The Pituitary Gland
If it was possible for you to look at the mirror and see inside yourself, you would probably find a line originating at the bridge of the nose and passing directly far from the back to your head’s center. Along this line, you could observe a minute organ approximately the dimension of a spotted bean (also called pinto bean). This organ is encircled by a bone and seems to be dangling from the bottom of your brain. In fact, this is the pituitary gland.
People have known the pituitary gland, which is among the minutest of all endocrine glands, for ages as the master gland. First and foremost, the pituitary gland is the main link that connects the nervous as well as endocrine systems. Secondly, this tiny gland makes and discharges an assortment of hormones, which regulate the performance of different endocrine glands. Last, but not the least, the pituitary gland also guides a number of basic processes of life. In fact, it is this gland that influences your height and how soon you will attain puberty.
This gland is made up of two separate sections. While the segment on the frontage is known as the anterior lobe, the part that is nearer to the skull’s rear is called the posterior lobe – together these two lobes have a dimension similar to that of a little acorn. Each of these segments work like independent gland and have their individual and dissimilar actions. While the anterior lobe makes up about 75 per cent of the pituitary gland, the posterior lobe comprises the remaining 25 per cent of this endocrine gland.
However, both the anterior lobe as well as the posterior lobe of this gland have a direct link with and is regulated by the section of the brain known as the hypothalamus, which controls the fundamental processes necessary for survival, such as thirst, hunger, self-defense as well as sexual reproduction. The pituitary gland is connected with the hypothalamus by means of a stem that comprises neurons as well as tiny blood vessels. Hence, the hypothalamus has a two-way communication with the pituitary gland – by means of the nerve impulses and through chemical messengers or hormones.
The hypothalamus sends instructions to the anterior lobe of the pituitary gland by releasing hormones. The hormones produced and released by the hypothalamus subsequently move by way of the blood. A specialized arrangement of the blood vessels propels the blood containing the hormones through the pituitary glands’ anterior lobe prior to going back to the heart. On the contrary, messages are sent to the posterior lobe of the pituitary gland by means of neural tissue and the nerve impulses regulate it.
It is worth mentioning here that the entire information that comes into the brain has got to pass via the hypothalamus. In effect, the pituitary gland has a pivotal role in the hypothalamus’ competence to work on the information passing through it and set off the appropriate physical reaction.
The main role of the anterior lobe of the pituitary gland is to produce hormones called tropic that has an effect on additional glands as well as organs. Therefore, ‘tropic’ in this case does not have any relation to the same term in geography that influences climatic conditions. In fact, the anterior lobe makes six vital tropic hormones, which include the growth hormone (GH), also known as the somatotropic hormone; adrenocorticotropic hormone (ACTH); thyroid-stimulating hormone (TSH), also called the thyrotropic hormone; lactotropic hormone (LTH) or prolactin; follicle-stimulating hormone (FSH), which is a gonadotropic hormone; and luteinizing hormone (LH), another gonadotropic hormone.
The hormones produced by the pituitary gland influence the dimension of the glands as well as the organs affected by them, in addition to the manufacture and release the hormonal products of these glands. For instance, if the anterior lobe starts producing as well as discharging any of the six tropic hormones in unusual amount, the consequences are obviously visible.
As mentioned earlier, ACTH or the adrenocorticotropic hormone is produced by the anterior lobe of the pituitary gland and it controls the functioning of the adrenal glands that are necessary for survival. Working in a way that is extremely analogous to that of the TSH or the thyroid-stimulating hormone, a subtle feedback system regulates the ACTH levels. It may be noted here that an element that stimulates the release of ACTH (also called the ACTH-releasing factor) is produced by the hypothalamus and it results in the pituitary gland secreting this tropic hormone into the blood circulation system. Specifically preset receptors found on the adrenal glands subsequently collect the ACTH. In addition, these receptors on the adrenal glands transmit signals to the nucleus of the cells to commence production as well as release of adrenal hormones. Eventually, the hormones are secreted into the bloodstream and the brain receives a message regarding their presence.
