/ Hypophysis cerebri, Histology of Suprarenal gland

Reading File

Finding Sources

Reading File

Finding Sources

Reading File

Finding Sources

Reading File

Finding Sources

Reading File

Searching Images

pituitary gland hypophysis histology adenohypophysis neurohypophysis

Reading File

I now have all the information needed for a comprehensive answer. Let me compile it:

Histology of Hypophysis Cerebri (Pituitary Gland)

Source: Junqueira's Basic Histology - Text and Atlas, 17e

Overview & Embryology

The pituitary gland (hypophysis) weighs ~0.5 g and measures ~10 × 13 × 6 mm. It sits in the sella turcica of the sphenoid bone, below the brain. It has a dual embryonic origin:

Neurohypophysis - downward bud from the floor of the diencephalon (neural tissue)
Adenohypophysis - upward outpocketing of oral ectoderm (Rathke's pouch)

Pituitary gland anatomy and sella turcica

Embryonic formation of pituitary from neurohypophyseal bud and Rathke's pouch

Two Major Divisions

Division	Parts	Origin
Adenohypophysis	Pars distalis, Pars tuberalis, Pars intermedia	Oral ectoderm (Rathke's pouch)
Neurohypophysis	Pars nervosa, Infundibulum (stalk)	Neural tissue (diencephalon)

Low-mag H&E section of entire pituitary showing PD, PI, PT, PN, IS

1. Adenohypophysis

Blood Supply: Hypothalamic-Hypophyseal Portal System

The adenohypophysis has NO direct arterial supply - it is entirely portal. Superior hypophyseal arteries form a primary capillary plexus in the median eminence/stalk, which drains into portal veins that branch as a secondary plexus throughout the pars distalis. This portal system transports hypothalamic releasing and inhibiting hormones to anterior pituitary cells.

Hypothalamic-hypophyseal tract and portal system diagram

A. Pars Distalis (75% of adenohypophysis)

Cords of secretory cells interspersed with fenestrated sinusoidal capillaries. Two major staining categories on routine H&E:

Chromophils (secretory, granule-filled cytoplasm):

Acidophils (orange-red on H&E / Gomori trichrome) - 2 types:
- Somatotrophs (~50% of all pars distalis cells) - secrete Growth Hormone (GH/Somatotropin)
- Lactotrophs - secrete Prolactin (PRL)
Basophils (violet on Gomori trichrome) - 3 types:
- Corticotrophs - secrete ACTH (from POMC precursor)
- Gonadotrophs - secrete FSH and LH (same cell secretes both)
- Thyrotrophs - secrete TSH (least numerous chromophils)

Chromophobes - poorly staining, granule-depleted cells (either resting chromophils or undifferentiated reserve cells)

Pars distalis H&E showing acidophils (A), basophils (B), chromophobes (C), sinusoids (S)

Gomori trichrome showing orange acidophils, violet basophils

Clinical note: Benign pituitary adenomas of somatotrophs cause gigantism (before epiphyseal closure) or acromegaly (in adults).

Hypothalamic Control (Table 20-2)

Hypothalamic Hormone	Action
TRH (3 aa peptide)	Stimulates TSH release
GnRH (10 aa peptide)	Stimulates FSH and LH release
GHRH (40/44 aa polypeptide)	Stimulates GH release
Somatostatin (14 aa)	Inhibits GH and TSH release
Dopamine	Inhibits Prolactin release
CRH	Stimulates ACTH release

Feedback loop: hypothalamic hormone → anterior pituitary → target organ hormone → negative feedback on both hypothalamus and pituitary.

Feedback loop - hypothalamus, pituitary, thyroid as example

B. Pars Tuberalis

Wraps around the infundibular stalk. Contains mainly gonadotrophs and portal blood vessels.

C. Pars Intermedia

Narrow zone between pars distalis and pars nervosa. Contains:

Corticotrophs (producing MSH, γ-LPH, β-endorphin from POMC, cleaved differently than pars distalis)
Colloid-filled Rathke's cleft cysts (remnants of hypophyseal pouch lumen)
Chromophobes
Best developed in fetal life; function in adults is unclear

Pars intermedia with colloid cysts (C), basophils (B), pars distalis (PD), pars nervosa (PN)

2. Neurohypophysis (Posterior Pituitary)

The pars nervosa does NOT contain the neurons that produce its hormones. It consists of:

~100,000 unmyelinated axons from supraoptic (ADH) and paraventricular (oxytocin) nuclei of the hypothalamus, running down via the hypothalamic-hypophyseal tract
Pituicytes - modified glial cells resembling astrocytes; the most abundant cell type
Herring bodies (neurosecretory bodies) - axonal dilatations visible by light microscopy as faintly eosinophilic swellings; contain membrane-bound granules storing ADH or oxytocin bound to carrier proteins neurophysin II and neurophysin I, respectively
Fenestrated capillaries for hormone uptake

Hormones released:

Hormone	Stimulus	Action
ADH (Vasopressin)	Increased blood osmolality	Increases water permeability of renal collecting ducts
Oxytocin	Suckling, parturition	Uterine contraction; mammary myoepithelial contraction (milk ejection)

Pars nervosa: pituicytes (P), Herring bodies (NB), capillaries (C)

Clinical note: Damage to posterior pituitary (trauma, tumor compression, gene mutation) → reduced ADH → Diabetes insipidus (polyuria + polydipsia).

