Endocrine Glands Prof Menna Abdel-Dayem THYROID GLAND Thyroid Gland Large endocrine gland in the front of the neck formed of 2 lobes connected by an isthmus. Thyroid Gland I. STROMA: ● Capsule: Outer false capsule of pretracheal fascia. Inner true capsule: C.T. cells & fibers, firmly adherent to the gland. ● Trabeculae ● Reticular framework Thyroid Gland II. PARENCHYMA: A. Thyroid Follicles: B. Interfollicular Tissue: A. Thyroid Follicles - The structural & functional units of the gland. - Rounded or oval in shape, surrounded by fenestrated blood capillaries. Lined with cubical epithelium, resting on thin basement membrane & surrounding a lumen filled with acidophilic colloid material (iodinated glycoprotein). Lined with 2 types of cells: 1. Follicular cells (98%) (endodermal): • LM: cuboidal cells with basophilic cytoplasm & central rounded nuclei. In hyperthyroidism, the cells become columnar & in hypothyroidism, the cells become flat squamous cells. 1. Follicular cells • EM: The apex of cells show short microvilli & adjacent cells joined by tight junctions. Have mitochondria, rER, supranuclear Golgi apparatus, ribosomes apical secretory vesicles & lysosomes. Function: secrete thyroid hormones (T3 & T4) under control of TSH. 2. Parafollicular cells C cells 2% Larger cells with paler cytoplasm, so called clear cells (stained with Ag). Present between the basement membrane and follicular cells. Do not reach the lumen of the follicle. 2. Parafollicular cells EM: have mitochondria, rER, Golgi apparatus & basal secretory granules. Function: secrete thyrocalcitonin (belong to APUD cells) →↓↓ blood calcium. B. Interfollicular Tissue: In-between thyroid follicles. ● Reticular C.T. ● Interfollicular cells (tangentially cut follicles), ● Occasional C-cells ● fenestrated blood capillaries. Parathyroid Gland Parathyroid Gland Parathyroid Gland I. STROMA: ● Capsule ● Trabeculae ● Reticular framework II. PARENCHYMA: Cells arranged in anastomosing cords separated by fenestrated capillaries. Two types of cells: chief cells and oxyphil cells. Parathyroid Gland (a) Chief (principal) cells (b) Oxyphil cells More numerous & small Less numerous but larger. No. ↑↑ with age. Polygonal cells with central Oval or rounded cells with eccentric rounded nuclei nuclei Have basophilic cytoplasm & Deeply acidophilic cytoplasm & vesicular nucleus dark nucleus Fine secretory granules Acidophilic granules Parathyroid Gland (a) Chief (principal) cells (b) Oxyphil cells EM: rich in mitochondria, rER, EM: mitochondria Golgi apparatus & secretory granules Function: secrete parathyroid Function not yet known hormone (parathormone) →↑↑ blood calcium .