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==The Parathyroid Glands==

==Introduction==

The parathyroid glands are small glands vital for [[Calcium|calcium homeostasis]].

The parathyroid glands are small glands, vital for [[Calcium|calcium homeostasis]].

==Anatomy==

==Anatomy==

The parathyroid glands are multiple (generally four) small glands approximately 1-2mm in length are located about the cranial trachea.

The parathyroid glands are multiple (generally four) small glands, approximately 1-2mm in length are located about the cranial trachea. Generally, there are two internal glands embedded within the [[Thyroid Gland - Anatomy & Physiology|thyroid Glands]], and two external glands are outside the thyroid tissue. However, all of the parathyroid tissue may be embedded within the thyroid gland itself. In the Horse, there are 'nests' of parathyroid tissue along the neck to the thoracic inlet.

Generally there are two internal glands embedded within the [[Thyroid Gland - Anatomy & Physiology|Thyroid Glands]], and two external glands are outside the thyroid tissue. However all of the parathyroid tissue may be embedded within the thyroid gland itself.

The parathyroid glands originate from the endoderm of pharyngeal pouches III and IV. The internal gland from pouch IV and the external from pouch III.

The parathyroid glands originate from the endoderm of pharyngeal pouches III and IV. The internal gland from pouch IV, external from pouch III.

===Histology===

===Histology===

* The parathyroids are histologically easy to distinguish from the [[Thyroid Gland - Pathology#Functional anatomy|thyroid]]. [[Image:Parathyroid Gland Active.jpg|thumb|right|350px|©RVC 2008]]

 

** The thyroid has a characteristic follicular structure.

The parathyroids are histologically easy to distinguish from the [[Thyroid Gland - Pathology#Functional anatomy|thyroid]]. [[Image:Parathyroid Gland Active.jpg|thumb|right|350px|©RVC 2008]]

** The parathyroid consists of densely packed cells, of two types:

 

**# Chief cells (Principal Cells)

The thyroid has a characteristic follicular structure, whereas the the parathyroid consists of densely packed cells, of two types:

**#* Are the predominant cell type

 

**#* Stain darker when active

1. '''Chief cells''' (Principal Cells)

**#* Are smaller than oxyphil cells

 

**#* Manufacture Parathyroid Hormone (PTH)

These are the predominant cell type. They stain darker when they are active and are smaller than oxyphil cells. They manufacture Parathyroid Hormone (PTH).

**# Oxyphil cells

 

**#* Are fewer in number than chief cells

2. '''Oxyphil cells'''

**#* Stain lighter

 

**#* Are larger than chief cells

These fewer in number than chief cells. They stain lighter and are larger than chief cells. They have an unknown function.

**#* Have unknown function

 

* Grossly, the parathyroids are difficult to differentiate from thyroid tissue or fat.

Grossly, the parathyroids are difficult to differentiate from thyroid tissue or fat. A parathyroid gland may be accidentally removed during thyroidectomy. Care must therefore be taken if the second thryoid is removed to leave the parathyroid intact, otherwise [[Parathyroid Glands - Pathology|hypoparathyroidism]] may ensue.

** A parathyroid gland may be accidentally removed during thyroidectomy. Care must therefore be taken if the second thryoid is removed to leave the parathyroid intact, otherwise [[Parathyroid Glands - Pathology|hypoparathyroidism]] may ensue.

====Histology Gallery====

====Histology Gallery====

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</gallery></center>

===Blood Supply and Innervation===

==Blood Supply and Innervation==

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===Physiology===

==Physiology==

* The sole function of the parathyroid gland is to maintain [[Calcium|Calcium Homeostasis]].

The sole function of the parathyroid gland is to maintain [[Calcium|Calcium Homeostasis]]. Calcium homeostasis is, amongst other things, important for maintaining the function of the [[Nervous and Special Senses - Anatomy & Physiology#Nervous System|nervous]] and [[Musculoskeletal System Overview - Anatomy & Physiology|muscular]] systems. When blood calcium levels drop below a certain point, calcium-sensing receptors in the parathyroid gland are activated to release [[Hormones - Anatomy & Physiology|hormone]] into the blood. The hormone produced by the parathyroid gland (Parathyroid Hormone) also has an effect on [[Phosphorus|phosphorus homeostasis]].

** Calcium homeostasis is, amongst other things, important for maintaining function of the [[Nervous and Special Senses - Anatomy & Physiology#Nervous System|nervous]] and [[Musculoskeletal System Overview - Anatomy & Physiology|muscular]] systems.  

* When blood calcium levels drop below a certain point, calcium-sensing receptors in the parathyroid gland are activated to release [[Hormones - Anatomy & Physiology|hormone]] into the blood.

*The hormone produced by the parathyroid gland (Parathyroid Hormone) also has an effect on [[Phosphorus|Phosphorus Homeostasis]].

==Test yourself with the Parathyroid Gland Flashcards==

==Links==

[[Parathyroid_Glands_Flash_Cards_- Anatomy & Physiology|Parathyroid Glands Flashcards]]

Click here for the [[Parathyroid_Glands_Flash_Cards_- Anatomy & Physiology|parathyroid glands flashcards]].

[[Category:Endocrine System - Anatomy & Physiology]]

[[Category:Endocrine System - Anatomy & Physiology]]

[[Category:To Do - A&P]]

[[Category:To Do - AimeeHicks]]