Information

Why is the pituitary gland located in the brain?

Why is the pituitary gland located in the brain?



We are searching data for your request:

Forums and discussions:
Manuals and reference books:
Data from registers:
Wait the end of the search in all databases.
Upon completion, a link will appear to access the found materials.

Why is the pituitary gland located in the brain in humans, instead of elsewhere in the body? Why would this be an evolutionary beneficial adaptation?


The evolutionary pressure on the location of the pituitary is likely not the reason why it resides at the basis of the brain. Instead, its (partly) neural origin makes it anatomically (and functionally) part of the brain. Why would it migrate out of the brain when it doesn't have to? What would the evolutionary pressure be on increasing the length of the axons connecting it to the other parts of the brain? It is part of the brain, hence it is located there. It clashes with the principle of parsimony to have the pituitary evolve to a structure located farther from the brain.

The neuroanatomy of the pituitary is schematically as follows (Fig. 1):


Fig. 1. Pituitary gland. Source: Imagekb.

The posterior lobe of the pituitary gland consists largely of extensions of processes (axons) from the hypothalamus and are part of the neurohypophyseal system. There are neural connections to the brain and other centres of the hypothalamus. Hence, the posterior lobe is neural tissue.

The cells constituting the anterior lobe of the pituitary gland are embryologically derived from an outpouching of the roof of the pharynx, known as Rathke's pouch.


Pituitary Glands: Origin, Location and Structure

The pituitary gland is located just below the hypothalamus. The pituitary gland is situated in a depression the sella turcica of sphenoid bone of the skull. The pituitary gland is the smallest endocrine gland.

It is about 1.3 cm in diameter and weighs about half a gram. The gland is attached to the brain by a stalk the infundibulum which is continuous with the hypothalamus above. The pituitary gland is formed of two main lobes of different origin.

These lobes are the much larger anterior lobe or adenohypophysis or pars distalis and the smaller posterior lobe or neurohypophysis or pars nervosa. Adenohypophysis originates as Rathke’s pouch from dorsal wall of stomodaeum in the embryo, but later its connection with the stomodaeum disappears.

The neurohypophysis originates as an outgrowth from the floor of the diencephalon. Thus the pituitary gland is dual in origin (from stomodaeum – foregut and diencephalon). A third lobe, called the intermediate lobe or pars inter-media is a part of adenohypophysis.

Adenohypophysis comprises about 75% part of the pituitary gland. The hypophysial portal veins carry blood containing neurohormones (releasing factors) from the hypothala­mus to the adenohypophysis. Neurohypophysis comprises about 25% part of the pituitary gland. The axons of neurosecretory cells (secretory neurons) extend into the neurohypo­physis where these axons terminate as axon terminals.

These terminals are embedded in a neuroglial tissue formed of large and branched cells called pituicytes. Obviously no hor­mones are synthesized in neurohypophysis but two hormones, synthesized in the hypotha­lamic neurosecretory cells remain stored in very small vesicles in the axons and terminals. These vesicles are called Herring bodies.

(a) Hormones of the anterior lobe:

The anterior lobe of the pituitary gland secretes the following hormones, most of them are trophic hormones.

(i) Growth hormone (STH or GH) or Somatotrophin (Soma— body, trophe— nourish­ment):

This hormone stimulates growth. Growth hormone promotes protein anabolism, the absorption of calcium from the bowel and the conversion of glycogen to glucose.

Various body cells which undergo growth.

(ii) Thyroid stimulating hormone (TSH) or Thyrotropin:

This hormone controls the growth and activity of the thyroid gland. It influences the uptake of iodine, the synthesis of the hormones, thyroxine and tri-iodothyronine by the thyroid gland and the release of stored hormones into the blood stream.

(iii) Adrenocorticotropic hormone (ACTH):

This hormone stimulates the cortex of the adrenal gland to produce its hormones.

(iv) Prolactin hormone (PRL) or Mammotropin hormone (MTH) or Luteotropic hormone (LTH):

Prolactin is also called the “hormone of maternity” because its main physiological effect is to activate growth of breasts during pregnancy and secretion of mammary glands after child birth. The name luteotrophic hormone (LTH) refers to because it also stimulates the corpus luteum of the ovary to secrete progesterone hormone.

