Glossary of Endocrine System Terms and Terminology

  • Hormones: Natural chemical substances that control, manage and coordinate several bodily functions throughout the body
  • Gland: An organ that secretes and releases a substance.
  • Exocrine gland: A gland that secretes a substance to the exterior part of the body
  • Endocrine gland: A gland that secretes and releases hormones into the blood which goes to target organ(s) in the body
  • Homeostasis: Bodily balance
  • The hypothalamus: Also referred to as the "master gland", this endocrine system gland is housed near the base of the skull just above the pituitary gland and it performs several roles
  • The pituitary gland: The endocrine system gland that is housed near the base of the skull just below the hypothalamus gland that performs several roles
  • The pineal gland: The small endocrine system gland that is in the brain and relatively close to the hypothalamus and the pituitary glands of the endocrine system and that regulates sleep and wake cycles
  • Circadian rhythm: The normal human being's 24 hour cycle of sleep and wakefulness.
  • Diurnal beings: Day time active and nighttime sleep beings
  • Nocturnal beings: Nighttime active and daytime sleep beings
  • The thyroid: The endocrine system gland that lies in the neck and secretes several endocrine hormones
  • The parathyroids: The four endocrine system glands that lie on both sides of the thyroid gland in the neck and that control the amount of circulating calcium and phosphorous, which are two electrolytes
  • Adrenal gland: The endocrine system glands that lies in the abdominal area above the diaphragm and just above the kidneys that secrete several hormones from its cortex and its medulla
  • Adrenal cortex: The outer layer of the adrenal glands that secretes androgen, aldosterone and cortisol
  • Adrenal medulla: The inner layer of the adrenal glands that secretes adrenaline, noradrenaline and catecholamine
  • The pancreas: The endocrine system gland that is located behind the stomach that plays an important role in our control of blood sugar with insulin from this gland
  • The ovaries: The endocrine system and reproductive system gland that produces progesterone, estrogen, inhibin and androstenedione
  • Progesterone: The ovarian hormone that is secreted by the ovaries and plays a role in the menstrual cycle and the preparation of the uterus for the implantation of the fertilized egg or ovum
  • Estrogen: The ovarian hormone that is secreted by the ovaries and plays a role in terms of the development of secondary sexual characteristics such as the breasts, at the time of female puberty, or pubescence
  • Inhibin: The ovarian hormone that is secreted by the ovaries and plays a role in the body in terms of the inhibition of follicle stimulating hormone among females
  • Androstenedione: The ovarian hormone that is secreted by the ovaries and plays a role as an androgen hormone
  • The testes: The endocrine system gland that produces androgens, particularly testosterone, and, as a reproductive organ, the testes also produces and manufactures sperm
  • Diabetes insipidus: A pituitary gland disorder
  • Acromegaly: A pituitary gland disorder
  • Gigantism: A pituitary gland disorder.
  • Syndrome of Inappropriate Antidiuretic Hormone Secretion (SIADH): A pituitary gland disorder
  • Hyperthyroidism: An overactive thyroid gland
  • Hypothyroidism: An underactive thyroid gland
  • Cushing's syndrome: Disorder that results from the over production of cortisol by the adrenal glands
  • Addison's disease: Disorder that results from the under production of cortisol by the adrenal glands

The Role of the Endocrine System

The role of the endocrine system, simply stated, is to provide the body with the hormones that are needed to sustain life with the provision of bodily functioning and hormonal balance and to create life. For example, the adrenal glands secrete hormones that are necessary for the "Fight and Flight" response to stress and the hormones secreted by the breast provide milk for a newborn baby.

This complex system of glands works primarily on the feedback it receives from the blood stream in terms of the current level of circulating hormones. For example, when the level of thyroid stimulating hormone drops, the pituitary gland is stimulated to produce more of thyroid stimulating hormone; and, when, the level of thyroid stimulating hormone is too high or elevated, the pituitary gland stops stimulating the thyroid to produce this hormone.

