The General Features of Human Cells

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The adaptation of cells to their functions,their size, and shape

1.THE GENERAL FEATURES OF HUMAN CELLS
The cell is the structural functional unit of all known living organisms it is the smallest unit of an organism that is classified as a living and is often called the building block of life .Like ourselves, the individual cell that forms our bodies can grow reproduce, process, information, respond to stimuli and carry out an amazing array of chemical reactions ,as the twenty first century opens we face an explosion of new data about components of cells what structures they contain how they touch and influence each other. The human body is composed of countless millions of units called cells .In an animal like a human there are many different types of cells, with different structures. They are specialised so that they can carry out particular functions in the body .Despite all the differences there are basic features that are the same in most cells (Lodish, 1999, Molecular Cell Biology)

THE RED BLOOD CELL

The red blood cells are the most common type of blood cells they are responsible for transporting oxygen around the body .They contain haemoglobin and protein which combines with oxygen from the lungs to form oxy haemoglobin, when transported to the tissues the oxy haemoglobin splits into its original constituents and the cells are able to release oxygen .There are 6 million red cells in every cubic centimetre of blood. The composition is a mixture of 2 components, 55% plasma (made of 90% water) and 45% blood cells also known as elements.

The cell has a distinctive shape it is shaped like a disc with a depression in the face of the disc and loses their nucleus before they work as oxygen transporters ,in order to make maximum space for haemoglobin in other vertebrates they are oval nucleated they are manufactured in the bone marrow in long bones like femur, this process is known as hematopoisesis.The bone marrow is found in the spongy tissue in the middle of the bones, in this tissue there are pluripotent hematopoietic stem cells. To become red blood cells the pluripotent hemapoietic stem cell must first become an uncommitted stem cell, it then forms a committed progenitor cells, and those progenitor cells can form red blood cells, lymphocytes , megakaryocytic and other white blood cells. To form red blood cells the committed progenitor cell must form an erythroblast then roticulocyte and then finally a red blood cell which has an average life span of 120 days in the body.(see appendix 1)

Haemoglobin
Haemoglobin is a protein based component of red blood cells which is primarily responsible for transferring oxygen from the lungs to the rest of the body it is actually the reason why red blood cells appeared. They also transport co2 as de oxy haemoglobin which make blood appear dark red. The protein contains two A chains and two B chains held by polypeptides bonds each chain contains an iron atom that binds easily with oxygen molecule of haemoglobin can transport up to four molecules of oxygen. The high carbon dioxide level in the tissues lowers the ph and the binding of haemoglobin to carbon dioxide causes a conformational change that facilitates the release of oxygen. The Co2 is then released once the red blood cells reach the lungs. LEUKOCYTES

White blood cells also called leucocytes a cellular component of the blood that lacks haemoglobin has a nucleus and are produced in the red bone marrow as well as in the lymph nodes .They defend the body by releasing antibodies which ingest foreign materials and cellular debris .A healthy human has between 4,500 and 11000 WBC per cubic mm of blood as living cells their survival depends on their continuous production of energy, the nucleus enables them to produce ribonucleic acid( RNA) which can synthesize protein.WBC are highly differentiated for their specialised functions and they do not undergo cell division...
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