HISTOLOGY - Endocrine System 2024-01.pdf

HISTOLOGY OF THE ENDOCRINE SYSTEM DR. DIANA VERA ESTRADA Modified by Dr. Flores and Dr. Yisel Guzmán Learning Objectives Identify the different types of cell secretion. Identify the histological, intracellular components and function of the organs that form the endocrine system. Pituitary gland. Thy...

HISTOLOGY OF THE ENDOCRINE SYSTEM DR. DIANA VERA ESTRADA Modified by Dr. Flores and Dr. Yisel Guzmán Learning Objectives Identify the different types of cell secretion. Identify the histological, intracellular components and function of the organs that form the endocrine system. Pituitary gland. Thyroid gland. Adrenal gland. Parathyroid glands. Endocrine Pancreas. Pineal body. Endocrine Cells and Tissue Specialization Endocrine cells are found in three distinct anatomic distributions: Forming endocrine glands Forming clusters in other organs Dispersed in epithelial tissues Pituitary Gland (Hypophysis) ANTERIOR LOBE: About 75% of the adenohypophysis is anterior lobe. Pars Distalis - comprises most of the anterior lobe (~75%) and contains five types of endocrine cells. Chromophils: are secretory cells in which hormone is stored in cytoplasmic granules. The chromophils are further subdivided into Acidophils (alpha cells). Somatotrophs - growth hormone (GH) Mammotrophs (Lactotrophs) - prolactin Basophils (beta cells). Corticotrophs - ACTH. Thyrotrophs - TSH. Gonadotrophs - FSH and LH. Chromophobes:with few or no secretory granules Photomicrograph: Pars distalis: acidophil cells (A), basophils (B), and chromophobes (C) in which the cytoplasm is poorly stained. Also shown are capillaries and sinusoids (S) Pars Tuberalis- The pars tuberalis is a smaller funnel-shaped region surrounding the infundibulum of the neurohypophysis. Most of the cells are gonadotrophs. Pars Intermedia - Contains basophils (corticotrophs), chromophobes, and small, colloid-filled cysts (rudiments of the Rathke pouch) Photomicrograph of the pituitary gland: The infundibular stalk (IS) and pars nervosa (PN), pars distalis (PD), pars intermediate (PI), and pars tuberalis (PT) (X30; H&E) Posterior lobe Neurohypophysis (PARS NERVOSA) Posterior lobe. Hypothalamohypophyseal tract (HT) (AXONS). Pituicytes (glial cells). Herring body (HB). Pituicytes (P) Herring bodies: Expanded terminals of the nerve fibers where the neurosecretory products vasopressin (antidiuretic hormone) and oxytocin are stored. Light micrograph of the pars nervosa of the pituitary gland x132 THYROID GLAND Macroscopically: It is a single gland that consists of large right and left lobes, connected in the middle by an isthmus. The thyroid gland is a unique endocrine organ in that its cells are arranged into spherical structures, called follicles, with the lumen filled with colloid. - Thyroid follicles The parenchyma of the thyroid is composed of millions of rounded epithelial thyroid follicles of variable diameter, each with simple epithelium and a central lumen densely filled with gelatinous acidophilic colloid Colloid: It is mostly the protein thyroglobulin (pink) and bound thyroid hormones (T3, T4) Follicles are lined by a simple cuboidal to columnar epithelium depending on functional activity. Secrete thyroid hormones when active. Parafollicular Cells are located at the periphery of follicles that secrete calcitonin. They stain poorly with H&E making identification difficult. 3 2 1 2 1 2 Thyroid gland follicles: canine (sectional view). Stain: hematoxylin and eosin. High magnification. Adrenal Glands The secretory parenchyma is organized into two distinct regions: THE CORTEX THE MEDULLA Adrenal at low magnification 95×. H&E. THE MEDULLA The cytoplasm appears clear, cells are larger and arranged into clumps. Polyhedral. Medullary parenchymal cells: Chromaffin cells which produce the catecholamines. Arise from neural crest cells. Are considered modified sympathetic postganglionic cells (no axons nor dendrites) & secretory cell. Parasympathetic ganglion cells. Parathyroid Gland ✓Are small endocrine glands closely associated with the thyroid. ✓These small oval glands arranged in two pairs constituting the superior and inferior parathyroid glands. They are embedded on the posterior surface of the thyroid gland but are separated from the thyroid gland by a thin connective tissue capsule. There are two types of cells in the parathyroid glands: Functional principal or chief cells. Oxyphil cells. Principal chief cells Oxyphil cells They appear after the first decade of life and are thought to be nonsecretory cells. Storage and secretes larges amounts of PTH. High-power micrograph of an H&Estained section of parathyroid 4 1 3 5 2 6 Thyroid and parathyroid glands: canine (sectional view). Stain: hematoxylin and eosin. Low magnification Endocrine Pancreas Composed of spherical aggregates of cells, known as islets of Langerhans , that are scattered among the acini. Islets of Langerhans Pancreatic islet (special preparation). Stain: Gomori chrome alum hematoxylin and phloxine. High magnification. Pineal Gland The pineal gland (pineal body, epiphysis cerebri) is a neuroendocrine gland: ✓ ✓ ✓ ✓ ✓ Regulates the circadian rhythm. Is located at the posterior wall of the third ventricle. Is a flattened, pinecone–shaped structure. Measures 5 to 8 mm high and 3 to 5 mm in diameter. Weighs between 100 and 200 mg. Cells and Structure - Pineal Gland The pineal gland contains two types of parenchymal cells: INTERSTITIAL (GLIAL) CELLS. Pinealocytes Are the chief cells of the pineal gland. Are the parenchymal cells of the pineal gland that are responsible for secreting melatonin The interstitial (glial) cells Constitute about 5% of the cells in the gland. They have staining and ultrastructural features that closely resemble those of astrocytes. Bibliography: Gartner, Leslie P. PhD. Textbook of histology. Endocrine system. 2017. 4TH Edition. Elsevier. Chapter 13. Pages 305-332. James S. Lowe B. Stevens & Lowe's Human Histology. Endocrine system. Fourth Edition. Elsevier. Chapter 14. Pages 263-285