(v) Gonadotropic hormones:

Follicle-stimulating hor­mone (FSH):

It stimulates growth of ovarian follicles and their secretion of oestrogens in the female, and spermatogenesis (formation of sperms) in the male.

(b) Luteinizing hormone (LH):

In female it stimulates the corpus luteum of the ovary to secrete progesterone. In male it activates the Leydig’s (interstitial) cells of the test is to secrete androgenes hence it may be called interstitial cell stimulating hormone (ICSH) in male.

Target Cells. Cells of gonads (testes and ovaries)

(b) Hormone of the Intermediate lobe:

The intermediate lobe of the pituitary gland secretes melanotrophin or melanocyte stimulating hormone (MSH). This hormone causes dispersal of pigment granules in the pigment cells, thereby darkening the colour in certain animals like fishes and amphibians. It is believed that it is associated with the growth and development of melanocytes in man which give colour to the skin.

Target Cells. Melanocytes in skin.

(c) Hormones of the Posterior lobe:

The secretion of the posterior lobe is known as pituitrin and it contains two hormones:

(ii) Antidiuretic hormone (ADH) or vasopressin. Once again it is reminded that the posterior lobe of the pituitary gland does not secrete any hormone. Its hormones are secreted in the hypothalamus.

Oxytocin promotes contraction of the uterine muscle and contrac­tion of the myoepithelial cells of the lactating breast, squeezing milk into the large ducts behind the nipple. In late pregnancy the uterus becomes very sensitive to oxytocin.

The amount secreted is increased just before and during labour and by sucking of the baby. Because of its role, oxytocin is called “birth hormone” and “milk ejecting hormone”. Milkmen inject synthetic oxytocin, called pitocin, into their cows and the buffaloes to get more milk.

(ii) Antidiuretic hormone (ADH) or Vasopressin or Pitressin:

This hormone has two main functions:

(a) Antidiuretic effect:

It increases the reabsorption of water in the distal convoluted tubule and collecting ducts of the nephrons of the kidneys. As a result, the reabsorption of water from the glomerular filtrate is increased,

(b) Pressor effect:

Involun­tary muscles in the walls of the intestine, gall bladder, urinary bladder and blood vessels are stimulated to contract by ADH. Contraction of the walls of the blood vessels raises the blood pressure and this may be its most important pressor effect.

The pituitary gland is also called “Master Endocrine Gland” of body or the “Chief Executive of Endocrine System” or “The Leader of Endocrine Orchestra” as it secretes the number of hormones (e.g., TSH, ACTH etc.) which regulate the working of other endocrine glands.

But it is not proper to call it as master endocrine gland because it is itself under the control of the releasing hormones secreted by the hypothalamus of the brain. Thus the hypothalamus is, in fact, the supreme commander of endocrine regulation.

Pituitary Disorders:

It is caused by the deficiency of growth hormones (GH) from childhood. It is characterised by small but well proportioned body and sexual immaturity. The dwarfs produced by the deficiency of growth hormone are different from those which are formed from the deficiency of thyroid hormone in having normal intelligence.

It is caused by excess of growth hormone from early age. It is characterised
by large and well proportioned body. If size of pituitary gland increases, it affects (suppresses) optic chiasma and ultimately affects vision.

(c) Acromegaly (Aero- extremity, megaly- large):

It is caused by excess of growth hormone after adult size is reached. It is characterised by disproportionate increase in size of bones of face, hands and feet.

It is caused by the deficiency of ADH. It is characterised by excessive dilute urine.

Cause — atrophy or degenera­tion of anterior lobe of pituitary gland. Symptoms— the skin of face becomes dry and wrinkled, premature ageing.

(f) High Blood Level of ADH:

It is caused by excessive secretion of ADH. It is characterised by excessively dilute blood and low plasma sodium.


Overview of the Endocrine System

The endocrine system is a system of glands called endocrine glands that release chemical messenger molecules called hormones into the bloodstream. Other glands of the body, including sweat glands and salivary glands, also secrete substances but not into the bloodstream. Instead, they secrete them through ducts that carry them to nearby body surfaces. These other glands are called exocrine glands.

