Why do hormones affect only certain cells

In essence, hormones serve as messengers, controlling and coordinating activities throughout the body. See also Endocrine Glands Endocrine Glands The endocrine system consists of a group of glands and organs that regulate and control various body functions by producing and secreting hormones. Upon reaching a target site, a hormone binds to a receptor, much like a key fits into a lock. Once the hormone locks into its receptor, it transmits a message that causes the target site to take a specific action.

Hormone receptors may be within the nucleus or on the surface of the cell. Ultimately, hormones control the function of entire organs, affecting such diverse processes as growth and development, reproduction, and sexual characteristics. Hormones also influence the way the body uses and stores energy and control the volume of fluid and the levels of salts and sugar glucose in the blood. Very small amounts of hormones can trigger very large responses in the body. Although hormones circulate throughout the body, each type of hormone influences only certain organs and tissues.

Some hormones affect only one or two organs, whereas others have influence throughout the body. For example, thyroid-stimulating hormone, produced in the pituitary gland Overview of the Pituitary Gland The pituitary is a pea-sized gland that is housed within a bony structure sella turcica at the base of the brain. The sella turcica protects the pituitary but allows very little room for expansion The two halves lobes of the gland are connected Insulin , secreted by the islet cells of the pancreas, affects the processing metabolism of glucose, protein, and fat throughout the body.

Others are steroids, which are fatty substances derived from cholesterol. To control endocrine functions, the secretion of each hormone must be regulated within precise limits. Hormones are chemical messengers secreted into blood or extracellular fluid by one cell that affect the functioning of other cells.

Most hormones circulate in blood, coming into contact with essentially all cells. However, a given hormone usually affects only a limited number of cells, which are called target cells.

A target cell responds to a hormone because it bears receptors for the hormone. In other words, a particular cell is a target cell for a hormone if it contains functional receptors for that hormone, and cells which do not have such a receptor cannot be influenced directly by that hormone. Reception of a radio broadcast provides a good analogy. Everyone within range of a transmitter for National Public Radio is exposed to that signal even if they don't contribute!

However, in order to be a NPR target and thus influenced directly by their broadcasts, you have to have a receiver tuned to that frequency.

This effect on the organ feeds back to the original signal to control any further hormone release. The pituitary gland is well known for its feedback loops. Numerous problems can occur in the endocrine system. These can be considered as excessive or deficient hormone production. Endocrine organs are also prone to tumours adenomas which can over produce hormones.

Some problems of the endocrine system include:. This page has been produced in consultation with and approved by:. Content on this website is provided for information purposes only.

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The State of Victoria and the Department of Health shall not bear any liability for reliance by any user on the materials contained on this website. Skip to main content. Hormonal system endocrine. Home Hormonal system endocrine. Hormonal endocrine system. Actions for this page Listen Print. Summary Read the full fact sheet.

On this page. Exocrine glands Functions of the endocrine system How hormones work Endocrine glands and organs Problems of the endocrine system Where to get help Things to remember. Exocrine glands An exocrine gland, unlike an endocrine gland, is a gland that secretes substances electrolytes, proteins or enzymes straight to a target site via ducts or tube. Some examples include: Salivary glands Sweat glands Sebaceous glands The pancreas.

Functions of the endocrine system Some of the roles of the endocrine system include: Growth Repair Sexual reproduction Digestion Homeostasis constant internal balance. Endocrine glands and organs The main glands and organs of the endocrine system include: Pituitary gland — is inside the brain. It oversees the other glands and keeps hormone levels in check. The pituitary gland is also connected to the nervous system through part of the brain called the hypothalamus. Thyroid gland — sits in the neck at the front of the windpipe.

It releases thyroid hormone T4 and T3 which is required for metabolism and body homeostasis. It is controlled by TSH which is produced by the pituitary gland through a feed-back loop.