pituitary gland. embryonic origin –anterior pituitary gland (adenohypophysis) rathke’s pouch...
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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 cell-
specific 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 female-equal 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
• 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 mRNA• 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 mRNA transcription
– Interaction with other factors to induce commitment of cells to differentiate (estrogen receptor, thyrotroph embryonic factor)
– Transcription of its own mRNA
• 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 m) • Small (150-250 m)
– Secretion of two distinct hormones by the same cells
• GnRH 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 m)