Endocrine system is the group of organs that helps to regulate the body through the use of chemical messengers called hormones . The organs of the endocrine system make hormones and secrete (release) them into the blood for delivery to the rest of the body. Hormones help to coordinate and control body processes. The endocrine system is one of the body’s major organ systems.
The endocrine system works with the nervous system to regulate such activities as metabolism , digestion , reproduction , and sleep . Together, the endocrine and nervous systems serve as the control systems of the body.
The major organs
of the endocrine system are called glands . Endocrine glands are different from other glands in the body, such as salivary glands. Such glands use tubes called ducts to transport their secretions. Endocrine glands, by contrast, secrete hormones directly into the bloodstream. The blood vessels carry the hormones throughout the body. The main endocrine organs include the pituitary gland , the two adrenal glands , the thyroid gland , the parathyroid glands , the pineal gland , and the gonads (sex glands).
The pituitary gland
is sometimes called the master gland. It secretes eight hormones that control many body functions, including the activities of other endocrine glands. The pituitary gland is about the size of a pea. It lies under the brain near the center of the skull.
The pituitary gland is divided into two lobes. The anterior (front) lobe makes and secretes six hormones: (1) growth hormone (GH), (2) thyroid stimulating hormone (TSH), (3) adrenocorticotropic hormone ( ACTH ), (4) prolactin (PRL), (5) follicle stimulating hormone (FSH), and (6) luteinizing hormone (LH). Most of these hormones control the activities of other hormone-releasing glands. Growth hormone regulates growth and helps control the way food is utilized. Prolactin stimulates milk production in nursing mothers.
The posterior (rear) lobe stores and secretes the hormones oxytocin and antidiuretic hormone (ADH), also called vasopressin. Vasopressin stimulates the kidneys to retain sufficient water for the body. Oxytocin is associated with reproduction and with social interaction.
The adrenal glands
sit atop each kidney. They secrete a group of hormones called corticosteroids that control water and mineral levels in the body as well as metabolism. The adrenal glands also secrete the hormones epinephrine (adrenaline) and norepinephrine, which help prepare the body for stressful situations.
The thyroid gland and parathyroid glands
are located in the front of the neck. The thyroid gland produces thyroid hormone, which increases metabolism in all cells of the body. This gland also secretes the hormone calcitonin, which regulates calcium in blood and bone tissue.
The four small parathyroid glands are located on the back surface of the thyroid gland. These glands secrete parathyroid hormone (PTH), which also regulates calcium in blood and bone tissue. Calcitonin decreases levels of calcium in the blood and increases bone production. PTH does the opposite, increasing blood calcium levels and decreasing bone production.
The pineal gland
is a small but important gland located in the brain. It secretes melatonin , a hormone important in the control of cycles of sleep and waking.
The gonads
or sex glands are the testes in males and the ovaries in females. These organs are part of the reproductive system as well as the endocrine system. Their endocrine function is to secrete hormones that help regulate reproduction. The testes secrete testosterone and the ovaries secrete estrogen and progesterone .
Other organs.
Many organs that are part of other body systems also secrete hormones and can be considered part of the endocrine system. These include the stomach, pancreas, liver, kidneys, and even the heart.
