Introduction (Psychology and Mental Health)
Hormones are loosely defined as chemical substances that are produced in certain parts of the body and then carried elsewhere by the bloodstream to perform their function. They include three general chemical types: short chains of amino acids, or proteins; derivatives of amino acids; and steroids. Many behaviors are regulated by hormones. Arguably, the most obvious behaviors are those associated with reproduction. For example, steroids secreted by the sex organs, or gonads, regulate both paternal and maternal behavior: aggression (testosterone), attraction for the opposite sex (pheromonea), uterine contraction (oxytocin), and so on.
The system that regulates hormone production is the neuroendocrine system, a series of ductless glands that secrete these chemicals directly into the blood. The pituitary gland is the central organ of the endocrine system. Slightly larger than a centimeter in diameter, it is located at the base of the brain in a bony cavity called the sella turcica. The gland is involved in the secretion of some ten different hormones.
The pituitary is formed from two distinct structures, the adenohypophysis (in the anterior portion of the gland) and the neurohypophysis, which forms the posterior lobe of the pituitary. Not only do the two portions function independently, but they also form independently during embryonic development. The adenohypophysis originates from the outer layer of embryonic tissue,...
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Neurosecretions and the Hypothalamus (Psychology and Mental Health)
Sets of secretions from the anterior pituitary play various roles in the body. The first set, which includes hormones such as adrenocorticotropic hormone (ACTH), thyroid-stimulating hormone (TSH), follicle-stimulating hormone (FSH), and luteinizing hormone (LH), regulate secretions from the adrenal gland, the thyroid, and the gonads. Two additional hormones from the anterior pituitary, prolactin and growth hormone (GH), have a variety of effects on breast tissue and bone growth, respectively.
Regulation of hormone secretion by the anterior pituitary is primarily the function of the hypothalamus. The hypothalamus is connected through a portal circuit, a connection involving two capillaries from the brain that merge to form the vein that feeds directly into the adenohypophysis. Neural secretions from the hypothalamus either stimulate or inhibit the appropriate cells in the adenohypophysis, allowing for a finely tuned method of regulation. For example, if a person’s fingers touch a hot stove, a sensory reflex allows the person to remove the hand quickly. At the same time, the anterior pituitary is “instructed” to secrete ACTH. The ACTH travels through the blood to the adrenals, which then secrete the appropriate steroids, which have an anti-inflammatory action. The rise in steroid level in the general circulation is monitored by the hypothalamus. At the appropriate level, a negative feedback results,...
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Role in Physiology of Behavior (Psychology and Mental Health)
Hormones of the endocrine system—in particular, those hormones associated with the pituitary gland—play a vital role in the physiology of behavior. This role may take several forms. For example, among the most obvious effects are those that result from systems that regulate body metabolism. Thyroid-stimulating hormone is produced within the anterior pituitary and is involved in regulating the secretion of thyroxin and trilodothyronine by the thyroid. Since thyroxin is particularly important in controlling the metabolic rate, overproduction of TSH may cause symptoms of nervousness, hyperactivity, and loss of sleep. On the other hand, lack of TSH production may result in hypothyroidism, an underactive thyroid. Individuals suffering from this condition are often mentally sluggish. It should be kept in mind, however, that an overactive or underactive thyroid may result from reasons other than inappropriate pituitary activity.
The activity of ACTH, the source of which is the anterior pituitary, is particularly illustrative of the multitude of effects associated with an individual hormone. The major activity of ACTH involves its effects on the adrenal glands. In response to ACTH production, the adrenal cortex (the outer region of the adrenal glands) begins production of a variety of steroid hormones. Several of these steroids, including cortisol, increase the rate of protein and fat metabolism. As in the example...
