Blood Composition And Its Functions PDF

BLOOD COMPOSITION AND ITS FUNCTIONS BLOOD COMPOSITION AND ITS FUNCTIONS  BLOOD COMPOSITION BLOOD: blood is the main circulating fluid in the human body. Study of blood is called HAEMATOLOGY. It is a fluid connective tissue derivedfrom mesoderm. Bright red in colour, sl...

BLOOD COMPOSITION AND ITS FUNCTIONS BLOOD COMPOSITION AND ITS FUNCTIONS  BLOOD COMPOSITION BLOOD: blood is the main circulating fluid in the human body. Study of blood is called HAEMATOLOGY. It is a fluid connective tissue derivedfrom mesoderm. Bright red in colour, slightly alkaline(pH7.4), salty, and heavier than water. The adult has 5lit of blood whichconstitute about 8% of the total bodyweight. Blood is divided into two constituents, 1.cellular composition 2.non-cellular composition  Blood Cellular Non-cellular composition composition Blood Plasma corpuscles RBCs WBCs platelets Granulocyte Agranulocyte Neutrophil Eosinophil Basophil Monocyte Lymphocyte  Cellular composition RBCs WBCs platelets  Functions of blood : TRANSPORTATION : REGULATION : PROTECTION: Respiration Regulates pH WBCs protects Nutrient carrierfrom Adjusts and maintain against diseaseby GIT body temperature phagocytosis Transportation of Maintains water Reservoir for hormones from contents of cells substances like endocrine glands water,electrolytes. Transportation of Performs metabolic waste. haemostasis. ERYTHROCYTE RBCs  They are circular , biconcave , enucleatedcells. A major function of red blood cells is to transport hemoglobin, which in turn carries oxygen from the lungs to the tissues. In healthy men, the average number of red blood cells per cubic millimeter is 5,200,000 (±300,000) In women, it is 4,700,000 (±300,000) Average life span is of 120days. LEUCOCYTES WBCs Leukocytes (White Blood Cells Mobile units of the body’s protective system. After formation, they are transported in the blood to different parts of the body where they are needed (areas of serious infection and inflammation).  WBCs Granulocytes Agranulocytes Neutrophil Eosinophil Basophil Monocyte Lymphocyte  The granulocytes and monocytes protect the body against invading organisms mainly by ingesting them (i.e., by phagocytosis). The lymphocytes and plasma cells function mainly in connection with the immune system. Concentrations of the Different White Blood Cells in the Blood Adult human being - 7000 WBC/ microliter of blood Polymorphonuclear neutrophils------ 62.0% Polymorphonuclear eosinophils------ 2.3% Polymorphonuclear basophils-------- 0.4% Monocytes--------------------------------- 5.3% Lymphocytes-------------------------------30.0% platelets------- 300,000 / microliter of blood.  The granulocytes and monocytes are formed only in the bone marrow. Lymphocytes and plasma cells are produced mainly in the various lymphogenous tissues— especially the lymph glands, spleen, thymus, tonsils, and various pockets of lymphoid tissue elsewhere in the body, such as in the bone marrow and in so-called Peyer’s patches underneath the epithelium in the gut wall. The life of the granulocytes after being released from the bone marrow is normally 4 to 8 hours circulating in the blood and another 4 to 5 days in tissues where they are needed. In times of serious tissue infection, this total life span is often shortened.  The monocytes also have a short transit time, 10 to 20 hours in the blood, before wandering through the capillary membranes into the tissues. Once in the tissues, they swell to much larger sizes to become tissue macrophages, and, in this form, can live for months unless destroyed while performing phagocytic functions.  Lymphocytes enter the circulatory system continually, along with drainage of lymph from the lymph nodes and other lymphoid tissue. After a few hours, they pass out of the blood back into the tissues by diapedesis.Then they reenter the lymph and return to the blood again and again. The lymphocytes have life spans of weeks or months, depending on the body’s need for these cells. The platelets in the blood are replaced about once every 10 days.  the neutrophils and tissue macrophages attack and destroy invading bacteria, viruses, and other injurious agents. Phagocytosis (cellular ingestion of the offending agent) First, most natural structures in the tissues have smooth surfaces, which resist phagocytosis. But if the surface is rough, the likelihood of phagocytosis is increased. Second, most natural substances of the body have protective protein coats that repel the phagocytes. Conversely, most dead tissues and foreign particles have no protective coats, which makes them subject to phagocytosis.  