Development of Cardiovascular System

Development of Cardiovascular System

Development of Cardiovascular System

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Heart's First Beat - Tube Twists & Turns

  • Primitive Heart Tube: Forms Day 21 from fused endocardial tubes (splanchnic mesoderm).
    • Layers: Endocardium, cardiac jelly, myocardium. Epicardium from proepicardial organ.
  • Segments & Derivatives (Cranial → Caudal):
    • Truncus Arteriosus → Aorta, Pulmonary Trunk.
    • Bulbus Cordis → Smooth RV (Conus arteriosus), Smooth LV (Aortic vestibule).
    • Primitive Ventricle → Trabeculated LV & RV.
    • Primitive Atrium → Trabeculated LA & RA.
    • Sinus Venosus → Smooth RA (Sinus venarum), Coronary sinus, Oblique vein of LA.
    • 📌 Mnemonic: To Be Perfectly At Sync. (TA, BC, PV, PA, SV)
  • Cardiac Looping (Dextral): Day 23-28.
    • Bulboventricular loop forms; crucial for chamber alignment & R-L asymmetry.
    • BC: Ventral, caudal, right. PV: Dorsocranial, left.
    • Defect: Dextrocardia (heart points right). Cardiac looping animation

⭐ The first heart beat occurs around day 22, often before maternal pregnancy awareness.

Dividing the Chambers - Walls Go Up!

  • Atrial Septation (Weeks 4-5):
    • Septum primum (↓ from atrial roof); ostium primum closes (fuses with endocardial cushions). Ostium secundum by apoptosis in SP.
    • Septum secundum (↓, muscular, right of SP); forms foramen ovale (in SS), for R→L fetal shunt.
    • Postnatally: ↑LA pressure closes foramen ovale (SP against SS) → fossa ovalis.
  • Ventricular Septation (Weeks 4-7):
    • Muscular IV septum (↑ from apex); interventricular foramen persists temporarily.
    • Membranous IV septum closes IV foramen; from endocardial cushion, conotruncal ridges, & muscular septum.
  • Outflow Tract (OFT) Septation (Weeks 5-8):
    • Aorticopulmonary (spiral) septum (neural crest cells vital) divides truncus arteriosus & conus cordis.
    • Forms Aorta & Pulmonary Trunk. Conus cordis forms smooth outflow tracts (infundibulum, aortic vestibule).

Cardiac Development Stages

⭐ VSD is most common congenital heart defect, often in membranous IV septum.

Plumbing the System - Pipes & Pathways

  • Aortic Arches (Arteries): 6 pairs from aortic sac.
    • 3rd: Common Carotid, prox. Internal Carotid. 📌 C for Carotid.
    • 4th: Left → Aortic Arch; Right → prox. Right Subclavian A. 📌 A for Aortic arch/subclavian Artery.
    • 6th ("Pulmonary"): Prox. → Pulmonary Arteries; Distal Left → Ductus Arteriosus. 📌 P for Pulmonary/PDA.
  • Major Veins:
    • Vitelline: Form portal system, hepatic sinusoids, part of IVC.
    • Umbilical: Left persists (→ Lig. teres hepatis); Ductus Venosus (→ Lig. venosum) bypasses liver.
    • Cardinal: Anterior → SVC; Posterior/Sub/Supracardinal system → IVC, Azygos.
  • Fetal Circulation Shunts:
    1. Ductus Venosus: Umbilical V. → IVC (bypasses liver).
    2. Foramen Ovale: RA → LA (bypasses lungs).
    3. Ductus Arteriosus: Pulmonary A. → Aorta (bypasses lungs).
  • Postnatal Remnants:
    • Umbilical V. → Lig. teres hepatis
    • Ductus Venosus → Lig. venosum
    • Foramen Ovale → Fossa ovalis
    • Ductus Arteriosus → Lig. arteriosum
    • Umbilical Arteries → Medial umbilical ligaments

⭐ Ductus arteriosus is kept patent by PGE2 (Prostaglandin E2) and low O2 tension. Indomethacin promotes closure.

Fetal Circulation Pathway and Shunts

When Blueprints Go Wrong - Cardiac Oopsies

  • Acyanotic (L→R Shunts):
    • VSD: Most common CHD.
    • ASD: Ostium secundum common.
    • PDA: Continuous "machinery" murmur.
  • Cyanotic (R→L Shunts): (📌 5 T's: Tetralogy, Transposition, Truncus, TAPVR, Tricuspid atresia)
    • Tetralogy of Fallot (TOF): (📌 PROVe: Pulmonary stenosis, RVH, Overriding aorta, VSD). Boot-shaped heart.

      ⭐ TOF is the most common cyanotic CHD beyond infancy.

    • TGA: Requires shunt for survival. "Egg on a string" X-ray.
  • Obstructive Lesions:
    • Coarctation of Aorta: ↑ upper limb BP, ↓ lower limb BP. Rib notching.

High‑Yield Points - ⚡ Biggest Takeaways

  • Heart development begins week 3; heart tube from splanchnic mesoderm.
  • Aortic arches (3, 4, 6) form major arteries (carotids, aortic arch, pulmonary artery).
  • Essential fetal shunts: ductus venosus, foramen ovale, ductus arteriosus.
  • Bulbus cordis forms ventricular outflow tracts; primitive ventricle forms trabeculated parts.
  • Neural crest cells are vital for aortico-pulmonary septation; endocardial cushions for AV septation.
  • Sinus venosus forms smooth RA (sinus venarum) and coronary sinus.
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Practice Questions: Development of Cardiovascular System

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Flashcards: Development of Cardiovascular System

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Congenital heart defects arise during embryogenesis, usually in weeks _____ through 8

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Congenital heart defects arise during embryogenesis, usually in weeks _____ through 8

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