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Sexual Behaviors (Psychology and Mental Health)
Directly or indirectly, sexual behaviors are also the result of pituitary activity. Production of follicle-stimulating hormone (FSH), and luteinizing hormone (LH) influences the sex organs to produce sperm or eggs and a variety of sex hormones. Well-known mating and sexual behaviors among humans are therefore influenced by pituitary hormones. In the male, this results from testosterone activity—sexual aggressiveness being a prime example. Whether aggressiveness in general among human males is primarily attributable to hormonal action or to environmental conditioning is not completely clear. Among other primates, however, fighting behavior is definitely a result of testosterone production. Sex hormones also regulate maternal activity among a variety of mammals. The “nesting instinct” and huddling behaviors exhibited by primates, including some humans, are controlled in this manner.
Communication behaviors that result from gonadal hormone production are well known. Visual signals include changes in skin color among female chimpanzees at the time of ovulation and the production of fat pads on the shoulders of male squirrel monkeys during mating season. Production of pheromones, chemicals that exhibit distinct odors, is also used to exhibit sexual receptivity. A male dog may be aware of any receptive female within a radius of hundreds of meters. The use of perfumes or musk is based, in part, on the belief that analogous...
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Oxytocin (Psychology and Mental Health)
The release of oxytocin by the posterior pituitary is also influenced by a variety of sexual and maternal behaviors. As described above, oxytocin is actually a neuropeptide, a short chain of amino acids that are released into the posterior pituitary from neural axons that originate in the hypothalamus. Oxytocin causes contraction of smooth muscle. During sexual intercourse, release of oxytocin may result in the uterine contraction known as “tenting.” This process may draw sperm into the uterus, increasing the likelihood of fertilization. In addition, the smooth muscle contraction in the male that occurs during ejaculation may be caused, in part, by the effects of oxytocin. The contraction of the uterus during labor and delivery is also caused by the effects of oxytocin. Finally, both oxytocin and prolactin, produced within the anterior pituitary, are activated by stimulation associated with suckling and result in milk production and letdown.
The pituitary gland is a principal component of the endocrine system. Hormones that originate within the anterior pituitary act on a variety of tissues and organs. The posterior pituitary, in turn, serves primarily as a “way station” for neuropeptides produced in the hypothalamus. In this manner, numerous physiological activities and behaviors are regulated by this set of glands.
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History of Study (Psychology and Mental Health)
Knowledge of pituitary function, like that of most tissues and organs in the body, evolved over the period of a millennium. Aristotle (in the fourth century b.c.e.) believed that the pituitary, as an extension of the brain, played a role in regulation of body temperature. He believed that the body humor known as phlegm (Latin pituita) passed through the gland into the nasal cavity. (Hence a person’s attitude, or humor, was related to the relative qualities of the four body fluids, or humours.) It was on this basis that Andreas Vesalius, the sixteenth century physician considered to be the founder of modern anatomy, named the gland “pituitary” in his classic work De humani corporis fabrica (1543; on the structure of the human body). This view continued to be held into the mid-nineteenth century.
The understanding of body functions is often associated with the correlation of behavioral or physiological changes with organ pathology. Such was the case with the pituitary gland. By 1850, it was recognized that pituitary tumors, particularly in children or young adults, often resulted in conditions such as gigantism, acromegaly, or sexual dysfunction. Furthermore, surgical removal of the gland, first in experimental animals and then in humans, resulted in numerous pathological changes. By the early twentieth century, it was clear that the pituitary played a key role in monitoring a variety of systems in the...
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Modern Research and Understanding (Psychology and Mental Health)
As knowledge of pituitary hormones increases, the interaction of these molecules with target sites on other organs or glands can be better understood at the molecular level. At the very least, this can allow treatment or prevention of behavioral or physiological changes associated with abnormalities of the endocrine system. This can include, for example, an improvement in the effectiveness or safety of birth control techniques; a pill that would inhibit sperm production could be used by men.
Oxytocin and ADH, the hormones released through the neurohypophysis, are functionally neurotransmitters. This example illustrates the close structural and functional relationship between different systems—in this case, the endocrine and nervous systems. Clearly, hormonal control is complex and finely controlled. Precise mechanisms of control, however, remain to be worked out. For example, negative feedback was discussed earlier as a means by which adrenal hormones regulate their own secretion. The exact region in the brain that responds to elevated levels of adrenal hormones remains a source of controversy. A similar situation exists for other hormones. Presumably, regulation involves a specific series of neurons with specialized neurotransmitters. As the control mechanisms become better understood, modulation of behavior through proper drug treatment will become more of a reality. For example, use of the drug...
