MCAR 2724 ‒ Heart, Pericardium, Mediastinum & Embryology

Vocabulary flashcards covering mediastinal anatomy, pericardium, heart structure, conduction, coronary circulation, embryological development, congenital anomalies and foetal circulation for MCAR Session 2 review.

Mediastinum

Central thoracic compartment between the two pleural cavities, extending from thoracic inlet to diaphragm and sternum to vertebral bodies.

Superior Mediastinum

Upper mediastinal region above the sternal angle; contains thymus, great veins, aortic arch, trachea, oesophagus, thoracic duct, vagus, phrenic and sympathetic nerves.

Anterior Mediastinum

Narrow space anterior to pericardium; holds fat, loose CT, lymphatics, internal thoracic vessels and sometimes thymic remnants.

Middle Mediastinum

Region occupied by pericardium, heart, roots of great vessels, phrenic nerves and pericardiophrenic vessels.

Posterior Mediastinum

Space posterior to pericardium (T5–T12); contains thoracic aorta, azygos system, oesophagus, thoracic duct, vagus, sympathetic trunks and splanchnic nerves.

Pericardium

Double-walled sac enclosing heart and proximal great vessels; consists of fibrous and serous layers.

Fibrous Pericardium

Tough outer pericardial layer anchoring heart to diaphragm and great vessels; prevents acute over-distension.

Serous Pericardium

Two-layered (parietal & visceral) thin membrane lining the fibrous sac and covering the heart.

Parietal Layer (serous pericardium)

Lines inner surface of fibrous pericardium; reflects onto great vessels to become visceral layer.

Visceral Layer / Epicardium

Serous layer directly on heart surface; forms outermost layer of heart wall.

Pericardial Cavity

Potential space between parietal and visceral serous layers, containing lubricating serous fluid.

Transverse Pericardial Sinus

Passage posterior to ascending aorta & pulmonary trunk, anterior to SVC; useful in cardiac surgery for clamping great vessels.

Oblique Pericardial Sinus

Blind U-shaped recess posterior to left atrium, bounded by pulmonary veins and IVC.

Pericardiophrenic Artery

Branch of internal thoracic artery supplying fibrous & parietal serous pericardium.

Pericardiophrenic Vein

Vein accompanying phrenic nerve; drains parietal pericardium to brachiocephalic or azygos systems.

Phrenic Nerve

C3–C5 nerve supplying motor to diaphragm and sensory to fibrous & parietal serous pericardium (referred pain to shoulder).

Crista Terminalis

Muscular ridge inside right atrium separating smooth sinus venarum from pectinate-muscle region.

Pectinate Muscles

Comb-like muscular ridges in atrial auricles and anterior right atrial wall.

Fossa Ovalis

Oval depression on interatrial septum—remnant of foetal foramen ovale.

Trabeculae Carneae

Irregular muscular ridges lining ventricular walls.

Moderator Band (Septomarginal Trabecula)

Muscular band in right ventricle carrying right bundle branch to anterior papillary muscle.

Conus Arteriosus

Smooth outflow tract of right ventricle leading to pulmonary valve.

Atrioventricular (AV) Valves

Leaflet valves between atria and ventricles (tricuspid & mitral) preventing back-flow during systole.

Tricuspid Valve

Right AV valve with anterior, posterior & septal cusps.

Mitral (Bicuspid) Valve

Left AV valve with anterior & posterior cusps.

Semilunar Valves

Pocket-like valves (aortic & pulmonary) guarding ventricular outflow tracts.

Aortic Valve

Left ventricular outflow valve with right, left (coronary) and posterior cusps.

Pulmonary Valve

Right ventricular outflow valve with anterior, right & left cusps.

Cardiac Skeleton

Fibro-cartilaginous rings and trigones providing attachment for valves and electrical insulation between atria & ventricles.

Fibrous Trigone

Strong connective tissue between aortic, mitral and tricuspid valve rings; left & right trigones anchor cardiac skeleton.

SA Node

Primary pacemaker located at junction of SVC & right atrium; intrinsic rate ≈ 70 BPM.

AV Node

Secondary pacemaker in interatrial septum near coronary sinus opening; delays impulse before ventricles.

AV Bundle (Bundle of His)

Only electrical connection through cardiac skeleton; divides into right and left bundle branches along IV septum.

Purkinje Fibers

Subendocardial conducting network distributing impulses to ventricular myocardium.

Coronary Arteries

Right and left arteries arising from aortic sinuses supplying myocardium and epicardium.

Right Coronary Artery (RCA)

Runs in right coronary sulcus; gives SA nodal (55%), right marginal, posterior interventricular (dominant in 85%) & AV nodal branches.

