Blood

Blood Composition Blood is the body’s only fluid tissue It is composed of liquid plasma and formed elements Formed elements include: Erythrocytes, or red blood cells (RBCs) Leukocytes, or white blood cells (WBCs) Platelets

Blood Composition

If blood is centrifuged Erythrocytes sink to the bottom (45% of blood, a percentage known as the hematocrit) Buffy coat contains leukocytes and platelets (less than 1% of blood) Buffy coat is a thin, whitish layer between the erythrocytes and plasma Plasma rises to the top (55% of blood)

Blood Plasma Composed of approximately 90% water Includes many dissolved substances Nutrients Salts (electrolytes) Respiratory gases Hormones Plasma proteins Waste products

Blood Plasma Blood plasma contains over 100 solutes, including: Proteins – albumin, globulins, clotting proteins, and others Lactic acid, urea, creatinine Organic nutrients – glucose, carbohydrates, amino acids Electrolytes – sodium, potassium, calcium, chloride, bicarbonate Respiratory gases – oxygen and carbon dioxide

Functions of Blood Blood performs a number of functions dealing with: Substance distribution Regulation of blood levels of particular substances Body protection

Functions of Blood Blood transports: Oxygen from the lungs and nutrients from the digestive tract Metabolic wastes from cells to the lungs and kidneys for elimination Hormones from endocrine glands to target organs

Functions of Blood Blood maintains: Appropriate body temperature by absorbing and distributing heat Normal pH in body tissues using buffer systems

Functions of Blood Blood prevents blood loss by: Activating plasma proteins and platelets Initiating clot formation when a vessel is broken Blood prevents infection by: Synthesizing and utilizing antibodies Activating WBCs to defend the body against foreign invaders

Photomicrograph of a Blood Smear Figure 10.2

Figure 17.2

Formed Elements Erythrocytes, leukocytes, and platelets make up the formed elements Only WBCs are complete cells RBCs have no nuclei or organelles, and platelets are just cell fragments Most formed elements survive in the bloodstream for only a few days Most blood cells do not divide but are renewed by cells in bone marrow

Formed Elements Erythrocytes (RBCs) Biconcave disks Essentially bags of hemoglobin Anucleate (no nucleus) Contain very few organelles

Erythrocytes (RBCs) Figure 17.3

Erythrocytes Because erythrocytes are anucleate they cannot: Make new proteins Continue cell division and grow

Formed Elements Erythrocytes (RBCs) Main function is to transport oxygen Hemoglobin Iron-containing protein Binds strongly, but reversibly, to oxygen

Production of Erythrocytes Hematopoiesis – blood cell formation Hematopoiesis occurs in the red bone marrow of the: Axial skeleton and girdles Epiphyses of the humerus and femur Hemocytoblasts give rise to all formed elements

Production of Erythrocytes Figure 17.5

Erythropoiesis Circulating erythrocytes – the number remains constant and reflects a balance between RBC production and destruction Too few RBCs leads to tissue hypoxia Too many RBCs causes undesirable blood viscosity Erythropoiesis is hormonally controlled and depends on adequate supplies of iron, amino acids, and B vitamins

Erythropoiesis Erythropoietin The hormone released by the kidneys Triggered by: Hypoxia due to decreased RBCs Decreased oxygen availability Increased tissue demand for oxygen

Homeostasis: Normal blood oxygen levels Increases O 2 -carrying ability of blood Erythropoietin stimulates red bone marrow Reduces O 2 levels in blood Kidney (and liver to a smaller extent) releases erythropoietin Enhanced erythropoiesis increases RBC count Stimulus: Hypoxia due to decreased RBC count, decreased amount of hemoglobin, or decreased availability of O 2 Start Erythropoietin Mechanism

Erythrocytes The life span of an erythrocyte is 100–120 days Old RBCs become rigid and fragile, and their Hb begins to degenerate Dying RBCs are engulfed by macrophages Heme and globin are separated and the iron is salvaged for reuse

Anemia Blood has abnormally low oxygen- carrying capacity Signs/symptoms include fatigue, paleness, shortness of breath, and chills Erythrocyte Disorders

Sickle-cell anemia Results from a defective gene coding for an abnormal Hb called hemoglobin S (HbS) This defect causes RBCs to become sickle- shaped in low oxygen situations Offspring must inherit two copies of the gene from their parents to have the disorder

