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3 thyroid gland final


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3 thyroid gland final

  1. 1. THYROID GLAND Captain Rishi Pokhrel
  2. 2. IntroductionUnique endocrine gland Located superficially Uses raw material – supplied externally ( Iodine ) Stores the product (2 months) Rich blood supply  5 ml/g/min  5 l/hr. 0.4% of body weight - 2% of total blood flow
  3. 3. Introduction – Historical background Eponymy – Gr. thyreos (Shield) Goiters were known long before the thyroid gland itself. God Bes of ancient Egypt – features of myxedema China 2700 B C Ayurveda 1400 BC – “galaganda”
  4. 4.  Hippocrates (460-337 BC) “...when glands of the neck become diseased themselves, they become tubercular and produce struma....” (struma – goiter) Hippocrates failed to differentiate between the thyroid and the cervical glands
  5. 5. Gallen (130-200 AD) described operations on two boys by ignorant physicians who removed tubercular nodes with their fingernails, rendering one boy mute and the other semi- mute.secretions of the thyroid lubricated the larynx & cartilage ; aphonia was provoked by cutting the laryngeal nerves
  6. 6.  Aetios 550 AD : goiter -> aneurysmBronchocele, elephantias is of the throat etc.
  7. 7. • Leonardo Da Vinci is generally credited as the first to draw the thyroid gland as an anatomical organ in 1508 AD
  8. 8. Andreas Vesalius (1514- 1564) correctly described the anatomy of thyroid gland in detailB. Eustachius (1520-1547) first used the term isthmusThomas Warton (1614- 1673) gave the gland its modern name of thyroid
  9. 9.  Robert James Graves, 1835 – hyperthyroidism – Grave’s disease Partial thyroidectomy - P.S. Dessault (1744- 1795) in Paris. Guillance Dupuytren 1808 - total thyroidectomy for tumor Ludwig Rehn, 1880, first successful thyroidectomy for exophthalmic goiter. Thyroxine was identified only in the 19th century In 1909, Theodor Kocher won Nobel Prize in Medicine "for his work on the physiology, pathology and surgery of the thyroid gland”
  10. 10. Development Starts from 3rd week of IUL -1st endocrine gland to develop Proliferation of cells from caudal end of Thyroglossal duct - endoderm PF or C cells – Ultimibranchial body – 4th/5th pharyngeal pouch – neural crest cells
  11. 11. Week 3 (day 24)  appears as midline vesicular structure at foramen cecum  form a duct like invagination of ventral pharyngeal endoderm  grows caudally to become thyroglossal duct
  12. 12. Week 7  finishes descent along midline – forms median isthmus & 2 lateral lobes  2 lateral anlagen develop from 4th-5th branchial pouch, which contains ultimobranchial body  midline and lateral portions of thyroid fuse  Thyroglossal duct disappears – remnants: Pyramidal lobe (50%) and levator muscles
  13. 13.  Week 9: cords and plates of follicular cells are formed Week 10:cords divide into small cellular groups, small follicular lumina appear Week 11-12: colloid secretion appears, thyroid becomes functional Week 14: well developed follicles are lined by follicular cells and contain thyroglobulin containing colloid in lumina Week 20: levels of TSH and T4 starts rising Week 35: TSH & T4 levels = adults Early growth and development is independent of TSH
  14. 14. Features Features Fleshy mass in the neck, in front of trachea, concealed by strap muscles of neck 2 symmetrical lobes united at isthmus. Lobes 5 x 3 X 2 cm; isthmus 1.25 x 1.25 cm 25 – 30 gms in wt. – variable, larger in females, varies with menstruation and pregnancy
  15. 15. Features Lobes – Pear shaped, triangular in cross section apex: oblique line of thyroid cartilage base: 4-6 tracheal ring Isthmus flat and square: against 2-4 tracheal rings Pyramidal lobe (50%) Levator Glandulae thyroidae
  16. 16. Coverings Inner true capsule: condensation of parenchyma Outer false capsule: formed by splitting of pretracheal layer of deep Cx fascia. Blood vessels ramify under true capsule Ligament of berry – condensation of PTF from false capsule to cricoid cartilage- RLN runs in it -> movement of thyroid gland with larynx
  17. 17. Deep cervical fascia
  18. 18. Relations Lobes: Δr in cross section – 3 surfaces: ant-lat, med & post Only posteromedial border is prominent. Med surface – 2 each; cartilage, muscle, tubes & nerves
  19. 19. Relations• Upper pole tucked b/w 2 muscles• Cannot extend sup.
