Pituitary gland (pituitary gland): anatomy, parts, and functions

With almost 16 billion neurons in the cerebral cortex and100 billion in the entire brain, it is normal for us to quickly and automatically attribute all the functions of our body to this fascinating and well-known organ. Even so, despite being the center of activities of the nervous system, not all the characteristics that condition us as a species are a direct product of the reactions in the brain tissue.

Beyond the brain, a mass of tissue that barely reaches 1.5 kilos (2% of our total weight) there are other structures of great interest, such as the pituitary gland, an essential gland forregulation and hormonal activityin our body.

We encourage you to continue reading, because today we unravel all the secrets of the pituitary: from growth to milk secretion, we assure you that this structure of essential importance will not leave you indifferent.

• We recommend you read: “Diencephalon: parts, structure and functions”

What is the pituitary and where is it located?

According to the Royal Spanish Academy of Language, the pituitary gland is defined as an organ of internal secretion, located in the excavation of the base of the skull called Turkish saddle, which is composed of two lobes, one anterior (glandular) and one posterior (nervous). From a slightly more biological point of view, we can say that it is anendocrine gland, that is, it pours messenger substances directly on the blood capillaries without the need for an excretory duct.

Beyond this, we can locate the pituitary at the base of the skull, in a depression of the sphenoid bone already named and known as “sella turcica”. The pituitary gland is closely related to the central nervous system through the hypothalamus (region of the brain that produces different hormones), as it establishes anatomical and functional relationships. In addition to all this, it is surprising to know that such an important gland has the size of a pea: 8 x 12 x 6 mm approximately in diameter and weighs about 500-600 milligrams in total, that is, little more than a pea.

Parts of the pituitary gland and their functions

Once we have located the pituitary gland in three-dimensional space and have gotten a little idea of its shape and size, it is time to dissect it into parts. The pituitary gland is composed of two main segments: adenohypophysis (adeno, Greek prefixal element meaning gland) and neurohypophysis (neuro, with the Greek meaning of nervous system). We tell you everything about these parts in the following lines, especiallytheir functions in the body.

1. Adenohypophysis

As its name suggests, we are facing the glandular part of the structure, which is why it belongs to the whole of the human endocrine system. It is located in the anterior lobe and represents80% of the weight of the gland, therefore, it is the dominant section.

The adenohypophysis secretes many hormones, of which six are especially relevant to body homeostasis. We show them to you in the following lines.

1.1 Growth hormone (GH)

Growth hormone, as its name suggests, stimulates infant growth (especially bone tissue) and helps maintain functional tissues and organs throughout the individual’s life. The amount of growth hormone secreted by the adenohypophysis decreases with age.

1.2 Prolactin (PL)

It stimulatesmilk secretionand the growth of mammary glands during pregnancy. It also promotes the synthesis of progesterone in the corpus luteum (a formation that appears in the ovary during the first trimester of gestation).

1.3 Gonadotropic hormones (FSH and LH)

Despite presenting four different types of them with different characteristics, we will limit ourselves to saying that they are a series of hormones essential for the reproduction process of vertebrates. They promoteovulation, spermatogenesisor estrogen production, among many other functions.

1.4 Thyroid-stimulating hormone (TSH)

TSH causes the thyroid gland, located in the front of the neck, to synthesize two different hormones: triiodothyronine (T3) and thyroxine (T4). These have various functions ofcontrol over the metabolism of theindividual.

1.5 Adrenocorticotropic hormone (ACTH)

This hormone, with such a complex name worthy of a tongue twister, is responsible for stimulating the cells of the adrenal cortex to synthesize mineralocorticoids and glucocorticoids. One of these glucocorticoids is cortisol, which is produced in the adrenal glands. Cortisol (and therefore ACTH) act onstress responses, prevent infections, regulate blood sugar and maintain blood pressure.

As we have seen in these lines, the function of the adenohypophysis is clear: to secrete hormones that either act directly on the body, or promote the synthesis of other hormones in another organ other than the pituitary. From growth to cortisol production, it is certainly clear to us that the adenohypophysis controls our bodily functions much more than we might at first believe.

2. Neurohypophysis

Maybe with so many terms you would have forgotten that we still had a whole section more to discover, but we remind you that in the posterior lobe of the pituitary gland is the neurohypophysis. This complex lobe can be divided into three sectors: median eminence, infundibulum and pars nervosa, of which only the latter seems to present secretory activity itself.

The neurohypophysis receives this name because it is defined by a series of characteristics much more “nervous” than the previous one, since it is communicated with the hypothalamus by the pituitary stem, a set of nerve fibers that acts as an anatomical link between both structures.

The neurohypophysis is formed by axon terminals of hypothalamic neurons, but despite this, it also presents a clear secretory activity. This phenomenon is known as neurosecretion, and below, we show you the two neurons synthesized in these cells.

2.1 Oxytocin

Of well-known name and fame, this hormone is known, mainly, for the stimulation of the mammary glands, which promotes the ejection of milk by the mother during breastfeeding. Beyond this, it is believed that it has a very important function on thefeeling of loveand well-being in the human being, since oxytocin and its receptors are also found in the heart.

2. 2 Antidiuretic hormone (ADH)

For its part, this hormone acts as a neurotransmitter, as a water-saving mechanism (causes an increase in water reabsorption in the kidneys), causes vasoconstriction and seems to be involved inmemoryand various cognitive processes.

Possible problems

As we have seen, the neurohypophysis is a prolongation of the hypothalamus and the adenohypophysis corresponds to the “glandular” part more properly speaking, but bothsecrete essential hormonesfor the proper functioning of the individual.

There are certain pathologies related to this pea-sized gland, such as pituitary insufficiency. In these cases, the pituitary gland does not produce one or more hormones or does so irregularly and insufficiently, which can result in tiredness, fatigue, hot flashes and many other symptoms depending on the hormone that is compromised.

On the other hand (and as surprising as it may seem),tumorscan also occur in the pituitary gland, that is, excessive cell growth. Some of them are not functional and do not promote the excessive production of certain hormones, while functioning tumors do translate into a higher hormonal concentration. Although impaired vision and headache are very common symptoms in these tumor processes, the patient’s signs will also depend largely on the hormone that is being produced in excess.