Changes

===Pars Intermedia===

===Pars Intermedia===

This is the residual lumen of '''Rathke's Pouch''' and consists of a series of small cystic cavities (follicles filled with colloid), with both basophillic and chromatophobic (poorly staining) cell types. These extend into the '''pars nervosa'''.T The pars intermedia separates the anterior and posterior lobes. Endocrine cells in this region are known as '''melanotropes'''. These  convert the [[Prohormones - Anatomy & Physiology|prohormone]] '''pro-opiomelanocorticotropin''' (POMC) to '''melanocyte stimulating hormone''' (a-MSH) and '''corticotropin-like intermediate lobe peptide''' (CLIP). The pars intermedia is innervated by dopaminergic neurones originating in the periventricular nucleus of the [[Hypothalamus - Anatomy & Physiology|hypothalamus]].

This is the residual lumen of '''Rathke's Pouch''' and consists of a series of small cystic cavities (follicles filled with colloid), with both basophillic and chromatophobic (poorly staining) cell types. These extend into the '''pars nervosa'''.T The pars intermedia separates the anterior and posterior lobes. Endocrine cells in this region are known as '''melanotropes'''. These  convert the [[Prohormones - Anatomy & Physiology|prohormone]] '''pro-opiomelanocorticotropin''' (POMC) to '''melanocyte stimulating hormone''' (a-MSH) and '''corticotropin-like intermediate lobe peptide''' (CLIP). The pars intermedia is innervated by dopaminergic neurones originating in the periventricular nucleus of the [[Hypothalamus - Anatomy & Physiology|hypothalamus]].

==Thyroid Gland==

==Thyroid Gland==

The pineal gland secretes [[Melatonin|melatonin]] in response to day length. The retina detects day length and sends an impulse via the [[Hypothalamus - Anatomy & Physiology|hypothalamus]], thoracic [[Spinal Cord - Anatomy & Physiology|spinal cord]] and cranial cervical ganglia to the pineal gland. The gland effectively acts as the body's '''biological clock''' and helps regulate the circadian rhythm, sleep and the seasonal and diurnal variations in [[:Category:Reproductive Behaviour|reproductive behaviour]]. In the horse,melatonin is inbitory on gonad function via its antigonadotrophic effects. Melatonin production is inhibited by light, therefore melatonin levels decrease in spring making horses 'long day breeders'.

The pineal gland secretes [[Melatonin|melatonin]] in response to day length. The retina detects day length and sends an impulse via the [[Hypothalamus - Anatomy & Physiology|hypothalamus]], thoracic [[Spinal Cord - Anatomy & Physiology|spinal cord]] and cranial cervical ganglia to the pineal gland. The gland effectively acts as the body's '''biological clock''' and helps regulate the circadian rhythm, sleep and the seasonal and diurnal variations in [[:Category:Reproductive Behaviour|reproductive behaviour]]. In the horse,melatonin is inbitory on gonad function via its antigonadotrophic effects. Melatonin production is inhibited by light, therefore melatonin levels decrease in spring making horses 'long day breeders'.