The Endocrine System

1. The Endocrine System

2. Pituitary Gland • The hypophysis (Gr. hypo, under, + physis, growth), or pituitary gland • Weighs about 0.5 g • It lies in a cavity of the sphenoid bone—the sellaturcica—an important radiological landmark • During embryogenesis, the hypophysis develops partly from oral ectoderm and partly from nerve tissue

4. Because of its dual origin, the hypophysis actually consists of two glands: • Neurohypophysis • Adenohypophysis • They are united anatomically but have different functions. • Neurohypohysis (Posterior Pituitary)neural part. Consists of: • Pars nervosa • Infundibulum(stalk and median eminence)

8. Adenohypophysis(Anterior Pituitary)glandular part: • It arises from oral ectoderm. • It is subdivided into three portions: • Pars Distalis • Pars Tuberalis • Pars Intermedia.

9. Adenohypophysis • Pars Distalis(anterior lobe) : • The largest part of adenohypophysis • The main components of the pars distalis are cords of epithelial cells . • Highly vascular stroma. • The hormones produced by these cells are stored as secretory granules. • Fibroblasts produce reticular fibers that support the cords of hormone-secreting cells.

10. The pars distalis accounts for 75% of the mass of the hypophysis. • Common stains allow the recognition of three cell types in the pars distalis: • Chromophobes(Gr. chroma, color, + phobos, fear) • Chromophils(Gr. chroma + philein, to love) • Two types of chromophils: • Basophils according to their affinity for basic dyes • Acidophilsaccording to their affinity for acid dyes • The subtypes of basophil and acidophil cells are named for the hormones they produce. • With the exception of the gonadotropic cell, which produces two hormones, the other cells produce only a single hormone. • Chromophobes(degranulated secretory cells) do not stain intensely and, when observed with an electron microscope, show two populations of cells.

11. Secretory Cells of the Pars Distalis

13. Pars Tuberalis • The pars tuberalis is a funnel-shaped region surrounding the infundibulum of the neurohypophysis . • Most of the cells secrete gonadotropins (follicle-stimulating hormone and luteinizing hormone) • Are arranged in cords alongside the blood vessels.

15. Pars Intermedia • Is a rudimentary region in humans • Made up of cords and follicles of weakly basophilic cells that contain small secretory granules. • It produces Melanocyte-stimulating hormone (α-MSH).

16. Neurohypophysis (Posterior pituitary) • It consists of • Pars nervosa • Infundibulum (neural stalk)stem and median eminence.that connects it to the hypothalamus.

17. The pars nervosa • Does not contain secretory cells. • Contains nonmyelinated axons and nerve endings of neurosecretoryneuron • The nerve endings have terminal dilations called Herring bodies

18. Pars Nervosa Neurosecretoryneurons have cell bodies that lie in the supraoptic & paraventricularnuclei in the hypothalamus The secretory neurons have all the characteristics of typical neurons The secretory neurons have well-developed Nissl bodies related to the production of the neurosecretory material Cells present in Pars Nervosa are: Pituicytes(glial cell) fibroblasts mast cells.