The endocrine system ( El sistema endocrí)

What Is the Endocrine System?
The foundations of the endocrine system are the hormones and glands. As the body's chemical messengers, hormones (pronounced: hor-moanz) transfer information and instructions from one set of cells to another.

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 of the mouth. Endocrine glands,


The hypothalamus (pronounced: hi-po-tha-luh-mus), a collection of specialized cells that is located in the lower central part of the brain, is the primary link between the endocrine and nervous systems.

growth hormone, which stimulates the growth of bone and other body tissues and plays a role in the body's handling of nutrients and minerals
prolactin (pronounced: pro-lak-tin), which activates milk production in women who are breastfeeding
thyrotropin (pronounced: thigh-ruh-tro-pin), which stimulates the thyroid gland to produce thyroid hormones
corticotropin (pronounced: kor-tih-ko-tro-pin), which stimulates the adrenal gland to produce certain hormones


The thyroid (pronounced: thigh-royd), located in the front part of the lower neck, is shaped like a bowtie or butterfly and produces the thyroid hormones thyroxine (pronounced: thigh-rahk-seen) and triiodothyronine (pronounced: try-eye-uh-doe-thigh-ruh-neen). These hormones control the rate at which cells burn fuels from food to produce energy.






What Does the Endocrine System Do?
Once a hormone is secreted, it travels from the endocrine gland 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. The special proteins act as carriers that control the amount of hormone that is available to interact with and affect the target cells. Also, 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 possess 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 or necessary amount, further secretion is controlled by important body mechanisms to maintain that level of hormone in the blood. This regulation of hormone secretion may involve the hormone itself or another substance in the blood related to the hormone. For example, if the thyroid gland has secreted adequate amounts of thyroid hormones into the blood, the pituitary gland senses the normal levels of thyroid hormone in the bloodstream and adjusts its release of thyrotropin, the pituitary hormone that stimulates the thyroid gland to produce thyroid hormones. Another example is parathyroid hormone, which increases the level of calcium in the blood. When the blood calcium level rises, the parathyroid glands sense the change and decrease their secretion of parathyroid hormone. This turnoff process is called a negative feedback system.