Growth hormone

The growth hormone or somatropine or somatotropine is a polypeptide Hormone secreted by the former part of the pituitary gland, which stimulates the growth and the cellular reproduction at the human S and the others Vertébré S.

At the Man, it has 191 amino-acid .

Terminology

Structure and gene of the molecule of the human hormone of growth

It is a polypeptide of 191 amino-acids at the man, it consists of two bridges disulfides (what enables him to be rolled up on itself). It consists of only one chain of 22 kDa. When GH is in the form of monomer it is more effective than in the oligomer shape (but the two types are present in circulation). GH has a half-life from 20 to 30 minutes.

Secretion of growth hormone

The secretion of the growth hormone by the adénohypophyse is pulsatile: night peaks after drowsiness and of the diurnal peaks spontaneous or supported by the meals, the stress or the effort. The basal concentration is weak. The regulation of this secretion is ensured by hypothalamic hormones. The somatolibérine or GHRH stimulates the secretion of GH (growth hormone) and the somatostatine or SIRH inhibits it. The somatolibérine is stimulated by hypoglycemia, the deep sleep, the stress and the exercise. The pulsatile secretion of GH is due to the alternation of secretion of GHRH and SIRH. There exists also a negative rétrocontrole by the GH on these hypothalamic hormones.

Functions of the growth hormone

Height growth in childhood is the best known effect off GH action, and appears to Be stimulated by At least two mechanisms. 1. GH directly stimulates division and multiplication off chondrocytes off cartilage. Thesis are the primary concealments in the growing ends (epiphyses) off children? S long bones (arms, legacy, digits). 2. GH also stimulates production off Insulin-like growth Factor 1 (IGF1, also known ace somatomedin C), has hormone homologous to proinsulin. The liver has off major target organ GH for this process, and is the principal site off IGF1 production. IGF1 has growth-stimulating effects one has wide variety off tissues. Additionally, nap IGF1 is generated within target tissues, making it apparently both endocrine year and year autocrine hormone.

Although height growth is the best known effect off GH, it serfs many other metabolic functions ace well. GH increases calcium retention, and strengthens and increases the mineralization off bone. It increases muscle farmhouse. Different It induces protein synthesis and growth off many organ systems off the body, resulting in has “positive nitrogen balances”.

GH stimulates the Immune system. It cross-country race reacts with prolactin receptors goal has physiologic role for this effect is uncertain.

GH plays has role in fuel homeostasis. GH reduces liver uptake off glucose, year effect that oppose that off insulin. GH also contributes to the maintenance and function off pancreatic islets. It tighten to promote lipolysis, which results in sum reduction off adipose tissue (body conceited) and rising amounts off free fatty acids and glycerol in the blood. --> Many factors come into play the growth. The genes, the hormones, food, rest - all these elements help the children to grow, of the birth at the adulthood. A key component of this process is the factor of release of the growth hormone or the factor of regulation of growth (GH-RF or GRF). This chemical messenger is produced in part of the brain called Hypothalamus. The GH-RF allows the Hypophyse (" main gland " who intervenes in the process of growth) to secrete the growth hormone, that is to say principal the Hormone responsible for the growth of a person. The growth is the increase in dimensions of the body. This phenomenon, characteristic of childhood, is related to the interaction between genetic factors and medium The Puberté represents the whole of the physical, psychic, emotional phenomena which characterizes the passage of the state of child to the state of adult leading to the function of reproduction." It is for this period that the rate of growth hormones secreted naturally reached its maximum".

The growth hormone or somatropine or somatotropine are a polypeptide hormone secreted by the former part of the pituitary gland, which stimulates the growth and the cellular reproduction at the human ones and the other vertebrate ones

But the GH (growth hormon) is not only implied in the phenomena of growth, it plays also a part in the fine regulation of the phenomena of reproduction as well in the male mammals as female.

At the male this hormone has actions extra-gonadiques among which one can quote the increase and the maintenance of the size of the penis, the differentiation of the spermatic channels at the teenager and the stimulation of the synthesis of enzymes in certain additional glands (seminal blisters and the prostate). This hormone has also effects on the gonadic functions among which we will retain the spermatogenèse, the stimulation of the synthesis of the androgens, the increase in the mobility of the spermatozoa.