The balance of hormones in the body should be sufficient enough to perform its roles but not over the normal limits of the hormone. Hypo, or low, and hyper, or high, secretion of the endocrine glands leads to physiological problems.

Some endocrine glands like the adrenal glands occur in bilateral pairs, other endocrine glands are the only ones in the human body and some adrenal glands are gender or sex related and others are not.

For example, the body has two adrenal glands; one is on the left side of the body above the kidney and the other is on the right side of the body above the right kidney; the human body has only one pituitary gland; and females have ovaries as endocrine glands and males have testes as endocrine glands. All endocrine glands, including the ovaries and the testes secrete hormones.

The hormones that the endocrine glands secrete are natural substances that control, manage and coordinate several bodily functions throughout the body.

Endocrine glands are distinctly different from exocrine glands. Endocrine glands secrete hormones to an internal part of the body; and exocrine glands secrete substances to the exterior or near the surface of the body. Salivary glands with the digestive process and sebaceous glands in the integumentary system, as previously discussed with the Gastrointestinal System and the Integumentary System are exocrine glands. Salivary glands secrete saliva into the mouth and not the blood and sebaceous glands secrete an oily substance on the skin.

The Parts of the Endocrine System

The endocrine system consists of hormones and the endocrine glands. Hormones are natural substances that control, manage and coordinate several bodily functions throughout the body.

The endocrine system consists of these glands:

  • The hypothalamus
  • The pituitary gland
  • The pineal gland
  • The thyroid
  • The parathyroid
  • The adrenal glands
  • The pancreas
  • The ovaries
  • The testes

In the past, the thymus was also considered an endocrine gland; however, it is not now considered an endocrine gland because, although the thymus plays a role in the immune system of the body, it does not secrete hormones.

The Hypothalamus

The hypothalamus performs several roles and functions. As you can see in the pictures above and below, the hypothalamus is seated within the cranium and the brain. The hypothalamus, as shown in the pictures above, lies in close anatomical proximity to and just above the pituitary gland, another endocrine gland, near the base or bottom of the brain.

The hypothalamus, quite similar to the pituitary gland, as discussed below, plays an important role in terms of the body's homeostasis, or normal balance. Again, like the pituitary gland, the hypothalamus secretes and releases hormones that slow down and stop the release of hormones from other endocrine glands and it stimulates the release of hormones from other endocrine glands, as based on the body's needs and the blood levels of these hormones in the blood.

When a particular hormone in the blood is too low, as based on the feedback that the hypothalamus gets, the hypothalamus, like the pituitary gland, releases a hormone to another endocrine gland to stimulate this gland to secrete and produce more of their hormone to raise the level of the particular hormone. Similarly, when a particular hormone in the blood is too high, the hypothalamus, like the pituitary gland, halts and stops the release of that stimulating hormone to another endocrine gland in order to lower the level of the particular hormone in the blood. This feedback maintains the body's hormonal homeostasis, or bodily balance.

The hypothalamus is the gateway from and to the nervous system and the endocrine system. For example, when sensory stimulation is received from the nervous system, this message is sent to the hypothalamus of the endocrine system.

The hypothalamus secretes the hormones, including its releasing hormones, as shown and listed in the picture above, and with these hormones, the hypothalamus controls and coordinates the:

  • Maintenance of the person's bodily temperature within its normal range
  • Maintenance of the person's fluid and electrolytes balances with antidiuretic hormone
  • Stimulation of the pituitary gland to release hormones, including its stimulating hormones
  • Gastrointestinal secretions from the intestines and the stomach
  • Ovarian and testicular functions with gonadotropin releasing hormone
  • Metabolism with corticotrophin releasing hormone and thyroid stimulating hormone
  • Human milk production with oxytocin and prolactin releasing hormone

The Pituitary Gland

Located at the base of the brain, the pituitary gland is protected by a bony structure called the Sella turcica of the sphenoid bone.

