CH 6 communication, integration, and homeostasis

CH 6 communication, integration, and homeostasis - CH 6:...

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CH 6: COMMUNICATION, INTEGRATION, AND HOMEOSTATSIS A combination of simple diffusion across small distances, widespread distribution of molecules through the circulatory system, and rapid, specific delivery of messages by the nervous system enables each cell in the body to communicate with most other cells and maintain homeostasis CELL-TO-CELL COMMUNICATION There are ~75 trillion cells in the human body - There are two basic types of physiological signals o Electrical signals, which are changes in a cell’s membrane potential o Chemical signals, which are molecules secreted by cells into the ECF Are responsible for most of the communication within the body - The cells that receive electrical or chemical signals are called target cells, or targets Our bodies use 4 basic methods of cell-to-cell communication - Gap junctions o Which allow direct cytoplasmic transfer of electrical and chemical signals between adjacent cells - Contact-dependent signals o Which occur when surface molecules on one cell membrane bind to surface molecules on another cell membrane - Local communication o Occurs via chemicals that diffuse through the ECF - Long distant communication o Which occurs through a combination of electrical signals carried by nerve cells and chemical signals transported in the blood GAP JUNCTIONS CREATE CYTOPLASMIC BRIDGES Gap junctions - Are protein channels that create cytoplasmic bridges between adjacent cells - Are the simplest form of cell-to-cell communication because direct transfer of electrical and chemical signals is allowed
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CH 6: COMMUNICATION, INTEGRATION, AND HOMEOSTATSIS - Form from the union of membrane-spanning proteins, called connexins, on two adjacent cells o The united connexins create a protein channel ( connexon ) that can open and close o When the channel is open, the connected cells function like a single cell that contains multiple nuclei (a syncytium ) When gap junctions are open - Ions, and small molecules such as amino acids, ATP, and cyclic AMP diffuse directly from the cytoplasm of one cell to the cytoplasm of the next - They provide the only means by which electrical signals can pass directly from cell to cell Large molecules cannot pass through gap junctions - Movement of molecules through gap junctions can be modulated or shut off completely Gap junctions are not all alike - In mammals, gap junctions are found in almost every cell type, including heart muscle, some types of smooth muscle, lung, liver, and neurons of the brain CONTACT-DEPENDENT SIGNALS REQUIRE CELL-TO-CELL CONTACT This type of cell-to-cell communication requires that surface molecules on one cell membrane bind to a membrane protein of another cell - This contact-dependent signaling occurs in the immune system and during growth and development o Such as when nerve cells send out long extensions that must grow from the central axis of the body to the distal ends of the limb - CAMs, cell adhesion molecules first known for their role in cell-to-cell adhesion o have now been shown to act as receptors in cell-to-cell signaling
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This note was uploaded on 04/07/2008 for the course BIOL 425 taught by Professor Tondi during the Spring '08 term at George Mason.

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CH 6 communication, integration, and homeostasis - CH 6:...

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