In addition, ACTH aids in regulating metabolism. For instance, glucocorticoids are hormones that assist in regulating the metabolism of our body; while mineralocorticoids are engaged in controlling the quantity of water in our body; and another hormone called progesterone is vital for reproduction, as it gets the uterus ready for receiving as well as the grounding the fertilized ovum.
Similar to several other hormones, adrenocorticotropic hormone (ACTH) is released in on a daily basis – i.e. once in about every 24 hours (also known as circadian pattern). Every individual has their personal internal circadian cadence, which actually decides on the amount of sleep required by an individual, when the individual would enjoy eating and the time when the individual is most watchful. Any kind of disturbance in this circadian rhythm has the potential to have an effect on the individual’s biological functioning and also his/ her mood as well as intellectual competence. It is understood that the jet lag experienced by an individual following a prolonged flight across numerous time zones is possibly the outcome of a disturbance of this circadian rhythm. It has been found that in the case of the majority of individuals, the levels of adrenocorticotropic hormone (ACTH) in the bloodstream are highest during the early part of the morning. It is important to note that the adrenal glands play a vital role in the manner an individual is able to deal with stress; the rapidity with which one is able to act as well as react; and whether the individual begins his/ her day with an energy or not.
As the name suggests, gonadotropic hormones target specific organs like the gonads, also known as the sex organs. Gonadotropic hormones are of two major types – the luteinizing hormones (also called LH) and the follicle-stimulating hormone (also called FSH). Perhaps, these hormones have been named very aptly. Each of these hormones performs double duties. On the one hand, they regulate the sex hormone secretion and, on the other, control eggs as well as mature sperm production. While the developing fetus encloses elevated levels of gonadotropic hormones FSH as well as LH, the production of these two hormones is very scant in infants and little kids. Next comes puberty or the teenage years. In the case of girls, on an average sexual maturation starts when they attain the age of 12 1/2 years, while in the case of boys, it begins after another two years.
It is the hypothalamus from where the signals are sent to the pituitary for producing gonadotropic hormones FSH as well as LH. However, it is yet to be ascertained as to how the hypothalamus decides when to start invigorating the secretion of gonadotropic hormones. Nevertheless, scientists have discovered that there is a specific connection between the inception of puberty as well as the development of bones. If you observe the girls studying in any class of a grade school you will be able to corroborate that they normally develop more rapidly compared to boys. Perhaps, this difference is related to the predisposition of the girls to attain puberty prior to the boys.
The FSH and LH both regulate the male organs related to sex, for instance, the testes. While FSH stimulates sperm production, LH is known to encourage testosterone production. While testosterone is frequently referred to as the hormone related to sex in males, it is not the whole truth. In fact, LH also plays a pivotal role in invigorating the adrenal glands as well as the ovaries in women to make a small amount of testosterone. Likewise, not only women produce estrogen, which is referred to as the hormone related to sex in women, in their ovaries, but it is also produced in very small amounts by the testes and adrenal glands in males. Therefore, when we are talking about sex hormones, we actually talk about the amount in which they are produced in males and females, and not which one is solely produced by one gender.
Right from the beginning of puberty or sexual maturity, males always secrete testosterone with a view to guarantee mature sperm production. In effect, the levels of this hormone are controlled by means of a negative feedback system that connects the pituitary, the brain as well as the body.
In the case of females, the discharge of gonadotropic hormones also regulates the secretion of sex hormones. However, in this instance, the sex hormone levels are basically cyclical, instead of being stable. The duration of such a cycle is called the menstrual cycle and, on average, lasts for 28 days. During each cycle, the females produce as well as release just a solitary mature egg. The levels of FSH reach the peak during ovulation. In effect, it is necessary that FSH as well as LH is present in the bloodstream of a woman to enable her ovaries to make estrogen.
