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Equine Endocrine System - Horse Anatomy (view source)
Revision as of 11:06, 20 November 2012
, 11:06, 20 November 2012→Pineal Glands
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==Hypothalamus==
==Hypothalamus==
The hypothalamus is a small area in the ventral diencephalon of the [[Forebrain - Anatomy & Physiology|forebrain]], in the floor of the third ventricle, and is a functional link between the [[Nervous and Special Senses - Anatomy & Physiology#Nervous System|nervous]] and [[Endocrine System Overview - Anatomy & Physiology|endocrine]] systems.
The hypothalamus controls most of the [[Endocrine System Overview - Anatomy & Physiology|endocrine glands]] within the body, largely through stimulation of the [[Pituitary Gland - Anatomy & Physiology|Pituitary Gland]] by secretion of [[Hormones - Anatomy & Physiology#Classifications of Hormones|neurohormones]]. It is a vital regulator of homeostasis, including [[Thermoregulation - Anatomy & Physiology| Thermoregulation]]. Further information on the physiology of the hypothalamus can be found [[Hypothalamus - Anatomy & Physiology|here]].
==Pituitary Gland==
==Pituitary Gland==
The pituitary gland, or '''hypophysis''' is an elongated appendage of the brain lying within a bony cavity of the [[Skull and Facial Muscles - Anatomy & Physiology#Sphenoid Bone (os sphenoidale)|sphenoid bone]] in the base of the skull - the '''Sella Turcica'''. The hypophysis is suspended ventral to the the [[Hypothalamus - Anatomy & Physiology|hypothalamus]] by a thin '''infundibular stalk'''. It lies between the more rostral '''optic chiasma''', and the more caudal '''mammillary bodies''', separated from the brain by a fold of dura mater known as the '''diaphragma sellae'''. The gland is divided into '''anterior and posterior''', with different embryological origins reflecting a difference in function.
The pituitary gland, or '''hypophysis''' is an elongated appendage of the brain lying within a bony cavity of the [[Skull and Facial Muscles - Anatomy & Physiology#Sphenoid Bone (os sphenoidale)|sphenoid bone]] in the base of the skull - the '''Sella Turcica'''. The hypophysis is suspended ventral to the the [[Hypothalamus - Anatomy & Physiology|hypothalamus]] by a thin '''infundibular stalk'''. It lies between the more rostral '''optic chiasma''', and the more caudal '''mammillary bodies''', separated from the brain by a fold of dura mater known as the '''diaphragma sellae'''. The gland is divided into '''anterior and posterior''', with different embryological origins reflecting a difference in function.
===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]].
This region of the hypothalamus is clinically important in horses. For more information see [[Equine Pituitary Pars Intermedia Dysfunction|Equine pituitary pars intermedia dysfunction]].
==Thyroid Gland==
==Thyroid Gland==
The thyroid gland lies in the neck, on either side of the second and third tracheal rings on their ventral aspect. It consists of left and right lobes, which are connected at their caudal aspect by a strand of connective tissue known as the '''isthmus'''. In the horse, the two lobes of the thyroid are oval in shape and roughly the size of a plumb.
Two types of hormones are produced by the thyroid gland. This first type is the iodine containing hormones; '''tri-iodothyronine'''(T3) and '''thyroxine''' (T4), which are produced by '''follicular cells'''. These thyroid hormones regulate the basal metabolic rate and are important in growth, regulation of body temperature and carbohydrate metabolism. Their release is stimulated by thyroid stimulating hormone (TSH) from the pituitary. The second type of hormone produced from '''parafollicular (C-cells)''' of 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.
===Vasculature===
The main blood supply is via the '''cranial thyroid artery''', which is a branch of the '''common carotid artery'''. There is a minor contribution from the '''caudal thyroid artery'''. Venous drainage is via the '''cranial and middle thyroid veins''', which drain into the '''external jugular vein'''.
===Lymphatics===
The thyroid drains to the '''deep cervical thoracic lymph node''' or the '''tracheal trunk'''.
