Endocrine System Histology

Pituitary Gland - Master Controller HQ

• Embryology: Adenohypophysis from Rathke's pouch (oral ectoderm); Neurohypophysis from neuroectoderm (diencephalon).
• Blood Supply: Superior & Inferior hypophyseal arteries; Hypophyseal portal system (long & short routes; connects hypothalamus to anterior pituitary).

Adenohypophysis (Pars Distalis)

• Cell types: Acidophils (40%), Basophils (10%), Chromophobes (~50%).

  Cell Type	Subtype	Hormone(s)	Staining
  Acidophils	Somatotrophs	GH	Eosinophilic
  	Lactotrophs	PRL	Eosinophilic
  Basophils	Corticotrophs	ACTH	Basophilic
  	Thyrotrophs	TSH	Basophilic
  	Gonadotrophs	FSH, LH	Basophilic
  Chromophobes	-	Minimal/No hormones	Poorly stains

• 📌 Mnemonic: B-FLAT (Basophils: FSH, LH, ACTH, TSH).

Neurohypophysis (Pars Nervosa)

• Stores & releases hypothalamic hormones: ADH (Vasopressin), Oxytocin.
• Contains Pituicytes (glial support cells), Herring bodies (axonal dilations).

Pars Intermedia

• Rudimentary; produces MSH. Site of Rathke's cysts (colloid-filled).

⭐ Herring bodies in the neurohypophysis are eosinophilic axonal dilatations containing stored ADH and oxytocin, visible with specific stains.

Thyroid & Parathyroid - Metabolic Twins

• Thyroid Gland:
  • Follicular cells (thyrocytes): Simple cuboidal, surround colloid (T3/T4 storage).
  • T3/T4 Synthesis: Iodide trapping → thyroglobulin synthesis → iodination → coupling (colloid).
  • Parafollicular (C) cells: Interfollicular/basal, not lumen; larger, pale; calcitonin.

    ⭐ Parafollicular (C) cells: neural crest origin via ultimobranchial body.

• Parathyroid Glands:
  • Chief cells: PTH; small, round nucleus, pale eosinophilic/clear cytoplasm (glycogen).
  • Oxyphil cells: Larger, intensely eosinophilic (mitochondria); function unknown; appear puberty, ↑ age.
• Embryology:
  • Thyroid: Foramen cecum (thyroglossal duct).
  • Parathyroids: 3rd pouch (inferior glands, thymus); 4th (superior glands, ultimobranchial body).

Thyroid Cell Comparison:

Adrenal Glands - Stress Central

• Adrenal Cortex: 📌 Mnemonic (Layers & Products): GFR - Salt, Sugar, Sex.

  Zone	% Thick	Cell Arrangement & Appearance	Product	Regulator
  Zona Glomerulosa (ZG)	15%	Rounded clusters; columnar/pyramidal	Aldosterone	Ang II/K+
  Zona Fasciculata (ZF)	75-80%	Straight cords; lg. polyhedral spongiocytes	Cortisol	ACTH
  Zona Reticularis (ZR)	5-10%	Anastomosing cords; smaller, eosinophilic, lipofuscin	Androgens	ACTH

• Adrenal Medulla:
  • Chromaffin cells: Modified sympathetic neurons; pale basophilic cytoplasm, granules.
  • Chromaffin reaction (brown with Cr salts). Epinephrine (↑) & Norepinephrine cells.
• Embryology: Cortex: Coelomic mesoderm. Medulla: Neural crest.
• Blood Supply: Capsular arteries → cortical sinusoids → medullary vessels → central medullary vein.

⭐ The Zona Fasciculata is the thickest layer (75-80%) of the adrenal cortex and its cells (spongiocytes) are characterized by abundant lipid droplets containing cholesterol for glucocorticoid synthesis.

Pancreas & Pineal - Sweet Dreams Team

Endocrine Pancreas (Islets of Langerhans):

• Pale, spherical/ovoid endocrine cell clusters in exocrine acini; rich capillaries.
• ID: Often IHC/special stains (e.g., Gomori's for beta cells).

Pineal Gland (Epiphysis Cerebri):

• Pinealocytes: Chief cells (~95%), large irregular nuclei; make melatonin.
• Interstitial (glial) cells: Astrocyte-like, darker, elongated nuclei.
• Corpora Arenacea ('brain sand'): Lamellated calcified concretions ($Ca$ phosphates & $CaCO_3$), ↑ with age, radiopaque.

⭐ Beta cells in the pancreatic Islets of Langerhans are the most abundant endocrine cell type and are typically concentrated in the central region of the islet.

High‑Yield Points - ⚡ Biggest Takeaways

• Pituitary: Acidophils (GH, Prolactin), Basophils (FSH, LH, ACTH, TSH); Herring bodies in neurohypophysis.
• Thyroid: Follicular cells (colloid for thyroglobulin); Parafollicular C-cells (Calcitonin).
• Parathyroid: Chief cells (PTH); distinctive eosinophilic Oxyphil cells.
• Adrenal Cortex: Glomerulosa (Aldosterone), Fasciculata (Cortisol), Reticularis (Androgens). Medulla: Chromaffin cells (Catecholamines).
• Pancreatic Islets: Central Beta cells (Insulin, most numerous); peripheral Alpha cells (Glucagon).
• Pineal Gland: Pinealocytes (Melatonin); characteristic Corpora arenacea (brain sand).