Pituitary gland

What is the pituitary gland?

The pituitary gland, or hypophysis, is a very small endocrine gland located inferior to the hypothalamus, at the base of the brain. This gland, sometimes referred to as the “master gland” is a link between the nervous and endocrine systems, and is responsible for regulating the hormonal functions of the other endocrine glands.

Location

The pituitary gland is located at the base of the brain, connected to, and directly beneath, the hypothalamus. It sits inside a bony hollow called the sella turcica which protects it. It is in the center of the skull right behind the bridge of the nose.

Anatomy: Structure of Pituitary gland

Picture 1: Location and Anatomy of Pituitary gland

The pituitary gland is about the size of a pea. It is composed of three lobes: 1) anterior lobe, 2) intermediate lobe, and 3) the posterior lobe. In humans, the intermediate lobe is almost absent.

Anterior Lobe

The anterior lobe, also called the adenohypophysis, accounts for 80% of the pituitary gland’s weight. It releases or inhibits the production of hormones after receiving instructions from the hypothalamus through connecting blood vessels. The anterior lobe is responsible for the production of seven important hormones: adrenocorticotropic hormone (ACTH), follicle-stimulating hormone (FSH), human growth hormone (hGH), luteinizing hormone (LH), melanocyte-stimulating hormone (MSH), prolactin (PRL), and thyroid-stimulating hormone (TSH). These hormones are involved in development of the body, sexual maturation, and reproduction.

Posterior Lobe

The posterior lobe, or neurohypophysis, is controlled by the hypothalamus through nerve impulses. It is actually an extension of nervous tissue from the hypothalamus which stores and releases two hormones produced in the hypothalamus. The hormones it releases are ADH (anti-diuretic hormone), which reclaims water from the kidneys and conserves it in the bloodstream (preventing dehydration) and oxytocin, which is responsible for contracting the uterus during childbirth as well as stimulating milk production.

Function

The hormones secreted by the pituitary gland control the following functions:

  • Aspects of pregnancy and childbirth (such as uterine contractions)
  • Blood pressure
  • Breast milk production
  • Growth
  • Metabolism
  • Pain relief
  • Sex organ functions in males and females
  • Temperature regulation
  • Thyroid gland function
  • Water and osmolarity regulation of the body
  • Water balance

Pathology

For a number of reasons, the pituitary gland may not function as it should. This could present as an overactive gland, called hyperpituitarism, or an inactive gland, called hypopituitarism.

In a case of hyperpituitarism, the pituitary gland produces too much of a hormone, elaborating the respective systems that said hormone affects. This is usually the result of a pituitary adenoma. Gigantism and acromegaly are examples of conditions caused by hyperpituitarism. In these cases, there is an excess of growth hormone (GH) causing excessive growth, and height significantly above average in children (Gigantism) and adults (acromegaly).

Hypopituitarism is when there is under function of the pituitary gland. This is when there is a decrease in the secretion of one or a few of the hormones that are produced by the pituitary gland. For example, hypothyroidism is caused by a deficiency of thyroid-stimulating hormone. Hypothyroidism can cause a whole host of symptoms including poor ability to tolerate cold, fatigue, constipation, depression, and weight gain.

Pituitary gland disorders

Pituitary Adenoma (tumor)

Picture 2: Pituitary gland tumor

The most common pituitary gland disorder occurs when a benign tumor, called an adenoma, develops in the gland. Benign is used to refer to a growth that is not cancerous. It is important to note that pituitary tumors are not brain tumors. In many cases, the tumor can go undetected for years without causing symptoms. In other cases, the tumor can cause headaches or visual problems; it can stop the production of one or more hormones; or it can generate too much of one or more hormones in the pituitary gland.

Often the symptoms are so general and vague, that diagnosis takes quite some time.

Symptoms of a pituitary tumor can include:

  • Acromegaly
  • Menstrual cycle change in women
  • Cushing’s syndrome, which includes sudden increase in weight, high blood pressure, diabetes mellitus, and susceptible to easy bruises.
  • Fatigue
  • Headaches
  • Impotence, or inability to maintain an erection
  • Infertility
  • Irritability
  • Mood changes
  • Vision problems

Increased Production of One or More Hormones:

When the tumor causes increased production in one or more hormones, this can result in a variety of different syndromes. Increased production of:

  • Adrenocorticotropic hormone: If there is an excessive release of this hormone, it can result in sudden weight gain, increase in blood pressure, increase in blood sugar levels, brittle bones, emotional changes, easy bruising and stretch marks.
  • Follicle-stimulating hormone and luteinizing hormone: In rare cases, too much of these hormones can result in infertility and irregular menstrual cycles in women.
  • Growth Hormone: Increased production of GH can result in gigantism or acromegaly which includes excessive growth of soft tissue and bones, high blood sugar, high blood pressure, heart problems, and many more symptoms.
  • Prolactin: Too much of this hormone can result in inappropriate production of breast milk (even in men). Other symptoms can include osteoporosis, lowered libido, irregular menstrual cycles, and impotence.
  • Thyroid-stimulating hormone: Overproduction of TSH can lead to various problems including nervousness and irritability, increased heart rate and high BP, hyperhidrosis, and sudden weight loss.

Decreased Production of One or More Hormones:

Sometimes, the pituitary tumor can press on the pituitary gland, causing it to produce too little of one or more hormones.

  • ACTH: Nausea, low energy, decrease in blood pressure, low blood sugar, and upset stomach, are all symptoms of not enough ACTH.
  • GH: When a person’s pituitary gland is not producing enough Growth hormone, is can cause late growth in children, poor muscle strength, weakening of bone structure, and an unwell feeling.
  • Prolactin: Decreased production of prolactin will present as an inability to breastfeed in postpartum women.
  • TSH: Not enough TSH can cause a person to experience fatigue, low energy, sensitivity to cold temperatures, constipation, and weight gain.

Vision Problems

In some cases, a pituitary tumor will press on the optic nerves causing loss of sight or double vision.

Treatment

A patient with a pituitary tumor will see an endocrinologist, a doctor who specializes in problems with the endocrine system, as well as a neurologist, a doctor who specializes and operates on the head, brain, and central nervous system.

A patient who is not presenting any symptoms that affect his/her daily life is usually put under surveillance. The patient is monitored closely to make sure that the tumor doesn’t grow or progress.

Surgery is the most common treatment for a pituitary adenoma. It is necessary in cases where the tumor is pressing on the optic nerves of it the tumor is over-producing certain hormones. The two main surgical options include an endoscopic transnasal transsphenoidal approach, where the surgeon goes through the nose and sinuses, and a transcranial approach, where the tumor is removed via an incision in the scalp.

Radiation therapy might be used after surgery or alone in cases where surgery is not an option.

In some cases, medications might be administered to block excess hormone secretion or shrink certain types of tumors.

During and after treatment for a pituitary tumor, the patient is observed closely to make sure that the tumor is not growing back, or in cases when it is not removed, that the tumor is not growing. There are many people walking around with pituitary tumors that are not aware they even have them because they do not affect their daily lives.

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