Textbook notes-Chapter 6-Communication Integration and Homeostasis

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University of Toronto Scarborough
Biological Sciences
Ingrid L.Stefanovic

Chapter 6- Communication, Integration, and Homeostasis Cell to Cell Communication N Electrical signals ,70.K,3J08L3,.0OO8202-7,30549039L,OZK070,8chemical signals are molecules secreted by cells into the ECF - Chemical signals are responsible for most communication within the body and the cells that receive electrical or chemical signals are called target cells, or targets for short N Our bodies use 4 basic methods of cell-to-cell communication 1. Gap junctions, which allow direct cytoplasmic transfer of electrical and chemical signals bw adjacent cells 2. Contact-dependent signals, which occur when surface molecules on one cell membrane bind to surface molecules on another cell membrane 3. Local communication by chemicals that diffuse through the ECF 4. Long-distance communication through a combo of electrical signals carried by nerve cells and chemical signals transported in the blood N A given molecule can function as a signal by more than one method Gap Junctions Create Cytoplasmic Bridges N The simplest form of cell-to-cell communication is the direct transfer of electrical and chemical signals through gap junctions, protein channels that create cytoplasmic bridges bw adjacent cells- Fig 6-1 (pg. 175) - A gap junction forms from the union of membrane-spanning proteins, called connexions on two adjacent cells - The united connexins create a protein channel (connexion) that can open and close N When the channel is open, the connected cells function like a single cell that contains multiple nuclei N When gap junctions are open, ions and small molecules like cyclic AMP diffuse directly from the cytoplasm of one cell to the cytoplasm of the next - As w other membrane channels, larger molecules cannot pass through gap junctions - Gap junctions are the only means by which electrical signals can pass directly from cell to cell - Movement of molecules through gap junctions can be modulated or shut off completely Paracrine and Autocrine Signals Carry Out Local Communication N Local communication is accomplished by paracrine and autocrine signalling - Paracrine signals are secreted by one cell and diffuse to adjacent cells - Autocrine signals act on the same cell that secreted them - In some cases a molecule may act as both an autocrine and a paracrine signal - Paracrine and autocrine signals reach their target cells by diffusing through the interstitial fluid - Distance is a limiting factor for diffusion, therefore the effective range of paracrine signals is restricted to adjacent cells - A good eg of a paracrine molecule is histamine, a chemical released from damaged cells Neural Signals, Hormones, and Neurohormones Carry Out Long-Distance Communication N All cells in the body can release paracrine signals, but most long-distance communication bw cells is the responsibility of the nervous and endocrine systems N The endocrine system communicated by using hormones, chemical signals that are secreted into the blood and distributed all over the body by the circulation - Hormones come in contact w most cells of the body, but only those cells w receptors for the hormone are target cells- Fig 6-2 (pg. 177) N The nervous system uses a combo of chemical and electrical signals to communicate over long distances - An electrical signal travels along a nerve cell (neuron) until it reaches the very end of the cell, where it is translated into a chemical signal secreted by the neuron (a neurocrine) - If a neurocrine molecule diffuses from the neuron across a narrow EC space to a target cell and has a rapid effect, it is called a neurotransmitter - If a neurocrine acts more slowly as an autocrine or paracrine signal, it is called a neuromodulator - If a neurocrine released by a neuron diffuses into the blood for distribution, it is called a neurohormone - The similarities bw neurohormones and classic hormones secreted by the endocrine system blur the distinction bw the nervous and endocrine systems, making them a continuum rather than two distinct systems 1 www.notesolution.com
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