Thus far, scientists have discovered six pituitary hormones and the last one to be found is called prolactin (also known as lactotropic hormone). As the name suggests, lactotropic hormone or prolactin promotes the production of breast milk by stimulating the mammary glands. However, this only happens in the case of women who have given birth recently. During this period, a complicated assortment of hormones sends signals to the brain’s hypothalamus to start secreting prolactin. Several scientists who have undertaken studies on this topic are of the view that there also exists a substance known as prolactin-inhibiting factor (in brief, PIF) that assists in putting off ill-timed lactation. Any drop in the PIF after childbirth is believed to cause its inhibition.
While the nursing infants are solely interested in one thing – being fed, and this is why they breast-feed and drain the milk from their mother’s breasts – in reality, they are also kindling a steady prolactin production. By doing so they are ensuring two things – maintain an instant and continued supply of their mother’s milk, and, at the same time, ensuring their subsequent meal.
Although it only happens rarely, occasionally, an excessive prolactin supply may cause an unusually high breast milk production and also put off the occurrence of menstruation in some women after childbirth.
The posterior pituitary
The posterior lobe of the pituitary gland releases two hormones – the first is called oxytocin (OT), while the other is called the antidiuretic hormone (also known as ADH). However, none of these hormones are made in the posterior lobe and they are generally produced in the hypothalamus inside the brain.
The hypothalamus is the production center for both oxytocin and antidiuretic hormone or ADH and sends them to the posterior lobe of the pituitary gland, where they are stored separately in granules bound by membranes. These hormones are only released when the hypothalamus sends nerve impulses to the posterior lobe of the pituitary gland.
In the case of women, the hormone oxytocin acts together with prolactin to provide breast milk to the nursing babies. Oxytocin also encourages the milk ducts’ contraction inside the breasts, which, in turn, assists in releasing milk from the breasts. This mechanism is called the letdown reflex. In addition, oxytocin also has a vital role in encouraging the uterus to contract during childbirth. Oxytocin is also used cathartically to encourage labor as well as to stop hemorrhage from the uterus. However, it is yet to be ascertained whether oxytocin has any function in men and if it does, what is its precise role.
Antidiuretic hormone (ADH)
Antidiuretic hormone, which is also referred to as vasopressin, primarily works to conserve water in the body. As ADH assists the kidneys in conserving water, it helps to sustain an appropriate level of fluids within the body. When water moves via the tubules within the two kidneys, the body may possibly absorb it again, or it may be expelled from the body in the form of urine. In fact, appropriate levels of water are absorbed by the body again only when the presence of ADH is adequate.
When the posterior lobe of the pituitary gland secretes very low levels of antidiuretic hormone (ADH) it may possibly result in a malady known as diabetes insipidus. In fact, expelling large amounts of urine is one of the most ordinary symptoms of diabetes insipidus. In such cases, the patient may pass urine very often in amounts as high as 10 quarts daily. While passing such large volumes of urine and that too very frequently is definitely extremely bothersome, it also results in dehydration soon. However, the good thing is that usually diabetes insipidus can be cured using an antidiuretic hormone (ADH) replacement.
It is worth noting that consumption of alcoholic beverages is one of the several factors that have the aptitude to slow down ADH secretion. Usually, people who might have consumed alcoholic beverages in excess urinate very often and also get up from sleep with an intense thirst. In effect, such people are themselves responsible for dehydrating them temporarily by disturbing their normal balance of hormones. Certain things like pain, exercise, sleep, morphine, barbiturates and nicotine are among the several things that have an effect that is just contrary to producing as well as secreting antidiuretic hormone (ADH).
As mentioned before, the pituitary gland is mainly responsible for deciding on the height of a child; when he/ she becomes an adult; the time when any girl will begin to menstruate; as well as whether a man or a woman would be able to conceive a baby or not. Any kind of imbalance in the secretion of its hormones may possibly affect the metabolic process in an individual; nurse a baby; or even things like getting out in the early morning. Hence, there is little doubt that this gland has been aptly named as the master gland – its insignificant size notwithstanding, the pituitary gland is of great significance in the life of humans – as it is essential for survival.