Blood PDF

Blood Ema Bexheti ( April 2022) Blood is a unique form of connective tissue in which cells are suspended in circulating fluid. It consists of formed elements, erythrocytes, leukocytes and platelets suspended in plasma. Blood cells also have limited life span and are continually replaced in the red...

Blood Ema Bexheti ( April 2022) Blood is a unique form of connective tissue in which cells are suspended in circulating fluid. It consists of formed elements, erythrocytes, leukocytes and platelets suspended in plasma. Blood cells also have limited life span and are continually replaced in the red bone marrow. It is circulated around the body by the heart and as a result if this circulation blood serves as a transport to gases, nutrients, waste product, cells, and hormones. The fluid is known as ***plasma*** and a typical sample is composed of 90% water, 8% protein, 1% inorganic salts, 0.5% lipids, 0.1% glucose and other minor components. The proteins are numerous and diverse, including albumin, blood coagulation factors, anti-proteases, transport proteins and antibodies (immunoglobulins). Collectively, these proteins exert a water-binding effect known as ***colloidal osmotic pressure*** which helps regulate the distribution of fluid between the plasma and the extracellular space, serving to keep the fluid in the circulation. Blood cell types **Erythrocytes** - Most numerous cells in blood. - They are nonnucleated cells that remain in blood. - Contains hemoglobin with iron molecules in the cytoplasm. - Carries oxygen as oxyhemoglobin and carbon dioxide are carbaminohemoglobin. - They have concave shape which increases the surface area to carry respiratory gases. - Life is about 120 days after which cells are phagocytosed on the spleen, liver, and bone marrow. **Platelets** - ***Thrombocytes*** are specialised cells which bind to and coat damaged vessel walls, plug small defects in blood vessel walls and help activate the blood-clotting cascade. They are essential for ***haemostasis***, the system that controls bleeding. - They don't have a nucleus **Leukocytes** - Contain nuclei and are subdivided into granulocytes and agranulocytes. - Granulocytes contain cytoplasmic granules, they are neutrophils, eosinophils, basophils. - Agranulocytes are without cytoplasmic granules; they are monocytes and lymphocytes. ***Granulocytes*** I. **Neutrophils** - Cytoplasm appears clear under microscope. - Nucleus contain several lobes connected by thin chromatin stands. - Short life span in blood or connective tissue, ranging from hours to days. - Very active phagocytes that are attracted to foreign material by chemotactic factors -- migration cellular stimulants. - Constitute about 60% to 70% of blood leukocytes. II. **Eosinophils** - Cytoplasm filled with large pink or eosinophilic granules. - Nucleus typically bilobed. - Short life span or connective tissue. - Phagocytic with affinity for antigen-antibody complexes. - Release a chemical that neutralizes histamine and other mediators of inflammatory reactions, - Constitute about 2% to 4% of blood leukocytes. III. **Basophils** - Cytoplasm contains dark blue or brown granules. - Short life span. - Nucleus stains palely basophilic, but is normally obscured. - Granules contain histamine and heparin. - Less than 1% of blood leukocytes Agranulocytes I. **Lymphocytes** - No granules in cytoplasm and vary in size from small to large. - Dense staining nucleus surrounded by a narrow cytoplasmic rim - Life span is from days to months. - Essential in immunologic defense of organism, - B lymphocytes form plasma cells in the connective tissue when exposed to specific antigen. - Constitute about 20% to 30% of blood leukocytes. II. **Monocytes** - Largest agranular leukocyte - Horseshoe shaped nucleus - Lives in connective tissue for months where they become powerful phagocytes. - Constitute about 3% to 8% of blood leukocytes. **Hemopoiesis** **Sites of Hemopoiesis** - Depend on the stage of development of the organism. - In Embryo, the initial hemopoietic site is the yolk sac. - Later in development, liver, spleen, lymph nodes, and bone marrow from the blood. - In adults, red marrow is limited to the skull, sternum, vertebrae, and pelvic bone. - Long bones contain yellow marrow and lose hemopoietic functions. - In this process, all blood cells originate from a common stem cell in the red bone marrow that is self-renewing. Because this stem cell type can produce all blood cell types, it is called the pluripotential hematopoietic stem cell.