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Sources for Further Study (Psychology and Mental Health)
Besedovsky, Hugo, George P. Chrousos, and Adriana Del Rey. The Hypothalamus-Pituitary-Adrenal Axis. Amsterdam: Elsevier Science, 2008. With a focus on the immune system, this text examines the relationship among the hypothalamus, the pituitary, and the adrenal gland and its role in regulation stress, digestion, mood. and sexuality.
Cotman, Carl W., and James L. McGaugh. Behavioral Neuroscience. New York: Academic Press, 1980. Originally developed as part of a course in neuroscience. The authors provide a broad overview of the topic without becoming bogged down in detail. Several chapters deal specifically with the endocrine system and associated clinical disorders.
Guillemin, Roger, and Roger Burgus. “The Hormones of the Hypothalamus.” Scientific American 227 (November, 1972): 24-33. An excellent article that deals primarily with the regulation of the pituitary gland. The methods by which hormones of the neurohypophysis have been isolated and studied are highlighted. Particularly useful are the clear diagrams. Description of experimental approaches is minimized.
Holmes, Clarissa S., ed. Psychoneuroendocrinology: Brain, Behavior, and Hormonal Interactions. New York: Springer-Verlag, 1990. Presents a thorough discussion of the interdependence of hormonal and psychological factors. Includes discussion of endocrine disease on growth disorders, academic development,...
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Structure and Functions (Magill’s Medical Guide, Sixth Edition)
The pituitary gland is similar in size to a pea and has two lobes: anterior (adenohypophysis) and posterior (neurohypophysis). The anterior lobe accounts for a greater proportion of the total weight, approximately 80 percent compared to 20 percent from the posterior lobe. The pituitary gland is involved in the release of numerous hormones that have a multitude of effects throughout the body; as a result, it is often referred to as the “master” gland. The functions of the hormones released from the pituitary gland include regulation of metabolic processes, reproductive functions (including childbirth and lactation), bone growth and development, and regulation of body temperature, water balance, circulation, and blood pressure. Therefore, a normally functioning pituitary gland is essential to the health and maintenance of homeostasis in humans.
Hormones released from the anterior lobe of the pituitary gland include thyroid-stimulating hormone (TSH) or thyrotropin, growth hormone (GH), adrenocorticotropic hormone (ACTH), follicle-stimulating hormone (FSH), luteinizing hormone (LH), and prolactin (PRL). The hypothalamus, which is located just superior to the pituitary gland, regulates the release of hormones from the anterior pituitary gland by releasing hormones that travel through a blood network called the hypophyseal portal system to the anterior pituitary. For example, the hypothalamus releases growth...
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Disorders and Diseases (Magill’s Medical Guide, Sixth Edition)
Pituitary dysfunction is typically characterized by an oversecretion or undersecretion of pituitary hormones. An overactive pituitary gland is an endocrine defect characterized by excessive growth in stature, mass, and a variety of other symptoms, depending upon which hormones are elevated. The increased hormone release from the pituitary gland is often attributed to a pituitary tumor. If this is the case, then the tumor may be treated with radiation therapy, surgical removal, or the use of an antagonist to decrease the release of pituitary hormones.
In contrast, individuals with underactive pituitary glands, or hypopituitarism, develop opposing characteristics such as short stature, low body mass, infertility or reproductive difficulties (including the inability to lactate following childbirth in women), low energy levels, perpetual feeling of cold due to an inability to regulate body temperature, and fatigue. Hypopituitarism may also be caused by a pituitary tumor, as well as injury to or infection of the hypothalamus or pituitary gland. The treatment for hypopituitarism involves stimulating the release of hormones from the target organs or tissues, instead of stimulating the pituitary gland itself.
