Ipofisi 
endocrine gland located at the base of the brain. This
gland, which produces various hormones
and monitors the activities of others, plays an important role in the relationship between
nervous system and endocrine system
.
The pituitary consists of two main parts, the anterior lobe or adenohypophysis and posterior lobe or neurohypophysis, they are all connected through the pituitary stalk '
hypothalamus, which controls, through the production of hormones with inhibitory function, or the issue, both the amount and the mode of liberation of the pituitary. The pituitary in turn controls, directly or indirectly, all the other endocrine glands. The pituitary gland is located in a small bony cavity at the center of
skull, the pituitary fossa, placed under the optic chiasm (the crossing point of
optic nerves), and for this reason, abnormal growths (such as tumors) affecting the pituitary gland can sometimes cause disturbances
view. In the adult, the pituitary gland weighs about 0.6 g, is larger in women than in man. In the embryo the anterior pituitary derives from '
ectoderm and formed by the same Once the tissue of the mouth, while the rear comes from a part of nervous tissue that also forms the embryonic portion of the brain
called diencephalon.
Although both lobes of the pituitary endocrine glands are intimately associated with the hypothalamus, they operate independently of each other in different groups of controlling body functions. However, because of their close proximity, often cancer and accidental injury affecting one lobe damage the other, causing illness and complex diseases.
In the anterior pituitary were identified five types of secretory cells, each of which produces one or more specific hormones. The production of these is controlled by specific factors or release of inhibition produced by '
hypothalamus. These releasing factors are secreted by
hypothalamic neurons in a region heavily vascularized and to act sull'ipofisi front, pass through a network of blood vessels connecting the two bodies.
Half of the cells of the anterior pituitary produces growth hormone or somatotropin
, under the influence of hormones and hypothalamic somatostatin release of growth hormone (growth hormone-releasing hormone, GHRH) . The somatotropin is responsible for the stimulation della produzione, nel
fegato , delle somatomedine (molecole coinvolte nella regolazione della crescita) che stimolano la moltiplicazione cellulare e la formazione della
cartilagine . L'ormone della crescita viene secreto durante la notte, in brevi episodi della durata massima di due ore. Nei bambini e negli adolescenti questi episodi sono più frequenti, quindi viene liberata una maggiore quantità di somatotropina. I livelli dell'ormone sono elevati dalla nascita ai quattro anni, poi diminuiscono assestandosi su un livello stabile che viene mantenuto fino alla fine della
pubertà , quando vengono raggiunti i livelli dell'adulto.
Circa il 20% delle cellule dell'ipofisi anteriore secerne l'ormone adrenocorticotropo o corticotropina,
ACTH (adrenocorticotrophic hormone), sotto l'influenza di un ormone ipotalamico, il fattore di liberazione della corticotropina (corticotrophin releasing factor, CRF). L'ACTH controlla la secrezione di diversi ormoni steroidei da parte della corticale del
surrene ; i principali sono il
cortisolo , l'aldosterone, il
testosterone e gli
estrogeni .
La prolattina viene prodotta da cellule che costituiscono circa il 10-20% del lobo anteriore dell'ipofisi. In condizioni normali, la secrezione della prolattina viene inibita da un fattore ipotalamico, called dopamine, while it can be stimulated by the secretion of a large amount of the factor of thyrotropin release by the hypothalamus and of estrogen by the ovaries
. The increase in the number of prolactin-producing cells, which occurs during pregnancy
, is probably due to the increase in estrogen that occurs at that time. Prolactin stimulates milk production after childbirth and, as with oxytocin, a posterior pituitary hormone, although its production is stimulated by the baby with the same suction. In addition, prolactin exerts an inhibitory effect on the release and action of gonadotrophic hormones
, which interferes with the appearance of
normal menstrual cycles and ovulation during lactation. Although the role of prolactin in males is unknown, it appears, however, sometimes functionally and structurally linked to growth hormone.
anterior pituitary hormone that controls the
thyroid stimulating hormone is called, TSH (thyroid stimulating hormone), or thyrotropin. The factor for the Liberation of thyrotropin (thyrotrophin-releasing factor, TRF) of hypothalamic origin, is the main factor that stimulates the secretion of this hormone. The production of thyrotropin varies over the course of 24 hours, that follows a circadian rhythm
, with a peak in the early morning hours (around 3) and a decline to very low levels in the afternoon. The stimulating hormone stimulates the production and release of thyroid hormones that regulate the rate of basal metabolism
the
thermoregulation and growth of the organism.
Other cells of the anterior lobe produce two gonadotropic hormones, follicle stimulating hormone, FSH (follicle stimulating hormone) and luteinizing hormone, LH (luteinizing hormone). These hormones are produced in both males and females in the act, respectively, on
testes and ovaries. The maximum secretion of these hormones occurs at puberty. They are responsible for the maturation of the reproductive organs, and the growth of the body that occurs during the 'teens
. In adulthood these hormones are secreted differently in males and females in both sexes, they nevertheless play an important role in stimulation of the gonads and production of gametes and some
sex steroids. In women, the level of FSH and LH produced by the anterior has a cyclical and varies in the 28 days of the menstrual cycle. At the beginning of the menstrual cycle is released FSH, which stimulates the growth of follicles in the ovaries. Then a follicle is transformed into a Graafian follicle, which produces the highest level of estrogen. The increase the first level of estrogen inhibits the secretion of FSH then stimulates the secretion of LH that causes rupture of the follicle, accompanied by the release of an egg and the formation of a corpus luteum. The latter secretes mainly progesterone inhibits the secretion of LH. In addition to the modulation of progesterone production of FSH and LH is also stimulated by a hypothalamic factor, the factor for the Liberation of gonadotrophin (gonadotrophin releasing hormone, GnRH).