This hormone exerts gonadic effects at the female among which one finds the stimulation of the synthesis of hormones stéroïdiennes, the induction of ovulation, recruitment and the follicular growth, the nuclear and cytoplasmic maturation of the ovocyte. This hormone exerts also extragonadic effects on the secretary activity of the epithelial cells of the female genital tract, on the placental growth and various aspects of lactation.

Still let us repeat to it these actions of the GH on the reproduction intervene on mechanisms of fine regulation.

The GH acts on the liver and stimulates the production of IGF (insulin growth Factor). The growth hormone has a lipolytic action (mobilization of greases), proteolytic via the IGF, hyperglysemic and diabetogene, it stimulates chondrogenesis and osteogenesis via the IGF, and is antinatriuretic.

Clinical problems: excess or deficiency

Excess of growth hormone: (Acromégalie and hypophyseal gigantism)

An excess of growth hormone (by hypophyseal hyperactivity, tumor or defect of inhibition by the somatostatine) before sexual maturity causes a gigantism. An excess acquired after puberty causes a acromégalie.

Deficiency in growth hormone

A lack of GH during childhood causes a harmonious nanism There are many causes off GH deficiency, including constrained changes off specific, congenital malformations involving the pituitary, and ramming to the pituitary from injury, surgery gold disease.

Diagnosis off GH deficiency involves has multiple step diagnosis process, usually culminating in has stimulation test to see yew the patient' S pituitary nipple will release has pulsates off GH when provoked by various stimuli.

GH deficiency is treated by replacing GH. All GH in current uses has synthetic Copy off human GH, manufactured by recombining DNA technology. As GH has broad protein molecule, it must Be injected into subcutaneous tissue gold muscle to get it into the blood. Patient When the has had has off length-standing deficiency GH, benefits off treatment rare are often dramatic and gratifying and side effects off treatment are.

This topic is treated more fully in the articles Growth hormone deficiency and Growth hormone treatment. -->

A deficit in growth hormone involves a reduction in the thin mass, an increase in the fatty mass, a stop of the growth of the cartilages and bones, a tendency depressive, and a reduction in the load-carrying capacity and cold. To diagnose it, it is necessary to carry out a dynamic test of stimulation by causing an insulinic hypoglycemia. In normal weather, a hypoglycemia causes an increase in the rate of GH.

Indications of the treatment by the growth hormone

Sometimes GH is used for other benefits than height. Conceited It has been shown to improve muscle strength and slightly reduce body in Prader-Willi syndrome, benefits more important to thesis children than increased height. It has also been shown to help maintain muscle farmhouse in AIDS wasting.

Use that are considered controversial include

GH treatment to reverse effects off Aging in older adults
GH treatment to aid muscle-building
GH treatment to enhance Weight loss in Obesity
GH treatment for Fibromyalgia -->

Risks related to the treatment by the growth hormone

The growth hormone produced before by extraction of pituitary glands of corpses because a certain number of contaminations by the prion, causing certain cases of diseases of Creutzfeldt-Jacob mortals. This risk disappeared since the production by genetic engineering.

It is used illegally as a doping or like “agent anti-age”, in particular by American. It involves a not very important reduction in the fatty mass and comprises many side effects (oedemas, joint pains, which have occurred of Diabète, increase in the size of the centres at the man…).

Its use (legal or not) in some breeding S agricultural in various countries and its possible presence upstream or downstream of Purification plants could make of it a Perturbateur endocrinien (EP), but few data seem available on this particular hormone, natural or synthetic unlike Oestrogène S, of Progestogène S, Androgène S, Phytoestrogène S, etc which are followed in the environment, at least in certain countries.

History

Ace off 2004, synthetic growth hormones available in the U.S. (and to their manufacturers) included Nutropin (Genentech), Humatrope (Lilly), Genotropin (Pfizer), Norditropin (Novo), and Saizen (Serono). The products are nearly identical in composition, efficacy, and cost, varying primarily in the formulations and delivery devices. -->

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