Do individual cells and our body as a whole attempt to maintain an optimal working environment?
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Just as you clean your apartment or house and determine what kind of stuff is found within your living area, so too will our cells clean and regulate the contents in their intracellular fluid. This allows each cell to maintain an optimal operating environment. Scientists often use the term homeostasis to describe the efforts associated with the maintenance of this optimal environment. Just as it is the responsibility of each cell to maintain its own ideal internal environment; at the same time many of our organs work in concert to regulate the environment within our body as a whole. These organs include the kidneys, lungs, skin, and liver. Many of our most basic functions, such as breathing, sweating, urinating, digesting, and the pumping of our heart, are actually functions dedicated to homeostasis (See Body Maintenance Table). Therefore, homeostasis is the housekeeping efforts of all our cells working individually as well as together to provide an environment conducive to optimal function. |
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What is the composition of the plasma membrane?
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Each cell is enveloped by a very thin membrane measuring only about 10 nanometers (nm) thick. A nanometer is one-billionth of a meter— pretty thin indeed. The makeup of the plasma membrane is a very clever combination of lipids and proteins with just a touch of carbohydrate and other molecules. Interestingly, plasma membranes use the basic principle of water solubility to allow for its barrier properties and it is the lipid that provides this character. Molecules that are somewhat similar to triglycerides (fat) called phospholipids are arranged to provide a water-insoluble capsule surrounding cells. What that means is that water-soluble substances such as sodium, potassium, and chloride, carbohydrates, proteins, and amino acids are not able to move freely through the membrane while some lipid substances and gases seem to move more freely. The plasma membrane will also contain the lipid substance cholesterol. Cholesterol appears to increase the stability of the plasma membranes |
Since the plasma membrane functions as a barrier between the outside and inside of the cell, there must be a means (or doorways) whereby many water-soluble substances can either enter or exit a cell. One of the roles of proteins in the plasma membrane is to function as doors, thereby allowing substances such as sodium, potassium, chloride, glucose, and amino acids to enter or exit a cell.
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