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24 Cards in this Set
- Front
- Back
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What is the origin of the thyroid?
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floor of primitive pharynx at foramen cecum
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When does the thyroid gland develop?
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4th week of gestation
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What are the functions of the thyroid gland? (3)
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make T4, T3, calcitonin
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What is the structure of the thyroid gland? (3)
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bilobed connected by isthmus
anterior to larnyx (10 lateral to trachea (2) extensive vascular supply (3) |
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Where exactly is the thyroid located relative to the trachea?
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lobes lateral to trachea extending from thyroid cartilage to the fifth or sixth tracheal ring
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What are the 4 main structures of the thyroid?
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1) spherical follicles
2) center of follicle containing colloid 3) fenestrated capillaries 4) parafollicular cells (C cells, clear cells) |
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What was the histology of the spherical follicles?
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cuboidal epithelium
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What effect does activity have on the spherical follicles?
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1) height varies between sqaumous or columnar depending on activity of gland
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What is colloid?
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accumulation of gelatin like material contained within the follicle specifically protein thyroglobulin
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What does the follicle secrete?
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thyroglobulin
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What is the purpose of thyroglobulin?
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storage form of thyroid hormones
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What is the origin of the parafollicular cells?
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originate from pharyngeal pouch endoderm
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Where are the parafollicular cells located?
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singly within follicular epithelium or in small clusters between follicles
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What do the parafollicular cells typically contain? (1)
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protein synthetic organelles and secretory granules (1)
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Are the parafollicular cells polarized?
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no
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What hormone does the parafollicular cell produce?
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calcitonin
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What are the two functions of calcitonin?
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1) inhibit bone resorption to decrese calcium levels
2) antagonist of parathyroid hormone |
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What is the function of the thyroid follicle cells? (2)
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1)release of thyroglobulin onto epithelial surface follicular lumen
2) reuptake and cleavage of precursor to release hormone |
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What What are the ultrastructure components of the follicle cells?
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1) basal lamina
2) apical microvilli 3)junctional complexes |
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What are the synthethic features of the follicular cells? (3)
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1) extensive ER
2) golgi 3) transport vesicles |
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What are the resorptive/degradative features? (2)
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1) psuedopodia to form resorption vacuoles
2) numerous lysosomes and phagosomes |
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What type of protein is thyroglobulin?
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glycoprotein
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What are the synthesis, secretion and storage steps of thyroglubulin?
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synthesis --> RER
glycosylation --> RER completion --> golgi released/stored --> lumen of follicle |
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What is a summary of T3 and T4 synthesis?
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1)thyroglobulin is synthesized and secreted into follicle lumen
2) iodide is actively pumped into follicle cell and transported to apical membrane 3) at apical membrane iodide is converted to iodine 4) iodine is released into lumne 5) iodine spontaneously adds to phenyl rings of tyrosin on thyroglobin to form either MIT or DIT 6)iodonated phenyl rings are rearranged forming diphenyl tyrosine (thyronines) which contain 4 iodidines (T4) or three iodines (T3) 7) iodinated thyroglobulin is taken back into follicle cells by pinocytosis 8) vacuoles containing thyroglobulin fuse with lysosomes 9) proteolytic enzymes digest the protein into its individual amino acids as well as T3 and T4 10) small thyroid hormones exit the cell via diffusion 11)MITs and DIts are de-iodinated and re-enter the general amino acid pool |