Endocrine hormones must travel through the bloodstream to the cells they affect, and this takes time. Because endocrine hormones are released into the bloodstream, they travel throughout the body wherever blood flows. As a result, endocrine hormones may affect many cells and have body-wide effects. Endocrine hormones may cause effects that last for days, weeks, or even months.


Pituitary Gland

Your pituitary (hypophysis) is a pea-sized endocrine gland at the base of your brain, behind the bridge of your nose and directly below your hypothalamus. It sits in an indent in the sphenoid bone called the sella turcica. The pituitary gland is one of eight interrelated major endocrine glands:

  • Pineal gland.
  • Pituitary gland.
  • Thyroid gland.
  • Thymus.
  • Adrenal gland.
  • Pancreas.
  • Ovary (women only).
  • Testis (men only).

The pituitary is often referred to as the “master gland” because it not only secretes its own hormones, it tells other glands to produce hormones.

Your pituitary gland is divided into two main sections: the front (anterior) lobe and the back (posterior) lobe. Connecting the hypothalamus and pituitary gland is a stalk of blood vessels and nerves. Through that stalk, the hypothalamus communicates with the anterior lobe via hormones and the posterior through nerve impulses.

The hypothalamus, which is above your pituitary gland, is the control center of some of your body’s basic operations. It sends messages to your body’s autonomic nervous system, which controls things like blood pressure, heart rate, respiration, body temperature, sleep-wake cycle and digestion. The hypothalamus also tells the pituitary gland to produce and release hormones.

What does the pituitary gland do?

Glands are organs that secrete hormones — the “chemical messengers” of the body — that travel through your bloodstream to different cells, telling them what to do. The major hormones produced by the pituitary gland are:

  • ACTH: Adrenocorticotrophic hormone. Stimulates the production of cortisol, a “stress hormone” that maintains blood pressure and blood sugar levels.
  • FSH: Follicle-stimulating hormone. Promotes sperm production and stimulates the ovaries to produce estrogen.
  • LH: Luteinizing hormone. Stimulates ovulation in women and testosterone production in men.
  • GH: Growth hormone. Helps maintain healthy muscles and bones and manage fat distribution.
  • PRL: Prolactin. Causes breast milk to be produced after childbirth. It also affects hormones that control the ovaries and testes, which can affect menstrual periods, sexual functions and fertility.
  • TSH: Thyroid-stimulating hormone. Stimulates the thyroid gland, which regulates metabolism, energy and the nervous system.
  • Oxytocin: Helps labor to progress, causes breast milk to flow, affects labor, breastfeeding, behavior and social interaction and the bonding between a mother and child.
  • ADH: Anti-diuretic hormone, or vasopressin. Regulates water balance and sodium levels.

Hormones are not released from the pituitary gland in a steady stream. They come in bursts, every one to three hours, and alternate between periods of activity and periods of inactivity.

What happens when the pituitary gland doesn’t work properly?

Your pituitary gland plays such an important role that a lot can go wrong if it overproduces hormones (hyperpituitarism) or under-produces hormones (hypopituitarism). Overproduction or underproduction can affect metabolism, growth, blood pressure, sex functions and more.

Pituitary disorders occur when your pituitary gland fails to function as it normally should, likely because of a tumor, which is an abnormal growth of cells. Expert endocrinologists determined that about one in five people will get a tumor in their pituitary gland (16% to 20% of the population). Thankfully, the tumors are usually noncancerous (benign). Cancers of the pituitary gland rarely happen. Sometimes a pituitary gland will even have a tumor for years that’s both benign and doesn’t cause any symptoms.

There are two types of tumors: functioning and nonfunctioning. A functioning tumor produces hormones itself and a nonfunctioning tumor does not. Nonfunctioning tumors are more common.

You should see an endocrinologist, a specialist in the pituitary gland, if you have a tumor. You may also need to see an ophthalmologist (eye doctor) and neurosurgeon (a surgeon who operates on the brain, the head and the nervous system).

What are the symptoms of a pituitary tumor?

Many symptoms may point towards a pituitary tumor. If the tumor is putting pressure on the gland, your symptoms could include:

If the pituitary gland is not producing enough hormones, your symptoms could include:

  • Fatigue.
  • Dizziness.
  • Dry skin.
  • Irregular periods (women).
  • Sexual symptoms (men).

