Endocrine Histology: strict examiner step-by-step topic order

1. Identify the organ
2. Give the staining and magnification, if stated
3. Describe capsule, stroma, and blood supply
4. Describe arrangement of cells
5. Name all cell types and their microscopic appearance
6. Name hormone secreted by each cell type
7. Correlate structure with function
8. Give 2-3 differentiating features from similar slides
9. Draw and label, if asked

1. General endocrine histology

Learn in this order

1. Definition: endocrine glands are ductless glands.
2. Hormones enter interstitial tissue and then blood.
3. Endocrine cells are closely associated with fenestrated capillaries/sinusoids.
4. General organization:
   • Cells arranged in cords, clumps, follicles, or nests
   • Rich vascular connective tissue stroma
   • No excretory ducts
5. Classify hormones:
   • Amino-acid derivatives
   • Peptides/proteins
   • Steroids

Strict viva questions

• Why are endocrine glands called ductless?
• Why are capillaries abundant and fenestrated?
• What is the difference between endocrine and exocrine secretion?
• Which endocrine cells produce steroid hormones? What organelles would they have?

2. Hypothalamus

Stepwise answer

1. Location: below thalamus, above pituitary, forms the neural-endocrine link.
2. Role: regulates anterior pituitary through releasing/inhibiting hormones.
3. Neurosecretory nuclei: supraoptic and paraventricular nuclei.
4. Hormones synthesized in hypothalamus:
   • ADH/vasopressin
   • Oxytocin
   • TRH
   • CRH
   • GnRH
   • GHRH
   • Somatostatin
5. Key distinction:
   • ADH and oxytocin are made in hypothalamic neurons.
   • They are transported down axons and released from posterior pituitary.

Examiner trap

3. Pituitary gland / Hypophysis

A. First identify the two major divisions

B. Adenohypophysis

Parts to name

1. Pars distalis: largest part, approximately 75%
2. Pars intermedia
3. Pars tuberalis

Pars distalis: answer in order

1. Cells arranged in cords/clumps.
2. Cords are separated by sinusoidal capillaries.
3. Identify three staining groups:
   • Acidophils
   • Basophils
   • Chromophobes

Cell types and hormones

Strict slide-identification points

• Acidophils: eosinophilic cytoplasm, stain pink/red.
• Basophils: basophilic cytoplasm, stain purple-blue.
• Chromophobes: pale cells with poorly stained cytoplasm.
• Sinusoidal capillaries: lie between cords of cells.

Pars intermedia

1. Lies between pars distalis and pars nervosa.
2. Identify colloid-filled cystic follicles.
3. In humans it is relatively small.

Examiner trap

• Thyroid has many uniformly distributed follicles throughout the gland.
• Pars intermedia has scattered cystic spaces between anterior and posterior pituitary.

C. Neurohypophysis / Pars nervosa

Answer in order

1. It is composed mainly of unmyelinated axons from hypothalamic neurons.
2. Supporting cells are pituicytes.
3. Dilated axonal swellings containing secretory granules are Herring bodies.
4. It stores and releases:
   • ADH/vasopressin
   • Oxytocin
5. These hormones are synthesized in the hypothalamus, not in the posterior pituitary.

Slide features

• Paler than pars distalis
• Fewer cells and more nerve fibers
• Pituicyte nuclei visible
• Herring bodies may be identified as eosinophilic dilatations

Strict differential diagnosis

• Pars distalis: more cellular, acidophils/basophils, numerous cords.
• Pars nervosa: paler, fibrous appearance, pituicytes and axons.

4. Thyroid gland

How to identify the slide

“This is thyroid gland because it contains numerous rounded follicles filled with eosinophilic colloid and lined by simple cuboidal follicular epithelium.”

Stepwise description

1. Thin connective-tissue capsule.
2. Numerous thyroid follicles of variable size.
3. Each follicle is lined by simple cuboidal epithelium.
4. Follicular lumen contains colloid.
5. Follicles are surrounded by rich capillary networks.
6. Interfollicular connective tissue is scant.
7. Identify:
   • Follicular cells / thyrocytes
   • Colloid
   • Parafollicular cells / C cells
   • Capillaries

Functional correlation

Functional states of follicular cells

• Inactive thyroid: flattened cells, large follicles, much colloid.
• Normal thyroid: cuboidal epithelium.
• Active thyroid: tall columnar cells, reduced/scalloped colloid.

Strict viva questions

• What is the structural and functional unit of thyroid?
  Thyroid follicle.
• Which endocrine gland stores hormone extracellularly?
  Thyroid gland, in colloid.
• Which cell produces calcitonin?
  Parafollicular or C cell.
• Does a C cell contact the follicular lumen?
  No. It lies basally within the follicular basement membrane.
• Which cells produce T3 and T4?
  Follicular cells.

Differential diagnosis

• Thyroid vs parathyroid: thyroid has colloid-filled follicles; parathyroid has solid cords of cells and no follicles.
• Thyroid vs pars intermedia: thyroid has many follicles throughout and a uniform pattern; pars intermedia has only scattered cystic spaces.

