Pituitary gland Pituitary gland Embryonic origin Anterior pituitary

Pituitary gland

Pituitary gland • Embryonic origin – Anterior pituitary gland (adenohypophysis) • Rathke’s pouch – Roof of the embryonic mouth – Glandular tissue containing secretory cells – Posterior pituitary gland (neurohypophysis) • Infundibulum/brain floor) – Part of the CNS – Contains axons of the hypothalamic neurons – Housed in a bony capsle called sella turcica

• Anterior lobe (predominant lobe) – Differentiation of cells • Spatiotemporal regulation – Expression of cellspecific transcription factor(s) at the specific stage of development – Concentration gradient of soluble factors • Sexually dimorphic – Gonadotrophs in male – predominantly LH secreting cells – Gonadotrophs in femaleequal distribution of LH and FSH secreting cells

• Pars tuberalis – Dorsal extension of anterior lobe • Surrounds the infundibulum • Pars Intermedia – Derived from anterior pituitary cells adjacent to infundibulum • May not be clearly defined in many species

• Pars nervosa – Posterior lobe – Extension of the CNS – Contains axons of hypothalamic neurons

• Blood vessels – Portal plexus from hypothalamus • Median eminence • Forms hypothalamic-portal circulation • Bidirectional flow of blood – Retrograde flow from the pituitary to hypothalamus (short -loop feedback system) – Systemic arteries • Inferior hypophyseal arterial blanches – Posterior pituitary gland

Regulation of hormone secretion • Hypothalamic level – Releasing/inhibitory factors • Transcription of m. RNA • Secretion of hormone • Peripheral hormones – Feedback system • Autocrine/paracrine factors • Net results – Pulstatile secretion of pituitary hormones

Role of transcription factors • Determination of cell type lineage – Temporal regulation of transcription cascade • Homeodomain transcription factors – Early differentiation • Expression of Rpx and Ptx • LIM homeodomain superfamily

• Ptx superfamily – Universal regulator of transcription within the anterior pituitary • Pit-1 – GH, PRL, TSH, and GHRH receptor m. RNA transcription – Interaction with other factors to induce commitment of cells to differentiate (estrogen receptor, thyrotroph embryonic factor) – Transcription of its own m. RNA • GATA-2 – Developmental regulation of alpha subunit expression – Interaction with SF-1 and DAX-1 triggers differentiation into gonadotrophs

Endocrine cells • Five types – Corticotrophs – Somatotrophs – Lactotrophs/mammotrophs – Thyrotrophs – Gonadotrophs • Staining characteristics – Acidphils (stained with acidic dye) – Basophils (stained with basic dye)

Endocrine cells • Corticotrophs – Basophils – 20 % of functional anterior pituitary gland cells – Appears the earliest • 8 weeks of gestation – Clustered mainly in central median pituitary wedge – Large, irregularly shaped cells

• Lactotrophs – Acidophils – Same stem cells as somatotrophs • Could give rise to mammosomatotrophs – Produce both GH and PRL – 15 -25 % of functional pituitary cells • Two types – Large polyhedral cells (found throughout the gland) – Smaller angulated elongated cells (lateral wings and median wedge)

• Gonadotrophs – Basophils – 10 -15 % of functional pituitary cells – Contains two types of secretory glanules • Large (350 -450 mm) • Small (150 -250 mm) – Secretion of two distinct hormones by the same cells • Gn. RH pulsatility

• Somatotrophs – Acidophils – 35 -45% of functional anterior pituitary cells – Same stem cells as lactotrophs • Mammosomatotrophs • Differentiation induced by TRH or dopamine along with estrogen – Large secretory granules (700 mm)

• Thyrotrophs – Basophils – 5 % of functional anterior pituitary cells – Smaller in size • Smaller secretory granules (120 -150 mm)