Adrenal Gland development

  • A= Adrenal cortex (A1= Zona Glomerulosa, A2= Zona Fasciculata, A3= Zona Reticularis; @GFR)
  • B= Adrenal medulla (consist of chromaffin cells which are formed by the migrating neural crest cells)
  • In the first picture, C= mesothelial cells
  • Adrenal cortex is derived from the mesothelial cells. During 4th week some of the mesothelial lining cells detach and invaginate into the mesoderm. These will surround the neural crest cells which have arrived in the urinary ridge to form the adrenal medulla.
  • With further development, the mesenchymal cells proliferate and so the cortex will engulf the medulla.
  • At birth, the cortex has two layers: zona glomerulosa and zona fasciculata
  • Only at the end of 3rd year, the zona reticularis layer can be identified, thus completing the 3 layers of an adult adrenal gland
  • Zona glomerulosa secretes mineralocorticoids, zona fasiculata secretes glucocorticoids and zona reticularis secretes gonadocorticoids (the mnemonics: the deeper you go the sweeter it gets–> salt, sugar and sex 😉

Caudal end of the embryo – Sagittal Section

  • A= Paramesonephric (Müllerian) duct
  • B= Mesonephric (Wolfian) duct
  • C= Vein (future venacava)
  • D= Umbilical artery
  • E= Metanephric blastema
  • F= Ureteric bud
  • G= Cloaca
  • H= Urorectal septum
  • I= Allantois
  • J= Phallus
  • K= Coccyx
  • L= Umbilicus
  • M= Umbilical vein
  • N= Hindgut
  • O= Dorsal mesentery

Development of Kidneys

Developing kidneys

  • The model shows:
    • At the lower pole: the segmented kidneys present in the new born and
    • At the upper pole: its later form
  • The kidneys in human develop from metanephric blastema.
  • The nephrons are formed from the cap of metanephrics blastema covering the branches of ureteric bud (which arise from the distal end of mesonephric duct).
  • The entire kidney develops as a segmented structure.
  • New nephrons are forming till birth, and even at birth the kidney is a segmented structure (at birth 1 million nephrons are present in each kidney)
  • After birth, the formation of new nephrons is stopped but their growth continues till infancy. Due to the growth of nephrons, the segments also grow in size and unite with one another. The result is that the kidney loses its segmented structure

Descent of testis and abnormalities: Congenital hernia, cyst and hydrocoele


  • The testes (also the ovaries) develop in the genital ridge present in the lumbar region during the embryonic period.
  • The testes, however, have to descend to their normal adult position in the scrotum.
  • They reach the inguinal canal at 12 weeks, migrate through the inguinal canal at 28 weeks and reach the scrotum at 33 weeks, so that the normal testes are present in the scrotum during birth (this process in affected by androgen and MIS- the Mullerian inhibiting substance)
  • When the testes are migrating, the abdominal peritoneum evaginates into the scrotal swelling, known as processus vaginalis
  • At birth or shortly thereafter (can take upto 1 years as well), the lumen of the processus vaginalis obliterates. (Model A)
  • If the lumen fails to obliterate, the intestinal content can herniate into the scrotum. This is called congenital inguinal hernia. (Model B)
  • Sometimes the lumen closes irregularly, so that at some places the lumen remains intact. These intact lumen can later start secreting fluid.
  • If the patent lumen is small, a cyst is formed (Model C- a spermatic cord cyst).
  • If the lumen is large and there is extensive fluid collection, it is called congenital hydrocele (Model D).

Caudal end of the embryo – Tansverse Section

Developing caudal end:

  • A= neural tube
  • B= Paraxial mesoderm
  • C= Notochord
  • D= Primitive aorta
  • E= Branch to mesonephros
  • F= Mesonephric tubule
  • G= Paramesonephric (Müllerian)duct
  • H= Mesonephric (Wolfian) duct
  • I= Primitive gonad
  • J= Dorsal mesentery
  • K= Hind gut
  • L= Vein (later becomes Inferior vena cava)
  • M= Artery (superior continuation of umbilical artery)

