Foregut, hindgut, Midgut

Development of Umbilical Cord and Gut Regions

Regions of Primitive Gut Tube

• FG – Foregut

• MG – Midgut

• HG – Hindgut

Folding of Embryo

• Folding causes incorporation of part of the yolk sac into the embryo as the gut tube.

Yolk Sac & Its Extensions

• Yolk sac remains outside the embryo.

• Vitello-intestinal duct (Vitelline duct) connects the yolk sac to the midgut.

• Allantois arises from hindgut (extends into umbilical cord).

Umbilical Cord Contents

• Contains: 1 vein & 2 arteries (70%)

Constituents	Function
2 umbilical arteries	Carry deoxygenated blood from fetus.
1 umbilical vein	Carries oxygenated blood to fetus. (SpO2 -80%)
Wharton's jelly	Gelatinous substance
Allantois	Early urine formation → becomes urachus
Vitello-intestinal duct	between yolk sac and midgut

• Single umbilical artery
• 5-10/1000 live births
• A/w ↑↑ risk of a renal anomaly in the baby

Order of Decreasing Saturation of O2

• Umbilical vein: 80%

• Inferior vena cava (IVC): 70%

• LV: 65% > RV: 55-60%

• Superior vena cava

Where would you place the pulse oximeter to measure preductal oxygen saturation in an infant who was born 3 minutes ago?

A. Left upper limb
B. Left lower limb
C. Right upper limb
D. Right lower limb

ANS

Right upper limb

Sensory supply

• Lies between L₃ & L₄.

• Supplied by T₁₀ fibres.

Pathology of Midgut

• Pain is referred to the umbilicus.

A → Ventral Mesogastrium

• Ventral → Lesser omentum + Falciform ligament

• Dorsal → Greater omentum + Spleen + related ligaments

Foregut Development

• Part of the primitive gut tube

• Derived from endoderm

• Extends from buccopharyngeal membrane to major duodenal papilla

• Rotates 90° clockwise during development

Derivatives of the Foregut

• Respiratory tube
• Forms trachea, bronchi, and lungs
• Epithelium: from foregut endoderm
• Smooth muscle: from ventral visceral lateral plate mesoderm

• Pharyngeal pouches

• Urogenital sinus (partial contribution)

• Esophagus

• Stomach

• Duodenum

Part of duodenum	Orgin
First part	foregut
Upper half of second part	foregut
Lower half of second part and beyond	midgut

SEPTUM TRANSVERSUM

• Undifferentiated LPM at the cranial end of the embryo

• Most cranial structure in the embryonic plate before Folding

• DERIVATIVES
1. Central Tendon of diaphragm
2. Fibrous Pericardium
3. Stroma of Liver including Kupffer cells
4. Ventral Mesogastrium — Lesser omentum.

Liver development

• Hepatic bud (endoderm):
• forms hepatocytes and biliary apparatus

• Septum transversum (mesoderm):
• forms liver stroma and Kupffer cells

Pancreas development

Origin	Structures derived
Ventral Pancreatic Duct + Distal part of Dorsal Pancreatic Duct	Duct of Wirsung (Main Pancreatic Duct)
Proximal part of Dorsal Pancreatic Duct	Duct of Santorini (Accessory Pancreatic Duct)
VPB	Lower head & uncinate pancreas
DPB	Upper head, neck, body, & tail of pancreas.

Derivatives of Mesogastrium

NOTE

• Ligamentum teres hepatis → Remnant of Left Umbilical vein

Arterial Supply

• Main artery: Celiac trunk
• Supplies structures from lower esophagus to major duodenal papilla
• Also supplies liver, pancreas, and spleen

• Left gastric artery (branch of celiac):
• supplies upper esophagus

Hindgut and Allantois

• Hindgut forms
• Rectum and anal canal.
• Cloaca is present between the hindgut and allantois.

Allantois/Urachus Remnant

• Allantois → (obliterated) → Urachus
• becomes MEDIAN umbilical ligament
• located at apex of bladder.
• Mneumonic: An Orange (urachus)

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NOTE: Umbilical Remnants:

• Umbilical arteries → 2
• Obliterate before birth.
• Remnant:
• Proximal part → Superior vesical artery.
• Distal part → Obliterated umbilical artery → Medial umbilical ligament
• NOTE
• Lateral umbilical ligament
• Remnant of Inferior Epigastric vessels

• Umbilical vein (left) → 1
• Obliterates after closure of umbilical artery.
• Remnant: Ligamentum teres hepatis.

---

Urine from umbilicus:

• Due to persistence of urachus or Allantois.

• Leads to weeping umbilical cord
• (urine dribbling from umbilicus)

Meconium from umbilicus:

• Due to persistence of Entire Vitello intestinal duct.

• NOTE: Proximal part only → Meckel’s diverticulum

Cloaca Division and Urorectal Septum

• Cloaca is divided by Urorectal septum (extraembryonic mesoderm) into:
• Anterior part → Urogenital sinus
• Posterior part → Primitive rectum

• Urogenital membrane lies at the distal end of the urogenital sinus.

• Anal canal forms from the posterior part.

