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Blood is a bodily fluid in animals that delivers necessary substances such as nutrients and oxygen to the cells and transports metabolic waste products away from those same cells.<br>
 
Blood is a bodily fluid in animals that delivers necessary substances such as nutrients and oxygen to the cells and transports metabolic waste products away from those same cells.<br>
 
In vertebrates, it is composed of blood cells suspended in blood plasma. Plasma, which constitutes 55% of blood fluid, is mostly water (92% by volume),and contains dissipated proteins, glucose, mineral ions, hormones, carbon dioxide, and blood cells themselves. Albumin is the main protein in plasma, and it functions to regulate the colloidal osmotic pressure of blood. The blood cells are mainly '''red blood cells''' (also called RBCs or erythrocytes) and '''white blood cells''', including leukocytes and '''platelets'''.<br>
 
In vertebrates, it is composed of blood cells suspended in blood plasma. Plasma, which constitutes 55% of blood fluid, is mostly water (92% by volume),and contains dissipated proteins, glucose, mineral ions, hormones, carbon dioxide, and blood cells themselves. Albumin is the main protein in plasma, and it functions to regulate the colloidal osmotic pressure of blood. The blood cells are mainly '''red blood cells''' (also called RBCs or erythrocytes) and '''white blood cells''', including leukocytes and '''platelets'''.<br>
The most abundant cells in vertebrate blood are red blood cells. These contain hemoglobin, an iron-containing protein, which facilitates transportation of oxygen. In contrast, carbon dioxide is almost entirely transported extracellularly dissolved in plasma as bicarbonate ion. Red blood cells are the body's oxygen transport systems. They are not true cells, as they do not have a nuclei or organelles. Their color ranges from bright red to dark red, depending on how much oxygen they are carrying. In the lungs, the oxygen binds to hemoglobin, a protein with four iron-containing sites for oxygen to bind to. Hemoglobin is also what gives the cells their red color.br>
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The most abundant cells in vertebrate blood are '''red blood cells'''. These contain hemoglobin, an iron-containing protein, which facilitates transportation of oxygen. In contrast, carbon dioxide is almost entirely transported extracellularly dissolved in plasma as bicarbonate ion. Red blood cells are the body's oxygen transport systems. They are not true cells, as they do not have a nuclei or organelles.Their life span is 100-120 days. Their color ranges from bright red to dark red, depending on how much oxygen they are carrying. In the lungs, the oxygen binds to hemoglobin, a protein with four iron-containing sites for oxygen to bind to. Hemoglobin is also what gives the cells their red color.The number of RBC varies from 4.5 to 5,5 million cells/cubic mm of blood.<br>
'''White blood cells''', or leukocytes, are the defense army within the blood tissue. They are the only true cells in the blood and are not limited to the blood stream. When called to defeat an infection or to dispose of a dead cell, they can squeeze through openings in the vessel walls. There, they can move through amoeboid action, meaning that they sprout cytoplasmic extensions that can move them. Leukocytes, along with platelets, usually make up less than 1% of blood.
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'''White blood cells''', or leukocytes, are the defense army within the blood tissue. They are the only true cells in the blood and are not limited to the blood stream. When called to defeat an infection or to dispose of a dead cell, they can squeeze through openings in the vessel walls. There, they can move through amoeboid action, meaning that they sprout cytoplasmic extensions that can move them. Leukocytes, along with platelets, usually make up less than 1% of blood.Their number varies from 6000 to 10000 cells/cubic mm of blood.<br>
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Platelets are actually cell fragments that help in blood clotting. When a tear occurs in the blood vessels, platelets stick to the exposed collagen at the site of injury. They produce fibrous protein that traps other blood cells in a clot that stops blood from flowing and helps to prevent excess blood loss. Some platelets also secrete substances that signal other platelets to the break, substances that constrict blood vessels, or substances that promote an inflammatory response. Once the clot is formed, the platelets contract and pull the opening back together, thus healing the break.
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Platelets are actually cell fragments that help in blood clotting. When a tear occurs in the blood vessels, platelets stick to the exposed collagen at the site of injury. They produce fibrous protein that traps other blood cells in a clot that stops blood from flowing and helps to prevent excess blood loss. Some platelets also secrete substances that signal other platelets to the break, substances that constrict blood vessels, or substances that promote an inflammatory response. Once the clot is formed, the platelets contract and pull the opening back together, thus healing the break.They are about 2,50,000 platelets in 1cc of blood.<br>
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Most of the blood cells contained in blood tissue don't last very long. Red blood cells only last about 100-120 days before they are disassembled, recycled, and disposed of. Platelets last about 10 days if they do not need to clot blood. The bone marrow makes and releases blood cells into the blood on a regular basis to replace old blood cells. Thus, the tissue is constantly being restored.
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Most of the blood cells contained in blood tissue don't last very long. Red blood cells only last about 100-120 days before they are disassembled, recycled, and disposed of. Platelets last about 10 days if they do not need to clot blood. The bone marrow makes and releases blood cells into the blood on a regular basis to replace old blood cells. Thus, the tissue is constantly being restored.<br>
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'''Lymph'''<br>
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Lymph is a colourless fluid similar to blood in structure.It differs from blood only in the absense of RBC and some plasma protiens.Lymph flows in a set of lymphatic capillaries.The lymph system is a network of organs, lymph nodes, lymph ducts, and lymph vessels that make and move lymph from tissues to the bloodstream. The lymph system is a major part of the body's immune system.<br>
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Lymph is a clear-to-white fluid made of:<br>
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*White blood cells, especially lymphocytes, the cells that attack bacteria in the blood.
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*Fluid from the intestines called chyle, which contains proteins and fats.<br>
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Lymph nodes are soft, small, round- or bean-shaped structures. They usually cannot be seen or easily felt. They are located in clusters in various parts of the body, such as the neck, armpit, groin, and inside the center of the chest and abdomen.<br>
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Lymph nodes make immune cells that help the body fight infection. They also filter the lymph fluid and remove foreign material such as bacteria and cancer cells. When bacteria are recognized in the lymph fluid, the lymph nodes make more infection-fighting white blood cells, which causes the nodes to swell. The swollen nodes are sometimes felt in the neck, under the arms, and groin.<br>
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The lymphatic system includes the tonsils, adenoids, spleen, and thymus.
    
===Activities===
 
===Activities===
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