AN52.1-8 | Histology & Embryology (Abdomen & Pelvis) — Summary & Reflection

REFLECT

A male newborn is found to have a single left kidney on neonatal ultrasound. His right ureter is absent. His right testis is undescended and his right vas deferens is absent.

What embryological event accounts for ALL these anomalies simultaneously? What is the key embryological relationship between the ureteric bud and the Wolffian duct? Why does absence of the ureteric bud predict absence of the ipsilateral kidney AND the ipsilateral vas deferens?

KEY TAKEAWAYS

Histology & Embryology of Abdomen and Pelvis — Key Points:

1. GIT histology keys: Brunner's glands = duodenum (submucosa); Peyer's patches = ileum; no villi = large intestine; Kupffer cells + space of Disse = liver
2. Liver zones: zone 1 (periportal) = hepatitis; zone 3 (centrilobular) = congestion/ischaemia/paracetamol toxicity
3. Testis: Sertoli cells (blood-testis barrier + AMH); Leydig cells (testosterone); Sertoli-cell-only = azoospermia
4. Corpus luteum: progesterone (large luteal cells) + oestrogen (small luteal cells); large pale folded cells on histology
5. Cardio-oesophageal junction: stratified squamous → simple columnar; site of Barrett's oesophagus
6. Diaphragm: 4 sources — septum transversum (main), pleuroperitoneal membranes, dorsal mesentery, body wall muscle; Bochdalek hernia = left posterolateral defect
7. Duodenal atresia: failure of recanalisation → double-bubble; associated with Down syndrome
8. Midgut rotation: 270° counterclockwise; malrotation → Ladd's bands + volvulus risk
9. Hirschsprung's disease: neural crest migration failure → distal aganglionosis → functional obstruction
10. Kidney development: ureteric bud (Wolffian duct) + metanephric mesenchyme; horseshoe kidney blocked at IMA; ARPKD = childhood, ADPKD = adults
11. Sex differentiation: SRY → Sertoli (AMH → Müllerian regression) + Leydig (testosterone → Wolffian + male genitalia); no SRY → female; undescended testis = orchidopexy before age 2