Pituitary gland

Pituitary glandEmbryonic originAnterior pituitary gland (adenohypophysis)Rathkes pouchRoof of the embryonic mouthGlandular tissue containing secretory cellsPosterior pituitary gland (neurohypophysis)Infundibulum/brain floor)Part of the CNSContains axons of the hypothalamic neuronsHoused in a bony capsle called sella turcica

Anterior lobe (predominant lobe)Differentiation of cellsSpatiotemporal regulationExpression of cell-specific transcription factor(s) at the specific stage of developmentConcentration gradient of soluble factorsSexually dimorphicGonadotrophs in male predominantly LH secreting cellsGonadotrophs in female-equal distribution of LH and FSH secreting cells

Pars tuberalisDorsal extension of anterior lobeSurrounds the infundibulumPars IntermediaDerived from anterior pituitary cells adjacent to infundibulumMay not be clearly defined in many species

Pars nervosaPosterior lobeExtension of the CNSContains axons of hypothalamic neurons

Blood vesselsPortal plexus from hypothalamusMedian eminenceForms hypothalamic-portal circulationBidirectional flow of bloodRetrograde flow from the pituitary to hypothalamus (short-loop feedback system)Systemic arteriesInferior hypophyseal arterial blanchesPosterior pituitary gland

Regulation of hormone secretionHypothalamic levelReleasing/inhibitory factorsTranscription of mRNASecretion of hormonePeripheral hormonesFeedback systemAutocrine/paracrine factorsNet resultsPulstatile secretion of pituitary hormones

Role of transcription factorsDetermination of cell type lineageTemporal regulation of transcription cascadeHomeodomain transcription factorsEarly differentiationExpression of Rpx and PtxLIM homeodomain superfamily

Ptx superfamilyUniversal regulator of transcription within the anterior pituitaryPit-1GH, PRL, TSH, and GHRH receptor mRNA transcriptionInteraction with other factors to induce commitment of cells to differentiate (estrogen receptor, thyrotroph embryonic factor)Transcription of its own mRNAGATA-2Developmental regulation of alpha subunit expressionInteraction with SF-1 and DAX-1 triggers differentiation into gonadotrophs

Endocrine cellsFive typesCorticotrophsSomatotrophsLactotrophs/mammotrophsThyrotrophsGonadotrophsStaining characteristicsAcidphils (stained with acidic dye)Basophils (stained with basic dye)

Endocrine cellsCorticotrophsBasophils20 % of functional anterior pituitary gland cellsAppears the earliest 8 weeks of gestationClustered mainly in central median pituitary wedgeLarge, irregularly shaped cells

LactotrophsAcidophilsSame stem cells as somatotrophsCould give rise to mammosomatotrophsProduce both GH and PRL15-25 % of functional pituitary cellsTwo typesLarge polyhedral cells (found throughout the gland)Smaller angulated elongated cells (lateral wings and median wedge)

GonadotrophsBasophils10-15 % of functional pituitary cellsContains two types of secretory glanulesLarge (350-450 mm) Small (150-250 mm) Secretion of two distinct hormones by the same cellsGnRH pulsatility

SomatotrophsAcidophils35-45% of functional anterior pituitary cellsSame stem cells as lactotrophsMammosomatotrophsDifferentiation induced by TRH or dopamine along with estrogenLarge secretory granules (700 mm)

ThyrotrophsBasophils5 % of functional anterior pituitary cellsSmaller in sizeSmaller secretory granules (120-150 mm)