Figure 10.3

Erythrocyte Disorders Polycythemia An abnormal excess of erythrocytes that increases blood viscosity Can occur naturally in individuals that live in high altitudes because there is less available oxygen Can be treated by removing some blood and replacing it with saline

Leukocytes Figure 17.10

Leukocytes The only blood components that are complete cells: Are less numerous than RBCs Make up 1% of the total blood volume Can leave capillaries via diapedesis Move through tissue spaces Leukocytosis – WBC count over 11,000 / mm 3 Normal response to bacterial or viral invasion

Figure 17.9

Neutrophils Most numerous leukocyte(50-70%) Are our body’s bacteria slayers Dramatic increase during acute bacterial infections Meningitis, appendictis Leukocytes

Eosinophils 2-4% of all leukocytes Lead the attack against parasitic worms that are too large to be phagocytized May also lessen the severity of allergies by inactivating the chemicals released Leukocytes

Basophils Rarest Contain histamine Inflammatory chemical that acts as a vasodilator and attracts other WBCs Antihistamines counter this effect Leukocytes

Lymphocytes 2 nd most numerous type There are two types of lymphocytes: T cells and B cells T cells function in the immune response –fight viruses and cancer cells B cells give rise to plasma cells, which produce antibodies

Monocytes 3-8% of all leukocytes Most numerous during chronic infections Leave circulation and enter tissues to become macrophages They ingest dead or damaged cells Activate lymphocytes for immune response Leukocytes

Leukocyte Disorders Leukemias Group of cancerous conditions involving leukocytes The bone marrow becomes overrun with immature leukocytes that cannot carry out normal functions Other blood cells are crowded out resulting in: Anemia and bleeding problems Most common cause of death is infection

Platelets Not true cells but fragments of the cytoplasm of cells called megakaryocytes Essential for the clotting process Are anucleate so they age quickly and die in about 10 days

Hemostasis “Stoppage of bleeding” Three steps occur: Vascular spasm Platelet plug formation Coagulation Commonly called blood clotting

Hemostasis Vascular Spasm Constriction of the damaged blood vessel It reduces blood loss for 20-30minutes This allow time for the platelet plug to form and blood clotting to take place

Hemostasis Platelet Plug Formation Platelets usually do not stick to each other or linings of blood vessels If endothelium is damaged, collagen fibers are exposed causing platelets to attach to them The platelets swell, become sticky and form spiky processes The platelets become activated and they begin to break down and release several chemicals

Hemostasis Platelet Plug Formation Platelet plugs are loosely knit but are reinforced by threads made up of fibrin Fibrin is a tough insoluble protein Effective for sealing the small tears in a blood vessel

Hemostasis Coagulation Remember, when a blood vessel is broken, platelets clump together and stick to the area of damage These platelets contain substances called clotting factors The clotting factors combine with a protein called prothrombin This is a clotting factor needed for normal blood clotting to occur

Hemostasis Coagulation Prothrombin is converted into an enzyme called thrombin Thrombin is needed to convert a plasma protein called fibrinogen into fibrin The fibrin strands glue the platelets together and make a web that forms the basis of a clot As the clot hardens, it forms a protective seal over the cut.

Hemostasis Coagulation Clot formation is usually completed within 3 to 6 minutes after the blood vessel is damaged Within minutes, clot retraction is induced Platelets have actin and myosin proteins that contract As they contract, they pull on the surrounding fibrin strands and squeeze out serum This helps to bring the edges of the blood vessel closer together

Hemostasis Disorders Thrombus A clot that develops and persists in an unbroken blood vessel Can block circulation, resulting in tissue death Embolus A thrombus freely floating in the blood stream Pulmonary emboli can impair the ability of the body to obtain oxygen Cerebral emboli can cause strokes

Substances used to prevent undesirable clots: Aspirin Heparin An anticoagulant used clinically for pre- and postoperative cardiac care Prevention of Undesirable Clots

Hemophilia Hereditary bleeding disorders caused by lack of clotting factors (X-linked disorder) Symptoms include prolonged bleeding and painful and disabled joints Treatment is with blood transfusions and the injection of missing factors Hemophilia A – most common type (83% of all cases) due to a deficiency of factor VIII Hemostasis Disorders