Hormones are the chemical messengers of the body. They are secreted by glands and travel through the circulatory system, where they act on target organs. There are several major endocrine glands in the human body: the pituitary regulates other endocrine glands; the thyroid controls the body's metabolism; the parathyroid regulates calcium levels; the adrenal gland responds to stress and low blood sugar; the pineal gland controls circadian rhythms; and the pancreas regulates blood glucose levels. In addition to these major endocrine glands, many other organs in the body also secrete hormones and have important endocrine functions.
At A Glance
- The endocrine system is made up of glands that secrete hormones that perform various functions including regulation of metabolism, blood sugar control, and maintenance of bone calcium levels.
- The hypothalamus sends chemical and neural signals to the pituitary gland, which then secretes hormones involved in growth, metabolism, fluid retention, and reproduction.
Thyroid hormones are involved in setting the body's metabolism and in the regulation of calcium; the parathyroid glands secrete hormones that assist with calcium homeostasis.
- The adrenal glands sit superiorly on each kidney and produce corticosteroids, androgen hormones, and catecholamines.
- The pineal gland is part of the epithalamus in the brain. It produces melatonin, which affects the sleep cycle.
- The pancreas is located between the stomach and small intestine and produces hormones that maintain homeostasis of blood glucose levels.
Several organs, including the kidneys, liver, thymus, heart, and skin, are not classified as primary endocrine organs but play important roles in endocrine function of the body.
- The stomach, small intestine, and adipose tissue have endocrine functions related to digestion.
- The testes, ovaries, and placenta produce hormones necessary for reproduction.