The Pituitary Gland

What is the Pituitary Gland (hypophysis)?

An explanation of the pituitary gland followed by their hormones.

Enclosed by bones, the Pituitary Gland hangs by a stalk from the base of the brain.

• The anterior pituitary’s hormonal output is regulated by the hypothalamus. It also synthesizes the two hormones that it sends to the posterior pituitary for storage and later release.
• The posterior pituitary which is an extension of the hypothalamus consists of the neural portion and the anterior pituitary is the hormone producing glandular portion.

Tropic hormones (four of the six adenohypophyseal hormones) regulate the function of other endocrine organs. There is a certain diurnal rhythm of release mostly anterior Pituitary Gland hormones and they are modified by the stimuli influencing the hypothalamus.

What is the pituitary gland

Hormones produced by the Pituitary Gland

The Pituitary Gland is broken up into two main lobe’s The Anterior pituitary lobe (adenohypophysis) and the Posterior pituitary lobe (neurohypophysis) see below for further details.
 

The Anterior pituitary lobe (adenohypophysis)

• Growth hormone (somatotropin)
• Thyroid-stimulating hormone (thyrotropin)
• Adrenocorticotropic hormone (corticotropin)
• Beta-endorphin
• Follicle-stimulating hormone
• Luteinizing hormone
• Prolactin
• Melanocyte-stimulating hormone

Posterior pituitary lobe (neurohypophysis)

• Oxytocin
• Vasopressin (antidiuretic hormone)

 
For a comprehensive list of Hormones and their functions please read Pituitary Gland Hormones

A list of Pituitary Gland Hormones

What is the endocrine system?

A comprehensive overview of the endocrine.

The Pituitary Gland is part of the endocrine system. The endocrine system is a system of glands where every gland secretes a particular type of hormone directly into blood so as to regulate the body. This system is in contrast to the exocrine system (the exocrine system secretes chemicals using ducts). “Endo” means within, inside and “Crinis” means to secrete.
 

Just like the nervous system, the endocrine system is also an information signal system though there are differences between the two systems as to their mechanism and effects. Quite contrary to the nervous system that sends information rapidly and where responses are short-lived, the effects of the endocrine system are slow to initiate and the responses are prolonged (normally lasts for hours to weeks). Hypophysis or Pituitary Gland is an endocrine gland about the size of a pea and weighs around 0.5g.
 

In order to generate a response, the endocrine tissue releases hormones (chemical mediators) into the blood and they travel to target tissue and generate the response. Various human functions like body growth, metabolism, mood and tissue functions are regulated by the hormones released by the endocrine glands. Endocrinology, a branch of internal medicine, is the study of the endocrine system and the various disorders associated with it.

For a comprehensive list of Disorders please read Pituitary Gland Disorders
 

Endocrine glands in the human head and neck and their hormones

What are the endocrine glands?

A break down on the endocrine gland.

The Endocrine glands are glands of the endocine system. The pancreas, the testes, the ovaries, the thyroid gland and the adrenal glands are the main endocrine glands. The hypothalamus is a neuroendocrine organ. Even the stomach, not so well known for its endocrine activity, produces endocrine hormones like ghrelin. The cells that are targeted by the hormones must respond to them properly. The presence of receptors makes it work.
 

The receptors present on the plasma membrane or within the cell binds with the hormone. The hormone receptors are quite dynamic in structure. Depending on the levels of the stimulating hormones, changes in number and sensitivity of hormone receptors occur. The balance between secretion and degradation (excretion) is reflected by the blood levels of hormone.
 

The major organs that carry out the degradation are the kidneys and the liver. The breakdown products are released through feces and urine. The duration of activity and hormone half-life are limited and vary from one hormone to the other.
 

The major endocrine organs

Major Endocrine Organs – A full summary of each gland is listed below.

This is a brief summary of what consists of the Endocrine glands. Below is an explanation of each gland and its hormone.

• Pituitary gland (hypophysis)
• Thyroid gland
• Parathyroid glands
• Pancreas
• Gonads
• Pineal gland

What is the hypothalamus?

The hypothalamus is a area of the brain which contains several tiny nuclei which has a variety of functions and capability’s.

The Pituitary Gland, a vital gland of the endocrine system protrudes or rather is a protrusion of the bottom of the Hypothalamus and is functionally connected to the hypothalamus by the median eminence via the pituitary stalk. The endocrine glands are ductless in nature. They are vascular and intracellular vacuoles or granules store their hormones.
 

Organs like the liver, kidney, gonads and heart have secondary endocrine functions. Renin and Erythropoietin are endocrine hormones secreted by the kidney. Glands of the endocrine system signal each other in sequence that is commonly referred to as an axis. The Hypothalamic – Pituitary Gland – Adrenal axis is one such sequence.
 

