HEMATOLOGY ANATOMY AND PHYSIOLOGY • Objectives • By the end of this lesson, you should be able to: • 1. Define blood • 2. Describe the composition of blood • 3. Describe the functions of blood • 4. Describe the composition and structure of the formed elements of blood • 5. Describe the composition and functions of plasma • Blood- is a specialized bodily fluid that delivers necessary substances (such as nutrients and oxygen) to the body's cells and transports waste products away from those same cells. It consists of a fluid and formed elements. • The fluid portion of blood (plasma), is one of the three major body fluids (interstitial and intracellular fluids are the other two). Whole blood constitutes about 8% of total body weight, plasma accounts for 55%, and the formed elements account for about 45% of the total blood volume. • FUNTIONS OF BLOOD • Blood performs many important functions within the body. These include: - • 1. Supply of oxygen to tissues (bound to hemoglobin, which is carried in red cells) • 2. Supply of nutrients such as glucose, amino acids, and fatty acids (dissolved in the blood or bound to plasma proteins (e.g., blood lipids) • 3. Removal of waste such as carbon dioxide, urea, and lactic acid • 4. Immunological functions, including circulation of white blood cells, and detection of foreign material by antibodies • 5. Coagulation, which is one part of the body's sel frepair mechanism (the act of blood clotting when you get cut to stop the bleeding.) • 6. Messenger functions, including the transport of hormones and the signaling of tissue damage • 7. Regulation of body pH (the normal pH of blood is in the range of 7.35–7.45) (covering only 0.1 pH unit) • 8. Regulation of core body temperature • 9. Hydraulic functions • How much blood does the body contain? • The amount of blood in the body is about 8% of total body weight in average-sized adults. • In a healthy young female, that amounts to about 4 to 5 liters and in a male about 5 to 6 liters. • In addition to gender, blood volume varies with age, body composition, and method of measurement. • A unit of blood is the amount (about 0.5 liter or just under 1 pint) that is collected from a blood donor for transfusion purposes. It constitutes about 10% of total blood volume in many adults FORMED ELEMENTS OF BLOOD They are as follows: • Red blood cells (RBCs) (erythrocytes) •White blood cells (WBCs)(leukocytes) • Platelets (thrombocytes) • FORMED ELEMENTS (CELLS) • One microliter of blood contains: 1) Erythrocytes (RBC) - 4.7 to 6.1 million (male), 4.2 to 5.4 million (female) : • In man, mature RBCs lack a nucleus and organelles. • They contain hemoglobin and distribute oxygen. • The proportion of blood occupied by RBCs is referred to as the hematocrit, and is normally about 45%. • Total surface area of RBCs of the human body roughly covers 2,000 times the body's exterior surface. • 2. Leukocytes • WBCs are part of the immune system; they destroy and remove old or aberrant cells and cellular debris, as well as attack infectious agents (pathogens) and foreign substances. • The cancer of leukocytes is called leukemia. • 3. Thrombocytes • Thrombocytes (platelets), are responsible for blood clotting (coagulation). They change fibrinogen into fibrin. This fibrin creates a mesh onto which red blood cells collect and clot, which then stops more blood from leaving the body and also helps to prevent bacteria from entering the body. • Red blood cells (RBCs; erythrocytes) • 1. Description of mature RBCs • a. They have no nucleus and are shaped like tiny biconcave disks • b. Do not contain ribosomes, mitochondria, and other organelles typical of most body cells • c. Their primary component of the cell is hemoglobin • d. They are the most numerous of the formed elements • Formation of blood cells • The hematopoietic stem cell serves as the original stem cell from which all formed elements of the blood are derived. • It is important to note that all five precursor cells, which ultimately produce the different components of the formed elements, are derived from the hematopoietic stem cell called a hemocytoblast. • The precursor cells are – Proerythroblast, myeloblast, lymphoblast, monoblast, megakaryoblast • Formation of red blood cells • Erythropoiesis— This is the entire process of RBC formation • a.RBC formation begins in the red bone marrow as hematopoietic stem cells and goes through several stages of development to become erythrocytes; entire maturation process requires approximately 4 days • b.RBCs are created and destroyed at approximately 100 million per minute in an adult; homeostatic mechanisms operate to balance the number of cells formed against the number of cells destroyed • Destruction of RBCs • Life span of a circulating RBC averages 105 to 120 days • b. Macrophage cells phagocytose the aged, abnormal, or fragmented RBCs c. Hemoglobin is broken down, and amino acids, iron, and bilirubin are released • White blood cells (leukocytes, WBCs) Granulocytes • a.Neutrophils— make up approximately 65% of total WBC count in a normal blood sample; highly mobile and very active phagocytic cells; capable of diapedesis; cytoplasmic granules contain lysosomes • b.Eosinophils — account for 2% to 5% of circulating WBCs; numerous in lining of respiratory and digestive tracts; weak phagocytes; capable of ingesting inflammatory chemicals and proteins associated with antigen-antibody reaction complexes; provide protection against infections caused by parasitic worms and allergic reactions • Basophils — account for only 0.5% to 1% of circulating WBCs; motile and capable of diapedesis; cytoplasmic granules contain histamine and heparin Agranulocytes • a. Lymphocytes—smallest of the WBCs; second most numerous WBC; account for approximately 25% of circulating WBCs; T lymphocytes and B lymphocytes have an important role in immunity—T lymphocytes directly attack an infected or cancerous cell, and B lymphocytes produce antibodies against specific antigens • b.Monocytes—largest leukocytes • Platelets • 1.Structure • a. In circulating blood, platelets are small, pale bodies that appear as irregular spindles or oval disks • b.They have 3 important properties - agglutination, adhesiveness, and aggregation • c. Platelet counts in adults average 250,000/mm3 of blood; normal range is 150,000 to 400,000/mm3 • 2.Funtions d. Important role in hemostasis and blood coagulation e.Hemostasis—refers to stoppage of blood flow; however, if injury is extensive, the blood-clotting mechanism is activated to assist Platelet plug formation • a.One to five seconds after injury to vessel wall, platelets adhere to damaged endothelial lining and to each other, forming a platelet plug - Temporary platelet plug is an important step in hemostasis b.Normal platelets (positive charge) adhere to damaged capillary wall and underlying collagen fibers, which both have a negative charge c. “Sticky platelets” form physical plug and secrete several chemicals involved in the coagulation process Formation and life span of platelets • The lifespan of platelets is 7 to 10 days • They are formed in red bone marrow, lungs, and spleen by fragmentation of megakaryocytes Megakaryoblast → Megakaryocytes → Platelets • BLOOD PLASMA • A.Plasma—liquid part of blood; clear, straw-colored fluid; made up of 90% water and 10% solutes • B.Solutes—6% to 8% of plasma solutes are proteins, consisting of three main compounds • 1.Albumins—help maintain osmotic balance of the blood • 2.Globulins—essential component of the immunity mechanism • 3.Fibrinogen—key role in blood clotting C. Plasma proteins have an essential role in maintaining normal blood circulation .