The pituitary gland or hypophysis is a gland of the endocrine system of the human body. It leans on the hypophyseal fossa of the sphenoid bone that is located in the center of the middle cranial fossa. In addition, this small but powerful gland is encircled by the sella turcica (a small bony cavity) and protected from above by a dural fold (diaphragma sellae).
This gland has one of the most important functions in the body, considering the span of their effects. The hormones it produces perform various tasks aimed at the control and regulation of the function of many organs in the human body.
What Is the Main Function of the Pituitary Gland?
The pituitary gland or the hypophysis senses the body’s needs and sends signals to different organs and glands throughout the body to maintain an appropriate environment for them and regulate their function. It secretes a variety of hormones into the bloodstream that act as neurotransmitters that relay the information from the pituitary gland to the distant cells in the brain.
These hormones regulate and control growth, blood pressure, all functions of the sex organs, and the thyroid glands. Furthermore, the hormones that are secreted by the pituitary gland also support the metabolism and many other vital processes in the body.
In addition, some aspects of pregnancy, childbirth, water/salt concentration in the kidneys, temperature regulation, breastfeeding, and pain relief, are also supported by this highly productive gland.
What Is the Structure of the Pituitary Gland?
The pituitary gland is comprised of three subdivisions, i.e. glandular lobes:
- The anterior glandular lobe
- The intermediate glandular lobe
- The posterior glandular lobe
The Anterior Glandular Lobe of the Pituitary
The anterior pituitary gland is affixed to the brain by short blood vessels. It regulates several physiological processes, including stress, growth, reproduction, and lactation.
This glandular lobe is composed of 3 sub-areas:
- Pars distalis – The majority of the hormone production of the pituitary gland occurs in this distal area of the hypophysis;
- Pars tuberalis – A part of the anterior lobe of the pituitary gland thatcontains both secretory and stellate cells and has a photoperiodic function;
- Pars intermedia – The boundary between the pars distalis and pars tuberalis, responsible for the production of melatonin.
Types of Cells Located in the Anterior Glandular Lobe
The anterior glandular lobe is comprised of several types of neuronal cells that produce and secrete hormones:
- Somatotrophes – This type of neuron cell secretes the human growth hormone (hGH). The somatotrophs are located predominantly in the anterior and the lateral regions of the gland and constitute almost 40% of the tissue.
- Corticotropes – This type of neuron cell secretes the adrenocorticotropin hormone (ACTH).
- Thyrotropes – This type of neuron cell secretes the thyroid stimulating hormone (TSH);
- Gonadotropes – This type of neuron cell secretes the gonadotropic hormone, i.e. both the luteinizing hormone (LH) and the follicle-stimulating hormone (FSH).
- Lactotropes – This type of neuron cell secretes the prolactin hormone (PRL).
The Intermediate Glandular Lobe of the Pituitary
This glandular lobe, unlike the anterior and posterior globular lobes, is not a distinct anatomic structure.
The intermediate glandular lobe of the pituitary synthesizes and secretes the melanocyte-stimulating hormone. It is composed of endocrine cells labeled as the melanotrophs. These neuron cells secrete several bioactive peptides, including alpha-melanocyte-stimulating hormone (alpha-MSH), as well as beta-endorphin.
The Posterior Glandular Lobe of the Pituitary
The posterior pituitary gland is a part of the brain itself. Under the command of the brain, it secretes hormones directly into the bloodstream.
This area of the pituitary gland is comprised of two sub-regions:
- Pars nervosa – This part of the posterior glandular lobe is where the hormones oxytocin and vasopressin are stored.
- Infundibular stalk – This structure of the pituitary gland is the connection between the hypothalamus and the posterior pituitary. This connection is labeled as the hypothalamo-hypophyseal tract or hypothalamo-neurohypophyseal tract.
The major stimulatory neurotransmitter in the posterior glandular lobe is the glutamate. Glutamate receptors create almost 25% of the synapses made with the magnocellular neurons of the pituitary gland.
One of the most important characteristics of the magnocellular pituitary gland system is the plasticity of the neurons, which occurs due to prolonged stimulation. This plasticity is of vital importance during the process of giving birth, as well as lactation.
Which Hormones Does the Pituitary Gland Produce?
Each pituitary hormone has a vital function in the endocrine system of the human body. The hormones that are produced by the pituitary gland are made by a separate type of neuron cell located within the pituitary gland. The exceptions are the follicle-stimulating and luteinizing hormones that are produced together by the same neuron cell.
Hormones Produced in the Anterior Pituitary Gland
The anterior pituitary gland produces the following hormones:
- The adrenocorticotropic hormone – A hormone responsible for stimulating the adrenal glands to secrete steroid hormones, mainly the cortisol hormone. Medical conditions that affect this hormone include Cushing’s disease (related to high levels of cortisol in the body), adrenal insufficiency (Addison’s disease), as well as hypopituitarism.
- Growth hormone (somatropin) – A peptide hormone responsible for the regulation of the growth, metabolism, as well as the composition of the body.
- Luteinizing hormone and follicle-stimulating hormone (also known as gonadotropins) – These hormones act on the ovaries or testes in order to stimulate the production of the sex hormone, thus influencing egg and sperm maturity;
- The prolactin hormone – This hormone stimulates the milk production in breastfeeding mothers, as well as the secretion of estrogen/progesterone.
