Pages Below:
| |
Thyroid Gland Histology
- development
- arises as invagination of endoderm from foramen cecum of tongue
- descends through tissues of neck to final position at end of
thyroglossal duct
- thryroglosal duct degenerates
- parathyroids arise on 3rd and 4th pharyngeal pouches
- exchange position as migrate to thyroid
- consist of two lateral lobes connected by isthmus
- pyramidal lobe may arise from isthmus
- follicles are structural unit
- filled with gel-like colloid
- contains thyroglobulin (storage form of hormones)
- follicular cells
- secrete T4 and T3
- arise from endoderm
- oxidise iodide from blood to iodine and release into colloid
- convert amino acids into thyroglobulin and release into colloid
iodination occurs nears microvilli
- cells have: lots of rER; well-developed Golgi complex; small
vesicles associated with Golgi; lysosomes; membrane limited colloid
resorption droplets
- hormone release stimulated by thyroid stimulating hormone (TSH)
- parafollicular (C) cells
- secrete calcitonin
- arise from neural crest cells
- calcitonin release stimulated by high calcium levels
- follicles surrounded by extensive network of fenestrated capillaries
- lymphatics also present and help transport hormones
| development of thyroid gland |
| gross and microscopic structure of thyroid gland;
vasculature |
| secretion of thyroid hormones; iodine economy of the
thyroid; action of TSH |
|