Genetics

Introduction to the Human Cell



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With few exceptions such as that which occurs with muscle cells and neurons of the nervous system in which case these cells connot regenerate or divide, all other cells of the body are able to regenerate and divide.  Cells in the human body have each a unique function.  In the human body cells are organized into tissues each of which is specialized for a different type of function.  Cells in the body that regenerate and divide do so by either dividing or through a process of differentiation.


Cellular division refers to multiplication of the cell into two cells by an organized well predicted process that leads to the formation of two new identical cells from precursor cell that divides its nucleus into two new nuclei.  The process of cellular differentiation does not refer to division but refers to a process in which precursor cells, that are referred to as blast cells, mature into specific cells by a predestined programmed process. 


An example of such a process occurs in the formation of red blood cells from precursor cells that are called reticulocytes.  These cells become mature red blood cells by expelling their nucleus.  Red blood cells do not have nucleus in their structure.  Therefore, they cannot divide and are obtained  from their precursor cells that are obtained in the red bone marrow.  Another example of a differentiation process occurs in cells of the immune system. 


Macrophages are a special type of immune cells that is able to perform immune function by phagocytizing microbes.  This type of cells is obtained from precursor cells that are called monocytes by a differentiation process.  Cells of the human body have special functions each that is characteristic of the tissue that forms it.  For example, liver cells have special and unique function in the body that is characterized by proteins sunthesis.


The liver cells have also other functions that are related to the immune system.  Liver cells are the first cells to encounter pathogens that enter the blood stream after the absorption process which occurs in the small intestine.  The kidney cells have another function that is related to its unique structure of the kidney itself.  For example, kidney cells are specialized in the filtration process of blood that occurs in the glomeruli of the nephrons.  Also the kidney cells have function that is related to red blood cells formation and vitamin D synthesis.


The pancreatic tissue has also special form of cells that each is specialized for different function.  An example are the pancreatic cells that synthesize and secrete the digestive enzymes to the intestinal tract.  Also other cell types of the pancreas, known as the endocrine pancreas, synthesize and secrete hormones to the blood circulation that have special function in controlling glucose level in the blood. 


Red blood cells are another type of human cells that have unique function of transporting oxygen from the lungs to the body tissues.  Red blood cells contain a special type of protein that is called hemoglobin which is the carrier of oxygen in the blood.  Cells of the immune system are another type of cells that perform an immunological function.  Immune cells can perform these functions in either one of two ways.  The first is by phagocytosis of microbes by engulfing them or by secreting antibodies or immunoglobulins to the blood circulation.  These antibodies recognize and bind to antigens and neutralize them.


Cells of the immune system are obtained in a differentiation process from precursor cells that are obtained in the bone marrow.  Other cells that have unique function in the body are cells of the endocrine glands.  These cells secrete hormones to the blood stream and which control the function of other endocrine glands.  An example of a gland which has cells that secrete hormones is the pituitary gland and the hypothalamus.  Hormones affect other cells in the body by binding to receptors on these cells and change the metabolic rate in these cells.

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