Third, the immune system of the body develops antibodies against infectious agents such as bacteria. The antibodies then adhere to the bacterial membranes and thereby make the bacteria especially susceptible to phagocytosis. Phagocytosis by Neutrophils. On approaching a particle to be phagocytized, the neutrophil first attaches itself to the particle and then projects pseudopodia in all directions around the particle. This creates an enclosed chamber that contains the phagocytized particle. Then the chamber invaginates to the inside of the cytoplasmic cavity to form a free-floating phagocytic vesicle (also called a phagosome). A single neutrophil can usually phagocytize 3 to 20 bacteria before the neutrophil itself becomes inactivated and dies. Phagocytosis by Macrophages. Macrophages are the end-stage product of monocytes that enter the tissues from the blood. When activated by the immune system, they are much more powerful phagocytes than neutrophils, often capable of phagocytizing as many as 100 bacteria. They also have the ability to engulf much larger particles, even whole red blood cells or, occasionally, malarial parasites, whereas neutrophils are not capable of phagocytizing particles much larger than bacteria. Also, after digesting particles, macrophages can extrude the residual products and often survive and function for many more months. Once Phagocytized, Most Particles Are Digested by Intracellular Enzymes. lysosomes and other cytoplasmic granules in the neutrophil or macrophage immediately come in contact with the phagocytic vesicle, and their membranes fuse, thereby dumping many digestive enzymes and bactericidal agents into the vesicle. Thus, the phagocytic vesicle now becomes a digestive vesicle, and digestion of the phagocytized particle begins immediately.  proteolytic enzymes( digesting bacteria and other foreign protein matter). The lysosomes of macrophages (but not of neutrophils) also contain large amounts of lipases, which digest the thick lipid membranes possessed by some bacteria such as the tuberculosis bacillus. neutrophils and macrophages contain bactericidal agents that kill most bacteria even when the lysosomal enzymes fail to digest them.  Much of the killing effect results from several powerful oxidizing agents formed by enzymes in the membrane of the phagosome or by a special organelle called the peroxisome. These oxidizing agents include large quantities of superoxide (O2 − ), hydrogen peroxide (H2 O2 ), and hydroxyl ions (OH− ), all of which are lethal to most bacteria, even in small quantities. Also, one of the lysosomal enzymes, myeloperoxidase, catalyzes the reaction between H2 O2 and chloride ions to form hypochlorite, which is exceedingly bactericidal. Monocyte-Macrophage Cell System Reticuloendothelial System  After entering the tissues and becoming macrophages, another large portion of monocytes becomes attached to the tissues and remains attached for months or even years until they are called on to perform specific local protective functions. They have the same capabilities as the mobile macrophages, and, when appropriately stimulated, they can break away from their attachments and once again become mobile macrophages. The total combination of monocytes, mobile macrophages, fixed tissue macrophages, and a few specialized endothelial cells in the bone marrow, spleen, and lymph nodes is called the reticuloendothelial system( monocyte- macrophage system). Tissue Macrophages in the Skin and Subcutaneous Tissues (Histiocytes). When infection begins in a subcutaneous tissue and local inflammation ensues, local tissue macrophages can divide in situ and form still more macrophages. Macrophages in the Lymph Nodes. Essentially no particulate matter that enters the tissues, such as bacteria, can be absorbed directly through the capillary membranes into the blood. Instead, if not destroyed locally in the tissues, they enter the lymph and flow to the lymph nodes located intermittently along the course of the lymph flow. The foreign particles are then trapped in these nodes in a meshwork of sinuses lined by tissue macrophages.  