The pituitary gland, as shown in the two pictures above, is also called the master gland because the pituitary gland, unlike other glands in the endocrine system, controls the secretion of several other glands included in the endocrine system.

For example, the pituitary gland plays an important role in the secretion of these hormones, among others, when the pituitary gland secretes its "simulating hormones:

  • Thyroid hormone from the thyroid glands when the pituitary gland secretes thyroid stimulating hormone
  • Cortisol from the adrenal glands when the pituitary gland secretes adrenocorticotropin

The pituitary gland also secretes other hormones, as listed in the picture above.

Anatomically, this tiny gland is housed at the base of the brain, as shown in the pictures above.

In summary, the pituitary gland controls and coordinates:

  • Bodily fluid balance
  • Blood pressure
  • The maturation of sexual organs
  • Growth
  • The labor process during childbirth
  • The production of human milk
  • Metabolism

The Pineal Gland

Diagram of pituitary and pineal glands in the human brain.

The pineal gland, as shown in the pictures above, is a small endocrine gland that lies in the area of the brain that is relatively close to the hypothalamus and the pituitary glands of the endocrine system.

The primary role that the pineal gland performs is the bodily control and coordination of sleep cycles and the internal clock of the body which is referred to as circadian rhythm. Simply defined, the circadian rhythm is the normal human being's 24 hour cycle of sleep and wakefulness. Humans are normal diurnal or day time activity beings and nighttime sleep beings, unlike nocturnal beings that have nighttime activity and daytime wakefulness.

The secretion of melatonin is stimulated and released with darkness, as sensed by the optic nerve, and it is inhibited when it is stimulated by light, as sensed by the optic nerve.

The Thyroid Gland

The human thyroid as viewed from the front, with arteries visible.

The thyroid gland, as shown in the picture above, is somewhat shaped like angel wings or a butterfly. It has one major section on each side of the throat just above the trachea. These bilateral major sections, or lobes, are connected to each other with a thin connecting area called the isthmus. Although it may appear upon first glance that there are two bilateral thyroid glands, there is only one.

The thyroid gland, as shown in the diagram below, performs several functions.

The thyroid hormones T3 and T4 have a number of metabolic, cardiovascular and developmental effects on the body. The production is stimulated by release of thyroid stimulating hormone (TSH), which in turn depends on release of thyrotropin releasing hormone (TRH). Every downstream hormone has negative feedback and decreases the level of the hormone that stimulates its release.

The thyroid gland produces and secretes triiodothyronine hormone that consists of T3 and T4, which are iodine containing hormones, and thyroxine when the thyroid gland is prompted and stimulated to produce and release these hormones by the thyroid stimulating hormone of the pituitary gland.

It also produces calcitonin which plays a role in the levels of blood circulating calcium. Simply states, the levels of calcitonin is lowered when the osteoclasts of the bones, as discussed above in the section entitled the Skeletal System, break down the bone in its normal process of bone regeneration. .

The thyroid gland plays a role in terms of the body's:

  • Metabolism
  • Basal metabolic rate
  • The cardiac system's function in terms of pulse rate, blood volume, bodily temperature, breathing, and oxygen utilization
  • Physical growth and growth rate
  • Sexual functioning

The Parathyroid Glands

Diagram showing structures in the human neck. The four green shaded areas represent the most common position of the parathyroid glands, which are generally four in number and situated behind the lateral lobes of the thyroid gland (shaded orange).

Thyroid and parathyroids as viewed from the back of the neck.

The parathyroid glands, as shown in the pictures above, are two pairs of glands found bilaterally on both sides of the neck area just behind the lobes of the thyroid gland. As a result of the proximity of the parathyroid glands and the thyroid gland, the parathyroid gland derives their name from "para" which means around and "thyroid" which is the thyroid gland.

The body has four parathyroid glands and this characteristic makes the parathyroid glands quite unique when compared and contrasted to the other glands of the endocrine system. ,

The primary and foremost role of the parathyroid glands is to control the amount of circulating calcium and phosphorous, which are two electrolytes. Calcium and phosphate play a vital role in terms of bone, teeth and the nervous system.

