activity.

Right Atrium in Focus: Veinous Return and Atrioventricular Connections

• Right atrium receives systemic venous blood: superior vena cava (head, neck, upper limbs, thorax), inferior vena cava (lower limbs, abdomen/pelvis), and coronary sinus (drains myocardium).
• Coronary sinus opens into the posterior RA; the foramen of the coronary sinus marks the venous drainage location.
• RA anatomy features include smooth surfaces with pectinate muscles on the anterior surface and in the RA auricle.

Right Ventricle in Focus

• RA → RV through tricuspid valve; chordae tendineae anchor valve leaflets to papillary muscles (anterior, posterior, septal).
• When RV contracts, pressure rises; papillary muscles contract to create tension on chordae to prevent valve prolapse and backflow.
• RV wall contains trabeculae carneae and a moderator band to reinforce structure and conduction.
• RV ejects into pulmonary trunk → lungs via left and right pulmonary arteries.
• Pulmonary semilunar valve sits at the base of the pulmonary trunk to prevent backflow into RV.

Left Atrium and Left Ventricle: Pulmonary Circuit and Systemic Output

• Pulmonary veins deliver highly oxygenated blood to the left atrium; LA has an auricle with pectinate muscles; no extensive pectinate muscles in the LA body.
• Blood flows from LA through the mitral valve to the LV; LV pumps into the aorta via the aortic semilunar valve.
• The left heart’s muscular wall is thicker to generate higher systemic pressure; LV also uses trabeculae carneae but lacks a moderator band.

Hemodynamics and Ejection Dynamics

• When ventricles contract, pressure rises and the AV valves close (prevent backflow into atria); the chordae tendineae hold valve leaflets in place; the semilunar valves open when pressure in ventricles exceeds arterial pressure.
• The difference in wall thickness between LV and RV reflects systemic vs pulmonary circuit resistance; LV generates greater pressure to overcome systemic vascular resistance.

Valve Pathophysiology: Clinical Implications

• Valvular insufficiency (regurgitation): valve fails to close, causing backward flow.
• Valve stenosis: valve becomes rigid, restricting forward flow and increasing cardiac workload.
• Valve prolapse: cusp(s) fall backward due to chordae or papillary muscle damage.
• Auscultation and imaging aid in diagnosing valve disorders; echo provides dynamic imaging of valve function.

Clinical Connections and Lifespan Implications

• CPR and heart position: knowledge of heart location guides manual chest compressions during CPR; standard recommends at least $5\ ext{cm}$ depth and $100\ \text{compressions/min}$; link to popular music tempo (e.g., Staying Alive) for pace guidance.
• Severe cardiac injury or tamponade necessitates rapid drainage to restore chamber filling and cardiac output.
• Congenital defects vary in severity; some may be tolerated for years or lifelong; others require early surgical correction.
• Myocardial infarction (MI) risk factors include LDL/HDL balance, hypertension, diabetes, obesity, smoking, exercise level, kidney disease, and drug use; management emphasizes rapid reperfusion and risk factor modification.
• Treatments for CAD/MI include pharmacologic therapy (antiplatelets, statins, anti-hypertensives), thrombolytics, angioplasty with stents, and bypass surgery; long-term management focuses on lifestyle changes and medications to reduce recurrence risk.

Quick Reference Terms and Concepts

• Pericardium, epicardium, myocardium, endocardium
• Auricle (atrial appendage); pectinate muscles; coronary sulcus; anterior/posterior interventricular sulci
• Fossa ovalis, foramen ovale, septa (interatrial, interventricular, atrioventricular)
• Cardiac skeleton; four valve annuli
• Chordae tendineae; papillary muscles (3 on right, 2 on left);
  moderator band; trabeculae carneae
• Tricuspid, mitral, pulmonary, and aortic valves; semilunar vs AV valves
• Coronary arteries: left coronary artery (LAD, circumflex), right coronary artery; coronary sinuses
• Coronary veins: great cardiac vein, middle cardiac vein, small cardiac vein, posterior cardiac vein, anterior cardiac veins; coronary sinus
• Myocardial infarction (MI); atherosclerosis; angina; STEMI vs non-STEMI; troponin and CK-MB
• Tetralogy of Fallot; patent foramen ovale; coarctation of the aorta; patent ductus arteriosus; blue baby
• Angioplasty, stents, bypass surgery; NSAIDs for PDA closure; prostaglandin E2 role
• Endothelins and vascular tone; role in contractility and vasoconstriction
• Cardiac conduction: relationship between the atrioventricular septum, skeleton, and conduction pathways

