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Organisation of cells animal tissues (view source)
Revision as of 02:51, 7 August 2014
, 02:51, 7 August 2014→Notes for teachers
http://upload.wikimedia.org/wikipedia/commons/3/34/Illu_compact_spongy_bone.jpg
http://upload.wikimedia.org/wikipedia/commons/3/34/Illu_compact_spongy_bone.jpg
'''Cross section of long bone showing both spongy and compact osseous tissue'''
'''Cross section of long bone showing both spongy and compact osseous tissue'''
'''Fluid connective tissue'''<br>
It is a type of connective tissue in which the matrix is in the liquid form. It is known as '''plasma'''. The plasma encloses different types of cells. Fibres are absent.Fluid connective tissue is distinguished into the following two types:<br>
*Blood
*Lymph<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>
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>
'''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.
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.
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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