Facial cleft: Cleft lip

  • It results from the failure of the fusion of the maxillary prominence with the corresponding median nasal prominence
  • It could be limited to the defect in the lip, or can extend deeper to cause upper jaw cleft, primary palate cleft (together these constitute anterior cleft as they lie anterior to the incisive foramen) or secondary palate cleft and cleft uvula(these are called posterior cleft as they lies posterior to the incisive foramen)
  • Remember the development of the face, which occurs from the following prominences:
Prominences Structures formed
Frontonasal (except this all other are paired) Forehead, nasal bridge, medial and lateral nasal prominence
Medial nasal Philtrum of lips, crest and tip of nose
Lateral nasal Alae of nose
Maxillary Cheeks and lateral part of upper lip
Mandibular Lower lip


Oblique facial cleft

  • Oblique facial cleft is formed due to the failure of fusion of the corresponding maxillary prominence and median and lateral nasal prominence.
  • Because nasolacrimal duct arises from the groove between the maxillary and lateral nasal prominence, in oblique facial cleft the nasolacrimal duct is either not formed at all or exposed
  • Remember the development of the face, which occurs from the following prominences:
Prominences Structures formed
Frontonasal (except this all other are paired) Forehead, nasal bridge, medial and lateral nasal prominence
Medial nasal Philtrum of lips, crest and tip of nose
Lateral nasal Alae of nose
Maxillary Cheeks and lateral part of upper lip
Mandibular Lower lip


Pharyngeal arches & development of tongue

  • The pharyngeal arches are numbered from I to VI
  • The pharyngeal pouches are numbered from 1 to 4
  • A= Lateral lingual swelling (1st pharyngeal arch)
  • B= Medial lingual swelling or Tuberculum impar (1st pharyngeal arch)
  • Large arrow= foramen caecum
  • C= Copula or hypobranchial eminence (formed by 2nd to 6th pharyngeal arches)
  • D= Epiglottic swelling (4-6th pharyngeal arch)
  • E= Arytenoid swelling (4-6th pharyngeal arch)
  • Small arrow= laryngeal orifice
  • The second picture is more advanced stage of the first picture. In this picture, A= fused lateral lingual swelling, rest of the labeling is same as the first picture.
  • The examiner will ask you to identify the structures present in the model, and then the structures that develop from the pharyngeal arches and the pouch.

Development of tongue:

  • Developmentally, the anterior 2/3rd tongue is different from the posterior 1/3rd portion
  • Anterior 2/3rd develops from the two lateral lingual swelling and tuberculum impar (First pharyngeal arch)
  • Posterior 1/3rd develops from the copula or the hypobranchial eminence (2nd to 6th pharyngeal arches)
  • The foramen caecum is the demarcation between the ant 2/3rd and post 1/3rd portion

Adult tongue:

  • A= Circumvallate papillae
  • B= Pharyngeal part of tongue (post. 2/3rd part)
  • C= Foliate papillae
  • Small arrow= Foramen caecum
  • Larger arrow= Sulcus terminalis
  • D= Epiglottis
  • E= Medial glossoepiglottis fold
  • F= Vallecula
  • G= Palatine tonsil
  • H= Lateral wall of oropharynx

Trilaminar germ disc: Neural tube folding

  • A= Neural crest cells
  • B= Ectoderm
  • C= Neuroectoderm
  • D= Paraxial mesoderm forming the somite
  • E= Intermediate mesoderm
  • F= Lateral plate mesoderm (parietal or somatic mesoderm)
  • G= Lateral plate mesoderm (visceral or splanchnic mesoderm)
  • H= Intra-embryonic cavity
  • I= Notochord
  • J= Endoderm
  • K= Yolksac
  • L= Probably, the mesoderm which gives rise to hemangioblasts. These later give rise to blood and blood vessels by vasculogenesis and angiogenesis

Neural crest migration

  • A= Neural crest cells
  • B= Migrating neural crest cells
  • C= Primitive aorta
  • D= Neural crest cells destined to form Preaortic ganglia
  • E= Neural crest cells migrating to gut wall to form enteric nerve plexus
  • F= Primitive gut
  • G= Visceral mesodermal lining epithelium (mesothelium)
  • H= Mesoderm
  • I= Primitive germ cells in gonadal ridge