Anal Canal Development

 

• Upper 2/3 from endoderm (primitive rectum)

• Lower 1/3 from ectoderm (Anal membrane)

• Dentate line marks the junction

Urogenital System Development

Endoderm → gives Urogenital sinus which forms

1. Bladder
• Except trigone of Bladder → Derived from mesonephric duct

2. Urethra (partly).

3. Lower 3rd of Vagina

Intermediate mesoderm forms

1. Genital ridge
• forms gonads
• (at 5 weeks of intrauterine life, testes before ovary).

2. Nephrogenic cord
• Kidney
• Mesonephric duct/Wolffian duct (from mesonephros)
• Ureteric bud
• Trigone of Bladder
• Paramesonephric duct / Mullerian duct

So, Bladder is formed from

• UGS

• Nephrogenic cord → trigone

Paramesonephric Duct (Müllerian duct) derivatives:

Females:

• Fallopian tube.

• Uterus.

• Upper part of vagina.
• Lower 1/3rd formed by UGS

Mullerian Duct in Males:

• Appendix of testes (hydatid of morgagni)

• Prostatic utricle

Appendix of Testis

• Small pedunculated structure on the upper pole of testis, beneath the tunica vaginalis

• Hydatid of Morgagni

• Remnant of paramesonephric (Müllerian) duct in males

• Homologue of the fallopian tube in females.

• Clinical relevance:
• Can undergo torsion → acute scrotal pain (esp. in children).

Prostatic Utricle

• Müllerian duct remnant

• male homologue of uterus + upper vagina

• Also know as masculine vagina

Exam pearl:

• Müllerian duct remnants → Appendix testis, Prostatic utricle

• Wolffian duct remnants → Appendix epididymis

Mesonephric Duct / Wolffian Duct

Derivatives:

• Ureteric bud and trigone.

• Males:
• Posterior wall of prostatic urethra
• till Ejaculatory Duct
• Spermatic Pathway:
• Vas deferens
• ejaculatory duct
• Appendix of epididymis
• seminal vesicle.

• Females:
• Posterior wall of urethra.
• Gartner’s Duct:
• Between broad ligament layers
• duct of epoophoron

Male Urethra

• Urethra:
• Prostatic Urethra:
• Mesonephric duct (mesoderm)
• Urogenital sinus (endoderm)
• Membranous Urethra & Spongy Urethra
• Urogenital sinus (endoderm).
• Terminal urethra
• in glans, ectoderm

Female Urethra:

• Endoderm: Anterior wall

• Mesoderm: Post. Wall

• No ectoderm (forms clitoris).

Terms

Development of Midgut

• Midgut extend from
• Junction of major duodenal papilla
• Between 2/3rd right and 1/3rd left of transverse colon

• Midgut development begins → 6th week

• Physiological Umbilical Hernia
• 6th week
• Return to abdomen (reduction) → at 10th week

Midgut Segments

• Pre-arterial segment
• Small Intestine

• Post-arterial segment
• Large Intestine

• Axis for rotation
• Superior Mesenteric Artery
  (SMA)

Midgut Rotation

1st Rotation

• 90° anti-clockwise

• Occurs at umbilical opening

• Pre-arterial segment → right side

• Post-arterial segment → left side

2nd Rotation

• 90° anti-clockwise

• (Pre-arterial segment overlaps post-arterial segment)

3rd Rotation

• 90° anti-clockwise

• Cecum moves to → sub-hepatic position
• then descends to right iliac fossa
• due to differential growth of posterior - abdominal wall

Total

• 90° × 3 = 270° anti-clockwise

Malrotation (Subpyloric Caecum)

Conditions	1st R	2nd R	3rd R	ㅤ
Non-Rotation	N	Abnormal	Abnormal	• SI on right side • LI on left side
Malrotation	N	N	Absent	• Subpyloric Caecum Persistence of Ladd band ↳ Duodenal obstruction ↳ Bilious vomiting ↳ Double bubble sign Very short mesentery ↳ High risk of volvulus
Reverse Rotation	N	180° clockwise	ㅤ	• In effect = 90 clockwise Transverse colon is overlapped by: ↳ Superior mesenteric artery ↳ Duodenum • Cause obstruction

• CT

 

• Contrast → Iohexol
• BARIUM NOT USED
• Corkscrew appearance

Ladd's Band

• m/c intestinal malrotation abnormality.

• Runs from Rt hypochondrium to caecum.

• Duodenal compression.

• Mx: Excision of band.

Non-Rotation

Reverse Rotation

Omphalocele

 

• Failure of reduction of physiological hernia.

• Sac present
• Cord attached to it.
• Comes through the midline
• Covering membrane of sac is present.

• Defect through umbilicus, (Sac → Central)
• Large defects (liver can herniate)

• Chronic

• Associated with congenital anomalies
• Beckwith Wiedemann syndrome
• Trisomy 13, 18, 21

Gastroschisis

 

• Defect is due to incomplete folding of embryo.

• Most common and acute and life threatening
• Risk of atresia, infection/perforation

• Split in the Anterior abdominal wall.
• Herniation from the defect
• Adjacent to the cord.

• Paraumbilical
• Defect adjacent to umbilicus

• Sac absent → Contain only intestinal loops
• (can get dry/shriveled)

• Fewer congenital anomalies

Management (Both): 

• Surgical (gradual closure to avoid abdominal compartment syndrome)