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For Further Information: (Magill’s Medical Guide, Sixth Edition)
Baylis, P. H. “Posterior Pituitary Function in Health and Disease.” Clinical Endocrinology and Metabolism 12, no. 3 (November, 1983): 747-770. A higher-level resource describing the roles of the posterior pituitary hormones as well as factors controlling their release.
Besser, G. M. “Pituitary and Hypothalamic Physiology.” Journal of Clinical Pathology. Supplement (Association of Clinical Pathologists) 7 (1976): 8-11. A great overview of the link between the hypothalamus and pituitary gland, including their functions and interactions.
Daniel, P. M. “Anatomy of the Hypothalamus and Pituitary Gland.” Journal of Clinical Pathology. Supplement (Association of Clinical Pathologists) 7 (1976): 1-7. Excellent resource for the anatomy of these structures.
Freeman, Susan, L. “The Anterior Pituitary.” In Endocrine Pathophysiology, edited by Catherine B. Niewoehner. 2d ed. Raleigh, N.C.: Hayes Barton Press, 2004. An excellent resource for general information about the endocrine system and the pituitary gland in particular. Information about endocrine and pituitary disorders and their treatment is also included. It is easy to follow and has a variety of tables and figures for improved comprehension.
Harris, G. W. “Neural Control of the Pituitary Gland. I. The Neurohypophysis.” British Medical Journal 2, no. 4731 (September, 1951): 559-564....
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Pituitary Gland (Encyclopedia of Nursing & Allied Health)
The pituitary gland is located at the base of the brain and is part of the endocrine system. It is sometimes called the hypophysis, from two Greek words that mean "to grow beneath." The pituitary is responsible for the hormonal regulation of several body processes, including water retention, breast milk synthesis and release, human growth, and thyroid gland secretions.
The pituitary is one of the most extensively researched glands in the endocrine system. In humans, it is located at the base of the brain just beneath the hypothalamus. There are three separate lobes (or sections) of the pituitary: the anterior lobe, the posterior lobe and the intermediate lobe. Therefore, it is sometimes considered as three different glands. In addition, there is a small stem called the pituitary stalk that connects the pituitary to the hypothalamus.
The pituitary gland is formed during early fetal development. An understanding of its formation explains its position in the endocrine system as well as its neurological importance. Early in the development of the fetus, a small sac of cells forms at the top of the oral cavity and moves upward. These cells are known as Rathke's pouch. At the same time, a small fold of neural tissue extends downward from the hypothalamus. During fetal development, the two structures continue to move toward each other; they meet and fuse to form the anterior (originally Rathke's pouch) and posterior (from the hypothalamus) lobes of the pituitary.
The hypothalamus, which is located just above the pituitary gland, is a region in the forebrain that is responsible for regulating all lobes of the pituitary. The pituitary releases, but does not necessarily synthesize, nine different hormones. Neurohormones are synthesized by the hypothalamus and transported to the posterior pituitary. The release of hormones from each lobe of the pituitary is regulated differently.
The anterior pituitary is sometimes called the adenohypophysis. It constitutes about 80% of the pituitary by weight. The cells of the anterior pituitary act like true endocrine cells. Instead of containing neurons, the anterior pituitary receives chemical signals through the blood and releases hormones in response. It has a direct connection with the hypothalamus through blood vessels. Various cells in the anterior pituitary release the following hormones:
- Gonadotrophs release luteinizing hormone (LH) and follicle-stimulating hormone (FSH).
- Lactotrophs release prolactin (PRL).
- Corticotrophs release adrenocorticotropic hormone (ACTH).
- Somatotrophs release growth hormone (GH).
- Thyrotrophs release thyroid-stimulating hormone (TSH).
The posterior pituitary is sometimes referred to as the neurohypophysis because it acts like an extension of the nervous system. As opposed to the anterior pituitary, which is connected to the hypothalamus via the circulatory system, the posterior pituitary receives nerve impulses from the same nerve cells that innervate the hypothalamus. The posterior pituitary releases oxytocin and antidiuretic hormone (ADH, or vasopressin).
