Insulin-like growth factor IGFformerly called somatomedinany of several peptide hormones that function primarily to stimulate growth but that also possess some ability to decrease blood glucose levels. IGFs were discovered when investigators began studying the effects of biological substances on cells and tissues outside the body.
The name insulin-like growth factor reflects the fact that these substances have insulin -like insulin-like growth factor-1 and cardiovascular in some tissues, though they are far less potent than insulin in decreasing blood glucose concentrations. Furthermore, their fundamental action is to stimulate growth, and, though IGFs share this ability with other growth factors—such as epidermal growth factorplatelet-derived growth factor, and nerve growth factor—IGFs differ from these substances in that they are the only ones with well-described endocrine actions in humans.
There are two IGFs: These two factors, despite the similarity of their names, are distinguishable in terms of specific actions on tissues because they bind to and activate different receptors. The major action of IGFs is on cell growth. Growth hormone stimulates many tissues, particularly the liverto synthesize and secrete IGF-1, which in turn stimulates both hypertrophy increase in cell size and hyperplasia increase in cell number of most tissues, including bone.
Serum IGF-1 concentrations progressively increase during childhood and peak at the time of pubertyand they progressively decrease thereafter as does growth hormone secretion. Children and adults with deficiency of growth hormone have low serum IGF-1 concentrations compared with healthy individuals of the same age. In contrast, patients with high levels of growth hormone e. The production of IGF-2 is less dependent on the secretion of growth hormone than is the production of IGF-1, and IGF-2 is much less important in stimulating linear growth.
Although serum IGF concentrations seem to be determined by production by the liver, these substances are produced by many tissues, and many insulin-like growth factor-1 and cardiovascular the same tissues also have receptors for them. In addition, there are multiple serum binding proteins for IGFs that may stimulate or inhibit the biological actions of the factors, insulin-like growth factor-1 and cardiovascular. It is likely that the growth-promoting actions of IGFs occur at or very near the site of their formation; in effect, they probably exert their major actions by way of paracrine acting on neighbouring cells and autocrine self-stimulating effects.
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Learn More in these related Britannica articles: Hormoneorganic substance secreted by plants and animals that functions in the regulation of physiological activities and in maintaining homeostasis, insulin-like growth factor-1 and cardiovascular. Hormones carry out their functions by evoking responses from specific organs or tissues that are adapted to react to minute quantities of them.
The classical view of hormones is that…. Glucoseone of a group of carbohydrates known as simple sugars monosaccharides. It is found in fruits and honey and is the major free sugar circulating in the blood of higher animals. It is the source of…. Cellin biology, the basic membrane-bound unit that contains the fundamental molecules of life and of which all living things are composed. A single cell is often a complete organism in itself, such as a bacterium or yeast.
Other cells acquire specialized functions as they mature. These cells cooperate with…. Insulinhormone that regulates the level of sugar glucose in the blood and that is produced by the beta cells of the islets of Langerhans in the pancreas.
Insulin is secreted when the level of blood glucose rises—as after a meal. When the level of blood glucose falls, secretion of…. Receptormolecule, generally a protein, that receives signals for a cell. Small molecules, such as hormones outside the cell or second messengers inside the cell, bind tightly and specifically to their receptors, insulin-like growth factor-1 and cardiovascular.
Binding is a critical element in effecting a cellular response to a signal and is influenced by a…. Help us improve this article! Contact our editors with your feedback. You may find it helpful to search within the site to see how similar or related subjects are covered. Any text you add should be original, not copied from other sources. At the bottom of the article, feel free to list any sources that support your changes, so that we can fully understand their context.
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