This control in the circulating blood is accomplished with the parathyroid glands' production and secretion of parathyroid hormone.

The Adrenal Glands

The adrenal glands, which are in the abdominal area, are located bilaterally just above the right and left kidneys and just above the diaphragm, as shown in the pictures above.

The adrenal glands consist of two major layers which are the cortex, the outermost layer of the adrenal glands, and the medulla which is the inner core of the adrenal glands. Each of these two layers performs a different role and they also secrete different hormones.

The cortex secretes:

  • Androgen which is a male hormone
  • Aldosterone which controls a person's blood pressure and fluid balance
  • Cortisol which regulates and coordinates metabolism

The medulla secretes stress reaction hormones such as:

  • Adrenaline
  • Noradrenaline
  • Catecholamine

The Pancreas

Anatomy of the pancreas.

The pancreas, as shown in the pictures above, is located in the abdominal cavity. Anatomically, it is located behind the stomach and the pancreas and it has three sections or parts which are the head of the pancreas, the neck of the pancreas and the body of the pancreas.

The pancreas has a somewhat different composition than other endocrine glands. A part of the pancreas serves as an endocrine gland and another part of the pancreas serves as a digestive organ and exocrine body, as discussed above in the previous section entitled The Digestive System. In this respect, the pancreas is often called a mixed gland because of these different functions.

As an endocrine gland, the islet cells of the pancreas, also referred to as the pancreatic islets and the islets of Langerhans, secrete glucagon, insulin, pancreatic polypeptide and somatostatin as listed in one of the pictures above. In terms of the pancreas' digestive system role, the pancreas produces and releases pancreatic, digestive enzymes and juices that break down foods as they enter the small intestine, as more fully described previously with the Digestive System.

The Testes & Ovaries

Blood supply of the human female reproductive organs. The left ovary is the oval shaped structure visible above the label "ovarian arteries".

The ovaries of the female are, in some ways, similar to the male gender's testes. Both the ovaries and the testes are endocrine glands and gonads, which is defined as a sex and reproduction glandular structure.

Like testes, females have two bilateral ovaries, each of which lie on either the left or right side of the uterus. One end of the ovary is at the fallopian tube and the other end of the ovary is attached to the uterus.

The ovaries, as an endocrine gland produces, progesterone, estrogen, inhibin and androstenedione, as listed in the picture above. Progesterone, secreted by the ovaries, plays a role in the menstrual cycle and the preparation of the uterus for the implantation of the fertilized egg or ovum; estrogen plays a role in terms of the development of secondary sexual characteristics such as the breasts, at the time of female puberty, or pubescence. Inhibin plays a role in the body in terms of the inhibition of follicle stimulating hormone among females and the inhibition of the development of sperm in the male and androstenedione, which is an androgen that is weaker than testosterone.

Diagram of male (human) testicles.

The testes, or testicles, of the male are, as suggested above, are similar to the female gender's ovaries. Both the ovaries and the testes are endocrine glands and gonads, which is defined as a sex and reproduction glandular structure.

Like ovaries, males have two bilateral testes, each of which lay on either the left or right side of the body next to the penis, as shown in the picture above.

The testes, as an endocrine gland produce androgens, particularly testosterone, and, as a reproductive organ, the testes also produces and manufactures sperm, the male cell of reproduction which joins with the ova, the female cell of reproduction, to procreate and fertilize the egg. These endocrine gland and reproductive functions of the testes are stimulated by the pituitary gland's secretion of luteinizing hormone, testosterone and follicle stimulating hormone, respectively.

Disorders Affecting the Endocrine System

  • Diabetes insipidus
  • Acromegaly
  • Gigantism
  • Syndrome of Inappropriate Antidiuretic Hormone Secretion (SIADH)
  • Hyperthyroidism
  • Hypothyroidism
  • Cushing's syndrome
  • Addison's disease

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