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Thyroid Gland - Anatomy & Physiology (view source)
Revision as of 17:46, 7 December 2022
, 17:46, 7 December 2022no edit summary
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==Introduction==
==Introduction==
The thyroid gland lies in the neck, in front of the upper part of the trachea. Two types of hormones are produced, which are the iodine containing hormones; '''tri-iodothyronine'''(T3) and '''thyroxine''' (T4). Thyroid hormones regulate the basal metabolic rate and are important in the regulation of growth of tissues, particularly nervous tissue. Release stimulated by TSH from the pituitary. The second type of hormone produced from the thyroid gland is '''[[calcitonin]]''', which regulates blood calcium levels along with parathyroid hormone and acts to reduce blood calcium by inhibiting its removal from bone.
The thyroid gland lies in the neck, in front of the upper part of the trachea. Two types of hormones are produced, which are the iodine containing hormones; '''tri-iodothyronine'''(T3) and '''thyroxine''' (T4). Thyroid hormones regulate the basal metabolic rate and are important in the regulation of growth of tissues, particularly nervous tissue. Release stimulated by TSH from the pituitary. The second type of hormone produced from the thyroid gland is '''[[calcitonin]]''', which regulates blood calcium levels along with parathyroid hormone and acts to reduce blood calcium by inhibiting its removal from bone.
== Embryological Origin ==
== Embryological Origin ==
The thyroid gland is a downgrowth from the pharyngeal endoderm of the developing [[Tongue - Anatomy & Physiology|tongue]]. The calcitonin producing cells are different and are derived from the fourth branchial pouch.
The thyroid gland is a downgrowth from the pharyngeal endoderm of the developing [[Tongue - Anatomy & Physiology|tongue]]. The calcitonin producing cells are different and are derived from the fourth branchial pouch.
===Ultrastructure and Histology===
===Ultrastructure and Histology===
The gland consists of varying sized follicles, which are bounded by a single layer of cuboidal epithelial cells ('''follicular cells'''} and a basement membrane, surrounding a central lumen filled with a homogenous protein rich colloid (thyrogloblin). The apical surface of the cell membranes is covered with numerous micovilli to increase surface area. The follicular cells are connected by tight junctions, and have a dense capillary network. The colloid is a store of thyroid hormones prior to secretion. The thyroid gland is the only endocrine gland to store its hormone in large quantities. In the active gland colloid is diminished and epithelial cells are tall and columnar.
The gland consists of varying sized follicles, which are bounded by a single layer of cuboidal epithelial cells ('''follicular cells'''} and a basement membrane, surrounding a central lumen filled with a homogenous protein rich colloid (thyrogloblin). The apical surface of the cell membranes is covered with numerous micovilli to increase surface area. The follicular cells are connected by tight junctions, and have a dense capillary network. The colloid is a store of thyroid hormones prior to secretion. The thyroid gland is the only endocrine gland to store its hormone in large quantities. In the active gland colloid is diminished and epithelial cells are tall and columnar.
:[[Reproductive System Overview - Anatomy & Physiology|'''Reproductive system''']] is affected by reduced levels of thyroid hormone causing irregular cycling and decreased libido.
:[[Reproductive System Overview - Anatomy & Physiology|'''Reproductive system''']] is affected by reduced levels of thyroid hormone causing irregular cycling and decreased libido.
:Finally, in the [[Alimentary System Overview - Anatomy & Physiology|'''alimentary system''']], thyroid hormone increases appetite and feed intake, increases secretion of [[Pancreas - Anatomy & Physiology|pancreatic]] enzymes and increases motility.
:Finally, in the [[Alimentary System Overview - Anatomy & Physiology|'''alimentary system''']], thyroid hormone increases appetite and feed intake, increases secretion of [[Pancreas - Anatomy & Physiology|pancreatic]] enzymes and increases motility.
===Influence of External Factors===
'''Euthyroid sick syndrome''': concurrent disease such as starvation, sepsis, trauma or stress can cause a depression in basal thyroid levels as a normal response, to minimise the catabolic effects of thyroid hormones.
This occurs in many species and may lead to false diagnoses of [[hypothyroidism]] or a missed diagnosis of [[hyperthyroidism]].
<u>'''In horses'''</u>, many factors influence the level of T3 and T4:
'''In foals''': thyroid hormone concentrations are up to 14 times higher than in horses over the age of 2.
During normal feeding, T3 and T4 levels increase within two hours of feeding. Undernutrition results in an increase in T4 but T3 levels are unchanged. Excess protein and energy result in a decreased T4 and an increased T3.
'''In adult horses''': undernutrition results in a decrease in both T3 and T4. Phenylbutazone is also known to decrease T4 levels.
Thyroid hormone levels increase with age, and are higher during pregnancy and times of low temperature.
==Problems associated with the Thyroid Gland==
==Problems associated with the Thyroid Gland==
Problems with the thyroid gland include enlargement, or [[Goitre|Goitre]] and also the effects of increased level of hormones in [[Hyperthyroidism|Hyperthyroidism]] or decreased levels of hormones in [[Hypothyroidism|Hypothyroidism]].
Problems with the thyroid gland include enlargement, or [[Goitre|Goitre]] and also the effects of increased level of hormones in [[Hyperthyroidism|Hyperthyroidism]] or decreased levels of hormones in [[Hypothyroidism|Hypothyroidism]].
==Test yourself with the Thyroid Gland Flashcards==
{{Template:Learning
|flashcards = [[Thyroid_Gland_Flash_Cards_- Anatomy & Physiology|Thyroid Gland]]<br>[[Equine Internal Medicine Q&A 21]]
|powerpoints = [[Endocrine Histology resource|Histology of the Endocrine system]]
|OVAM = [http://www.onlineveterinaryanatomy.net/content/feline-thyroid-gland-histology Feline Thyroid Gland Histology]
|Vetstream = [https://www.vetstream.com/canis/Content/Factsheets/FactSheet020.asp Hypothyroidism]
}}
{{review}}
==Webinars==
<rss max="10" highlight="none">https://www.thewebinarvet.com/endocrinology/webinars/feed</rss>
[[Category:Endocrine System - Anatomy & Physiology]]
[[Category:Endocrine System - Anatomy & Physiology]]
[[Category:A&P Done]]
[[Category:A&P Done]]