lymph entering through the lymph node capsule by way of afferent lymphatics, then flowing through the nodal medullary sinuses, and finally passing the hilus into efferent lymphatics that eventually empty into the venous blood. Large numbers of macrophages line the lymph sinuses, and if any particles enter the sinuses by way of the lymph, the macrophages phagocytize them and prevent general dissemination throughout the body. Alveolar Macrophages in the Lungs. Another route by which invading organisms frequently enter the body is through the lungs. Large numbers of tissue macrophages are present as integral components of the alveolar walls. They can phagocytize particles that become entrapped in the alveoli. If the particles are digestible, the macrophages can also digest them and release the digestive products into the lymph.  If the particle is not digestible, the macrophages often form a “giant cell” capsule around the particle until such time—if ever—that it can be slowly dissolved. Such capsules are frequently formed around tuberculosis bacilli, silica dust particles, and even carbon particles.  Macrophages (Kupffer Cells) in the Liver Sinusoids. Still another route by which bacteria invade the body is through the gastrointestinal tract. Large numbers of bacteria from ingested food constantly pass through the gastrointestinal mucosa into the portal blood. Before this blood enters the general circulation, it passes through the liver sinusoids, which are lined with tissue macrophages called Kupffer cells. Almost none of the bacteria from the gastrointestinal tract passes from the portal blood into the general systemic circulation ( phagocytosis of a single bacterium in less than 1 / 100 of a second). Macrophages of the Spleen and Bone Marrow. If an invading organism succeeds in entering the general circulation, there are other lines of defense by the tissue macrophage system, especially by macrophages of spleen and bone marrow. In both these tissues, macrophages become entrapped by the reticular meshwork of the two organs and when foreign particles come in contact with these macrophages, they are phagocytized.  The spleen is similar to the lymph nodes, except that blood, instead of lymph, flows through the tissue spaces of the spleen. A small artery penetrates from the splenic capsule into the splenic pulp and terminates in small capillaries. The capillaries are highly porous, allowing whole blood to pass out of the capillaries into cords of red pulp. The blood then gradually squeezes through the trabecular meshwork of these cords and eventually returns to the circulation through the endothelial walls of the venous sinuses. The trabeculae of the red pulp are lined with vast numbers of macrophages, and the venous sinuses are also lined with macrophages. Inflammation: Role of Neutrophils and Macrophages  When tissue injury occurs, multiple substances are released that cause secondary changes in the tissue. These substances increase local blood flow and the permeability of the capillaries, which cause large quantities of fluid to leak into the interstitial spaces, the migration of large numbers of granulocytes and monocytes into the tissues, and local swelling. One of the first results of inflammation is to “wall off” the area of injury from the remaining tissues. The tissue spaces and lymphatics in the inflamed area are blocked by fibrinogen clots, so fluid barely flows through these spaces. This walling- off procedure delays the spread of bacteria or toxic products. The intensity of the inflammatory process is usually proportional to the degree of tissue injury. Some of the many tissue products that cause these reactions are histamine, bradykinin, serotonin, prostaglandins, several different reaction products of the complement system. reaction products of the blood clotting system, lymphokines that are released by sensitized T cells. 1. The Tissue Macrophage Is the First Line of Defense against Invading Organisms. Within minutes after inflammation begins, the macrophages present in the tissues immediately begin their phagocytic actions. Many sessile macrophages break loose from their attachments and become mobile in response to chemotactic factors. These macrophages migrate to the area of inflammation and contribute their activity. 2. Neutrophil Invasion of the Inflamed Tissue Is a Second Line of Defense During the first hour or so after inflammation large numbers of neutrophils invade the inflamed area as a result of products in the inflamed tissue that attract these cells and cause chemotaxis toward that area. Within a few hours after the onset of severe acute inflammation, the number of neutrophils increases by as many as four-to fivefold. This neutrophilia is caused by inflammatory products that are transported in the blood to the bone marrow, where neutrophils from the marrow capillaries are mobilized and move into the circulating blood. This process results in more neutrophils being made available to the inflamed tissue area  3.A Second Macrophage Invasion of the Inflamed Tissue Is the Third Line of Defense monocytes from the blood enter the inflamed tissue and enlarge to become macrophages. The number of monocytes in the circulating blood is low, and the storage pool of monocytes in the bone marrow is much less than that of the neutrophils. The buildup of macrophages in inflamed tissue is much slower than that of neutrophils. After several days to several weeks, the macrophages become the dominant phagocytic cell in the inflamed area because of the increased bone marrow production of monocytes. 