5. Parathyroid gland

How to identify the slide

“This is parathyroid gland because there are densely packed cords of chief cells separated by numerous capillaries, with no colloid-filled follicles.”

Stepwise description

1. Thin connective-tissue capsule.
2. Septa extend inward.
3. Cells arranged in anastomosing cords/nests.
4. Numerous capillaries or sinusoids between cell cords.
5. Two cell types:
   • Chief cells
   • Oxyphil cells
6. In adults, adipocytes may be present in the stroma.

Cell types

Functional correlation

• PTH increases serum calcium.
• It acts on bone, kidney, and indirectly on intestine through vitamin D activation.

Strict viva questions

• Which cell is more numerous?
  Chief cell.
• Which cell is absent or very rare in children and becomes more evident with age?
  Oxyphil cell.
• Which hormone is produced by chief cells?
  Parathyroid hormone, PTH.
• How do you differentiate parathyroid from thyroid?
  Parathyroid has cords of chief cells and no colloid; thyroid has follicles with colloid.

6. Adrenal / suprarenal gland

How to identify the slide

“This is adrenal gland because it has a thick capsule, an outer cortex divided into three zones, and a central medulla.”

First state the basic organization

1. Thick connective-tissue capsule.
2. Outer cortex.
3. Inner medulla.
4. Cortex and medulla are functionally distinct endocrine organs.

A. Adrenal cortex

Always name zones from outside inward

1. Zona glomerulosa
2. Zona fasciculata
3. Zona reticularis

Use this table exactly

Mnemonic

• Glomerulosa: salt, aldosterone
• Fasciculata: sugar, cortisol
• Reticularis: sex, androgens

Important structural correlation

• Cortical cells produce steroids.
• Therefore, they have abundant smooth endoplasmic reticulum and lipid droplets.
• Lipid droplets dissolve during routine processing, giving zona fasciculata its spongy appearance.

ACTH correlation

• Zona fasciculata and zona reticularis depend on ACTH.
• Zona glomerulosa is primarily regulated by the renin-angiotensin-aldosterone system and serum potassium.

B. Adrenal medulla

Stepwise answer

1. Located centrally.
2. Cells arranged in clusters/cords with capillaries and venules.
3. Main cells are chromaffin cells.
4. They are modified postganglionic sympathetic neurons.
5. They secrete catecholamines:
   • Adrenaline/epinephrine
   • Noradrenaline/norepinephrine
6. Called chromaffin cells because their granules react with chromium salts.

Strict viva questions

• Which layer is widest?
  Zona fasciculata.
• Which cells are called spongiocytes and why?
  Cells of zona fasciculata; lipid dissolution creates vacuolated cytoplasm.
• Which adrenal zone produces aldosterone?
  Zona glomerulosa.
• Which zone produces cortisol?
  Zona fasciculata.
• Which zone produces adrenal androgens?
  Zona reticularis.
• Which part produces catecholamines?
  Adrenal medulla.
• Which part is essential for life?
  Adrenal cortex.

7. Practical slide checklist from your PDF

Slide: Hypophysis, low power

1. Pars distalis
2. Pars intermedia
3. Pars nervosa
4. Capsule, if visible
5. Blood vessels/sinusoids

Slide: Pars distalis, high power

1. Acidophil
2. Basophil
3. Chromophobe
4. Sinusoidal capillary
5. Cell cords

Slide: Pars intermedia

1. Pars intermedia
2. Cystic/colloid follicles
3. Sinusoidal capillary
4. Adjacent pars distalis or pars nervosa, if visible

Slide: Pars nervosa

1. Pituicyte nucleus
2. Unmyelinated nerve fibers
3. Herring body
4. Capillary

Slide: Thyroid with parathyroid

1. Thyroid follicle
2. Colloid
3. Follicular cells
4. Parafollicular/C cells
5. Capillary
6. Parathyroid tissue
7. Chief cells
8. Blood vessel

Slide: Adrenal gland, low power

1. Capsule
2. Zona glomerulosa
3. Zona fasciculata
4. Zona reticularis
5. Medulla
6. Central vein, if visible

Slide: Adrenal gland, high power

1. Spongiocytes of zona fasciculata
2. Sinusoidal capillaries
3. Reticularis cell cords
4. Chromaffin cells, if medulla included

8. Last-minute strict examiner revision order

1. General endocrine features and capillaries
2. Pituitary divisions
3. Pars distalis cell types with hormones
4. Pars intermedia and pars nervosa
5. Thyroid follicle, colloid, follicular cell, C cell
6. Differentiate thyroid from parathyroid
7. Parathyroid chief cell and oxyphil cell
8. Adrenal cortex zones from outside inward
9. Hormones of each adrenal zone
10. Adrenal medulla and chromaffin cells
11. Draw pituitary, thyroid-parathyroid, and adrenal gland from memory
12. Practice slide identification using only 3 diagnostic points per slide