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Body Fluids, Composition and Functions of Blood

Blood serves as connective tissue when in a fluid state. As it circulates continuously, it facilitates constant communication between distant tissues.
Blood serves as connective tissue when in a fluid state. As it circulates continuously throughout the body, it facilitates constant communication between distant tissues. There are several different types of blood cells suspended in the clear, straw-colored liquid called plasma in which the blood is composed. The volume of blood is normally composed of 55% plasma. About 45% of blood is composed of cellular components. Using gravity and centrifugation, blood cells are separated from plasma. Any sample containing cells sinks to the bottom due to their weight.

About 91% of plasma is water. Plasma makes up the liquid part of the blood. Due to the solvent property of water, plasma can transport many types of substances. Glucose, amino acids, and minerals absorbed in the digestive tract are transported throughout the body. A variety of waste products from the tissues are excreted in the urine by the kidneys, including urea and creatinine. The plasma carries hormones produced by the endocrine glands as well as antibodies to their target organs. The carbon dioxide emitted by the cells is carried by the plasma as bicarbonate ions (HCO3- ). During the process of blood re-formation, CO2 diffuses into the alveolus and exits the body.

A plasma protein can also be found in plasma. Blood clots are formed by the liver synthesizing clotting factors such as prothrombin and fibrinogen following a rupture or injury to an artery or vein. A large amount of plasma protein is albumin. A liver enzyme synthesizes it too. This pull of tissue fluid into capillaries is governed by osmotic pressure created by albumin in the blood.

To keep blood pressure and volume normal, this is necessary. Globulins are another type of plasma protein. Beta and alpha globulins are produced by the liver to transport fat molecules. Lymphocytes produce gamma globulin antibodies. Immunity is achieved through the destruction of pathogens by antibodies. Body heat is also carried by plasma. As part of cellular respiration (the process in which ATP is produced), heat is a by-product. As the blood passes through the active liver and muscles, the blood is heated. The blood circulates through the body and distributes this heat to the cooler parts.

Blood cells
Blood cells are usually present in three types such as white blood cells, red blood cells, and lastly platelets. Derived from stem cells, hemopoietic tissue makes blood cells. Essentially, it is the red bone marrow of the sternum, the hip bone, and the vertebrae found after birth. The thymus gland, spleen, and lymph nodes are body parts where lymphocytes mature and divide. Besides stem cells in the thymus, other lymphatic tissues also produce lymphocytes from stem cells.

Red blood cells
A red blood cell (RBC) is called an erythrocyte because it has a biconcave disc shape, meaning the center is thinner than its edges. As red blood cells mature, their nuclei dissolve and are no longer needed for the cells to function normally. There are 4.5 to 6.0 million red blood cells per microliter (L) of blood in a normal human. In general, men tend to have higher RBC counts while women tend to have lower counts. Haematocrit is another measure of the number of RBCs.

About 120 days is the lifespan of red blood cells. Hemoglobin (Hb), a protein found in red blood cells, is responsible for carrying oxygen through the body. The oxygen molecules which bond to each hemoglobin molecule in every red blood cell are approximately 300 million in number.
White blood cells

The leukocytes are commonly called white blood cells (WBC), which are blood cells. Generally speaking, there are five kinds of WBC, each of which is nucleated when mature and larger than RBCs. As a whole or in segments, the nucleus may appear either whole or divided. WBC counts (part of a complete blood count) usually range from 5,000 to 10,000 per liter. Five different types of white blood cells are produced in the red bone marrow (and some lymphocytes are produced in lymphatic tissues as well) and may be grouped into two categories: granular and agranular.

Granular leukocytes consist of neutrophils, eosinophils, and basophils that show distinct colors when stained, and their nuclei are usually organized into more than one lobe or segment. A neutrophil's granules are light blue, and eosinophils are red, and basophils are dark blue. In agranular leukocytes, there is a single nucleus, as in lymphocytes and monocytes. Lymphocytes are usually smaller than monocytes. A CBC represents types of leukocytes by measuring how many white blood cells (a component) are present.

A thrombocyte, which is a more formal term for platelets, is a fragment or piece of a whole cell. Stem cells in the red bone marrow can develop into large cells named megakaryocytes, which then break apart into smaller cells that circulate. Platelets are small, oval, circulating cells that last for up to nine days if not used before then. Blood platelet production is boosted by thrombopoietin, a hormone produced in the liver. An average platelet count (part of a complete blood count) ranges from 150,001 to 300,000/L (the high end may be as high as 500,000). A certain condition arises when the level of platelets is low, it is called thrombocytopenia. To prevent blood loss, platelets are vital for hemostasis. Blood clotting, platelet plugs, and vasoconstriction are the three mechanisms involved in platelets.
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