Connections to Foundational Principles and Real-World Relevance

• Structure–function relationship: heart anatomy (chamber arrangement, valve design, muscle layering) directly supports efficient unidirectional blood flow and high-output pumping under varying physiological demands.
• Pulmonary vs systemic circuits illustrate the principle of gas exchange coupled to systemic nutrient delivery, and how pressure differences drive flow.
• Coronary circulation emphasizes the necessity of continuous, high-volume perfusion to metabolically active myocardium, highlighting why coronary artery disease is particularly dangerous.
• Clinical relevance spans congenital defects, acquired valvular disease, ischemic heart disease, and emergent care (CPR, MI management).
• Ethical and practical implications of CPR training: high-quality chest compressions save brain function by maintaining cerebral perfusion; improper technique can cause harm, underscoring the importance of proper CPR education and recertification.

Equations and Numerical References (LaTeX)

• Average heart rate: $75 \, \text{contractions per minute}$
• Contractions per day (approximate): $75 \times 60 \times 24 = 108{,}000$
• Contractions per year (approximate): $108{,}000 \times 365 \approx 3.94 \times 10^{7}$
• Blood pumped per cycle per ventricle (resting adult): $70 \rm \,mL$
• Blood pumped per minute (both ventricles at rest): $70 \rm \,mL \times 2 \times 75 = 1{,}050{,}000 \rm \,mL/min = 5.25 \rm \,L/min$
• Blood per day (two ventricles at rest): $5.25 \rm \,L/min \times 60 \rm \,min/h \times 24 \rm \,h = 7{,}560 \rm \,L/day$ (note: the text cites approximately 14,000 L/day; values can vary with assumptions about resting vs peak flow.)
• Blood per year (rounded): $7{,}560 \times 365 \approx 2.76 \times 10^{6} \rm \,L \,/\, year$ ~ consistent with “about 2.6 million gallons” per year when converting units.
• Cardiac cycle depth and compression guidance: not a mathematical formula, but therapeutic depth is about $5 \text{ cm}$ and rate $100\ \text{compressions/min}$.
• Atherosclerotic plaque and ischemia: not a numerical equation, but conceptually relates plaque burden to reductions in lumen area and flow; anastomoses provide limited collateral support in the heart.

Hypothetical Scenario Highlights

• If a patient develops acute tamponade after chest trauma, rapid pericardial drainage could be lifesaving to restore diastolic filling.
• In Tetralogy of Fallot, early surgical repair can improve oxygenation and survival; remaining defects may still require follow-up interventions.
• In CAD, a patient with chest pain and dyspnea may undergo echocardiography, ECG, and troponin testing to distinguish STEMI from non-STEMI and guide reperfusion therapy.
• For a patient with PDA in infancy, NSAIDs may help close the ductus, while larger defects may necessitate coils or surgical closure to prevent pulmonary overcirculation and heart failure.

Practical Takeaways for Exam Preparation

• Know the four chambers and their basic functions, plus the sequence of blood flow through the heart and lungs.
• Be able to identify and describe the layers of the heart wall and pericardium, including the epicardium, myocardium, endocardium, and the pericardial cavity.
• Understand the valve anatomy and the role of chordae tendineae, papillary muscles, and the moderator band in ensuring one-way flow and preventing regurgitation.
• Distinguish atrioventricular vs semilunar valves in terms of structure, mechanical operation, and presence of chordae/papillary muscles.
• Recognize major coronary arteries and veins, their courses, and how occlusion leads to myocardial infarction; know basic treatments and risk factors.
• Be familiar with common congenital heart defects (foramen ovale closure, PDA, coarctation, Tetralogy of Fallot) and their clinical implications.
• Recall CPR guidelines and the rationale behind chest compressions in maintaining brain perfusion during cardiac arrest.
• Appreciate how the heart’s anatomy supports its function as a dynamic pump and how disease can disrupt this critical system.