Histology of the Endocrine System I Dr Jack

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 Neurohypophysis

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

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

Subdivisions of Pituitary

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

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

Acidophils Smaller cells, more numerous Types – Somatotropes (75%) – Mammotropes (25%)

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

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

Larger than Acidophils Granules stain with PAS Types – Thyrotropes – Gonadotropes – Corticotropes Basophils

Thyrotropes v. Secrete thyroid stimulating hormone (TSH)

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

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

Mnemonic A : Acidophils – Smart : Somatotrope – Move : Mammotropes By : Basophils – The : Thyrotropes – Girls : Gonadotropes

Adenohypophysis Pars tuberalis – Contains gonadotropes only – Consists of a collar of cells surrounding the infundibulum

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

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

Control of adenohypophysis secretion

Control of adenohypophysis secretion 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.

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

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

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)

Hormone release Hormones – Results. Neurohypophyseal from action potential in hypothalamic neuron – Causes release of “neurotransmitter”

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