The hypothalamus contains the below Endocrine hormones:

• Thyrotropin-releasing hormone
• Gonadotropin-releasing hormone
• Growth hormone-releasing hormone
• Corticotropin-releasing hormone
• Somatostatin
• Dopamine
• Vasopressin
• Oxytocin

What is Hypothalamus and contains the Endocrine hormones

What are the functions of the pituitary gland?

Hormones secreted by the Pituitary Gland have a lot of functions in the human body such as:

• Production of breast milk
• Thyroid gland function
• Temperature regulation
• Blood pressure regulation
• Metabolism (converting food to energy)
• Sex organ functions in both female and male
• Growth (excess HGH secretion leads to gigantism and acromegaly)
• Few aspects of pregnancy and childbirth
• Maintaining water balance by controlling re-absorption by kidneys
• Water and osmolarity regulation in body

An overview of the hormones and their functions

An explanation of the hormones

• Growth Hormone (GH) / Somatotropic hormone is a type of anabolic hormone that stimulates growth of all body tissues though its effect is more on the bone and skeletal muscle. The insulin-like growth factors (IGFs) helps in its action. The action might be direct or indirect. Fats are mobilized by the GH. It also inhibits glucose uptake, stimulates protein synthesis and aids metabolism. The secretion of the GH in the Pituitary Gland is regulated by the growth hormone releasing hormone (GHRH) and growth hormone inhibiting hormone (GHIH) or somatostatin.
• Hypersecretion of the Pituitary Gland hormone causes gigantism in children and acromegaly in adults. On the other hand, hyposecretion in children causes pituitary dwarfism. The thyroid gland’s activity and normal development is carried out by the Thyroid-stimulating hormone (TSH).
• Thyrotropin-releasing hormone (TRH) stimulates the secretion of the hormone while a negative feedback of the thyroid hormone inhibits it. The adrenal cortex releases corticosteroids when stimulated by Adrenocorticotropic hormone (ACTH). Again, the ACTH release is triggered by corticotrophin-releasing hormone (CRH). Rising glucocorticoid levels inhibits the release.
• Luteinizing hormone (LH) and follicle-stimulating hormone (FSH) regulate the functions of gonads in both male and female.
• Prolactin (PRL) promotes milk production in human females. Two hypothalamic hormones (oxytocin and antidiuretic hormone, ADH) are both stored and released by the neuropophysis. ADH excites the kidney tubules to reabsorb and preserve water, resulting in small volumes of highly concentrated urine and decreased plasma osmolarity. Hyposecretion of ADH results in diabetes insipidus. Oxytocin is a positive feedback mechanism as it stimulates powerful uterine contractions that cause labor and delivery of an infant and milk ejection in nursing women.
• Pituitary Gland also makes endorphin to relieve pain and alter mood.

Pituitary hormones and their functions

Thyroid Gland

The thyroid gland and its functions

The anterior throat hosts the thyroid gland. Colloid containing thyroglobulin is stored by the thyroid follicles. The thyroid hormone is derived from thyroglobulin (a glycoprotein).

The cellular metabolism rate is increased by the thyroid hormone (TH) containing triiodothyronine (T3) and thyroxine (T4). Oxygen use and heat production also rise consecutively. In order to inhibit the Pituitary Gland and hypothalamus, rising levels of thyroid hormone supply back. In the target tissues, most T4 is converted to T3, which is the more active form. Hyperthyroidism causes Grave’s disease. Cretinism in infants and myxoedema in adults are caused by hyposecretion.
 

Parathyroid gland

The parathyroid gland and its functions

The parathyroid hormone (PTH) that by targeting bones, kidneys and intestine increases blood calcium levels is secreted by the parathyroid gland situated on the dorsal end of the thyroid gland. Calcitonin finds its rival in PTH. Falling blood calcium levels triggers PTH release and rising levels inhibits the PTH.
 

Pancreas

The pancreas and its functions

The Pancreas is both an exocrine and endocrine gland. It is located close to the stomach, in the abdomen. Islets of langerhans (the endocrine portion) releases glucagon and insulin and other smaller amounts of hormones to the blood. When glucose levels in blood are not enough, Glucagon is released by the alpha cells which in turn stimulate the liver to release glucose in blood. The beta cells release insulin when blood levels of amino acids and glucose are rising. It makes the body cells increase the rate of glucose uptake and metabolism. Diabetes mellitus disease is the result of hypo-secretion of insulin. The cardinal signs are polydipsia, polyuria and polyphagia.
 

Gonads

The gonads and its functions

The female ovaries located in the pelvic cavity release two main hormones. Under the influence of FSH, estrogen secretion by the ovarian follicles begins at puberty. The maturation of the female reproductive system and development of the secondary sex characteristics are brought about by estrogen. Progesterone is released as a result of high blood levels of LH. The menstrual cycle comes to life when progesterone works with estrogens. Similarly, the male testes produce testosterone at puberty in response to LH. Maturation of male reproductive organs and development of secondary sex characteristics are brought about Testosterone. It also helps in the production of sperm.
 

