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

Origin and Location of Thyroid Gland Develops during the 4th week of gestation Forms in the floor of the primitive pharynx Thyroid diverticulum is the anlagen Foramen cecum of the tongue is the site of its origin

Origin and Location of Thyroid Gland Develops during the 4th week of gestation Forms in the floor of the primitive pharynx Thyroid diverticulum is the anlagen Foramen cecum of the tongue is the site of its origin

Origin and Location of Thyroid Gland Develops during the 4th week of gestation Forms in the floor of the primitive pharynx Thyroid diverticulum is the anlagen Foramen cecum of the tongue is the site of its origin

Functions A. Synthesizes thyroxine (tetraiodothyronine T4) and triiodothyronine (T3) for metabolic regulation B. Synthesizes calcitonin, lowers blood calcium levels

Anatomy of the Thyroid Gland Bilobed gland anterior to larynx Lobes connected by an isthmus of tissue Lobes lie lateral to trachea and extend from thyroid cartilage to fifth or sixth tracheal ring Extensive vascularization

Composed of spherical follicles. Follicular or principal cells Composed of spherical follicles Follicular or principal cells height varies from squamous to columnar Center of follicle contains colloid proteinaceous, gelatin-like material, held in follicle: thyroglobulin, a glycoprotein ` thyroglobulin secreted by follicle cells Contains modified tyrosine (aa) in the primary sequence, a storage form of thyroid hormone. Fenestrated Capillaries

Parafollicular cells (C Cells, Clear Cells). -Neural crest origin Parafollicular cells (C Cells, Clear Cells) -Neural crest origin -Single or in clusters between follicles -High in protein synthetic machinery, non-polar -Secrete Calcitonin -Inhibits bone resorption, lowers blood Ca++ levels -Secretion stimulated by high blood Ca++ levels

Thyroglobulin is produced and secreted to follicle lumen Cells have polarity Organelles for protein synthesis Resorptive and degradative features

Histophysiology of follicle cells Synthesis, secretion and storage of thyroglobulin in follicle Iodination of tyrosines on thyroglobulin Rearrangement of tyrosines to form thyroid hormones

Histophysiology of follicle cells Re-uptake of iodinated thyroglobulin, hydrolysis and release of thyroid hormone from follicle cells

Follicle Epithelial Cells   Feature Active Follicle Inactive Follicle Follicle Epithelial Cells Cuboidal to Columnar Squamous Amount Colloid (Thyroglobulin) Reduced Extensive Mitoses Present Absent      

Regulation of the Thyroid Gland

Diseases of the Thyroid Gland Hyperthyroidism (Grave’s Disease) Hypothyroidism Myxedema (adult) Cretinism (childhood) Iodine Deficiency Goiter

Histology of the Parathyroid Gland Embryology Derived from portions of 3rd and 4th pharyngeal pouches Gross Anatomy Two pairs (superior/inferior on posterior surface of thyroid Embedded in CT capsule of Thyroid Ellipsoid, 6x1x2mm, tan in color Number and location may vary Functions Increase blood Ca++ via parathyroid hormone (PTH) PTH acts on osteoclasts, renal tubule cells, intestinal epithelial cells

Microscopic Anatomy of the Parathyroid Stroma Thin CT capsule with septae (trabeculae) that divide gland into lobes Adipose Tissue which may be up to 70% of the gland in aged individuals Fenestrated capillaries

Parenchyma Chief (principal) cells Oxyphilic Cells Major cell type; arranged in cords Secrete PTH Oxyphilic Cells Large cells found singly or in clumps Heterochromatic nucleus and intensely eosinophilic cytoplasm (high in mitochondria) No secretory granules Function not known

How PTH Regulates Blood Ca++ Levels High Ca++ Low Ca++ Decreased PTH, Ca++ Deposition Increased PHT, Ca++ Mobilization and Increased Absorption

Histology of the Adrenal Gland Gross Anatomy: 4-6 cm x 4-6 cm Cortex: derived from mesoderm Medulla: derived from neural crest cells Cortex: General Cell Characteristics Large numbers of cytoplasmic lipid droplets Large amount of SER Mitochondria with tubular cristae Secretion by diffusion, not stored products

Anatomical Zones of Adrenal Cortex Zona Glomerulosa (15%): Just beneath CT capsule Cells in round clusters Secrete Mineralcorticoids (aldosterone) Zona Fasiculata (80%); Middle and largest layer Rows of cells perpendicular to capsule; alternating sinusoidal capillaries Cells appear highly vacuolated (lipid droplets) Secrete Glucocorticoids (corticosterone, cortisol, androgens and estrogens) Zona Reticularis (5%): Deepest cortical layer Cells in anastomosing chords Secretions same as in fasiculata

Organization of Adrenal Medulla Neural Crest Derivative; Sympathetic Ganglion Cells Arranged in Cords or Clumps Chromaffin Cells Synthesize and release Epinephrine and Norepinephrine Synthesize Products Stored in Dense Core Granules Merocrine Secretion of Products Innervated by Preganglionic Sympathetic Fibers

Organization of Adrenal Medulla Neural Crest Derivative; Sympathetic Ganglion Cells Arranged in Cords or Clumps Chromaffin Cells Synthesize and release Epinephrine and Norepinephrine Synthesize Products Stored in Dense Core Granules Merocrine Secretion of Products Innervated by Preganglionic Sympathetic Fibers

Organization of Adrenal Medulla Neural Crest Derivative; Sympathetic Ganglion Cells Arranged in Cords or Clumps Chromaffin Cells Synthesize and release Epinephrine and Norepinephrine Synthesize Products Stored in Dense Core Granules Merocrine Secretion of Products Innervated by Preganglionic Sympathetic Fibers

Organization of Adrenal Medulla Neural Crest Derivative; Sympathetic Ganglion Cells Arranged in Cords or Clumps Chromaffin Cells Synthesize and release Epinephrine and Norepinephrine Synthesize Products Stored in Dense Core Granules Merocrine Secretion of Products Innervated by Preganglionic Sympathetic Fibers

Chromaffin cell of the Adrenal Medulla

Pineal Gland Regulates daily body rhythm Develops from neuroectoderm of posterior roof of diencephalon Located at posterior wall of 3rd ventricle Pine cone-shaped, 5x3 mm

Capsule composed of pia mater CT septa penetrate gland Sympathetic axons and blood vessels enter with septa

Pinealocytes Major cell type Euchromatic with nucleolus Cytoplasmic processes end at a capillaries Secrete melatonin

Interstitial cells Similar to astrocytes in brain Nucleus more heterochromatic Contain intermediate filaments Found throughout the gland

Corpora arenacea (brain sand) Globular accumulations of calcium phosphate and carbonates in interstitial space Used to determine midline in radiographic and CT scans

Function of Pineal gland Timekeeper of the body regulating circadian rhythm Retinal stimulation by light relayed to pineal via sympathetic innervation from superior cervical ganglion Melatonin is released in the dark, inhibited by light Melatonin affects neurons in the hypothalamus that produce Gonadotropin releasing factors, thus in animals it influences seasonal sexual activity. Tumors that destroy the pineal lead to precocious (early onset) puberty

http://www. path. uiowa. edu/virtualslidebox/ Table of Contents http://www.path.uiowa.edu/virtualslidebox/ Table of Contents Endocrine System Thyroid-parathyroid #92 Parathyroid #SP02 Adrenal gland #160 http://java.vcu.edu/som-histology/