Endocrine - Thyroid Development: Difference between revisions
No edit summary |
|||
Line 43: | Line 43: | ||
Childhood hypothyroidism delays ossification and bone mineralization. | Childhood hypothyroidism delays ossification and bone mineralization. | ||
==Iodine Deficiency== | |||
Iodine deficiency disorder (IDD) is the single most common cause of preventable mental retardation and brain damage in the world (More? Abnormal Development - Iodine Deficiency). It is required for synthesis of thyroid hormone, which in turn regulates aspects of neural development. | |||
Worldwide: | |||
1.6 billion people are at risk | |||
IDD affects 50 million children | |||
100,000 cretins are born every year | |||
It causes goiters and decreases the production of hormones vital to growth and development. Children with IDD can grow up stunted, apathetic, mentally retarded and incapable of normal movement, speech or hearing. IDD in pregnant women cause miscarriage, stillbirth and mentally retarded children. | |||
A teaspoon of iodine is all a person requires in a lifetime, but because iodine cannot be stored for long periods by the body, tiny amounts are needed regularly. In areas of endemic iodine deficiency, where soil and therefore crops and grazing animals do not provide sufficient dietary iodine to the populace, food fortification and supplementation have proven highly successful and sustainable interventions. | |||
Iodized salt programs and iodized oil supplements are the most common tools in the fight against IDD. | |||
(Data: ICCIDD) | |||
Prolonged intake of large amounts (excess) of iodide can increase the incidence of goiter and/or hypothyroidism in humans. African Congo appears to be the only country that appears to have a dietary excess. | |||
== References == | == References == |
Revision as of 14:09, 25 April 2010
Introduction
The boundary endoderm in the floor region forms a pocket (marked by the foramen cecum) that separates from the surface and forms the thyroid. Cells originate on the surface of the floor and descend into mesoderm above aortic sac and into the hypopharyngeal eminence as "cords". These cells continue to descend until they reach their final destination in the neck adjacent to the thyroid cartilage.
This pathway forms a temporary duct (thyroglossal duct). There are abnormalities of incomplete or excessive descent of these thyroid precursor cells. The thyroid is one of the earliest endocrine organs to differentiate and has an important hormonal role in embryonic development. The early bundle of cells then forms the thyroid by first dividing to form 2 lobes separated by a narrow connecting isthmus.
| Lecture - Head Development | original page
- Functions from wk10, required for neural development, stimulates metabolism (protein, carbohydrate, lipid), reduced/absence = cretinism (see abnormalities)
Hormones - (amino acid derivatives) Thyroxine (T4), Triiodothyronine (T3)
Thyroid Development
- thyroid median endodermal thickening in the floor of pharynx, outpouch – thyroid diverticulum
- tongue grows, cells descend in neck
- thyroglossal duct - proximal end at the foramen cecum of tongue thyroglossal duct
- thyroid diverticulum - hollow then solid, right and left lobes, central isthmus
Thyroid Timeline
- 24 days - thyroid median endodermal thickening in the floor of pharynx, outpouch – thyroid diverticulum
- Week 11 - colloid appearance in thyroid follicles, iodine and thyroid hormone (TH) synthesis
growth factors (insulin-like, epidermal) stimulates follicular growth
Fetal Thyroid Hormone
- Initial secreted biologically inactivated by modification, late fetal secretion develops brown fat
- Iodine deficiency- during this period, leads to neurological defects (cretinism)
- Birth - TSH levels increase, thyroxine (T3) and T4 levels increase to 24 h, then 5-7 days postnatal decline to normal levels
Abnormalities
Congenital hypothyroidism - approximately 1 in 3000 births, associated with neurological abnormalities.
Lingual thyroid gland - failure of thyroid descent.
Thyroglossal cyst - persistance of thyroglossal duct.
Thyroglossal fistula - partial degeneration of the thyroglossal duct.
Abnormal development of the thyroid - incomplete or excessive descent.
Pyramidal lobe - from isthmus (50% of people) attached to hyoid bone distal end of thryoglossal duct.
Childhood hypothyroidism delays ossification and bone mineralization.
Iodine Deficiency
Iodine deficiency disorder (IDD) is the single most common cause of preventable mental retardation and brain damage in the world (More? Abnormal Development - Iodine Deficiency). It is required for synthesis of thyroid hormone, which in turn regulates aspects of neural development.
Worldwide:
1.6 billion people are at risk IDD affects 50 million children 100,000 cretins are born every year It causes goiters and decreases the production of hormones vital to growth and development. Children with IDD can grow up stunted, apathetic, mentally retarded and incapable of normal movement, speech or hearing. IDD in pregnant women cause miscarriage, stillbirth and mentally retarded children.
A teaspoon of iodine is all a person requires in a lifetime, but because iodine cannot be stored for long periods by the body, tiny amounts are needed regularly. In areas of endemic iodine deficiency, where soil and therefore crops and grazing animals do not provide sufficient dietary iodine to the populace, food fortification and supplementation have proven highly successful and sustainable interventions.
Iodized salt programs and iodized oil supplements are the most common tools in the fight against IDD.
(Data: ICCIDD)
Prolonged intake of large amounts (excess) of iodide can increase the incidence of goiter and/or hypothyroidism in humans. African Congo appears to be the only country that appears to have a dietary excess.
References
Reviews
Articles
Search PubMed
Search April 2010
- Endocrine Development - All (14277) Review (4620) Free Full Text (3140)
Search Pubmed: thyroid development
Additional Images
Adult Histology
Terms
Glossary Links
- Glossary: A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z | Numbers | Symbols | Term Link
Cite this page: Hill, M.A. (2024, June 27) Embryology Endocrine - Thyroid Development. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Endocrine_-_Thyroid_Development
- © Dr Mark Hill 2024, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G