The intermediate lobe is not a complete "lobe" in humans. Instead it is a simple structure comprised of just a few cells. The intermediate pituitary is an important structure in many lower vertebrates, but it has very little significance in humans. In lower vertebrates, the intermediate
Acromegalybnormal enlargement of such parts of the body as the hands, face, head, and feet.
Adenohypophysisnother name for the anterior lobe of the pituitary.
Antidiuretic hormone (ADH) hormone released by the posterior lobe of the pituitary gland that increases the absorption of water by the kidneys. It is also known as vasopressin.
Diabetes insipidus disorder characterized by increased urine production resulting from inadequate levels of ADH.
Gonadotropinsormones that affect the development or activity of the ovaries or testes.
Hypophysisnother name for the pituitary gland.
Hypopituitarism condition produced by deficient activity of the anterior lobe of the pituitary gland. It is characterized by obesity, incomplete sexual maturation, and in extreme cases, dwarfism.
Hypothalamus region in the forebrain that regulates the functions of the autonomic nervous system by vascular communication. The hypothalamus governs the functions of both lobes of the pituitary gland.
Neurohypophysisnother name for the posterior lobe of the pituitary.
Oxytocin hormone produced by the posterior pituitary that stimulates the movement of breast milk from the sacs in which the milk is produced to the larger ducts from which the milk is ejected.
Peptide compound containing two or more amino acids, in which the carboxyl group of one acid is linked to the amino group of the other.
Vasopressinnother name for ADH.
pituitary releases melanocyto-stimulating hormone. This hormone stimulates the growth of melanocytes, which are cells that produce a dark pigment called melanin.
The pituitary gland is an organ that is part of the endocrine system, along with many other glands and organs. It is regulated by the hypothalamus, and it in turn regulates the secretion of many different hormones that are essential to human health.
Role in human health
Hormones released from the anterior and posterior pituitary have far-reaching effects on many different organ systems and physiological processes.
Hormones of the anterior pituitary
Luteinizing hormone and follicle stimulating hormone are called gonadotropins. As the name suggests, the target tissues of these hormones are the gonads (ovaries and testes). They have two main functions. The first is to promote the development and maturation of sperm and eggs. Second, they stimulate the production and release of such sex steroid hormones as estradiol and testosterone in women and men respectively.
Prolactin is responsible for stimulating cells in the female breast to produce milk. Therefore, lactotrophs located in the anterior pituitary of women that are breast-feeding are large and numerous, indicating an increased amount of prolactin production. These lactotrophs comprise about 30% of the cells in the anterior pituitary. The pituitary in women doubles in size during pregnancy because of the increase in size and number of lactotrophs.
The target tissue of adrenocorticotropic hormone is the adrenal cortex (part of the adrenal gland that is located above the kidney). ACTH stimulates the production of cortisol and also causes the cells of the adrenal gland to grow. Cortisol has many effects on metabolism in various tissues.
Growth hormones have many different target tissues and promote the growth of each of them. For this reason human growth hormone (GH) is considered an anabolic hormone, indicating that it is responsible for building tissue proteins. For example, GH directly increases protein synthesis in muscles and the liver; and it decreases the size of adipose tissue. It also has an indirect effect by stimulating other hormones. Growth hormones indirectly affect the bones by increasing protein synthesis, collagen synthesis and cell proliferation. In many other tissues, the indirect effects of growth hormone are responsible for protein, RNA and DNA synthesis. The overall effect of growth hormone is to promote skeletal growth and a lean body mass.
As its name implies, thyroid-stimulating hormone (TSH) promotes cell growth in the thyroid gland. TSH also triggers the secretion of thyroid hormones that affect many metabolic processes in the body.
Hormones of the posterior pituitary
Both oxytocin and antidiuretic hormone (ADH) are peptide hormones that are synthesized in the cell bodies of the nerves originating in the hypothalamus and then delivered through the axons to the posterior pituitary. Thus, they are good examples of neuroendocrine hormones.
