The function of the endocrine system: glands and hormones
Information travels through our bodies in two forms: as electrical signals, or as chemical signals. The chemical signals are created and carried throughout the body using the endocrine system. This system works more slowly than the electrical signals, and is made up of glands that secrete hormones (the carriers of the information) in the bloodstream.
Although we rarely think about the endocrine system, it influences almost every cell, organ, and function of our bodies. The endocrine system plays a role in regulating mood, growth and development, tissue function, metabolism, and sexual function and reproductive processes.
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 affects almost every organ and cell in the body.
In general, the endocrine system is in charge of body processes that happen slowly, such as cell growth. Faster processes like breathing and body movement are controlled by the nervous system. But even though the nervous system and endocrine system are separate systems, they often work together to help the body function properly.
The foundations of the endocrine system are the hormones and glands. As the body’s chemical messengers, hormones transfer information and instructions from one set of cells to another. Although the hormones circulate throughout the body, each type of hormone is targeted toward certain organs and tissues. The endocrine system gets some help from organs such as the kidney, liver, heart and gonads, which have secondary endocrine functions. The kidney, for example, secretes hormones such as erythropoietin and renin.
A gland is a group of cells that produces and secretes, or gives off, chemicals. A gland selects and removes materials from the blood, processes them, and secretes the finished chemical product for use somewhere in the body.
Some types of glands release their secretions in specific areas. For instance, exocrine (pronounced: EK-suh-krin) glands, such as the sweat and salivary glands, release secretions in the skin or inside the mouth. Endocrine glands, on the other hand, release more than 20 major hormones directly into the bloodstream where they can be transported to cells in other parts of the body.
Where are Endocrine Glands Located in the Human Body?
Hypothalamus – The hypothalamus links our endocrine and nervous systems together. The hypothalamus drives the endocrine system.
Pituitary gland – The pituitary gland receives signals from the hypothalamus. This gland has two lobes, the posterior and anterior lobes. The posterior lobe secretes hormones that are made by the hypothalamus. The anterior lobe produces its own hormones, several of which act on other endocrine glands.
Thyroid gland – The thyroid gland is critical to the healthy development and maturation of vertebrates and regulates metabolism.
Adrenal glands – The adrenal gland is made up of two glands: the cortex and medulla. These glands produce hormones in response to stress and regulate blood pressure, glucose metabolism, and the body’s salt and water balance.
Pancreas – The pancreas is responsible for producing glucagon and insulin. Both hormones help regulate the concentration of glucose (sugar) in the blood.
Gonads – The male reproductive gonads, or testes, and female reproductive gonads, or ovaries, produce steroids that affect growth and development and also regulate reproductive cycles and behaviors. The major categories of gonadal steroids are androgens, estrogens, and progestins, all of which are found in both males and females but at different levels.
So how are the endocrine and nervous system linked? The brain structure known as the hypothalamus connects these two important communication systems. The hypothalamus is a tiny collection of nuclei that is responsible for controlling an astonishing amount of behavior. Located at the base of the forebrain, the hypothalamus regulates basic needs such as sleep, hunger, thirst and sex in addition to emotional and stress responses. The hypothalamus also controls the pituitary glands, which then controls the release of hormones from other glands in the endocrine system.
What Does the Endocrine System Do?
Once a hormone is secreted, it travels from the endocrine gland that produced it through the bloodstream to the cells designed to receive its message. These cells are called target cells. Along the way to the target cells, special proteins bind to some of the hormones. These proteins act as carriers that control the amount of hormone that is available for the cells to use.
The target cells have receptors that latch onto only specific hormones, and each hormone has its own receptor, so that each hormone will communicate only with specific target cells that have receptors for that hormone. When the hormone reaches its target cell, it locks onto the cell’s specific receptors and these hormone-receptor combinations transmit chemical instructions to the inner workings of the cell.
When hormone levels reach a certain normal amount, the endocrine system helps the body to keep that level of hormone in the blood. For example, if the thyroid gland has secreted the right amount of thyroid hormones into the blood, the pituitary gland senses the normal levels of thyroid hormone in the bloodstream. Then the pituitary gland adjusts its release of thyrotropin, the hormone that stimulates the thyroid gland to produce thyroid hormones.