The thyroid gland is a butterfly-shaped organ and is composed of two cone-like lobes or wings - lobus dexter (right lobe) and lobus sinister (left lobe) - connected with the isthmus.Hormones in animals are often transported in the blood. Cells respond to a hormone when they express a specific receptor for that hormone. The hormone binds to the receptor protein, resulting in the activation of a signal transduction mechanism that ultimately leads to cell type-specific responses.
Lymphatic drainage passes frequently the lateral deep cervical lymph nodes and the pre- and parathracheal lymph nodes. The gland is supplied by sympathetic nerve input from the superior cervical ganglion and the cervicothoracic ganglion of the sympathetic trunk How to reference and link to summary or text, and by parasympathetic nerve input from the superior.The venous blood is drained via superior thyroid veins, draining in the internal jugular vein, and via inferior thyroid veins, draining via the plexus thyroideus impar in the left brachiocephalic vein.
The thyroid and thyrotropes form a negative feedback loop : TSH production is suppressed when the T4 levels are high, and vice versa. The TSH production itself is modulated by thyrotropin-releasing hormone (TRH which is produced by the hypothalamus and secreted at an increased rate in situations such as cold (in which an accelerated metabolism.You can share it by copying the code below and adding it to your blog or web page. a href"http psychologydictionary. org/thyroid-gland title"THYROID GLAND " THYROID GLAND /a Edited and fact checked by Pam: Google.
The thyroid gland also makes the hormone calcitonin, which is involved in calcium metabolism and stimulating bone cells to add calcium to bone. See also Calcitonin; Hyperthyroid; Hypothyroidism ; Thyroid stimulating hormone; Thyroxine; Triiodothyronine.During migration, the thyroid remains connected to the tongue by a narrow canal, the thyroglossal duct. Follicles of the thyroid begin to make colloid in the 11th week and thyroxine by the 18th week.
Physiology Edit The primary function of the thyroid is production of the hormones thyroxine (T4 triiodothyronine (T3 and calcitonin. Up to 80 of the T4 is converted to T3 by peripheral organs such as the liver, kidney and spleen.Iodine is captured with the "iodine trap" by the hydrogen peroxide generated by the enzyme thyroid peroxidase (TPO) 6 and linked to the 3' and 5' sites of the benzene ring of the tyrosine residues on TG, and on free tyrosine.
For example, thyroid-stimulating hormone (TSH) causes growth and increased activity of another endocrine gland, the thyroid, which increases output of thyroid hormones. A recently-identified class of hormones is that of the "hunger hormones" - ghrelin, orexin and PYY 3-36 - and "satiety hormones" - e.g., leptin, obestatin, nesfatin-1.Parafollicular cells produce calcitonin in response to hypercalcemia. Calcitonin stimulates movement of calcium into bone, in opposition to the effects of parathyroid hormone (PTH). However, calcitonin seems far less essential than PTH, as calcium metabolism remains clinically normal after removal of the thyroid, but not the parathyroids.
Different tissue types may also respond differently to the same hormonal signal. Because of this, hormonal signaling is elaborate and hard to dissect. Interactions with receptors Edit Most hormones initiate a cellular response by initially combining with either a specific intracellular or cell membrane associated receptor protein.In order to bind their receptors these hormones must cross the cell membrane. The combined hormone-receptor complex then moves across the nuclear membrane into the nucleus of the cell, where it binds to specific DNA sequences, effectively amplifying or suppressing the action of certain genes, and affecting protein synthesis.
It is inappropriate to demarcate the gland's upper and lower border with vertebral levels as it moves position in relation to these during swallowing. The thyroid gland is covered by fibrous sheath, the capsula glandulae thyroidea, composed of an internal and external layer.Relay and amplification of the received hormonal signal via a signal transduction process: This then leads to a cellular response. The reaction of the target cells may then be recognized by the original hormone-producing cells, leading to a down-regulation in hormone production.
T3 is about ten times more active than T4. 5 T3 and T4 production and action Edit Main thyroid hormones) Thyroxine is synthesised by the follicular cells from free tyrosine and on the tyrosine residues of the protein called thyroglobulin (TG).Embryological development Edit In the fetus, at 3-4 weeks of gestation, the thyroid gland appears as an epithelial proliferation in the floor of the pharynx at the base of the tongue between the tuberculum impar and the copula linguae at a point latter indicated by the foramen cecum.
The effects of pharmacologic doses of hormones may be different from responses to naturally-occurring amounts and may be therapeutically useful. An example is the ability of pharmacologic doses of glucocorticoid to suppress inflammation.In this region the recurrent laryngeal nerve and the inferior thyroid artery pass next to or in the ligament and tubercle. Between the two layers of the capsule and on the posterior side of the lobes there are on each side two parathyroid glands.
Thyroxin The hormone secreted by the thyroid gland. thyroxine, thyroxin ( th-rok'sn, -sin ) The active iodine compound existing normally in the thyroid gland and extracted therefrom in crystalline form for therapeutic use; also prepared synthetically; used for the relief of congenital hypothyroidism, and myxedema.It may even be used on biopsy samples from suspicious lesions (e.g. swollen lymph nodes ) to establish whether they are metastasis of the original cancer. Calcitonin can be used therapeutically for the treatment of hypercalcemia or osteoporosis.
Chemical classes of hormones Edit Vertebrate hormones fall into three chemical classes: Pharmacology Edit Many hormones and their analogues are used as medication. The most commonly-prescribed hormones are estrogens and progestagens (as methods of hormonal contraception and as HRT thyroxine (as levothyroxine, for hypothyroidism ) and steroids (for autoimmune diseases and several respiratory disorders ).T4 Tf TBG. The amount is very small and difficult to estimate so that the amount present in serum is not used as a more accurate indicator of thyroxine status than T4. thyroxine-binding globulin (TBG) most (99.95) of the thyroxine in plasma is bound to globulin and a small amount bound to prealbumin.
2 However, it has been shown that not all steroid receptors are located intracellularly, some are plasma membrane associated. 3 An important consideration, dictating the level at which cellular signal transduction pathways are activated in response to a hormonal signal is the effective concentration of hormone-receptor complexes that are formed.The number of receptors at the cell surface of the receiving cell can also be varied as can the affinity between the hormone and its receptor. Physiology of hormones Edit Most cells are capable of producing one or more molecules, which act as signaling molecules to other cells, altering their growth, function, or metabolism.
It may be used diagnostically as a tumor marker for a form of thyroid cancer (medullary thyroid adenocarcinoma in which high calcitonin levels may be present and elevated levels after surgery may indicate recurrence.The classical hormones produced by cells in the endocrine glands mentioned so far in this article are cellular products, specialized to serve as regulators at the overall organism level. However they may also exert their effects solely within the tissue in which they are produced and originally released.
The thyroid isthmus is variable in presence and size, and can encompass a cranially extending pyramid lobe ( lobus pyramidalis or processus pyramidalis remnant of the thyroglossal duct. The thyroid is one of the larger endocrine glands, weighing 2-3 grams in neonates and 18-60 grams in adults, and is increased in pregnancy How to reference.Cyclic AMP ). Some protein hormones also interact with intracellular receptors located in the cytoplasm or nucleus by an intracrine mechanism. For hormones such as steroid or thyroid hormones, their receptors are located intracellularly within the cytoplasm of their target cell.