development of piatiyutari gland or mbbs student for6 mars question
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Development of the Pituitary Gland (Hypophysis)
MBBS Embryology - 6 Marks Answer
Key Concept: Dual Origin
The pituitary gland is unique because it develops from two completely different embryological sources that grow toward each other and fuse.
| Component | Embryological Origin | Structure Formed |
|---|---|---|
| Rathke's pouch | Oral ectoderm (stomodeum / roof of primitive mouth) | Adenohypophysis (anterior pituitary) |
| Infundibulum | Neuroectoderm (floor of diencephalon / 3rd ventricle) | Neurohypophysis (posterior pituitary) |
Step-by-Step Development
Week 3
- Rathke's pouch appears as an upward evagination (outpocketing) of the ectoderm of the stomodeum (primitive oral cavity), just in front of the oropharyngeal membrane.
- Simultaneously, the floor of the diencephalon sends a downward projection called the infundibulum.
- Both structures grow toward each other.
End of Week 6
- The connection of Rathke's pouch with the oral cavity disappears (the stalk is obliterated).
- Rathke's pouch is now in close contact with the infundibulum and lies completely enclosed within the cranium.
By End of Month 2
- Rathke's pouch loses its connection with the oral cavity entirely.
- Cells in the anterior wall of Rathke's pouch proliferate rapidly → form the anterior lobe (pars distalis) - the bulk of the adenohypophysis.
- The posterior wall of Rathke's pouch becomes the thin pars intermedia (rudimentary in humans).
- A small extension of the anterior wall grows upward around the infundibular stalk → pars tuberalis.
- The infundibulum gives rise to the infundibular stalk and pars nervosa (posterior lobe / neurohypophysis).
Final Parts of the Pituitary Gland
Adenohypophysis (from Rathke's pouch - oral ectoderm):
- Pars distalis - largest part; bulk of anterior lobe; from thickened anterior wall of Rathke's pouch
- Pars tuberalis - wraps around the infundibular stalk; from anterior wall extension
- Pars intermedia - thin strip adjacent to posterior lobe; from posterior wall of Rathke's pouch
Neurohypophysis (from infundibulum - neuroectoderm of diencephalon):
- Pars nervosa (posterior lobe) - composed of neuroglial cells (pituicytes) + nerve fibers from hypothalamus
- Infundibular stalk - connects pituitary to hypothalamus
Developmental Diagram
Fig: (a) 6-week embryo: Rathke's pouch (red) grows up from oropharynx; neuroectoderm (blue) grows down from diencephalon. (b) 10 weeks: Rathke's pouch nearly detached from oropharynx, merging with infundibulum. (c) Mature pituitary: anterior lobe (red) and posterior lobe (blue) within sella turcica of sphenoid bone.
Location
The fully formed pituitary gland lies in the sella turcica (the "Turkish saddle") - a bony fossa of the sphenoid bone. It is connected to the hypothalamus by the infundibular stalk.
Clinical Correlation - Craniopharyngioma ⭐
This is a high-yield exam point!
If the stalk of Rathke's pouch is not completely obliterated, remnants of oral epithelium persist along the path of migration. These epithelial remnants can give rise to a craniopharyngioma - a benign but locally invasive suprasellar tumor derived from squamous epithelium of Rathke's pouch remnants. It is the most common suprasellar tumor in children.
Summary Table for Quick Revision
| Feature | Adenohypophysis | Neurohypophysis |
|---|---|---|
| Origin | Oral ectoderm (Rathke's pouch) | Neuroectoderm (diencephalon) |
| Appears | ~Week 3 | ~Week 3-4 |
| Parts | Pars distalis, pars tuberalis, pars intermedia | Pars nervosa, infundibular stalk |
| Cell type | Endocrine secretory cells | Pituicytes (modified astrocytes) + axon terminals |
| Hormones | GH, TSH, ACTH, FSH, LH, Prolactin | ADH, Oxytocin (produced in hypothalamus, stored here) |
Sources: Langman's Medical Embryology, Junqueira's Basic Histology 17e, Ganong's Review of Medical Physiology 26e, Histology: A Text and Atlas (Ross)
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