Thyroid gland (edited v.)


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  •  TEM of the follicular epithelium shows pseudopodia and microvilli extending from the follicular cells (F) into the colloid of the lumen (L). The cells have apical junctional complexes, much RER, well-developed Golgi complexes, and many lysosomes. Inside the basement membrane (BM) of the follicle, but often not contacting the colloid in the lumen, are occasional C or parafollicular cells (C). To the left and right of the two C cells seen here are capillaries intimately associated with the follicular cells, but outside the basement membrane
  • A TEM of a C cell, with its large Golgi apparatus (G), extensive RER, and cytoplasm filled with small secretory granules containing calcitonin.
  • Thyroid gland (edited v.)

    1. 1. THYROID GLAND<br />
    2. 2. THYROID GLAND<br />Located in the anterior neck region adjacent to the larynx and trachea<br />Consists of two lateral lobes united by an isthmus<br />Develops from the endodermal lining of the floor of the primitive pharynx<br />Composed of connective tissue septa and follicles<br />
    3. 3. MAIN FUNCTION<br />Synthesize the thyroid hormones<br /><ul><li>Thyroxine (Tetra – iodothyronine or T4)
    4. 4. Tri – iodothyronine (T3)
    5. 5. Calcitonin</li></li></ul><li>LOCATION<br />Located in the anterior neck region adjacent to the larynx and trachea<br />
    6. 6. STROMA<br />Thin loose areolar connective tissue capsule<br /><ul><li>Forming connective tissue septa</li></ul>Coarse and fine collagenous fibers<br />Presence of fibroblasts and blood vessels<br />
    7. 7. STROMA<br />A low-power micrograph of thyroid gland shows the thin capsule (C), from which septa (S) with the larger blood vessels, lymphatics, and nerves enter the gland<br />
    8. 8. FOLLICULAR EPITHELIUM<br />Surrounds each follicle<br />Composed of reticular fibers and network of capillaries<br />Can be simple squamous, cuboidal, or low columnar epithelium<br />
    9. 9. THYROID FOLLICLE<br /><ul><li>Structural unit
    10. 10. Roughly spherical cyst-like compartment
    11. 11. Wall formed by follicular epithelium
    12. 12. Central cavity contains a gelatinous substance called colloid
    13. 13. large glycoprotein thyroglobulin, precursor for the active thyroid hormones</li></li></ul><li>THYROID FOLLICLE<br />Surrounded by 2 types of cells<br /><ul><li>Follicular cells
    14. 14. Parafollicular cells</li></li></ul><li>THYROID FOLLICLE<br />The lumen (L) of each follicle is surrounded by a simple epithelium in which the cell height ranges from squamous to low columnar. Also present are large pale-staining parafollicular or C cells (C).<br />
    15. 15. FOLLICULAR CELLS<br />Principal cells<br />Most numerous cell type<br />Cuboidal in shape with spherical nucleus<br />Periods of increased activity – cells are more columnar and colloid is less abundant<br />
    16. 16. FOLLICULAR CELLS<br />Periods of decreased activity – cells are squamous and colloid content increases<br />Exhibit organelles <br /><ul><li>active protein synthesis and secretion, phagocytosis and digestion
    17. 17. Synthesize, release, and store their product outside their cytoplasm
    18. 18. Secretion and synthesis of T3 and T4</li></li></ul><li>FOLLICULAR CELLS<br />RED– Follicle with colloid<br />BLUE – Follicular cells<br />PINK - Connective tissue septa<br />
    19. 19. PARAFOLLICULAR CELLS<br />C (clear) cells<br />Larger than follicular cells<br />Contain secretory granules<br />Can occur either alone or in clumps<br />Synthesize and secrete calcitonin<br />
    20. 20. PARAFOLLICULAR CELLS<br />RED– Follicle with colloid<br />BLUE – Parafollicular cells<br />PINK – Retracted or distorted colloid<br />
    21. 21. FOLLICULAR AND C CELLS<br />C cells may be part of the follicular epithelium or present singly or in groups outside of follicles. Follicular cells (F) can usually be distinguished from C cells (C) by the smaller size and darker staining properties. Unlike follicular cells, C cells seldom vary in their size or pale staining characteristics. <br />
    22. 22. FOLLICULAR AND C CELLS<br />
    23. 23. FOLLICULAR AND C CELLS<br />
    24. 24. ULTRASTRUCTURE (Follicular and C cells)<br />
    25. 25. ULTRASTRUCTURE (Follicular and C cells)<br />
    26. 26. HORMONES<br /><ul><li>Thyroxine (Tetra – iodothyronine or T4)
    27. 27. Tri – iodothyronine (T3)
    28. 28. Calcitonin</li></li></ul><li>THYROXINE (T4) and TRI - IODOTHYRONINE (T3)<br />Growth<br />Cell differentiation<br />Control of the basal metabolic rate and oxygen consumption in cells<br />Affect protein, lipid, and carbohydrate metabolism<br />
    29. 29. CALCITONIN<br />Lower blood calcium levels through inhibition of bone resorption<br />Secretion is triggered by elevation of blood calcium concentration<br />
    30. 30. HORMONES<br />