Ts of thyroid gland of mammal

All vertebrates have a thyroid gland. In mammals, it is usually bilobed and located just caudal to the larynx, adjacent to the lateral surface of the trachea. The two lobes may be connected by a fibrous isthmus (eg, ruminants, horses), or a connecting isthmus may be indistinct (eg, dogs, cats). The gland is extremely vascular. In birds, it is found within the thoracic cavity; both lobes are located near the syrinx, adjacent to the carotid artery near the origin of the vertebral artery. Ectopic or accessory thyroid tissue is relatively common in most species, especially dogs and cats. It may be located anywhere from the larynx to the diaphragm and may be responsible for maintaining normal thyroid function after surgical thyroidectomy. In addition, ectopic thyroid tissue occasionally is the site of hyperplasia or neoplasia. Physiology of the Thyroid Gland in Animals Thyroid hormones are the only iodinated organic compounds in the body. Thyroxine (T 4) is the main secretory product of the normal thyroid gland. However, the gland also secretes 3,5,3′-triiodothyronine (T 3), reverse T 3, and other deiodinated metabolites. T 3 is ~3–5 times more potent than T 4, whereas reverse T 3 is thyromimetically inactive. Thyroid hormone secretion is regulated primarily via negative-feedback control through the coordinated response of the hypothalamic-pituitary-thyroid axis: thyrotropin-releasing hormone (TRH) binds to the thyrotroph cell in the pituitary and stimulates secretion of thyrot...

Thyroid gland is externally covered by connective tissue sheath or capsule. From the capsule, number of septa called trabeculae arise, which divide the thyroid gland into several lobules.The lobules contain about 3 million thyroid follicles.Each thyroid follicle is oval in shape and varies in size.Larger follicles are present towards periphery, whereas smaller ones are present in the interior.The follicles are surrounded by a connective tissue called interfollicular tissue which contains bloodvessels and nerve fibres.Each follicle is lined by a single layer of cuboidal glandular epithelium which rest on a very thin basement.The follicular cavity or acinus is filled by dense amorphous semisolid substance called colloid,which is thyroglobulin, a precursor of thyroid hormone, thyroxine.Other cells bigger than follicular cells are also present singly or in groups in the connective tissue. These are called parafollicular or ‘C’ cells. They secrete hormone thyrocalcitonin.

Your This happens most often because your thyroid gland makes too much. That’s a condition called Causes Graves’ disease: This condition is the most common cause of hyperthyroidism -- and thyrotoxicosis. It leads your Nodules: Growths called nodules can develop on your thyroid and affect how much hormone the gland makes. A single hyperfunctioning nodule is called toxic nodular adenoma., while multinodular goiter or Plummer’s disease means you have a number of them. Struma ovarii: This is a rare type of ovarian tumor that’s made mostly of thyroid tissue. In some cases, it can cause hyperthyroidism. Thyroiditis: A virus or bacteria, certain Thyroid supplement: Some people take thyroid hormone in pill form to treat a medical condition, like hypothyroidism (when your thyroid doesn’t make enough hormone). You can have too much in your blood if your prescription is off or you don’t take the medication as directed. Symptoms Normally, thyroid hormones help you burn energy at the right speed. High levels can affect your body in lots of different ways. In general, they speed things up -- like your Graves’ disease can also trigger thyroid eye disease with red, watery Diagnosis Your doctor will ask about your symptoms and medications you take, and check to see if your pulse is too fast or your thyroid is too big. After that, a simple blood test that measures the amount of thyroid stimulating hormone, or TSH, in your blood can help your doctor know for sure if you have thyrotoxicosis. ...

An enlarged thyroid gland is, by definition, a goiter. Non-neoplastic and noninflammatory enlargements of the thyroid gland develop in all domestic mammals as well as birds. . Goiter must be differentiated from other causes of upper neck swelling, including enlargements of the salivary glands or lymph node. Many animals with goiter appear to remain euthyroid, but clinical signs of hypothyroidism may develop in some, especially in newborns. Thyroid hyperplasia due to iodine deficiency was common in many goitrogenic areas throughout the world before the widespread supplementation of iodized salt to animal diets. Although outbreaks of iodine-deficient goiter are now sporadic, and fewer animals are affected, iodine deficiency is still responsible for most non-neoplastic goiters seen in large domestic animals in which a definitive cause is determined. Many goiters are idiopathic. Iodine atoms are a part of the thyroid hormones thyroxine and triiodothyronine; thus, insufficient iodine reduces the ability of the thyroid to make these hormones. With reduced circulating thyroid hormone levels, the pituitary secretes more thyroid-stimulating hormone (TSH), which acts as a stimulus for hyperplasia of the thyroid gland and subsequent development of a goiter. The hyperplastic gland may, and usually does, compensate for the reduced availability of iodine; therefore, goiter is in no way synonymous with hypothyroidism. Fetal thyroid glands are more susceptible to the effects of high or lo...