Additional symptoms include:

  • Mood changes.
  • Irritability.
  • Muscle weakness.
  • Depression.
  • Menstrual cycle changes.
  • Erectile dysfunction.
  • Infertility.
  • Inappropriate breast growth.
  • Inappropriate production of breast milk.

There are several conditions that involve the pituitary gland:

    : Hypopituitarism is when the pituitary gland doesn’t make enough hormones.
  • Acromegaly (Gigantism): Gigantism is a very rare disorder caused when the pituitary gland produces too much growth hormone (GH). : This is a disorder affected by vasopressin, the antidiuretic hormone (ADH). If you have this disorder, your kidneys can’t retain water, which results in increased urination and increased thirst.
  • Hypogonadism: Also known as testosterone deficiency, this condition is a failure of the testes to make testosterone and/or sperm.
  • Prolactinoma: This is a type of tumor that causes the pituitary gland to produce too much of the prolactin hormone.
  • Galactorrhea: Galactorrhea is when a man or a woman produces breast milk when they’re not breastfeeding.
  • Cushing’s syndrome: This rare condition can happen when your body makes too much ACTH, which causes another gland in the body, your adrenal glands, to make too much cortisol. This condition can affect almost any tissue in the body.
  • Adult GH deficiency syndrome: Problems resulting from this syndrome include changes in body composition due to changes in fat and muscle, bad cholesterol levels and loss of energy and/or interest in hobbies and social activities.
  • Empty sella syndrome: The sella turcica is the bone structure that surrounds and protects the pituitary gland. Empty sella syndrome means that nothing appears, at first, to be inside that bone structure. The pituitary gland may be flat, smaller than normal, or regressed within the cavity because of an injury.
  • Sheehan’s syndrome (postpartum hypopituitarism): Sheehan’s syndrome occurs when a woman has severe uterine hemorrhage during childbirth. Such severe blood loss causes some of the pituitary gland tissues to die.
  • Craniopharyngioma: A craniopharyngioma is a rare tumor that puts pressure on the hypothalamus.
  • Multiple endocrine neoplasia (MEN): MEN causes multiple glands to develop tumors.
  • Lymphocytic hypophysitis: This is caused by immune cells that inflame the pituitary gland.

How are pituitary tumors treated?

Radiotherapy, medications and surgery may be necessary to treat a pituitary tumor.

  • Radiotherapy — which may be performed before or instead of surgery — uses highly focused x-rays (Gamma knife or X-knife Linac), usually over several weeks.
  • Medications are used to either reduce the levels of a particular hormone or replace a hormone that is under-produced.
  • Surgery is called transsphenoidal surgery where the neurosurgeon makes an incision inside your nostril or under your upper lip. You’ll stay in the hospital for about five days after the tumor is removed. Recovery times vary. It could be as short as four weeks to as long as eight weeks. Regular follow-ups will be required.

Pituitary tumors can regrow.

Your pituitary gland affects vital areas of your body. If your pituitary gland doesn’t function properly, your skin, brain, reproductive organs, vision, mood, energy, growth and more could all be negatively affected. Your body depends on the hormones it produces and releases.

Contact your healthcare provider to address any symptoms that might point towards your pituitary gland.

Last reviewed by a Cleveland Clinic medical professional on 10/08/2020.

References

  • The Pituitary Society. Pituitary Disorders. Accessed 9/18/2020.
  • ASCO/Cancer.net. Pituitary Gland Tumor: Symptoms and Signs. Accessed 9/18/2020.
  • Hormone Health Network. Pituitary Tumors. Accessed 9/18/2020.
  • The Pituitary Foundation. What is the Pituitary Gland? Accessed 9/18/2020.
  • Hormone Health Network. Pituitary Gland. Accessed 9/18/2020.
  • The Pituitary Network Association. Okay… Now, Where Do I Start? Accessed 9/18/2020.
  • The Society of Endocrinology. Pituitary Gland. Accessed 9/18/2020.
  • The Pituitary Network Association. Is it All in Your Head? Pituitary Disorders. Accessed 9/18/2020.
  • Merck Manuals. Overview of the Pituitary Gland. Accessed 9/18/2020.
  • NIH. National Cancer Institute. Pituitary & Pineal Gland. Accessed 9/18/2020.
  • Health Direct. Pituitary Gland. Accessed 9/18/2020.
  • American Cancer Society. What are Pituitary Tumors? Accessed 9/18/2020.
  • The Pituitary Society. Pituitary Gland Function. Accessed 9/18/2020.
  • NIH. National Cancer Institute. Endocrine Glands & Their Hormones. Accessed 9/18/2020.
  • Merck Manual. Galactforrhea. Accessed 9/18/2020.