Pineal Gland (epiphysis)

The pineal gland and its functions

Located in the diencephalon, the pineal gland’s primary hormone is melatonin, which influences daily rhythms and may have an antigonadotropic effect in humans.
 

What can go wrong with the pituitary gland?

The underlining problems associated with a pituitary dysfunction

Most problems associated with the Pituitary Gland are the result of the development of a tumor. A pituitary tumor is an abnormal growth in the Pituitary Gland. The tumors might produce excessive amounts of a particular pituitary hormone while at the same time reduce or rather hinder the production of other hormones and also compress neighboring tissues. Most of the pituitary gland tumors are generally benign.
 

The Pituitary Gland is in close proximity to optic nerves and blood vessels. Compression of tumors can cause visual impairment, massive headaches, fatigue, loss of vision and seizures. There are numerous other signs and symptoms related to diminished hormone production. Up to 20% of people have pituitary tumors though in many, the tumors don’t cause any problems and may not be even diagnosed in the person’s lifetime.
 

The gradual growth of the tumor results in the damage of pituitary’s hormone-releasing cells causing hypopituitarism. The causes of the tumors are not really known though some Pituitary Gland tumors are the part of a hereditary disorder called Multiple Endocrine Neoplasia I (MEN I). There are various other types that can be found in the same part of the head as a pituitary tumor. They are Cysts, Metastatic tumors that spread from cancer in another part of the body, Germinomas tumors and Craniopharyngiomas tumors.
 
For a comprehensive read about Tumors of the pituitary please read Pituitary Tumors

An overview of the pituitary gland

Conditions Related to Pituitary Dysfunction

Other disorders of the Pituitary Gland are:

• Hyperprolactinemia: It is either caused by a pituitary tumor that produces prolactin or a tumor that stops the regulation of prolactin production. It can cause galactorrhea and amenorrhea, and in men reduced sex drive and impotence.
• Growth Hormone Deficiency: Also occurs due to a variety of causes. In children it causes late growth and a short stature and in adults it can lead to decreased bone mass, muscular weakness, obesity and fatigue.
• Empty Sella Syndrome: The structure that surrounds the pituitary gland is called the sella. An increase in the size of the sella puts pressure on the Pituitary Gland. As a result, the pituitary gland may shrink in response and hormone production decreases leading to hypopituitarism.
• Hypopituitarism: It can be caused due to various reasons including trauma, infection, tumors, decreased pituitary blood supply, radiation, sarcoidosis, an autoimmune process, surgical removal of the pituitary, or a side effect of pituitary surgery. These result in a general decrease in pituitary hormone production.
• Craniopharyngioma: the most common benign tumor puts pressure on the pituitary causing hypopituitarism, headaches, visual disturbances, and delayed growth.
• Cushing’s syndrome: caused as a result of excess ACTH production by a pituitary tumor.
• Nelson’s syndrome: due to the removal of both adrenal glands because of Cushing’s syndrome.
• Diabetes insipidus: due to decreased production of ADH by the hypothalamus.
• Kallman’s syndrome: irregular release of gonadotropin-releasing hormone (GnRH) leading to deficient FSH and LH production.
• Multiple Endocrine Neoplasia I (MEN I): is a disorder which leads to an imbalance in the Endocrine glands.
• Sheehan’s syndrome: caused due to the increase of the Pituitary Gland during pregnancy.
• Pituitary Infarction: caused by restricted blood supple to the pituitary.

 
For a comprehensive list of Disorders please read Pituitary Gland Disorders
 

If you find to be suffering from any of the above symptoms, get immediate medical attention as it might be that your Pituitary Gland is not functioning properly. Other rare pituitary disorders are Acromegaly and Gigantism caused due to excess growth hormone production usually because of a tumor.

Conditions related to a pituitary dysfuntion

Hormone replacement if the body is not making enough?

If the Pituitary Gland is not producing enough hormones and causing hypopituitarism, the doctor may advise hormone replacement. The process no doubt is a complex one and might be seen as a burden but hypopituitarism is a serious problem and though hormone replacements may not be perfect, at least they can restore some part of your health, improve your well-being and aid in better circulation of target gland hormones.
 

Endoscopic Pituitary Surgery

Endoscopic Pituitary Surgery is done to treat acoustic craniopharyngiomas, arachnoid cysts, neuromas, meningiomas, pineal tumors, trigeminal neuralgia and hemifacial spasm. These techniques result in less complication, less pain and faster recovery than ‘open brain’ craniotomies. Discuss with your doctor the expected benefits and the desired outcome as it will help the patient cope up with the problem better.