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The Endocrine System

FEBRUARY 24, 2016

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What Is the Endocrine System?
In general, the endocrine system is in charge of body processes that happen slowly, such as cell growth. Faster processes like breathing and body movement are controlled by the nervous system. They often work together to help the body function properly. It influences almost every cell, organ, and function and plays a role in regulating mood, growth and development, tissue function, metabolism, and sexual and reproductive processes.

The foundations of the endocrine system are the hormones and glands. As chemical messengers, the hormones transfer information and instructions from one set of cells to another. Many different hormones move through the bloodstream as each type of hormone is designed to affect only certain cells.

Endocrine glands shouldn’t be confused with exocrine glands. Exocrine glands, such as sweat and salivary glands, secrete externally and internally via ducts. Endocrine glands secrete hormones internally, using the bloodstream.


A gland is a group of cells that produces and secretes chemicals. A gland selects and removes materials from the blood, processes them, and secretes the finished chemical product for use in the body.

Some types of glands release their secretions in specific areas. For instance, exocrine glands like the sweat and salivary glands release secretions in the skin or inside the mouth. Endocrine glands, on the other hand, release more than 20 major hormones directly into the bloodstream where they can be transported to other body parts.

The Endocrine System
The endocrine system is made of many glands. These glands secrete hormones to regulate many bodily functions, including growth and metabolism. Simply put, the endocrine system is a network of glands that secrete chemicals called hormones to help the body function properly.

The endocrine system helps control the following processes:

1. Growth and development
2. Homeostasis (the internal balance of body systems)
3. Metabolism (body energy levels)
4. Reproduction
5. Response to stimuli (stress and/or injury)

Major Endocrine Glands

The hypothalamus in the brain releases hormones that control hunger, thirst, body temperature and anger. These hypothalamus’ "releasing" hormones regulate the secretion of other hormones in the pituitary gland, which in turn affects other endocrine glands. The hypothalamus’ “inhibiting” hormones turn off the secretion of some hormones from the pituitary.

The pituitary gland is located in the brain, directly under the hypothalamus. It plays a large role in the endocrine system as it releases the maximum number of hormones, which affect the secretions of other glands as well. That's why, the pituitry is know as the Master Gland in the body.     

Anterior Pituitary Gland
The hormones from the anterior pituitary gland are responsible for growth (growth hormone), reactions to stress (adrenocorticotrophic hormone- ACTH), metabolism (thyroid stimulating hormone) and reproductive function (follicle stimulating hormone and luteinizing hormone). Hormones from the anterior pituitary also stimulate the release of hormones from the gonads, thyroid and adrenal glands. Finally, the anterior pituitary secretes a hormone called prolactin, which stimulates milk production in breasts.

Posterior Pituitary Gland
The posterior pituitary gland produces a hormone (anti-diuretic hormone) to regulate the level of water in the body. This gland also secretes a second hormone oxytocin that aids in childbirth (parturition) and stimulates the release of milk from a nursing mother.

Pineal Gland
The pineal gland, in the brain, secretes the hormone melatonin, which plays a role in the sleep-wake cycle.

Thyroid Gland
The thyroid glands, on either side of the throat, secrete two hormones - thyroxine and triodothyronine. These hormones play a role in metabolism, body temperature, cell growth, and cell differentiation.

Parathyroid Gland
The parathyroid glands are tiny glands at the back of the thyroid glands. They secrete parathyroid hormone which regulates the levels of calcium.

Adrenal Glands
There are two adrenal glands, one above each kidney. They produce the hormones cortisol and aldosterone. Cortisol is released when the body undergoes stress or exercise, and it aids in metabolism. Aldosterone regulates the levels of sodium in the body and this, in turn, influences the amount of water in the body.

The adrenal gland produces epinephrine and norepinephrine, also called adrenaline and noradrenaline. The primary hormone released during excitement or stress is epinephrine. This release is commonly known as an “adrenaline rush” and is an important part of the fight-or-flight response.

The pancreas secretes digestive juices to help break down foods. Its endocrine function is to control blood sugar levels by releasing the hormones insulin and glucagon. Insulin transports glucose from the bloodstream into the cells, thereby decreasing blood sugar levels. Glucagon, on the other hand, causes stored glucose from the cells and the liver to be released into the bloodstream, raising the sugar levels.

The gonads refer to the reproductive organs. Male gonads are known as testes and female gonads are called ovaries. The testes secrete a hormone called testosterone, which stimulates the production of sperm and secondary male sex characteristics, such as facial and body hair.  The ovaries secrete several hormones, namely estrogen and progesterone. Estrogen stimulates the maturation of eggs in the ovaries. Together, estrogen and progesterone regulate breast development during puberty and the menstrual cycle.

The thymus is just behind the breastbone and secretes thymosins, which helps regulate immune function.


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