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Cardiovascular & Upper Respiratory Anatomy – Key Vocabulary

Atria – The Receiving Chambers

  • General
    • Two thin-walled chambers: right atrium (RA) & left atrium (LA) – each a "receiving" chamber
    • RA receives de-oxygenated blood from
    • Superior vena cava (SVC)
    • Inferior vena cava (IVC)
    • Coronary sinus (venous drainage of heart wall)
    • LA receives oxygenated blood from lungs via {4} pulmonary veins (paired right & left, 2 each)
  • Internal landmarks (mostly visible in RA)
    • Pectinate (trabeculated) muscle gives a rough anterior wall; smoother in LA
    • Fossa ovalis
    • Thin, oval depression in inter-atrial septum
    • Remnant of fetal foramen ovale; closes at birth to prevent inter-atrial shunt
    • Openings of venae cavae & coronary sinus clearly identifiable in RA

Ventricles – The Discharging Chambers

  • Overview
    • Right ventricle (RV): pumps de-oxygenated blood to pulmonary circuit via pulmonary trunk → pulmonary arteries
    • Left ventricle (LV): pumps oxygenated blood to systemic circuit via aorta
  • Ventricular-specific wall features (test favorite!)
    • Papillary muscles – conical muscles protruding from ventricular wall
    • Chordae tendineae – tendon-like "heart-strings" anchoring valve cusps to papillary muscles
    • Trabeculae carneae – ridged muscular folds giving internal roughness (analogous to pectinate muscle of atria)
  • Thickness gradient of myocardium
    • LV myocardium is the thickest; it must generate systemic pressure sufficient to send blood "toe to head"
    • RV thinner; only needs to propel blood to nearby lungs

Valves of the Heart

  • Atrioventricular (AV) valves – between atria & ventricles; prevent back-flow into atria
    • Right AV = Tricuspid ( 3 cusps )
    • Left AV = Bicuspid / Mitral ( 2 cusps )
    • Papillary muscle contraction via chordae tendineae prevents cusp prolapse when pressure rises in ventricles
  • Semilunar (SL) valves – at ventricular exits; prevent back-flow into ventricles
    • Pulmonary SL – RV → pulmonary trunk
    • Aortic SL – LV → aorta
  • Heart sounds
    • "Lub" = simultaneous closure of both AV valves
    • "Dub" = simultaneous closure of both SL valves

Layers of the Heart Wall

  • Endocardium – thin, endothelial inner lining in contact with blood; contains trabeculae carneae / pectinate muscle
  • Myocardium – cardiac muscle; contraction layer
    • Relative thickness: LV > RV > atria
  • Epicardium (visceral serous pericardium)
    • Outermost layer; houses coronary vessels supplying myocardium

Great Vessels (Anterior View Reference)

  • Superior vena cava – far right; returns blood from head, neck, upper limbs (also receives azygos vein)
  • Aorta – central; arches over pulmonary trunk
  • Pulmonary trunk – most leftward; bifurcates quickly into right & left pulmonary arteries carrying de-oxygenated blood
  • Inferior vena cava – ascends through diaphragm at T8; enters RA inferiorly
  • Pulmonary veins ( 4 ) – oxygenated; open into posterior LA

Coronary Circulation (Arterial)

  • Origin: immediately above aortic SL cusps
  • Right coronary artery (RCA)
    • Courses in coronary sulcus between RA & RV (anterior)
    • Branches
    • Right marginal artery (inferior border)
    • Posterior interventricular artery (posterior IV sulcus)
  • Left coronary artery (LCA)
    • Very short; passes posterior to pulmonary trunk, then bifurcates into
    • Anterior interventricular artery (LAD / "widow-maker") – anterior IV sulcus between ventricles
    • Circumflex artery – wraps around left AV groove to posterior heart
  • Venous return
    • Great, middle & small cardiac veins → coronary sinus → RA

Intrinsic Conduction System (Electrical)

  1. Sino-atrial (SA) node – natural pacemaker (in RA near SVC); sets rate modulated by ANS
  2. Atrioventricular (AV) node – inter-atrial septum; receives SA impulses
  3. Bundle of His (AV bundle) – penetrates fibrous skeleton into IV septum
  4. Right & left bundle branches – descend septum toward apex
  5. Purkinje fibres – sub-endocardial network distributing impulse through ventricular myocardium
  • Autonomic modulation
    • Sympathetic (fight/flight) ↑ heart rate & force
    • Parasympathetic (rest/digest; vagus) ↓ heart rate

Fetal Circulation – Temporary Shunts & Post-Natal Remnants

  • Umbilical vein – carries oxygenated blood from placenta → fetus; post-natal remnant = round ligament of liver (ligamentum teres)
  • Ductus venosus – shunts blood from umbilical vein to IVC, bypassing immature liver; remnant = ligamentum venosum
  • Foramen ovale – RA → LA inter-atrial shunt; closes to become fossa ovalis
  • Ductus arteriosus – pulmonary trunk → aortic arch, bypassing fetal lungs; remnant = ligamentum arteriosum
  • Umbilical arteries ( 2 ) – return de-oxygenated blood from fetus to placenta; proximal remnants persist as superior vesical arteries, distal portions fibrose to medial umbilical ligaments

Comprehensive Blood-Flow Pathway (Adult)

  1. Systemic veins → RA via SVC & IVC (plus coronary sinus)
  2. RA → tricuspid valve → RV
  3. RV → pulmonary SL valve → pulmonary trunk → R/L pulmonary arteries → lungs (gas exchange)
  4. Lungs → R/L pulmonary veins → LA
  5. LA → bicuspid valve → LV
  6. LV → aortic SL valve → aorta → systemic arteries

Beginning of Respiratory System (Conducting Division)

  • Functional divisions
    • Conducting: nasal cavity → terminal bronchioles (no gas exchange)
    • Respiratory: respiratory bronchioles → alveoli (gas exchange)
  • Nasal cavity
    • Three conchae (superior, middle, inferior) create turbulence; functions:
    • Warm, moisten & filter incoming air
    • Meatuses beneath conchae receive drainage from paranasal sinuses & nasolacrimal duct (→ sniffles when crying)
  • Pharynx – common aero-digestive chamber; three zones
    1. Nasopharynx – solely air; contains pharyngeal tonsil ("adenoids"), Eustachian tube opening
    2. Oropharynx – air + food/fluid; contains palatine & lingual tonsils
    3. Laryngopharynx – air + food/fluid; ends where paths diverge (anterior larynx vs. posterior esophagus)
  • Larynx (voice box)
    • Cartilaginous skeleton keeps airway patent
    • Thyroid cartilage (Adam’s apple; laryngeal prominence)
    • Cricoid cartilage (complete ring, inferior)
    • Epiglottis (elastic cartilage flap; folds over glottis during swallowing)
    • Arytenoid cartilages (paired, pyramidal; anchor vocal cords & pivot to change tension)
    • Vocal folds
    • Superior vestibular folds = "false"; protective/resonance
    • Inferior true vocal folds = vocal cords; phonation; abduct/adduct for pitch

Key Clinical / Practical Connections

  • LV hypertrophy can follow chronic hypertension because myocardium must overcome higher systemic resistance
  • LAD occlusion (widow-maker) commonly fatal due to large territory supplied
  • Valve incompetence (e.g.
    • Mitral prolapse when chordae/papillary fail)
  • ASD / VSD persistence (failure of fetal shunts to close) → cyanosis
  • Auscultation points correspond to valve flow directions, not anatomic position
  • Middle-ear infections in children often follow URIs because pathogen-laden mucus traverses the auditory (Eustachian) tube from nasopharynx to middle ear