Cellular Biology

Overview of Mammalian Cells



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The cell is the basic unit of the human body.  It is also the most fundamental functional entity that sustains life in it.  The cell has all the machinery within it for maintaining life and to survive.  It does this by one of two ways: either by division such as occurs in mitosis and meiosis or through differentiation from mother cells such as occurs in red blood cells which are differentiated from precursor cells that are called reticulocytes.


The cell is separated from the environment through a membrane which is composed of phospholipid bilayer.  This membrane is permeable to fatty material but not to polar compounds.  An exception to this rule is the molecule water.  Water usually can enter or exit the cell via a process which is called diffusion. 


Diffusion across the cellular membrane is dependent on the osmolality of the extracellular fluid in addition to the osmolality of the cell interior.  The amount of water inside the cell is kept within a very narrow range which guarantees a proper functioning of the cell.  The osmolality is determined mainly by the amount of proteins and electrolytes mostly sodium ions.


The physiological concentration of electrolytes in the blood guarantee that the cell does not contract or rupture.  Thus preventing cellular death.  This is especially important in these patients that are doing infusion od saline solutions to dehydrated patients.  It is important in these patients to infuse an isotonic solution of NaCl to that of the blood. 


A hypertonic solution can cause contraction of the cells due to drawing water out of the cell with subsequent death of the cell.  On the other hand infusing a hypotonic solution is likely to cause rupture of the cells due to the flow of water inside the cells.


The cell membrane despite its being permeable only to lipidlike compounds can allow for other compounds to enter the cell by a process which is called active transport.  Molecules such as glucose which is important as an energy source for the body is transported into the cell via the assistance of the hormone insulin.


This process is especially important due to its role in diabetes mellitus in which the lack of the hormone insulin prevents the process of glucose entering into the cell.  Thus preventing the production of energy via the glycolytic pathway.  In these patients an alternative pathway occurs in which fatty acids are usedas fuel instead of glucose to generate energy. 


This process occurs also inside the cell and leads to the formation of ketone bodies which in these patients give the urine a smell like acetone which is a useful diagnostic tool to the presence of diabetes in these affected individuals. 


Active transport occurs not only for chemical compounds but also it occurs for electrolytes such as sodium and potassium and calcium.  Sodium in particular is important along with potassium for the normal functioning of nerves and muscle tissues.  Active transport across the cellular membrane of these cells guarantees the existence of electric potential which can be depolarized and hyperpolarized by openning and closing of ion channels Based on a stimulus from outside the cell such as the neurotransmitter acetylcholine. 


If the process of active transport of ions stops such as in the case of inhibiting the enzymes responsible for this process we are likely to die of the consequences due to the dysfunction of the nervous system and the muscular system. 


Sodium ions in these processes of active transport are kept outside the cell where their concentration there is higher thatn that inside the cell.  Potassium ions on the other hand, are kept inside the cell where their concentration there is higher than that outside the cell.   

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