Cleveland Clinic is a non-profit academic medical center. Advertising on our site helps support our mission. We do not endorse non-Cleveland Clinic products or services. Policy

Cleveland Clinic is a non-profit academic medical center. Advertising on our site helps support our mission. We do not endorse non-Cleveland Clinic products or services. Policy

Cleveland Clinic is a non-profit academic medical center. Advertising on our site helps support our mission. We do not endorse non-Cleveland Clinic products or services. Policy

Cleveland Clinic is a non-profit academic medical center. Advertising on our site helps support our mission. We do not endorse non-Cleveland Clinic products or services. Policy

Cleveland Clinic is a non-profit academic medical center. Advertising on our site helps support our mission. We do not endorse non-Cleveland Clinic products or services. Policy

Cleveland Clinic is a non-profit academic medical center. Advertising on our site helps support our mission. We do not endorse non-Cleveland Clinic products or services. Policy

Cleveland Clinic is a non-profit academic medical center. Advertising on our site helps support our mission. We do not endorse non-Cleveland Clinic products or services. Policy

Cleveland Clinic is a non-profit academic medical center. Advertising on our site helps support our mission. We do not endorse non-Cleveland Clinic products or services. Policy


Pituitary gland anatomy and function

This small, bean-shaped gland is located below the brain in the skull base, in an area called the sella turcica. The pituitary gland is regulated by a brain region called the hypothalamus which is connected to the pituitary gland by a thin delicate vascular connection called the pituitary stalk or infundibulum.

The pituitary is divided into a larger anterior region (adenohypophysis) and smaller posterior region (neurohypophysis). Directly above the pituitary are the optic nerves and the optic chiasm as they project to the eyes.

On each side of the pituitary is the cavernous sinus which is a venous channel through which runs the carotid arteries that carry blood to the brain, and important nerves that control eye movements and facial sensation.

Because of the proximity of the pituitary to these major intracranial nerves and blood vessels, and the vital hormonal control the pituitary provides, disorders of the pituitary can cause a wide spectrum of symptoms, both hormonal and neurological.

Pituitary Gland and Related Structures

Thyroid Gland

The thyroid gland, the largest endocrine gland, is responsible for the production of the hormones T3, T4, and calcitonin.

Learning Objectives

Describe the hormones produced by the thyroid and explain how their production is regulated

Key Takeaways

Key Points

  • The thyroid gland is made up of thyroid follicles, which produce three main hormones.
  • T3 and T4 hormones increase the metabolic activity of the body‘s cells while calcitonin helps regulate calcium concentrations in body fluids.
  • T3 and T4 release is controlled by thyroid stimulating hormone however, calcitonin release is controlled by calcium ion concentrations.

Key Terms

  • thyroglobulin: a globulin, produced by the thyroid gland, that has a role in the production of the thyroid hormones
  • thyroxine: a hormone (an iodine derivative of tyrosine), produced by the thyroid gland, that regulates cell metabolism and growth
  • thyrocalcitonin: a hormone, secreted by parenchymal cells, that regulates calcium and phosphate metabolism
  • triiodothyronine: the most powerful thyroid hormone, affecting almost every process in the body, including body temperature, growth, and heart rate

Thyroid Gland

The thyroid gland, one of the largest endocrine glands in the body, is located in the neck, just below the larynx and in front of the trachea. It is a butterfly-shaped gland with two lobes that are connected by the isthmus. It has a dark red color due to its extensive vascular system. When the thyroid swells due to dysfunction, it can be felt under the skin of the neck.

Thyroid gland: The location of the thyroid gland is in the neck below the larynx and in front of the trachea it is the largest endocrine gland in the body, producing T3, T4, and calcitonin.

