CorpusHuman Anatomy
EndocrineOrgan part

Anterior pituitary (adenohypophysis)

Adenohypophysis; lobus anterior hypophysis

Also known as: adenohypophysis, pars distalis

The glandular, epithelial lobe of the pituitary that secretes six tropic hormones — GH, prolactin, TSH, ACTH, FSH and LH — under control of hypothalamic hormones delivered by portal blood.

Show on body map Hypothalamic–Pituitary Axis

Overview

The adenohypophysis consists of cords and clusters of endocrine cells between wide fenestrated sinusoids (the secondary capillary plexus of the portal system). Classical histology divides the cells into acidophils (eosinophilic granules: somatotrophs and lactotrophs), basophils (PAS-positive glycoprotein granules: thyrotrophs, gonadotrophs and corticotrophs) and chromophobes (degranulated or undifferentiated cells); immunohistochemistry and transcription factors (PIT-1, TPIT, SF-1) are now used to classify cells and tumours.

TSH, FSH and LH (and placental hCG) are glycoprotein hormones sharing a common α-subunit with a hormone-specific β-subunit. ACTH is cleaved from pro-opiomelanocortin (POMC), which also yields β-lipotropin, β-endorphin and (in the intermediate lobe of animals) α-MSH. GH and prolactin are related single-chain proteins acting through JAK–STAT cytokine receptors.

Location

Anterior part of the pituitary in the sella turcica; the pars tuberalis wraps the stalk.

Parts & subdivisions

  1. Somatotrophs (≈40–50 %)
    Acidophils; secrete growth hormone. Stimulated by GHRH and ghrelin, inhibited by somatostatin and IGF-1.
  2. Lactotrophs (≈15–25 %)
    Acidophils; secrete prolactin. Tonically inhibited by dopamine; stimulated by TRH and estrogen; hyperplasia in pregnancy.
  3. Corticotrophs (≈15–20 %)
    Basophils; process POMC to ACTH. Stimulated by CRH and ADH; inhibited by cortisol.
  4. Gonadotrophs (≈10 %)
    Basophils; secrete FSH and LH (often from the same cell). Stimulated by pulsatile GnRH; inhibited by sex steroids and inhibin.
  5. Thyrotrophs (≈5 %)
    Basophils; secrete TSH. Stimulated by TRH; inhibited by T3/T4, somatostatin and dopamine.
  6. Folliculostellate cells
    Non-secretory supporting cells with paracrine roles.
  7. Pars intermedia
    Rudimentary in adult humans; Rathke cleft cysts arise here.

Anatomy

Arterial supply

Portal blood from the long and short hypophyseal portal veins; little or no direct arterial supply.

Histology

Cords of polygonal cells around fenestrated sinusoids; acidophils (orange-G/eosin), basophils (PAS-positive), chromophobes. Reticular fibre framework.

Development

Rathke's pouch — an evagination of the roof of the stomodeum (oral ectoderm) in week 3–4 that detaches and meets the infundibulum.

Function

  • Secretes GH (growth, metabolism via IGF-1).
  • Secretes prolactin (milk synthesis).
  • Secretes TSH, ACTH, FSH and LH (control of the thyroid, adrenal cortex and gonads).
Regulation

Hypothalamic releasing/inhibiting hormones (TRH, CRH, GnRH, GHRH stimulate; somatostatin and dopamine inhibit) and negative feedback from peripheral hormones.

Clinical significance

Functioning adenomas

Prolactinoma (commonest), somatotroph adenoma (acromegaly), corticotroph adenoma (Cushing disease), and rarely thyrotroph adenoma (TSH-oma: hyperthyroidism with non-suppressed TSH). Non-functioning gonadotroph adenomas present with mass effect.

Compiled from standard anatomy and physiology references — see the Endocrine System sources. For education only; not medical advice.