A gland is an organ which produces and releases substances that perform a specific function in the body. Though we have many glands throughout the body, they fall into two types: endocrine and exocrine.
Endocrine glandsEndocrine glands are ductless glands and release the substances that they make (hormones) directly into the bloodstream. These hormones are chemicals that affect a lot of the bodily functions ranging from: growth and development, metabolism, mood, reproduction etc.
1) Pituitary glandThe pituitary gland is a pea-sized gland at the base of the brain, just behind the bridge of the nose. It's controlled by the hypothalamus, which sits just above it.
The pituitary gland is often called the master gland because it controls a number of other hormone glands, including: thyroid, adrenal gland, testes ovaries etc.
It consists of an anterior portion that produces hormones and a posterior portion that has many neural links.
The pituitary gland stimulates the adrenal gland to secrete cortisol, a steroid hormone that controls a range of activities from controlling the body's metabolism to stimulating blood pressure.
Metabolism is a term that is used to describe all chemical reactions involved in maintaining the living state of the cells and the organism. Metabolism can be conveniently divided into two categories:
Catabolism: the breakdown of molecules to obtain energy
Anabolism: the synthesis of all compounds needed by the cells
The pituitary gland also secretes prolactin, which stimulates the production of milk.
2) Thyroid glandYour thyroid gland is located in the front of neck, just below the larynx. It measures approximately two inches and has a shape similar to a butterfly.
It secretes hormones that affect virtually every tissue in your body. Thyroid hormones egulate your metabolism (T3 and T4), heart, and digestive function. They also play a role in brain and nerve development, muscle control, and mood.
Your thyroid function is controlled by the pituitary, which is a small gland at the base of the brain.
3) Parathyroid glandsThere are four parathyroid glands that are embedded in the thyroid gland. The parathyroid gland secretes a hormone called parathormone which helps to regulate calcium and phosphate levels in the blood.
Sometimes, when the gland produces excess parathyroid hormones, it can have negative effects such as brittle bones and kidney stones.
4) Adrenal glandThe adrenal glands are located at the top of each kidney and are not larger than a walnut. They produce over 150 hormones, some of which include: cortisol, aldosterone, adrenaline, androgens etc.
The hormones produced by the adrenal glands have several important functions: control blood sugar, burn fat and protein, regulate blood pressure, react to stressors.
Adrenaline is a hormone released from the adrenal glands that prepares the body for fight or flight.
It is a stress hormon that helps the body to either face a dangerous situation or to avoid it altogether. It does this by - increasing blood sugar levels, increasing the blood supply to the muscles, dilating (wider) the pupils, increasing the heart rate and tightening the jaw muscles.
5) PancreasThe pancreas is a long (6 inches), flat organ located in your abdomen, it is made up of two types of glands: exocrine and endocrine. The pancreas is surrounded by the small intestine, stomach, liver, gallbladder, and spleen.
The pancreas plays an important role in converting the food you eat into fuel for your body's cells. It does this by producing digestive enzymes that are released into your small bowel to break down and digest food.
It also produces hormones such as insulin and glucagon - Insulin is produced by the β cells in the pancreas and it helps in regulating the blood glucose levels in the body from getting too high. The lack of insulin causes type 1 and type 2 diabetes.
The hormone glucagon is produced by α cells of the pancreas and it helps the body to prevent the glucose levels from dropping too low. Lack of glucagon leads to hypoglycemia.
Insulin becomes active when the blood glucose levels are high, and glucagon become active only when blood glucose levels are low.
6) Pineal glandThe pineal gland is located deep in the center between two halves of brain. It's function is not completely understood, but we do know that it secretes and regulates certain hormones, including melatonin.
Melatonin helps regulate the sleep patterns, which are also known as circadian rhythms.
The pineal gland also plays a role in the regulation of female hormones, which affect the menstrual cycle and fertility.
7) Hypothalamus glandThe hypothalamus functions as a communication center for the pituitary gland, sending signals and messages to the pituitary to produce and release hormones that trigger the production and release of other hormones.
It influences a number of your body's functions, including: temperature regulation, food intake, sleep and wakefulness, thirst, memory and emotional behavior.
8) GonadsSome glands are specific to males or females - the ovaries are specific to females and are located in the pelvic cavity, ovaries produce estrogen that is important for reproduction and female sex characteristics.
While the testes are specific to males, testes produce testosterone that is responsible for male sex characteristics.
Below are some examples of hormones that are produced by the endocrine system.
|adrenaline||adrenal||increases blood pressure, heart rate, and metabolism in reaction to stress|
|aldosterone||adrenal||controls the body?s salt and water balance|
|cortisol||adrenal||plays a role in stress response|
|dehydroepiandrosterone sulfate (DHEA)||adrenal||aids in production of body odor and growth of body hair during puberty|
|estrogen||ovary||works to regulate menstrual cycle, maintain pregnancy, and develop female sex characteristics; aids in sperm production|
|follicle stimulating hormone (FSH)||pituitary||controls the production of eggs and sperm|
|glucagon||pancreas||helps to increase levels of blood glucose|
|insulin||pancreas||helps to reduce your blood glucose levels|
|luteinizing hormone (LH)||pituitary||controls estrogen and testosterone production as well as ovulation|
|melatonin||pineal||controls sleep and wake cycles|
|oxytocin||pituitary||helps with lactation, childbirth, and mother-child bonding|
|parathyroid hormone||parathyroid||controls calcium levels in bones and blood|
|progesterone||ovary||helps to prepare the body for pregnancy when an egg is fertilized|
|prolactin||pituitary||promotes breast-milk production|
|testosterone||ovary, teste, adrenal||contributes to sex drive and body density in males and females as well as development of male sex characteristics|
|thyroid hormone||thyroid||help to control several body functions, including the rate of metabolism and energy levels|
Exocrine glandExocrine glands produce other substances - not hormones, that are released through ducts to the exterior of your body, such as sweat, saliva, and tears.
Exocrine glands do things like: regulate body temperature, protect skin and eyes, and even help mothers feed babies by producing breast milk.
1) Lacrimal GlandsThe lacrimal gland (tear gland) is an exocrine gland located above the eyeball, in the anterior part of the upper outer aspect of each orbit.
It secretes lacrimal fluid (tear fluid), a watery fluid isotonic to plasma, onto the surface of the eyeball.
This fluid forms the aqueous portion of a multilayered tear film that lubricates, protects and provides nutrients to the conjunctiva and cornea.
The lacrimal fluid ultimately drains through a series of ducts into the nasal cavity.
When produced in excess, lacrimal fluid forms tears.
2) Salivary GlandsThe salivary glands are exocrine glands that are positioned in the head, in and around the oral cavity and secrete their salivary contents into the mouth.
They contribute to digestion through the enzymes they excrete with saliva, mainly amylase that starts the digestion of carbohydrates.
3) LiverBile is a fluid that is made and released by the liver and stored in the gallbladder. Bile helps with digestion. It breaks down fats into fatty acids, which can be taken into the body by the digestive tract.
4) Mammary GlandsThe mammary gland is a highly evolved and specialized organ present in pairs, one on each side of the anterior chest wall.
The organ's primary function is to secrete milk. Though it is present in both sexes, it is well developed in females and rudimentary in males.
It is also a vital accessory organ of the female reproductive system.
5) Eccrine Sweat GlandsThe skin has two types of sweat glands: eccrine and apocrine. Eccrine glands occur over most of the body and open directly onto the surface of your skin.
Apocrine glands open into the hair follicle, leading to the surface of the skin. Apocrine glands develop in areas abundant in hair follicles, such as on the scalp, armpits and groin.