Plasma:
Plasma (any thing formed or molded) is the straw coloured liquid part of the blood. In mammals plasma is about 90 percent water and provides the solvent for dissolving and transporting nutrients.
A group of proteins (albumen, fibrinogen and globulin) comprises another 7 percent of the plasma. The concentration of these plasma proteins influences the distribution of water between the blood and extra cellular fluid. Albumen is about 60 percent of the total plasma proteins and it plays important role with respect to water movement. Fibrinogen is necessary for blood coagulation (clotting). Globulins include immuno globulins and various metal binding proteins. Serum is plasma from which the protein involved in blood clotting has been removed.
Gamma globulin portion functions in the immune response because it consists mostly of antibodies. Remaining 3 percent of plasma is composed of electrolytes, amino acids, glucose and other nutrients, various enzymes, hormones, metabolic wastes and traces of many inorganic and organic molecules.
Formed elements:
Cellular component of vertebrate blood consists of erythrocytes (red blood cells i.e. RBC), leucocytes (white blood cells i.e. WBC) and platelets (thrombocytes). White blood cells are present lower number than are red blood cells, 1 to 2 percent of blood by volume. White blood cells are divided into agranulocytes and granulocytes. Two types of agranulocytes are lymphocytes and monocytes.
Three types of granulocytes are eosinophils, basophils and neutrophils. Fragmented cells are called platelets (thrombocytes).
Red blood cells:
Erythrocytes (Erythros=red cells) vary in size shape and number of different vertebrates.
Mammalians RBC are enucleated (without nucleus).
Some fishes and amphibians also have enucleated RBC. Salamander (Amphiuma) has largest RBC.
Avian RBC is oval shaped nucleated and larger than mammalian RBC. Among birds ostrich has largest RBC. Most mammalian RBC is biconcave disks but camel and Llama have elliptical RBC. The shape of biconcave disk provides larger surface area for gas diffusion.
Lower vertebrates tend to have fewer but larger RBC than higher invertebrates. Entire mass of a RBC consists of hemoglobic (haeme=blood + globules=little globe) an iron-containing protein. Major function of an erythrocytes to pick up oxygen from the environment, bind it to haemoglobin to form oxy-haemoglobin is bright red. As oxygen diffuses into the tissue, blood becomes larger and blue when observed through the blood vessel wall. When this less oxygenated blood is exposed to oxygen (such as when a vein is cut and a mammal begins to bleed), it turns bright red. Haemoglobin also carries waste carbon dioxide (in the form of carbamino haemoglobin) from the tissues to the lungs (or gills) for removal from the body.
White blood cells:
White blood cells or leucocytes are scavengers that destroy the microorganisms at infection sites, remove foreign chemicals and remove debris that results from dead or injured cells. All WBC are derived from immature cells called stem cells in bone marrow by a process called haematopoiesis.
Among the gramulocytes is phagocyte and ingest foreign proteins and immature complexes rather than bacteria. In mammals cosinophils also release chemicals that counteract the effects of certain inflammatory chemicals released during allergic reactions.
Basophils are the least numerous WBC. When they react with a foreign substance, their granules release histamine and heparin. Histamine causes blood vessels to dilate and lead fluid at a site of inflammation and heparin prevents blood clotting.
Neutrophils are the most numerous of white blood cells. They are chemically attracted to sites of inflammation and are active phagocytes.
Two types of agranulocytes are monocytes and lymphocytes. Two types of lympocytes are B cells and T cells, both of which are central to the immune response. B cells originate in the bone marrow and colonized the lymphoid tissue where they mature, when B cells are activated. They divide and differentiate to produce plasma cells. T cells are associated with and influenced by thymus gland before they colonize lymphoid tissue and play their role in immune response.
Platyleles (Thrombocytes):
Platylets or thrmocotyes (thrombus=clot + cells) are dise shaped cells fragments that initiate blood clotting. When a blood vessel is injured, platelets immediately move to the site and clump, attaching themselves to the damaged area, and thereby beginning the process of blood coagulation.
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