pituitary gland n.
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Pituitary gland

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Pituitary gland

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  1. Pituitary gland

  2. 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

  3. 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

  4. 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

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

  6. 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

  7. 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

  8. 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

  9. 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

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

  11. 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

  12. 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)

  13. 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 • GnRH pulsatility

  14. 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)

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