!Thyroid
!!Anatomical overview
The butterfly-shaped thyroid is one of the largest ((Endocrine - System Overview|endocrine glands)) in the body, in the neck below the larynx and behind the cricoid cartilage. The thyroid gland is covered by a __thin fibrous sheath__, composed of an internal and external layer. The gland is covered in front by infrahyoid muscles and at the sides with the sternomastoid muscle (SCM). On the backside, the gland is fixed to the ((Musculoskeletal - Cartilage|cartilage)) of the trachea. The thyroid gland's firm attachment to the underlying ((Respiratory - Bronchial Mucosa and Muscle|trachea)) is the reason behind its movement with swallowing.

The thyroid has 2 lobes which consist of many __follicles__, in which __thyrocytes__ are arranged like alveoles. Here, __triiodothyronine__ (T3), __thyroxine__ (T4), and __calcitonin__ are produced and stored. The hypothalamus controls their release via a feedback loop with the ((Endocrine - Pituitary Gland - Anterior Lobe|pituitary)). The hormones __stimulate metabolism and growth__: heart rate, blood pressure and excitability of ((Nervous - System Overview|nerves)) increase. 

The ((Endocrine - Thyroid - Parathyroid Glands|parathyroid glands)) are 4 small endocrine glands in the neck that produce __parathyroid hormone__ to control the amount of __calcium__ in the ((Circulatory - Blood|blood)) and within the ((Musculoskeletal - Bones|bones)).

Embryologically the thyroid derived from the head gut - endodermal tissue - and traveled through the __thyreoglossal duct__ to it's remaining location. The duct closes and regresses after passage. If this happens incompletely, a medial cervical cyst remains. 

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!!Brain
In the Brain Stem, the __primeval ring structure__ is reflected: organ tissue relays with assimilative and digestive functions from oesophagus to small intestines are situated in the right brain stem, while excretory organs from caecum to rectum are relayed in the left brain stem. Medial on both sides are the relays of mouth/pharynx, middle ears and lacrimal glands, as well as the pineal and pituitary glands and the __thyroid__.

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!!!Relay:
__Brain Stem__   ( + / - ) posterior central, for ((Endocrine - Thyroid - Follicular Epithelium|Thyroid Follicular Epithelium)) and ((Endocrine - Thyroid - Parathyroid Glands|Parathyroid Glands))
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__Cerebral Cortex__ (-/+) prefrontal sensory area, for ((Endocrine -Thyroid - Archaic Excretory Ducts|Thyroid "Ductal Pattern"))
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