Left Coronary Artery (LCA)

Short stem splitting into LAD and circumflex branches.

Left Anterior Descending (LAD)

Anterior interventricular branch of LCA; supplies anterior IV septum, anterior ventricles and apex.

Circumflex Artery

LCA branch in left coronary sulcus; gives left marginal branch; may supply SA/AV nodes in left dominance.

Right Marginal Branch

RCA branch along acute margin of heart to supply right ventricle.

Posterior Interventricular Branch

Terminal branch in dominance pattern; supplies posterior IV septum and adjacent ventricles.

Coronary Sinus

Main venous channel in posterior coronary sulcus opening into right atrium.

Great Cardiac Vein

Runs with LAD then circumflex; drains areas supplied by LCA to coronary sinus.

Middle Cardiac Vein

Accompanies posterior interventricular artery; drains to coronary sinus.

Small Cardiac Vein

Runs with right marginal artery; empties into coronary sinus.

Anterior Cardiac Veins

Small veins crossing right coronary sulcus to empty directly into right atrium.

Veins of Thebesius (Venae cordis minimae)

Tiny intramyocardial veins that drain directly into all heart chambers.

Coronary Dominance

Artery (RCA or circumflex) that gives rise to posterior interventricular branch; determines blood supply to AV node/IV septum.

Referred Cardiac Pain

Visceral afferents travel with sympathetic fibers (T1–T4), producing pain in chest, shoulder, medial arm.

Embryonic Heart Tube

Straight tube formed in week 3 that folds to create cardiac loop and primitive chambers.

Cardiac Loop

Bending of heart tube placing atria posterior-superior and ventricles anterior-inferior by day 28.

Septum Primum

First crescentic septum growing from atrial roof toward endocardial cushions.

Septum Secundum

Thicker right-side septum with incomplete formation leaving the foramen ovale.

Foramen Ovale

Foetal interatrial opening allowing right-to-left shunt; closes after birth to become fossa ovalis.

Atrial Septal Defect (ASD)

Persistent interatrial communication, often from patent foramen ovale or ostium secundum defect; typically acyanotic left-to-right shunt.

Interventricular Septum

Composite muscular (ventricular walls) and membranous (endocardial cushion) partition between ventricles.

Interventricular Foramen

Temporary opening above muscular septum before membranous part forms.

Ventricular Septal Defect (VSD)

Most common congenital heart defect; failure of septum closure causing left-to-right shunt—acyanotic unless Eisenmenger develops.

Endocardial Cushions

Neural-crest-derived swellings in AV and conotruncal regions forming septa and AV valves; defects linked to facial anomalies.

Truncus Arteriosus

Primitive arterial outflow that divides into aorta & pulmonary trunk via conotruncal septum.

Conus Cordis

Outflow tract of ventricles forming infundibula and proximal great vessels.

Transposition of the Great Vessels

Failure of conotruncal septum to spiral; aorta from RV, pulmonary trunk from LV—cyanotic.

Tetralogy of Fallot

Pulmonary stenosis, VSD, overriding aorta, right ventricular hypertrophy—cyanotic conotruncal defect.

Patent Ductus Arteriosus (PDA)

Persistence of foetal ductus between pulmonary trunk & aorta; produces continuous murmur, acyanotic left-to-right shunt.

Ligamentum Arteriosum

Fibrous remnant of ductus arteriosus after functional & anatomical closure postnatally.

Ductus Venosus

Foetal shunt bypassing liver; becomes ligamentum venosum after birth.

Umbilical Arteries

Foetal vessels returning deoxygenated blood to placenta; distal portions form medial umbilical ligaments.

Umbilical Vein

Carries oxygenated blood from placenta; becomes ligamentum teres hepatis in falciform ligament.

Coarctation of the Aorta

Localised narrowing (pre- or post-ductal) of aortic arch; collateral intercostal circulation and upper-limb hypertension.

Double Aortic Arch

Persistence of both right & left dorsal aortae forming vascular ring compressing trachea/oesophagus.

Aberrant Right Subclavian Artery

Right subclavian arises distally and passes posterior to oesophagus; may cause dysphagia lusoria.

Eisenmenger Syndrome

Reversal of long-standing left-to-right shunt owing to pulmonary hypertension, producing cyanosis.

Cyanotic Heart Defect

Congenital lesion causing right-to-left shunt or mixing, leading to systemic desaturation and central cyanosis.

Acyanotic Heart Defect

Lesion with left-to-right shunt or obstruction without systemic desaturation; cyanosis absent until complications arise.