- Thyroid-stimulating hormone – This hormone stimulates the thyroid gland to secrete thyroid hormones.
The hormones that are produced in the anterior pituitary lobes are proteins consisting of one or two long polypeptide chains. The thyroid-stimulating hormone, luteinizing hormone, and the follicle-stimulating hormone are called glycoproteins because they contain complex carbohydrates, labeled as glycosides.
How Is the Production of These Hormones Regulated?
Peptides, such as the thyrotropin-releasing hormone (TRH), corticotropin-releasing hormone, gonadotropin-releasing hormone, and growth-hormone-releasing hormone, are responsible for the production and secretion of each of the major anterior pituitary hormones.
Hormones Produced in the Posterior Pituitary Gland
There are two hormones that are produced by the hypothalamus, after which they are stored in the posterior pituitary gland before they are secreted into the bloodstream:
- The antidiuretic hormone (also labeled as vasopressin) – This hormone controls and regulates the water balance in the body, as well as blood pressure. It also increases the reabsorption of water from the kidneys in order to prevent dehydration of the body.
- The oxytocin hormone – This hormone stimulates the contractions of the uterus during labor, as well as the secretion of milk during breastfeeding.
These hormones are synthesized in the neurosecretory granules that are located in the cell bodies of the nuclei. The hormones are released into the circulatory system in response to the chemical or electrical nerve signals that originate in the hypothalamus. From here, they are relayed to the posterior pituitary lobe.
Hormones Produced in the Intermediate Pituitary Gland
The neuron cells of the intermediate pituitary gland produce the melanocyte-stimulating hormone. This hormone stimulates the production of melanin in the skin cells.
What Happens When the Pituitary Gland Is Dysfunctional?
The conditions under which the pituitary gland operates are subject to change. Due to these changes, the regular functioning of the gland can become impaired, which can lead to some severe medical conditions or diseases of the pituitary gland.
The conditions that affect the proper functioning of the pituitary gland include:
- Conditions that result in overproduction of one or more hormones (this can result in Acromegaly, Cushing’s disease, or Prolactinoma).
- Conditions that result in underproduction of one or more hormones (this can result in an adult-onset growth hormone deficiency, Diabetes insipidus, or Hypopituitarism).
- Conditions that can lead to altering the size or shape (or both) of the pituitary gland (which can result in the empty sella syndrome).
These conditions can lead to diseases and disorders of the pituitary gland, such as:
- Addison’s disease
- Cushing’s disease
Addison’s disease
This endocrine disorder is labeled as primary adrenal insufficiency and hypocortisolism. It’s a potentially lethal condition due to insufficient production of the steroid hormones cortisol and aldosterone.
Some of the key symptoms of this disorder include fatigue, gastrointestinal abnormalities, changes in skin color (vitiligo), as well as behavior and mood changes in the affected individual.
Vitiligo is a condition related to the appearance of white patches on different areas of the body. This discoloration of the skin may vary from one or two small spots on the skin to multiple and larger affected areas.
Cushing’s disease
Prolonged exposure of the body to increased cortisol levels results in Cushing’s disease. The affected individuals typically get a round ‘moon-like’ face, gain weight mostly around the midsection and upper back, bruise easily or feel fatigued, tired, and sad.
What Are the Symptoms of a Dysfunctional Pituitary Gland?
In case of a dysfunctional pituitary gland, the affected individual can experience the following symptoms:
- Weakness;
- Feeling cold;
- An increased amount of urine;
- Nausea and vomiting;
- Less frequent or no menstrual periods;
- Unintended weight loss;
- Unintended weight gain.
Fun Facts
Did you know?
- The pituitary gland is called the master gland due to the fact that the hormones it produces control and regulate many different processes in the human body.
- Without the pituitary gland, the body wouldn’t be able to reproduce, wouldn’t grow properly, and many of the bodily functions wouldn’t function which could bring one’s life in danger.
- This pea-sized (but oh-so-powerful) gland thrives on Vitamins D and E, which are found in high-protein meats, fish, eggs, and nuts. This is why it’s important that these foods are regularly found on our menu.
- The production of the human growth hormone can be promoted by eating a diet rich in fruits and vegetables (fiber) and fats containing omega-3 fatty acids and monounsaturated fats, and by reducing salt intake.
- The tumors of the pituitary gland can change the affected individual’s personality by causing overproduction or underproduction of hormones. In turn, this can alter the behavior, mood, emotions, and the body weight of the individual, which can influence some aspects of their personality.
- The pituitary gland weighs merely 0.5 grams.
- Adenohypophysis or Pars anterior are other names of this major gland of the endocrine system in the human body.
- Photoperiodism refers to the functional or behavioral response of an organism to the changes of the duration of light and darkness in daily, seasonal, or yearly cycles. For instance, photoperiodism occurs when a plant doesn’t bloom due to the increased darkness in the winter.
- The term hypophysis cerebri originates from the Latin language and means “growth below the cerebrum.”
- Fenderson’s funnel, infundibulum, or a pituitary stalk, are other names of the infundibular stalk of the posterior glandular lobe.