Endocrine System Introduction
From MyMCAT
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[edit] Introduction
Much like the nervous system, the endocrine system is used as an information signaling system throughout the body. The endocrine system however is capable of relaying signals to various cell types and organs throughout the body, Unlike the nervous system, which transmits signals between sensory cells, receptor cells, muscles, and neurons, the endocrine system relays signals that can act on any cell, tissue, or organ in the body with the corresponding receptors for that signal.
Where the nervous system uses nerves to conduct information, the endocrine system uses the blood vessels and communicates its messages through hormones. Typical endocrine glands are ductless and secrete their hormones directly into the blood supply that passes through them. These hormones can then travel to distant organs or cells to regulate their target function.
In general, the endocrine system is in charge of slow processes such as cell while faster processes, like breathing and skeletal 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.
[edit] The Flow of Information
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 many different hormones circulate throughout the bloodstream, each one affects only the cells that are genetically programmed to receive and respond to its message. Thus, target cells can be selectively "listening" with their receptors for specific hormonal signals from elsewhere in the body.
A gland is a group of cells that produces and secretes, or gives off, chemicals. Some types of glands release their secretions in specific areas. For instance, exocrine glands, such as the sweat and salivary glands, release secretions in the skin or inside of the mouth. Endocrine glands, on the other hand, release hormones into the bloodstream where they can be transported to cells in other parts of the body.
[edit] Types of Messages
Endocrine signals can have a variety of effects on different cells, tissues, and organs and they can be classified to be either paracrine, autocrine, or endocrine (although in a general sense, they are all forms of endocrine signaling).
[edit] Paracrine
When the target cells are close to or next to the signal releasing cell, it is called paracrine signaling. In this case, the hormone merely diffuses away from the source cell and adjacent target cells pick up the signal and respond.
[edit] Autocrine
If the target cell is in fact also the cell that released the signal the process is called autocrine signaling. An example of this self-stimulation is when cytokine interleukin-1 is released from monocytes in response to an external stimuli. The produced cytokine can actually bind cell-surface receptors on the same cell that produced it.
[edit] Endocrine
The classic example of endocrine signaling is that of a hormone being released into the blood stream where target cells in distant regions can respond to the signal. Insulin, produced by the pancreas has the affect of stimulating muscle and adipose cells to uptake glucose and stimulates the liver to store glucose in the form of glycogen. This is also an example of how different cell types respond to the same hormone differently.
[edit] The Glands of the Endocrine System
The endocrine glands of the human body consist of the Pineal gland, the Pituitary gland, the Thyroid gland, the Thymus, the Adrenal gland, the Pancreas and the sex organs (the Ovaries and Testes). See Glands of the Endocrine System for the specifics of each of these glands.
[edit] Homeostasis and the Endocrine System
A pivotal role of the endocrine system is to maintain homeostasis. That is, the endocrine system is used to regulate the activities of most cellular and bodily processes to ensure every day operation. Too much or too little of any hormone can be harmful to the body. For example, if the pituitary gland produces too much growth hormone, a child may grow excessively tall. If it produces too little, a child may be abnormally short. In extreme cases, if a hormone is not produced at all, as in the case of insulin production by the pancreas in type 1 diabetes, the individual may die unless regular hormone supplements can be maintained.