  20. 20. RelationsPara thyroids lie in post. Surface b/w 2 capsulesCapsule is thinner posteriorlyGland enlargement – extends posteriorly & inferiorly
  21. 21. Blood Supply
  22. 22. Blood Supply
  23. 23. Venous DrainageVeins – wide lumenNo valves in lumenKocher’s vein - variable
  24. 24. Lymphatic Drainage
  25. 25. Microscopic Structure Stroma: – Fibroelastic true capsule -> septae -> ill defined lobules -> Pseudolobulated – Septae: blood vs, nerves lymphatics – Intralobular loose CT
  26. 26. Parenchyma Follicles: arrangement of cells in hollow spherical or short cylindrical masses 0.2- 0.9 mm - Structural & functional units Filled with gel like substance - colloid- Thyroglobulin Simple Principal/Follicular cells Parafollicular or ‘C’ cells
  27. 27. Resting Follicle Active Follicle
  28. 28. Principal/Follicular cellsNuclei- Spherical, 1-2 nucleoliGolgi, rER - prominentCytoplasm – basophilicApical vacuolesMicrovilli
  29. 29.  Thyroglobulin - Stored follicle – iodine trapping and iodination - reuptake (Scalloped margins) – lysosmes - broken into T3 & T4 - secreted
  30. 30. (calcitonin)– Lie beside follicle– Enclosed in same BM but not reaching lumen– Larger, rounded & paler– Nucleus round /oval, eccentric– Secretory granules – Calcitonin (PTH Antagonist)
  31. 31. Phylogeny• Thyroid gland evolution -> adapt to the terrestrial ecosystem with less supply of iodine.• Jellyfish lack thyroid gland• Endostyle of non-vertebrate chordates -> homologous to thyroid (Endostyle: longitudinal ciliated groove on ventral wall of the pharynx – produces mucus to gather food particles)• In lampreys, the larval endostyle transforms into adult thyroid gland during metamorphosis• Most primitive vertebrates - follicular thyroid gland but non capsulated• Thyroid is encapsulated in cartilaginous fish• In the higher vertebrate forms, the thyroid is a one- or two-lobed encapsulated structure.
  32. 32. Thyroid hormones Primary function of the thyroid - production of T3, T4, and calcitonin T3 & T4 – essential for normal growth, development & metabolism T4 -> T3 by peripheral organs like liver, kidney, spleen T3 is 4 - 10 X more active than T4 Hypothalamo – pitutary – thyroid axis
  33. 33. Physiology Thyrocytes (follicular cells) have four functions: – collect and transport iodine – they synthesize thyroglobulin and secrete it into the colloid – fix iodine to the thyroglobulin to generate thyroid hormones – remove the thyroid hormones from thyroglobulin and secrete them into the circulation.
  34. 34. Synthesis of thyroid hormones
  35. 35.  Thyroglobulin is synthesized in the rough endoplasmic reticulum and follows the secretory pathway to enter the colloid in the lumen of the thyroid follicle by exocytosis. Meanwhile, a sodium-iodide (Na/I) symporter pumps iodide (I-) actively into the cell, which previously has crossed the endothelium by largely unknown mechanisms. This iodide enters the follicular lumen from the cytoplasm by the transporter pendrin, in a purportedly passive manner In the colloid, iodide (I-) is oxidized to iodine (I0) by an enzyme called thyroid peroxidase. Iodine (I0) is very reactive and iodinates the thyroglobulin at tyrosyl residues in its protein chain (in total containing approximately 120 tyrosyl residues). In conjugation, adjacent tyrosyl residues are paired together. The entire complex re-enters the follicular cell by endocytosis. Proteolysis by various proteases liberates thyroxine and triiodothyronine molecules, which enters the blood by largely unknown mechanisms.
  36. 36. Calcitonin• 32 - aa linear polypeptide - C cells• Not under control of hypothalamus or pitutary• Secretion -> Ca2+, gastrin and pentagastrin• not essential for life – no replacement required following thyroidectomy unlike parathyroids.• antagonist to PTH - reduces Ca2+ level• Inhibits: Ca2+ absorption by intestine, osteoclast activity in bone & renal tubular cell reabsorption of Ca2+• Agonist to PTH -> Inhibits phosphate reabsorption by the kidney• Used clinically for Tt of hypercalcemia & osteoporosis
  37. 37. Applied AnatomyCongenital thyroid disorders  Aberrant thyroid tissue  Lingual thyroid  Thyroglossal cyst  50% close to or just inferior to body of hyoid bone  Thyroglossal fistula – secondary to rupture of cyst
  38. 38. Hyperthyroidism Vs. thyrotoxicosis Graves’ disease—an autoimmune disease involving autoantibody stimulation of TSH receptors. Toxic multinodular goiter — nodular enlargement of the thyroid in the elderly. Toxic nodule—autonomously functioning thyroid nodule; most are adenomas Lymphocytic thyroiditis /Hashimoto’s thyroiditis—inflammation causes release of stored hormones (followed by hypothyroid phase). Subacute (de Quervain’s) thyroiditis — thyroiditis associated with a painful goiter.
  39. 39. HypothyroidismMyxedema Cretinism
  40. 40. Thyroid lumps Thyroid cysts. Nodule of multinodular goiter. Follicular adenoma. Malignancy – 20% • Papillary • Follicular • Medullary – C cells -> PNPS • Malignant lymphoma • Anaplastic
  41. 41. Applied anatomyThyroidectomy lobe, subtotal, total Transverse skin incision 2.5 cm above jugular notch Gap b/w ST & SH opened up – trachea & isthmus exposed Muscles retracted laterally or divided at upper ends – preserve nerve supply from ansa cervicalis
  42. 42.  Later lobes displayed Plane of cleavage: b/w 2 capsules Vessels ligated and divided – STA right at the lower pole; ITA at some distance from lower pole During removal of gland  Ligament of berry released – RLN injury  Wedge shaped areas on post-medial surface is left behind- PT
  43. 43. Complications ELN injury – CT paralysis, hoarseness of voice, temporary until the other side takes over RLN injury – all intrinsic muscles except CT paralyzed, no recovery
  44. 44. What’s Your Message?POWERPOINT 2011