The endocrine system is the collection of glands that produce hormones that regulate metabolism, growth and development, tissue function, sexual function, reproduction, sleep, and mood, among other things.

The word endocrine derives from the Greek words “endo,” meaning within, and “crinis,” meaning to secrete.  In general, a gland selects and removes materials from the blood, processes them and secretes the finished chemical product for use somewhere in the body.

The endocrine system is based on the ductless gland that secrete their hormone directly into blood stream. The pituitary gland is known as master gland of endocrine system.

• Hypothalamus
• Pineal Gland
• Pituitary Gland
• Thyroid
• Parathyroid
• Thymus
• Adrenal
• Pancreas
• Ovaries
• Testes

Hypothalamus

• The hypothalamus  is a portion of the brain. Hypothalamus is to link the nervous system to the endocrine system via the pituitary gland (hypophysis).
• The hormones from the hypothalamus govern physiologic functions such as temperature regulation, thirst, hunger, sleep, mood, sex drive, and the release of other hormones within the body.

Pituitary Gland

The pituitary gland is a pea-sized structure located at the base of the brain, just below the hypothalamus, to which it is attached via nerve fibers.

That is main endocrine gland. It is a small structure in the head. It is called the master gland because it produces hormones that control other glands and many body functions including growth. The pituitary consists of :

1. Anterior Pituitary Gland
2. Posterior Pituitary Gland

Anterior Pituitary Gland

The anterior pituitary ( adenohypophysis) is the glandular and present in anterior lobe of pituitary. It secretes following hormones:-

Growth Hormone (GH):- The growth hormone stimulate growth of bones and muscle. It stimulate cell function.

Thyroid Stimulating Hormone (TSH):-  It produce two hormones: triiodothyronine (T3) and thyroxine (T4). T3 and T4 help control your body’s metabolism.

Adrenocorticotropic Hormone (ACTH):-  Its stimulate the production and release of cortisol from the cortex of the adrenal gland.

Melanocyte Stimulating Hormone (MSH):- The MSH stimulates melanocytes for the production of melanin which is responsible for darkening of skin.

Luteinizing Hormone (LH):- The LH stimulates the production of testosterone in males and progesterone in female.

Prolactin:- The prolactin provides stimulation for milk production in mammary glands of female after child birth.

Posterior Pituitary Gland

The back portion of the pituitary, a small gland in the head called the neurohypophysis.  It secretes following hormones:-

Antidiuretic Hormone (Vasopressin):- A pituitary hormone which acts to promote the retention of water by the kidneys and increase blood pressure. Diabetes insipidus is caused by a lack of antidiuretic hormone (ADH), also called vasopressin, which prevents dehydration, or the kidney’s inability to respond to ADH. ADH enables the kidneys to retain water in the body.

Oxytocin:- A hormone released by the pituitary gland that causes increased contraction of the uterus during labour and stimulates the ejection of milk into the ducts of the breasts.

Thyroid Gland

The thyroid gland is a butterfly-shaped organ located in the base of neck. It releases hormones that control metabolism. Calcitonin is also secreted by the thyroid gland that reduces the concentration of blood calcium level when it has risen to an above normal level.

When the thyroid gland is overactive known as hyperthyroidism. The body’s processes speed up and can cause nervousness, anxiety, rapid heartbeat, hand tremor, excessive sweating, weight loss, and sleep problems, among other symptoms.

When the thyroid gland is underactive called hypothyroidism. Its deficiency of thyroid hormones can disrupt such things as heart rate, body temperature and all aspects of metabolism. Hypothyroidism is most prevalent in older women.

Parathyroid Gland

Parathyroid glands are small glands of the endocrine system which are located in the neck behind the thyroid. Parathyroid glands control the amount of calcium in bones and blood.

Calcium is the most important element in our bodies , so calcium is regulated very carefully. Parathyroid glands control the calcium.

Hyperactivity of parathyroid gland may cause hyperparathyroidism whereas the parathyroid gland is underactive called hypoparathyroidism.

Adrenal Gland

The adrenal glands are two glands that present on the top of kidneys that are made up of two distinct parts.

• The adrenal cortex—the outer part of the gland—produces hormones that are vital to life, such as cortisol (which helps regulate metabolism and helps your body respond to stress) and aldosterone (which helps control blood pressure).
• The adrenal medulla—the inner part of the gland—produces nonessential hormones, such as adrenaline which helps your body react to stress.

Adrenal glands are also known as suprarenal glands and secreting the hormone adrenaline, which rapidly prepares body to spring into action in a stressful situation.

The adrenal cortex is divided into following three layers:

1. Mineralocorticoids: The most important of which is aldosterone and secreted by outer layer. This hormone helps to maintain the body’s salt and water levels which, in turn, regulates blood pressure.
2. Glucocorticoids: predominantly cortisol and secreted by middle layer. This hormone is involved in the stress response and also helps to regulate body metabolism. Cortisol stimulates glucose production by mobilising amino acids and free fatty acids. Cortisol also has significant anti-inflammatory effects.
3. Adrenal androgens: male sex hormones mainly dehydroepiandrosterone (DHEA) and testosterone and secreted by inner layer.

Addisons’disease is caused by deficiency of adrenal cortex hormone and overactivity of adrenal cortex hormone may cause cushing syndrome.

Pancreas

The pancreas is an organ located in the abdomen. It plays an essential role in converting the food into fuel for the body’s cells. The pancreas has two main functions: an exocrine function that helps in digestion and an endocrine function that regulates blood sugar.

The pancreas contains exocrine glands that produce enzymes important to digestion. These enzymes include trypsin and chymotrypsin to digest proteins; amylase for the digestion of carbohydrates; and lipase to break down fats. 

The endocrine component of the pancreas consists of islet cells (islets of Langerhans) that create and release important hormones directly into the bloodstream. Two of the main pancreatic hormones are insulin, which acts to lower blood sugar, and glucagon, which acts to raise blood sugar. 

Testis and Ovaries

The testes secrete testosterone, which is necessary for proper physical development in boys. In adulthood, testosterone maintains libido, muscle strength, and bone density. Disorders of the testes are caused by too little testosterone production.

The ovaries  are the female gonads. The ovaries are paired organs that are found in the pelvic cavity. The ovaries are the organs that produce the egg.

The ovaries also produce steroid hormones, Estrogen is a steroid hormone that helps control and guide female sexual development.

Thymus Gland

The thymus is composed of two identical lobes and is located anatomically in the anterior superior mediastinum, in front of the heart and behind the sternum.

The thymus gland, located behind sternum and between lungs, is only active until puberty. After puberty, the starts to slowly shrink and become replaced by fat.

Thymosin is the hormone of the thymus, and it stimulates the development of disease-fighting T cells.

Pineal Gland

The pineal gland, also known as the “pineal body,” is a small endocrine gland. It is located on the back portion of the third cerebral ventricle of the brain, which is a fluid-filled space in the brain.

The pineal gland produces the hormone melatonin that helps to regulate the human sleep-wake cycle known as the circadian rhythm.