4.The Fourth Line of Defense is the Greatly Increased Production of Both Granulocytes and Monocytes by Bone Marrow This process results from stimulation of the granulocytic and monocytic progenitor cells of the marrow. it takes 3 to 4 days for the newly formed granulocytes and monocytes to reach the stage of leaving the marrow area. Factors Involved in the Feedback Control of the Macrophage and Neutrophil Response (produced by activated macrophages and T cells in the inflamed tissues) 1. Tumor necrosis factor (TNF) 2. Interleukin-1 (IL-1) 3. Granulocyte-monocyte colony-stimulating factor (GM-CSF) 4. Granulocyte colony-stimulating factor (G-CSF) 5. Monocyte colony-stimulating factor (M-CSF) Formation of Pus When the neutrophils and macrophages engulf large numbers of bacteria and necrotic tissue, essentially all the neutrophils and many of the macrophages eventually die. The combination of various portions of necrotic tissue, dead neutrophils, dead macrophages, and tissue fluid is commonly known as pus. When the infection has been suppressed, the dead cells and necrotic tissue in the pus gradually autolyze over a period of days and are absorbed into the surrounding tissues until most of the evidence of the tissue damage is gone. EOSINOPHILS  Eosinophils Are Produced in Large Numbers in Persons with Parasitic Infections. Most parasites are too large to be phagocytized. The eosinophils attach themselves to the surface of the parasites and release substances such as hydrolytic enzymes, reactive forms of oxygen, and larvicidal polypeptides called major basic proteins, which then kill many of the invading parasites. The eosinophils normally constitute about 2% of all the blood leukocytes.  In addition to combating parasitic infections, eosinophils have a propensity to collect in tissues in which allergic reactions have occurred. This results from the release of eosinophil chemotactic factor from mast cells and basophils. The eosinophils are believed to detoxify some of the inflammation-inducing substances released by the mast cells and basophils and destroy allergen-antibody complexes, thus preventing spread of the inflammatory process. BASOPHILS  Basophils Are Circulating Mast Cells. Mast cells and basophils liberate heparin into the blood, which prevents blood coagulation. These cells release histamine, bradykinin and serotonin, which contribute to the inflammation process. The mast cells and basophils play an important role in some allergic reactions.  The immunoglobulin E (IgE) class of antibodies (those responsible for allergic reactions) has a propensity to become attached to mast cells and basophils. The resulting attachment of the allergic antigen to the IgE antibody causes the mast cells or basophils to rupture and release exceedingly large quantities of histamine, bradykinin, serotonin, heparin. These substances in turn cause the local vascular and tissue reactions that are characteristic of allergic manifestation. PLATELETS : This are small fragments of bone marrow cellsand therefore not really classified as cells themselves.  Functions : 1.vasoconstriction. 2.form temporary platelet plug tostop bleeding. 3.secrete procoagulants to promote blood clotting. 4. digest and destroy bacteria. 5. Secrete some chemicals to attract neutrophil and monocyte to the site ofinflammation. 6. secrete growth factor to maintain the lining of blood vessel. Non – cellular composition Plasma  Plasma : It is straw coloured , slightly , alkaline , viscous fluid. It contains 90-92 %water , 10% of solutes and 7%of protein. Plasma proteins such as serum albumin , serum globulin , heparin , fibrinogen and prothrombin. Other nutrients such as glucose , amino acids, & glycerols. Nitrogenous waste as urea , uric acid , ammonia, and creatinine. Gases like oxygen,carbon-dioixde , nirtogen. Regulatory substances such as enzymes and hormones. Inorganic substances like bicarbonates , chlorides, phosphates, sulphates, Na, K, Ca& Mg ions, etc.