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Histology of the Endocrine System I

Histology of the Endocrine System I. Dr. Jack L. Haar Department of Anatomy and Neurobiology. Embryology of the Pituitary Gland. Origins of the Pituitary Gland (4 -6 weeks gestation) Stomodeal ectoderm – Rathke’s pouch Adenohypophysis Evagination of diencephalon - Neuroectoderm

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Histology of the Endocrine System I

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  1. Histology of the Endocrine System I Dr. Jack L. Haar Department of Anatomy and Neurobiology

  2. Embryology of the Pituitary Gland • Origins of the Pituitary Gland (4 -6 weeks gestation) • Stomodeal ectoderm – Rathke’s pouch • Adenohypophysis • Evagination of diencephalon - Neuroectoderm • Neurohypophysis

  3. Pituitary Organization Set in sella turcica of sphenoid bone Separated from hypothalamus by diaphragm sella (stalk passes through) Surrounded by dense CT capsule Extensive capillary beds associated with gland

  4. Pituitary Organization Set in sella turcica of sphenoid bone Separated from hypothalamus by diaphragm sella (stalk passes through) Surrounded by dense CT capsule Extensive capillary beds associated with gland

  5. Subdivisions of Pituitary

  6. Adenophypophysis • Pars distalis • Structure • Forms majority of pituitary gland • Glandular, with cells in cords, protein secreting • Reticular fiber framework • Fenestrated capillaries

  7. Cell Types • Chromophobes • No secretory granules • Reserve/Degranulated cells • Chromophils • Secretory granules with protein hormone • Acidophils (eosin affinity granules) • Basophils (hematoxylin affinity granules)

  8. Acidophils • Smaller cells, more numerous • Types • Somatotropes (75%) • Mammotropes (25%)

  9. Somatotropes • Secrete somatotropin (growth hormone) • Stimulates epiphyseal plate • Gigantism/Dwarfism; Acromegaly may result

  10. Mammotropes • Secrete prolactin • Simulates milk secretion • Galactorrhea, continuous milk production (tumor)

  11. Basophils • Larger than Acidophils • Granules stain with PAS • Types • Thyrotropes • Gonadotropes • Corticotropes

  12. Thyrotropes • Secrete thyroid stimulating hormone (TSH)

  13. Gonadotropes • Secrete leutinizing hormone (LH) and follicle stimulating hormone (FSH) • Same cell secretes both hormones having similar structure

  14. Corticotropes • Secrete adrenocorticotropic hormone (ACTH), lipotropin, melanocyte stimulating hormone (MSH) and endorphin • Primary sequence of each hormone within a precursor protein: proopiomelanocortin

  15. Mnemonic • A : Acidophils • Smart : Somatotrope • Move : Mammotropes • By : Basophils • The : Thyrotropes • Girls : Gonadotropes

  16. Adenohypophysis • Pars tuberalis • Contains gonadotropes only • Consists of a collar of cells surrounding the infundibulum

  17. Adenohypophysis • Pars Intermedia • <2% of adenohypophysis • Composed of corticotropes only • Cells surrounding cystic remnants of Rathke’s pouch • Some cells migrate into pars nervosa

  18. Adenohypophysis • Pars Intermedia • <2% of adenohypophysis • Composed of corticotropes only • Cells surrounding cystic remnants of Rathke’s pouch • Some cells migrate into pars nervosa

  19. Control of adenohypophysis secretion

  20. Hypothalamic releasing hormones move down axons of hypothalamic neurons Releasing factors are secreted in capillary beds of infundibulum at median eminence Capillary beds drain into hypophyseal portal vessels, ending in pars distalis capillaries Hypothalamic releasing factors exit capillaries to either stimulate or inhibit release of hormones in pars distalis acidophils or basophils Negative feedback occurs at multiple levels. Control of adenohypophysis secretion

  21. Neurohypophysis • Infundibulum • Connects hypophysis with hypothalamus • Axons from supraoptic and paraventricular nuclei forming hypothalamic-hypophyseal tract

  22. Neurohypophysis • Pars nervosa • Axons from hypthalamus terminate (Herring bodies) • Pituicytes also present • Glial cells, highly polymorphic • In humans may have pigment and resemble Herring bodies

  23. Control of Neurohypophyseal secretion • No synthesis of hormone in pars nervosa • Oxytocin and ADH/Vasopressin stored in axon terminals (Herring bodies) of neurons in the paraventricular and supraoptic nuclei of hypothalamus (sites of synthesis)

  24. Neurohypophyseal Hormones • Oxytocin • Synthesized in paraventricular nucleus • Stimulates smooth muscle contraction • Antidiuretic hormone (ADH/vasopressin) • Synthesized in the supraoptic nucleus • Increases water retention • Hormone release • Results from action potential in hypothalamic neuron • Causes release of “neurotransmitter”

  25. http://www.path.uiowa.edu/virtualslidebox/ Table of Contents Endocrine System Pituitary gland #91 H&E Pituitary gland (Demo) Masson’s stainhttp://java.vcu.edu/som-histology/

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