Quotes from The Merck Veterinary Manual Sixth Edition describing the roles of the Pituitary and Thyroid glands, both of which can play a part in pituitary dwarfism.Description of a Dwarf GSD
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Pituitary dwarfs vary in color and have no primary (guard) hair. The puppy coat consists of secondary hair and is retained until it is lost. This loss of hair can begin to occur anywhere from 6 months of age onward varying with each individual dwarf. It was believed that tufts of hair remained around the feet and on the ears but this information is false. In Trisha's case she lost all hair on her feet and her ears. Hair on the trunk of her body turned very wooly in texture and went from its original black and silver colors to that of liver/brown and cream. The hair on her tail was lost entirely leaving her with a "rat-like" tail.
It is said that after this state of alopecia the skin tends to become scaly and wrinkled and goes from grey to black in coloration. To a degree this is correct. The color of the skin does turn blackish in areas where there were sores in the process of hair loss. But the texture of the skin can be smooth feeling in areas as well. Trisha's croup and hip area has a very smooth surface where she has lost her hair. The skin is scaly only in areas where she had scores under the spots of hair loss. The skin literally disintegrated in some areas. She went through periods of skin shed where she had black dandruff-like flaking. I would sit and scratch this off and she would sit there and fall asleep so I can only assume she itched and my scratching relieved the itching.
Quotes from The Merck Veterinary Manual Sixth Edition describing the roles of the Pituitary and Thyroid glands, both of which can play a part in pituitary dwarfism.
The Pituitary Gland
The pituitary gland rests in the sella turcica at the base of the brain and is enveloped by an extension of the dura mater. The pituitary gland (hypothysis) is subdivided anatomically into the adenohypophysis ("anterior lobe") and neurohypophysis ("posterior lobe").
This is a lot of mumbo jumbo medical jargon but I think the lay person can get an idea of the thyroid functionin connection with pituitary dwarfism and why it is a concern. (Mainly in hair loss and weight gain.)
The Thyroid Gland
The thyroid gland is present in all vertibrates. It is intimately related to the aortic sac in its development and this association leads to the frequent occurrence of accessory thyroid parenchyma in the mediastinum, particularly in adult dogs. This accessory thyroid tissue may undergo neoplastic transformation. A portion of the thyroglossal duct, which is am embryological connection between pharyngeal plate and the migrating thyroid tissue, may persist postnatally and for a cyst due to accumulation of proteinaceous material secreted by its epithelial lining. The ductal epithelium also may undergo neoplastic transformation.
The synthesis of thyroid hormones is unique among endocrine glands because the final assembly of hormone occurs extracellularly within the follicular lumen, which is made possible by a unique protein (thyroglobulin). The constituent amino acids ( tyrosine and others) and carbohydrates (mannose, galactose) of thyroglobulin are derived from the circulation. Tyrosine is an essential component of thyroid hormones. Iodine is bound to tyrosyl residues in thyroglobulin to form, successively, monoiodotyrosine (MIT) and diiodotyrosin (DIT), which combine to form the 2 biologically active iodothyronines (thyroxine [T4] , triiodothgyronine [T3]) secreted to the thyroid gland.
Negative feedback control of thyroid hormone secretion is accomplished by the coordinated response of the adenohypophysis and certain hypothalamic nuclei to circulating levels of T4 and T3. Thyrotropin-releasing hormone (TRH) binds to isoreceptors on the plasma membrane of thyrotropic basophils in the adenohypophysis, and results in discharge of thyrotropin (TTH)-containing secretion granules. TTH is conveyed to thyroid follicular cells where it increases the rate of biochemical reactions concerned with the biosynthesis and secretion of thyroid hormones.
Action of the Thyroid Hormones: Thyroxine and triiodothyronine, once released into the circulation, act on many different target cells in the body. The overall function of T4 and T3 are similar though much of the biological activity may be the ressult of monodeiodination to 3,5,3'-triiodothyronine prior to interacting with target cells. Under certain conditions (protein starvation, neonatal animals, liver and kidney disease, febrile illness, etc) thyroxine is preferentially monodeiodinated to 3,3',5'-triiodothryonine ("reverse T3"). Since this form of T3 formed by target cells is biologically inactive, monodeiodination to form "reverse T3" provides a mechanism to attenuate the metabolic effects of thyroid hormones.
The overall physioligical effects of the active thyroid hormones are to; 1) increase the basal metabolic rate; 2) make more glucose available to meet the elevated metabolic demands by increasing glysolysis, gluconeogenesis, and glucose absorption from the intestine; 3) stimulate new protein synthesis; 4) increase lipid metabolism and conversion of cholesterol into bile acids and other substances, activation of lipoprotein lipase, and increase sensitivity of adipose tissue to lipolysis by other hormones; 5) stimulate the heart rate, cardiac output, and blood flow; 6) increase neyral transmission, cerebration, and neuronal development in young animals.
This page last updated on May 13, 1999
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