Microscopic Anatomy of Endocrine Glands

Pituitary Gland - Master Controller's Micro-View

Comprises Adenohypophysis (anterior) & Neurohypophysis (posterior).

• Adenohypophysis (Pars Distalis): Cellular cords & sinusoidal capillaries.

  Staining	Cells & Hormones	Mnemonic
  Acidophils	Somatotrophs (GH), Lactotrophs (PRL)	📌 GPA
  Basophils	Corticotrophs (ACTH), Thyrotrophs (TSH), Gonadotrophs (FSH, LH)	📌 B-FLAT
  Chromophobes	Minimal granules; reserve/degranulated cells.

• Pars Intermedia: Basophilic cells (MSH), Rathke's cysts.
• Neurohypophysis (Pars Nervosa):
  • Unmyelinated axons from hypothalamus.
  • Herring bodies: Axonal dilations with ADH, Oxytocin.
  • Pituicytes: Glial support cells.

⭐ Adenohypophysis develops from Rathke's pouch (oral ectoderm); Neurohypophysis from neuroectoderm (diencephalon floor).

Thyroid & Parathyroid - Neck's Hormone Factories

• Thyroid Gland:
  • Follicles: Functional units. Lined by simple cuboidal epithelium; lumen contains colloid (thyroglobulin reservoir).
  • Parafollicular cells (C cells): Between follicles; secrete calcitonin (regulates $Ca^{2+}$ homeostasis, ↓ serum $Ca^{2+}$).

    ⭐ Parafollicular cells (C cells) are neural crest derivatives, originating from the ultimobranchial body.

• Parathyroid Glands:
  • Chief cells (Principal cells): Predominant; basophilic; secrete Parathyroid Hormone (PTH) (regulates $Ca^{2+}$ homeostasis, ↑ serum $Ca^{2+}$).
  • Oxyphil cells: Larger, acidophilic (eosinophilic) cytoplasm; numerous mitochondria; appear around puberty, function uncertain.

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Adrenal Gland - Stress Response Central

• Adrenal Cortex (Zonation & Products):
  • Zona Glomerulosa (Outer): Secretes Mineralocorticoids (e.g., Aldosterone $\rightarrow$ Salt balance).
  • Zona Fasciculata (Middle, largest): Secretes Glucocorticoids (e.g., Cortisol $\rightarrow$ Sugar metabolism, stress). Cells: Spongiocytes (foamy, lipid-rich).
  • Zona Reticularis (Inner): Secretes Androgens (e.g., DHEA $\rightarrow$ Sex characteristics).
  • 📌 Mnemonic: GFR (Layers) $\rightarrow$ Salt, Sugar, Sex (Products). "Deeper you go, sweeter it gets."
• Adrenal Medulla (Core):
  • Composed of Chromaffin cells (modified postganglionic sympathetic neurons).
  • Secretes Catecholamines: Epinephrine (Adrenaline) and Norepinephrine (Noradrenaline) $\rightarrow$ fight-or-flight.

⭐ The Adrenal Medulla is derived from neural crest cells, similar to sympathetic ganglia, and functions as part of the sympathetic nervous system.

Pancreas (Islets) & Pineal - Sugar Boss & Sleep Clock

• Pancreas (Islets of Langerhans): Endocrine cell clusters (1-2% of pancreas mass) regulating glucose.
  • Islet Cells & Hormones:

    Cell	Hormone	Location	Primary Action
    Alpha (α)	Glucagon	Periphery	↑ Blood glucose
    Beta (β)	Insulin	Central	↓ Blood glucose
    Delta (δ)	Somatostatin	Scattered	Inhibits A & B cells
    PP/Gamma (γ)	Pancreatic Polypeptide	Periphery	Regulates GI/endo

  • 📌 Insulin INside Beta cells (most numerous).
• Pineal Gland: Midline brain structure; melatonin for circadian rhythm.
  • Pinealocytes: Chief cells; produce melatonin from serotonin.
  • Corpora arenacea (brain sand): Calcified concretions; ↑ with age. No known function.

⭐ Corpora arenacea (brain sand) in the pineal gland are calcified concretions that increase with age and are radiopaque.

High‑Yield Points - ⚡ Biggest Takeaways

• Pituitary: Acidophils (GH, Prolactin), Basophils (FSH, LH, ACTH, TSH); Herring bodies in neurohypophysis.
• Thyroid: Follicles with colloid; Parafollicular C-cells secrete calcitonin.
• Parathyroid: Chief cells (PTH) and larger, eosinophilic Oxyphil cells.
• Adrenal Cortex: Zonation: Glomerulosa (aldosterone), Fasciculata (cortisol), Reticularis (androgens).
• Adrenal Medulla: Chromaffin cells (modified neurons) produce catecholamines.
• Pancreatic Islets: Beta cells (insulin) are central; Alpha cells (glucagon) peripheral.
• Pineal Gland: Pinealocytes (melatonin) and characteristic Corpora arenacea (brain sand).