Function of the endocrine system
Maintaining homeostasis within the body requires the coordination of many different systems and organs.
The endocrine system is one of communication mechanisms between neighboring cells, and between cells and tissues in distant parts of the body.
This communication occurs through the release of chemicals called hormones.
Hormones are released into body fluids, usually blood, which carries them to their target cells where they elicit a response.
The cells that secrete hormones are often located in specific organs, called endocrine glands.
The cells, tissues, and organs that secrete hormones make up the endocrine system.
Some of the regulatory functions of the endocrine system include:
- the control of heart rate,
- the control of blood pressure,
- immune response to infection,
- emotional state,
- the overall growth and development of the body.
Parts of the endocrine system
The endocrine system consists of
- the pituitary gland,
- thyroid and parathyroid glands,
- the adrenal glands,
- the thymus gland,
- the pineal gland,
- the pancreas,
- reproductive tissues (ovaries and testes).
Many other organs, such as the liver, skin, kidney, and parts of the digestive and circulatory systems, produce hormones in addition to their other physiological functions.
Endocrine vs. exocrine glands
Examples of exocrine glands are sweat glands, salivary glands, and tear (lacrimal) glands.
Video: Endocrine glands and hormones review
Different types of hormones in human body - steroid vs. nonsteroid hormones and their mechanisms of action
The endocrine system produces two main types of hormones:
- steroid hormones
- nonsteroid hormones
Steroid hormones, such as cortisol, are manufactured from cholesterol.
Each type of steroid hormone is composed of a central structure of four carbon rings attached to distinctive side chains that determine the hormone’s specific and unique properties.
Within the endocrine cells, steroid hormones are synthesized in the smooth endoplasmic reticulum (ER).
Since steroid hormones are hydrophobic, they combine with a protein carrier that transports them through the bloodstream.
Fat-soluble steroid hormones can pass through the membrane of a target cell.
Once inside the target cell, steroid hormones attach to a protein receptor molecule in the cytoplasm. This hormone- receptor complex then enters the nucleus, where it binds with and activates a specific gene on the cell’s DNA molecule.
The activated gene then produces an enzyme that initiates the desired chemical reaction within the cell.
Nonsteroid hormones, such as adrenaline, are composed of either proteins, peptides, or amino acids.
These hormone molecules are not fat-soluble, so they usually do not enter cells to exert their effect. Instead, they bind to receptors on the surface of target cells.
This combination substance then triggers a specific chain of chemical reactions within the cell.
Video: Endocrine system - Types of hormones
Organs of the endocrine system, their hormones and functions
|Endocrine Gland||Associated Hormones||Effect|
|Pituitary (anterior)||growth hormone||promotes growth of body tissues|
|prolactin||promotes milk production|
|thyroid-stimulating hormone||stimulates thyroid hormone release|
|adrenocorticotropic hormone||stimulates hormone release by adrenal cortex|
|follicle-stimulating hormone||stimulates gamete production|
|luteinizing hormone||stimulates androgen production by gonads in males;
stimulates ovulation and production of estrogen and progesterone in females
|Pituitary (posterior)||antidiuretic hormone||stimulates water reabsorption by kidneys|
|oxytocin||stimulates uterine contractions during childbirth|
Thyroid and Parathyroid glands
|calcitonin||reduces blood Ca2+ levels|
|Parathyroid||parathyroid hormone||increases blood Ca2+ levels|
|aldosterone||increases blood Na+ levels|
|increase blood-glucose levels|
|stimulate fight-or-flight response|
|Pancreas||insulin||reduces blood-glucose levels|
|glucagon||increases blood-glucose levels|
|Pineal gland||melatonin||regulates circadian rhythms|
|Thymus gland||thymosin||stimulates the development of T cells|