===Innervation===
*Sympathetic: Supply from the cranial cervical ganglion.
*Parasympathetic: Supply from branches of cranial and caudal laryngeal nerves, which themselves branch from the vagus nerve.
==Parathyroid Glands==
==Parathyroid Glands==
The parathyroid glands are multiple (generally four) small glands, approximately 1-2mm in length are located about the cranial trachea. There are two internal glands embedded within the cranial [[Thyroid Gland - Anatomy & Physiology|thyroid glands]], and two external glands along the trachea, close to the caudal deep cervical lymph nodes. The parathyroid glands produce '''parathyroid hormone (PTH)''', which regulates serum [[Calcium|calcium]] and [[Phosphorus|phosphorus]] concentrations.
===Vasculature===
The parathyroid glands are surrounded by a '''capillary network''' which arises from branches of the '''common carotid artery'''. Venous drainage is via the '''jugular vein'''.
===Lymphatics===
The parathyroid glands drain to the '''deep cervical lymph nodes'''.
===Innervation===
*Sympathetic: From the cranial cervical ganglion
*Parasympathetic: Run with branches of the caudal laryngeal nerve
==Adrenal Glands==
==Adrenal Glands==
The adrenal glands are paired bodies lying cranial to the kidneys within the retroperitoneal space. The glands consist of two layers; the '''cortex''' and '''medulla'''.
The '''adrenal cortex''' is red to light brown in colour and is composed of three zones. These zones all produce hormones derived from cholesterol, which is abundant in the cells. From the outer to inner, the layers are:
1. Zona Glomerulosa: Secretes '''[[Adrenal Glands - Anatomy & Physiology#Mineralocorticoids|mineralocorticoids]]'''
2. Zona fasciculata: Secretes '''[[Adrenal Glands - Anatomy & Physiology#Glucocorticoids|glucocorticoids]]'''
3. Zona Reticularis: Secretes sex steroids or '''[[Adrenal Glands - Anatomy & Physiology#Androgens|androgens]]'''
The '''adrenal cortex''' represents 80-90% of the adrenal gland.
The '''[[Adrenal Glands - Anatomy & Physiology#Adrenal Medulla|adrenal medulla]]''' is primarily involved in the production of catecholamines; '''epinephrine and norepinephrine'''. In fetal life, the [[Adrenal Glands - Anatomy & Physiology#Adrenal Medulla|adrenal medulla]] plays a role in the autonomic nervous system. The medulla acts as a sympathetic ganglion with the postganglionic cells lacking axons. Through sympathetic preganglionic fiber stimulation, the medullary cells secrete catecholamines. The [[Adrenal Glands - Anatomy & Physiology#Adrenal Medulla|adrenal medulla]] represents only 10-20% of the adrenal gland.
[[Image:Adrenal Gland Schematic..jpg|700px|small>'''Schematic Diagram of the Adrenal Gland</small>|frameless]]
===Vasculature===
The adrenal glands receive blood supply from the '''abdominal aorta''', '''renal artery''', '''cranial abdominal artery''' and '''caudal phrenic artery'''. Capillaries from these branch to form a '''capsular and medullary network'''. There is a '''central vein''', where venous blood pools, before flowing via satellite veins to join the '''caudal vena cava'''.
===Lymphatics===
The lymphatic network within the adrenal glands drains into the '''lumbar aortic lymph nodes'''.
===Innervation===
The parenchyma of the adrenal medulla is specialised for neurohormonal release, itself being a modified sympathetic ganglion. It is innervated by preganglionic fibres of the splanchnic nerve. The cortical cells are modified postganglionic neurones.
==Pineal Glands==
==Pineal Glands==
The pineal gland is an unpaired organ located immediately behind the [[thalamus]]. It is part of diencephalon and lies dorsally to it, attached to it via the '''habenulae''' and a short peduncle. It is innervated by the '''postganglionic sympathetic fibres''' from the '''cranial cervical ganglion'''.
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'.
[[Category:To Do - AP Review]]
[[Category:Horse Anatomy]]