The primary target organ of ADH is the kidney. ADH is responsible for increasing water retention by the kidney, resulting in an increase in extracellular fluid and a decrease in urine volume. Receptors in the hypothalamus called osmoreceptors can sense the concentration of water in the extracellular fluid through changes in extracellular fluid osmolarity. The osmoreceptors in turn determine the release of ADH by the posterior pituitary. The consumption of alcohol decreases the amount of ADH released. As a result, more fluid is lost through urination, resulting in excessive water loss and thirst.
The primary site of action of oxytocin is female breast tissue. Oxytocin stimulates the contraction of smooth muscle cells in the breast, transferring milk from the place of synthesis to the larger ducts of the breast. Oxytocin is secreted by the stimulation of touch sensors when an infant is suckling. Other psychological factors, such as the sound of a baby crying, can stimulate the release and action of oxytocin. The role of oxytocin in the onset of labor contractions is not fully clear. There is no known stimulus for the secretion of oxytocin in the human male.
Common diseases and disorders
Disorders of the pituitary gland can have severe effects on normal growth and sexual maturation. A general condition known as hypopituitarism, also known as pituitary dwarfism, is characterized by a decrease in one or more of the hormones produced by the anterior pituitary. Sexual immaturity and metabolic dysfunction leading to obesity are symptoms of this syndrome. When hypopituitarism occurs in childhood, growth is slowed. Tumors are often the cause of hypopituitarism; however, sometimes there is no identifiable cause. If there is a decrease in the levels of hormones released from the hypothalamus, then hypopituitarism results. The symptoms vary according to the number and amount of hormones that are deficient. The most effective treatment is the administration of replacement hormones.
The overproduction of growth hormone during childhood produces a condition known as gigantism or acromegaly. Excessive secretion of anterior pituitary hormones is known as hyperpituitarism. Growth hormone influences the overgrowth of the skeleton and all other tissues. A person may grow to 8 ft (2.4 m) or more in height. It is still unclear, but researchers think that over-production of growth hormone may be caused by an adenoma (tumor) on the anterior pituitary. Sometimes, this condition occurs in more than one member of the family, suggesting that there is a genetic component. Gigantism is treated by removing the tumor and administering medications (bromocriptine and octreotide) that inhibit the production of growth hormone.
A disorder related to both the hypothalamus and the posterior lobe of the pituitary is diabetes insipidus, not to be confused with diabetes mellitus. Diabetes insipidus, or DI, is caused by a deficiency of antidiuretic hormone (ADH). As a result, water is rapidly released from the body through large volumes of urine (30 quarts per day). DI may result from an inherited trait; from damage to the hypothalamus, which synthesizes ADH; or from damage to the posterior pituitary, which stores the ADH. Diabetes insipidus occurs more frequently in men than in women. In mild cases, no treatment is necessary other than water replacement. In extreme cases, the patient can be treated by hormone replacement therapy.
Cahill, Matthew, ed. Professional Guide to Diseases. 6th ed. Springhouse, PA: Springhouse Corporation, 1998.
Greenspan, Francis S., and David G. Gardner. Basic and Clinical Endocrinology. 6th ed. New York: Lange Medical Books/McGraw-Hill, 2001.
"Hypothalamic-Pituitary Relationships." Chapter 6 in The Merck Manual of Diagnosis and Therapy, edited by Mark H. Beers, MD, and Robert Berkow, MD. Whitehouse Station, NJ: Merck Research Laboratories, 1999.
Martin, John H., PhD. Neuroanatomy: Text and Atlas. 2nd ed. Norwalk, CT: Appleton & Lange, 1996.
"Pituitary Disorders." Chapter 7 in The Merck Manual of Diagnosis and Therapy, edited by Mark H. Beers, MD, and Robert Berkow, MD. Whitehouse Station, NJ: Merck Research Laboratories, 1999.
Vander, Arthur, et al, eds. Human Physiology: The Mechanisms of Body Function, 7th ed. Boston, MA: WBC/McGraw-Hill, 1998.
Sally C. McFarlane-Parrott