Changes

==Anatomy==

==Anatomy==

 

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.

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.

==Embryology==

==Embryology==

==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 parathyroids are histologically easy to distinguish from the [[Thyroid Gland - Pathology#Functional anatomy|thyroid]].  

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

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

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

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

2. '''Oxyphil cells'''

2. '''Oxyphil cells'''

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

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

 

 

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.

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 thyroid is removed to leave the parathyroid intact, otherwise [[Parathyroid Glands - Pathology|hypoparathyroidism]] may ensue.

====Histology Gallery====

====Histology Gallery====

<center><gallery>

<center><gallery>

Image:Parathyroid Gland Low Power 2.jpg|<p>'''Parathyroid Gland Low Power 2'''</P>^{©RVC 2008}

Image:Parathyroid Gland Low Power 2.jpg|<p>'''Parathyroid Gland Low Power 2'''</P>^{©RVC 2008}

Image:Parathyroid Gland Active.jpg|<p>'''Parathyroid Gland with active Principal Cells'''</P>^{©RVC 2008}

Image:Parathyroid Gland Active.jpg|<p>'''Parathyroid Gland with active Principal Cells'''</P>^{©RVC 2008}

Image:normalparathyroid.jpg|<p>'''Normal Parathyroid Gland'''</P> ^{Image courtesy of of Biomed Image Archive.}

Image:normalparathyroid.jpg|<p>'''Normal Parathyroid Gland'''</P> ^{Image courtesy of Biomed Image Archive.}

</gallery></center>

</gallery></center>

==Physiology==

==Physiology==

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]].

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]].

==Links==

==Links==

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

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

[[Category:To Do - AimeeHicks]][[Category:To Do - Review]]

[[Category:A&P Done]]