Histology of Suprarenal (Adrenal) Gland

Source: Junqueira's Basic Histology - Text and Atlas, 17e

Overview

The paired adrenal (suprarenal) glands lie at the superior poles of the kidneys, each ~4-6 cm long, 1-2 cm wide, ~8 g total weight. Each is enclosed in a dense connective tissue capsule with thin trabeculae projecting inward. The stroma is reticular fibers.

Each gland has two concentric regions of completely different embryologic origin:

Region	Color (gross)	Embryologic Origin
Cortex (outer)	Yellowish	Embryonic mesoderm (intermediate mesoderm / coelomic epithelium)
Medulla (inner)	Reddish-brown	Neural crest cells

Adrenal gland cross-section diagram showing cortex layers and medulla with tissue samples

Adrenal Cortex

Cortical cells are arranged in three concentric zones, all producing steroid hormones. Steroids are not stored in granules - as small lipid-soluble molecules they diffuse freely through the plasma membrane when synthesized.

Ultrastructural features common to all steroid-secreting cells:

Lipid droplets (cholesterol ester stores)
Mitochondria with tubular/vesicular cristae (not lamellar) - for steroidogenesis
Abundant smooth ER (SER)
Autophagosomes (remove organelles between active periods)

Zone 1: Zona Glomerulosa (outermost, ~15% of cortex)

Immediately beneath the capsule
Cells: columnar or pyramidal, arranged in rounded/arched cords or ovoid clusters
Many capillaries
Hormone: Mineralocorticoids → Aldosterone (principal product)
Aldosterone regulates salt balance: stimulates Na+ reabsorption in distal convoluted tubules
Control: primarily angiotensin II, also elevated plasma K+; only weakly by ACTH

Zone 2: Zona Fasciculata (middle, ~65-80% of cortex)

Thickest zone
Cells: large polyhedral cells in long straight cords (1-2 cells thick) separated by sinusoidal capillaries
Cells are filled with lipid droplets → appear vacuolated/spongy on routine H&E ("spongiocytes")
Hormone: Glucocorticoids → Cortisol (principal product) + small amounts of androgens
Cortisol: stimulates gluconeogenesis, glycogen synthesis in liver; suppresses immune functions; fat mobilization; muscle proteolysis
Control: ACTH with negative feedback

Zone 3: Zona Reticularis (innermost, ~10% of cortex)

Cells: smaller, in irregular anastomosing network of cords with wide capillaries
Cells are more darkly stained than zona fasciculata (fewer lipid droplets, more lipofuscin pigment)
Hormone: mainly weak androgens (DHEA - dihydroepiandrosterone, converted to testosterone in peripheral tissues) + some cortisol
Control: ACTH with regulatory feedback

Adrenal cortex - H&E and Mallory trichrome showing zones G, F, R, and medulla (M)

Mnemonic for hormones: GFR = Salt, Sugar, Sex (Glomerulosa=Salt/mineralocorticoids; Fasciculata=Sugar/glucocorticoids; Reticularis=Sex/androgens)

Clinical note: Addison disease - usually autoimmune degeneration of adrenal cortex → loss of glucocorticoids, mineralocorticoids, or androgens.

Adrenal Medulla

The medulla is composed of large, pale-staining polyhedral chromaffin cells arranged in cords or clumps, supported by reticular fibers with a profuse sinusoidal capillary supply. A few parasympathetic ganglion cells are also present.

Chromaffin cells:

Derived from neural crest cells (like sympathetic postganglionic neurons)
Considered modified sympathetic postganglionic neurons - lack axons and dendrites, specialized for secretion
Contain electron-dense granules (150-350 nm) storing catecholamines bound to chromogranins (49 kDa proteins) with Ca2+ and ATP
Innervated by preganglionic sympathetic neurons (direct preganglionic control, unlike other postganglionic neurons)
Two subtypes by TEM:
- Epinephrine-secreting cells - smaller, less electron-dense granules (~80% of secretion)
- Norepinephrine-secreting cells - larger, more electron-dense granules

Key biochemistry: The conversion of norepinephrine → epinephrine occurs ONLY in adrenal medullary chromaffin cells (via PNMT enzyme, stimulated by cortisol from cortical venous blood).

Hormonal effects - Fight-or-Flight:

Epinephrine: ↑ heart rate, dilates bronchioles, dilates arteries of cardiac/skeletal muscle
Norepinephrine: vasoconstricts gut/skin vessels, ↑ blood flow to heart/brain/muscle
Both: stimulate glycogenolysis → ↑ blood glucose

Adrenal medulla - chromaffin cells in H&E and TEM showing epinephrine (E) and norepinephrine (NE) granules

Clinical note: Pheochromocytoma - benign tumor of chromaffin cells; periodically secretes high catecholamines → episodic swings between hypertension and hypotension.

Summary Comparison

Feature	Adrenal Cortex	Adrenal Medulla
Origin	Mesoderm	Neural crest
Cell type	Epithelial steroid-secreting cells	Chromaffin cells (modified neurons)
Hormone class	Steroids (aldosterone, cortisol, androgens)	Catecholamines (epinephrine, norepinephrine)
Storage	Not stored (diffuse freely)	Stored in dense-core granules
Control	ACTH, angiotensin II, K+	Preganglionic sympathetic neurons
Organelle hallmark	Tubular mitochondrial cristae, SER, lipid droplets	Dense-core secretory granules, chromogranins

Junqueira's Basic Histology - Text and Atlas, 17e, pp. 999-1027

This is a shared conversation. Sign in to Orris to start your own chat.