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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.
  • Transcript

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