In adult male hypothalamus produces GnRH and anterior pituitary produces a constant amount of FSH and LH. LH stimulates the interstitial cells of the testis to produce testosterone and other androgens
and then also called interstitial cell stimulating hormone (interstitial cell stimulating hormone, ICSH) and FSH exerts an important effect on the steady production of sperm.
Based on what has been described, we can say that the production and secretion of hormones from the anterior pituitary are partly regulated by hypothalamic releasing factors and, in part, by hormones that regulate their own secretion (such as cortisol, estrogen and progesterone) with a mechanism called 'negative feedback regulation' (or feedback, where the hormone inhibits the secretion of that hormone releasing factors) necessary for the maintenance of '
omeostasi , cioè dei sistemi utilizzati dall'organismo per conservare il proprio equilibrio biologico.
I disturbi del lobo anteriore dell'ipofisi si riflettono, generalmente, in un eccesso o in un difetto di produzione o di secrezione degli ormoni ipofisari che possono, a loro volta, comportare una serie di patologie dell'individuo. Ad esempio, se durante l'infanzia vengono prodotte quantità insufficienti di ormone della crescita, l'individuo affetto da questa alterazione può essere colpito da
nanismo o comunque rimanere di bassa statura, a meno che la carenza di ormone della crescita non venga corretta farmacologicamente. Una quantità eccessiva di ormone della crescita during childhood or puberty causes gigantism
, while at the adult stage because
acromegaly.
If adrenocorticotropic hormone is produced in quantities exceeding the standard, it may give rise to Cushing's syndrome
, much more rarely it may be, however, produced in insufficient quantities, causing a variety of events. If prolactin secretion is deficient, after pregnancy does not occur the milk, which is the first production of milk. In both sexes, the occurrence of a
pituitary tumor may, among other things, to lead to excessive secretion of prolactin, which in turn can cause a form of infertility
still curable.
pituitary disorders that prevent the release of thyrotropin cause events similar to those of thyroid
diseases, including mental retardation and growth (if the deficiency relates to an infant), cold intolerance, lethargy and slowing of mental processes (If the deficiency relates to an adult). An excess of these hormones cause emotional instability, weight loss and heat intolerance. Lack of FSH and LH can result in both sexes, a form of infertility treatable with therapy
hormone.
The posterior lobe dell'ipofisi è collegato all'ipotalamo da neuroni particolari, detti neurosecretori. Gli ormoni ipotalamici passano attraverso queste cellule per raggiungere l'ipofisi posteriore, dove vengono liberati nella
circolazione sanguigna . Gli ormoni che vengono secreti in questo modo sono la vasopressina o ormone antidiuretico, ADH (antidiuretic hormone) e l'ossitocina.
La vasopressina esercita i suoi effetti sul
rene , aumentando il riassorbimento di acqua da parte dei tubuli e dei dotti collettori e provocando una riduzione della quantità di
urina prodotta. La quantità di questo ormone secreta dall'ipofisi posteriore dipende dalla concentrazione dei sali dissolved in body fluids. When the salt concentration of body fluids increases (or decreases the volume of the liquid itself), as happens after you sweat a lot, the amount of water present in the body is insufficient is, therefore, vasopressin secretion, which reduces the excretion urinary, and thus the amount of liquids that could be further lost. When the opposite occurs, that is when the body fluids are more dilute or volume increases, as occurs after drinking very heavily, decreases the secretion of vasopressin and thus the volume of urine produced increases.
Oxytocin plays an important role in female durante la
gravidanza e l'allattamento, mentre non se ne conosce il ruolo nel maschio. La produzione di quantità elevate di ossitocina dà inizio al travaglio e, dopo il parto, contribuisce a controllare la liberazione del latte in risposta alla stimolazione esercitata dal neonato con la suzione.
Entrambi gli ormoni secreti dal lobo posteriore dell'ipofisi possono venire prodotti in quantità eccessive o insufficienti. Una bassa concentrazione di ossitocina provoca l'impossibilità di un allattamento adeguato, mentre la secrezione carente di vasopressina è responsabile dell'insorgenza del
diabete insipido , che si manifesta con una produzione eccessiva di urina. Treatment depends on the cause that led to the alteration of the level of vasopressin, but in any case, unlike other forms of diabetes, diabetes insipidus not treated with the 'insulin
but with the administration of vasopressin.
If excessive amounts of vasopressin are produced, they form an insufficient volume of urine. This causes water retention, which gives rise to various manifestations calls, in general, water intoxication. These conditions can be caused, inter alia, by a pituitary tumor. Treatment usually consists in identifying and eliminating the cause, and in limiting the intake of water and other liquids from the patient.
source: MSN Encarta
