Pituitary hormones


Nine vital hormones are secreted via the pituitary gland. Seven of the nine hormones are actually released by the anterior portion of the pituitary. One of those seven literally come directly from what was (in fetal development) the pars intermedia, and the final two hormones are actually created by the hupothalamus. The final two are still released by the pituitary, after traversing via axons and the infundibulum to reach the posterior portion of the pituitary.The posterior portion of the pituitary then expels the hormones into the bloodstream.


Trophic hormones, which are released into the bloodstream by the pars distalis, is a term given to the hormones meaning “food.” This term is associated with these particular hormones due to their ability to increase the size of their target glands. A lack of these hormones causes shrinking of the target glands. Thus, these hormones are said to “feed” the glands.

The growth hormone, somatotropin, is responsible for regulating cell growth as well as regulating mitotic activity. The hypothalamus releases either a growth hormone-releasing hormone or a growth hormone-inhibiting hormone based on whether more or less enticed growth (or division of cells) is required. It has not yet been determined exactly how the growth hormone releases or inhibits, and exactly how it conducts itself within the bloodstream. What is apparent is that it directly influences the activity of amino acids throughout the cells. It also seems to have a direct relation to the synthesis of proteins via amino acid origins. This is evident in both dwarfism and gigantism. In dwarfism, there is obvious and chronic limitation of the release of the growth hormone and an excessive release of growth hormone-inhibiting hormone. In gigantism, the opposite is evident, where there is an abnormal release of growth hormone-release hormone. In the scenario of either hypersecretion (too much secretion) or hyposecretion (too little secretion) there is distortion of regular body features such as the hands and jaws. In an adult body (after the fusion of epiphysis) acromegaly, a serious distortion relating to joint fusion areas, becomes evident.


Pituitary Hormones
Image: Pituitary Hormones


The thyroid stimulating hormone is frequently referred to as the thyrotropin. Its main responsibility is to provide regulation of the thyroid gland. A secondary hormone assists in the regulation of the thyroid gland, known as the thyrotropin-releasing hormone, which is secreted by the hypothalamus. The thyroid-stimulating hormone can be influenced by external elements such as the cold. Illness as well as emotional upheaval can influence the release of the thyroid-stimulating hormone, usually causing an additional amount of secretion. Responsible for the regulation of the adrenal cortex is the hormone, adrenalcorticotropic. This hormone also assists in the breakdown of fats in targeted cells. The hypothalamus administers the adrenalcorticotropic-releasing hormone. Additional levels of adrenalcorticotrpoic hormones can be released with emotional upheaval.

The follicle-stimulating hormone acts variably depending on whether it is addressing a female body or a male body. In the male body, the follicle-stimulating hormone is responsible for encouraging the testes to produce viable sperm cells. In the female body, the follicle-stimulating hormone is responsible for regulating the monthly cycle, egg development, and the production and release of estrogen. Working cohesively with the follicle-stimulating hormone is the luteinizing hormone. Together, these two hormones target the cells located within the reproductive system. Often referred to as the gonadotrophins, these two hormones are vital in the reproductive cycle and in females by stimulating and initiating ovulation as well as initiating the formation of the corpus luteum. Progesterone, an additional female sex hormone, is stimulated into secretion via the luteinizing hormone. In the male body, the luteinizing hormone is referred to as the interstitial cell-stimulating hormone and takes on the job of producing and administering testosterone. There is an additional mechanism that controls the release rate of the gonaotrophins, although there is little information understood about this hormone. Rather, it has been determined that a post pubescent body has a releasing agent that secretes gonadotrophin-releasing hormones that are responsible for the regulation of the luteinizing hormone and the follicle-stimulating hormones.


Although the hormone prolactine is found in both male and female bodies, its main responsibility is to encourage lactation in females after birth. Prolactine works in conjunction with other hormones to stimulate the production of breast milk. Prolactine is regulated by the hypothalamus, which releases the prolactine inhibiting hormone known as dopamine. When the hypothalamus releases dopamine, prolactine does not release throughout the body, but when lactation is required, the hypothalamus ceases the release of dopamine so that lactation can occur.

The melanocyte-stimulating hormone has not been thoroughly understood by medical science as of yet. Rather, it has been determined that it does play a role in the darkening of skin through the release of melanin granules. These granules are found within the melanocytes. The hypothalamus plays a critical role in secreting the two hormones which seem to compliment the melanocyte hormone, corticotrophin (which enhances the secretion process) and dopamine (which inhibits the secretion process.)


The hypothalamus is also responsible for the secretion of oxytocin. Oxytocin comes from specialized cells within the hypothalamus and then journeys through the axons of the infundibulum until it reaches the lobus nervosa. The lobus nervosa serves as a storage unit for the oxytocin and it is released as needed by additional impulses sent out from the hypothalamus. Once the oxytocin is released by the hypothalamus impulses, it travels into the female reproductive system with the intent of causing contractions at the end of fetal gestation. Post partum, oxytocin is responsible for assisting with the ejaculation response of the mammary glands and the areola to assist with the lactation process. In the male body, ejaculation and elevated levels of oxytocin have been determined to coincide, but there has not been a discernable need for the rise in this hormone in a male body.

The antidiuretic hormone is produce and released in the same manner as oxytocin, however, its function is completely different. Just like oxytocin, the antidiuretic hormone is a polypeptide but its target cells are in the kidneys. The antidiuretic hormone’s main function is to control or limit the production of water in the kidneys. High levels of antidiuretic hormone can cause vasoconstriction, and thus is known as a vasopressin.

The posterior pituitary is responsible for the release of both oxytocin and the antidiuretic hormones. However, each hormone is created within the hypothalamus, in the supraoptic nuclei and the paraventricular nuclei. These particular nuclei are thus defined as glands of the endocrine system. The hormones which they are responsible for secreting traverse the axons of the hypothalamo-hypophyseal tract which takes them to the posterior portion of the pituitary gland. The posterior pituitary gland is then able to keep them and maintain them until it is time for their release into the body.

Neuroendocrine reflexes are responsible for the ultimate release of oxytocin and antidiuretic hormones into the body’s system. This can be controlled or contributed to by external stimuli. For example, a lactating woman would require the stimuli caused by suckling in order for the hormone oxytocin to be released via nerve impulses from the hypothalamus.

Antidiuretic hormones are controlled and regulated via various stimuli, the most obvious being the osoreceptor neurons in the hypothalamus. These receptors respond directly to a rise in blood osmotic pressure which can be inhibited or increased depending on the blood volume detected by the stretch receptors of the left atrium.

The anterior section of the pituitary gland was often referred to as the “master gland.” It received this honorary nickname in light of its responsibility of secreting the majority of the hormones that regulate the bulk of the endocrine glands. This includes the thyroid-stimulating hormone, which regulates the thyroid, the adrenocorticotrophic hormone, which regulates the adrenal cortex, and the gonadotrophic hormone, which is responsible for regulating the gonads. These glands are reliant upon the anterior pituitary for their overall health and function. This nickname is misleading however, as the anterior pituitary relies on the hypothalamus to secrete the hormones which permit the anterior pituitary to do it job. Hormones that are secreted by the hypothalamus are either inhibiting or enhancing hormones, which in turn regulate the anterior pituitary, after they traverse hypothalamo-hypophyseal portal to reach the anterior pituitary. An incredible network of various primary capillaries thus receive the hormones secreted via the hypothalamus, which initially enters the median eminence. Secondary capillaries that are positioned within the anterior pituitary receive venous drainage from the pituitary stalk. The two individual sets of capillaries qualifies this system as a portal for neuron or hormonal transport.
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