The thyroid gland is made up of many spherical thyroid follicles which are lined with a simple cuboidal epithelium. These follicles contain a viscous fluid, called colloid, which stores the glycoprotein thyroglobulin. This glycoprotein is the precursor to the thyroid hormones. The follicles produce hormones that can be stored in the colloid or released into the surrounding capillary network for transport to the rest of the body via the circulatory system.

The thyroid gland produces the hormones T3 (triiodothyronine) and T4 (thyroxine). These hormones increase the metabolic activity of the body‘s cells. Follicle cells are stimulated to release stored T3 and T4 by thyroid-stimulating hormone (TSH), which is produced by the anterior pituitary. These thyroid hormones increase the rates of mitochondrial ATP production.

Another hormone produced by the thyroid gland, thyrocalcitonin, or calcitonin, decreases the concentration of calcium in the blood. Most of the calcium removed from the blood is stored in the bones. Calcitonin is produced by parafollicular cells of the thyroid, either releasing hormones or inhibiting hormones. The hormone’s release is not controlled by TSH, but instead is released when calcium ion concentrations in the blood rise. Calcitonin functions to help regulate calcium concentrations in body fluids. It acts in the bones to inhibit osteoclast activity and in the kidneys to stimulate excretion of calcium. The combination of these two events lowers body fluid levels of calcium.


Research and Facts

"1 in 5 individuals may have an abnormal growth on their pituitary gland, causing significant health complications that, if left undiagnosed and untreated, can impair normal hormone function and result in a reduced lifespan."
Shereen Ezzat, M.D., Professor of Medicine, University of Toronto

Some have estimated nearly 30%. In reviewing dozens of studies over the past 80 years on the Prevalence of Pituitary Tumors, the consensus was reached that at least 16.7% of the population develop or harbor pituitary tumors. Supported by the PNA and published by the American Cancer Society June 2004, the systematic review abstract "The Prevalence of Pituitary Adenomas.
PDF full text file available here Prevalence_Of_Pituitary_Adenomas.pdf


Reasons for endoscopic pituitary surgery

Endoscopic pituitary surgery is done to remove certain types of tumors that start to grow in your pituitary gland:

Hormone-secreting tumors. These growths secrete chemical messengers that travel through the blood.

Nonhormone-secreting tumors. These growths, also called endocrine inactive pituitary adenomas, are removed by surgery because as they increase in size they may cause headache and visual disturbances.

Cancerous tumors. These growths may be treated with a combination of surgery, cancer drugs, and X-ray treatment.


What causes empty sella syndrome?

Empty sella syndrome can be due to primary or secondary causes. Primary empty sella syndrome occurs in people who have a weakness in the membrane (diaphragma sellae) that normally covers the pituitary gland. Cerebrospinal fluid is the fluid that flows around the brain. As a result of the weakened membrane, this fluid can leak into the sella turcica and apply pressure on the gland. This can lead to either a flattening of the pituitary gland or expansion of the sella turcica, giving the appearance of an empty sella.

In secondary empty sella syndrome, the pituitary fossa becomes empty because the pituitary gland has been removed through surgery or shrunk through radiation treatment or pituitary apoplexy.


References

[1] Lavrentaki A, Paluzzi A, Wass JA, Karavitaki N. Epidemiology of acromegaly: review of population studies. Pituitary. 201720(1):4–9.

[2] Chanson P, Salenave S, Kamenicky P. Acromegaly. In: Fliers E, Korbonits M, Romijn JA, eds. Handbook of clinical neurology. Vol 124. 1st ed. Waltham, MA: Elsevier B.V. 2014:197–219.

[3] Katznelson L, Laws ER Jr, Melmed S, et al. Acromegaly: an endocrine society clinical practice guideline. Journal of Clinical Endocrinology and Metabolism. 201499(11):3933–3951.

[4] Paragliola RM, Salvatori R. Novel somatostatin receptor ligands therapies for acromegaly. Frontiers in Endocrinology. 20189:78.

This content is provided as a service of the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), part of the National Institutes of Health. The NIDDK translates and disseminates research findings to increase knowledge and understanding about health and disease among patients, health professionals, and the public. Content produced by the NIDDK is carefully reviewed by NIDDK scientists and other experts.