Blood: An Introduction to Blood and the Cardiovascular System - PDF

Chapter 19: Blood An Introduction to Blood and the Cardiovascular System Cardiovascular system consists of... - A pump (the heart) - Series of conducting hoses (blood vessels) - Fluid connective tissue (blood) 19-1 Blood, composed of plasma and formed elements, provides transport, regula...

Chapter 19: Blood An Introduction to Blood and the Cardiovascular System Cardiovascular system consists of... - A pump (the heart) - Series of conducting hoses (blood vessels) - Fluid connective tissue (blood) 19-1 Blood, composed of plasma and formed elements, provides transport, regulation, and protective services to the body. **[Blood:]** specialized connective tissue that contains cells suspended in a fluid matrix. **Functions of blood** - Transporting dissolved gases, nutrients, hormones, and metabolic wastes. - Regulating pH, ion composition of interstitial fluids. - Restricting fluid losses at injury sites. - Defending against toxins and pathogens. - Stabilizing body temperature. **Characteristics of blood** - 38ºC (100.4ºF). - High viscosity. - Slightly alkaline (pH of 7.35--7.45). - Blood volume (liters) = 7 percent of body weight (kilograms). - A 75-kg (165-lb) person would have approximately 5.25 liters (5.4 quarts) of blood. **Whole blood** - **[Plasma ]** - Fluid containing many proteins. - **[Formed elements ]** - Cells and cell fragments. **[Fractionation:]** process of separating whole blood into plasma and formed elements. **Plasma** - Makes up about 55% of blood volume. - More than 90% of plasma is water. - Also contains dissolved plasma proteins and other solutes. - Similar in composition to interstitial fluid. - Because water, ions, and small solutes are exchanged across capillary walls. **Plasma Proteins** **Albumins (60%)** - Major contributors to plasma osmolarity. - Transport fatty acids, thyroid hormones, some steroid hormones, etc. **Globulins (35%)** - Antibodies (immunoglobulins). - Transport globulins including hormone-binding proteins, metalloproteins, apolipoproteins (lipoproteins), and steroid-binding proteins. **Fibrinogen (4%)** - Soluble protein that functions in clotting. - Converted to insoluble fibrin. - Conversion of fibrinogen to fibrin leaves serum (fluid) in blood sample. **Other plasma proteins (1%)** - Varying concentrations of enzymes and hormones. **Origins of plasma proteins** - More than 90% made in liver. - Including all albumins, fibrinogen, most globulins, and various proenzymes. - Antibodies made by plasma cells. - Peptide hormones made by endocrine organs. **Formed elements** - Red blood cells- **erythrocytes** - White blood cells- **leukocytes** - Cell fragments (platelets)- **thrombocytes** **[Hemopoiesis:]** process of producing formed elements. 19-2 red blood cells, formed by erythropoiesis, contain hemoglobin that transports respiratory gases. **Red blood cells (RBCs)** - Also called **[erythrocytes]**. - Make up 99.9 percent of formed elements. - **[Hemoglobin:]** red pigment that gives whole blood its color. - Binds and transports oxygen and carbon dioxide. **[RBC count:]** number of RBCs per microliter of whole blood. - Adult male: 4.5--6.3 million - Adult female: 4.2--5.5 million **[Hematocrit:]** percentage of formed elements in blood, packed cell volume (PCV). - Adult male: 46 - Adult female: 42 **Structure of RBCs** - Small, highly specialized cells. - **[Biconcave discs:]** thin central region and thicker outer margin. **Important effects of RBC structure on function** - Large surface-area-to-volume ratio. - Quickly absorb and release oxygen. - **[Rouleaux:]** formed stacks. - Smooth blood flow through narrow blood vessels. - Bend and flex when entering small capillaries. - 7.8-µm RBC can pass through a 4-µm capillary. **Mature RBCs** - **[Anucleate:]** lack nuclei. - Lack mitochondria and ribosomes. - Unable to divide, synthesize proteins, or repair damage. - Live about 120 days. **Hemoglobin (Hb or Hgb)** - Protein in RBCs that transports respiratory gases. - Normal hemoglobin - Adult male: 14--18 g/dL whole blood - Adult female: 12--16 g/dL whole blood - Complex quaternary structure. - Four globular protein subunits. - Two alpha (α) chains and two beta (β) chains. - Each with one molecule of **[heme]**. - Each heme contains one iron ion. - Iron interacts with oxygen to form **[oxyhemoglobin, HbO2]**. - Dissociate easily to form **[deoxyhemoglobin]**. **Fetal hemoglobin** - Form of hemoglobin in embryo or fetus. - Binds oxygen more readily than does adult hemoglobin. - Takes up oxygen from maternal blood at placenta. **Hemoglobin function** - Each RBC contains about 280 million Hb molecules. - Each RBC can carry over a billion molecules of O2. - In peripheral capillaries, where O2 is low, hemoglobin. - Releases O2. - Binds CO2, forming **[carbaminohemoglobin]**. - At the lungs, where O2 is high, hemoglobin. - Binds O2. - Releases CO2. **[Anemia:]** results when hematocrit or Hb content of RBCs is reduced. - Interferes with oxygen delivery to peripheral tissues. **RBC formation and turnover** - 1 percent of circulating RBCs are replaced per day. - About 3 million new RBCs enter bloodstream each second. **[Erythropoiesis:]** red blood cell formation. - In embryos, embryonic blood cells move from bloodstream to liver, spleen, thymus, bone marrow. - Differentiate into **[stem cells]**. - That divide to produce blood cells. - In adults, occurs only in **[myeloid tissue:]** red bone marrow. **[Hemocytoblasts]**, also called hematopoietic stem cells (HSCs) - Stem cells in myeloid tissue that divide to produce... - **[Myeloid stem cells:]** become RBCs and some WBCs. - **[Lymphoid stem cells:]** become lymphocytes. Hematologists have identified several stages of RBC maturation... - Myeloid stem cell - Proerythroblast - Erythroblast stages - Reticulocyte - Mature RBC **[Erythropoietin (EPO):]** hormone that stimulates erythropoiesis. - Secreted by kidneys and liver when oxygen in peripheral tissues is low (**[hypoxia]**). **[Blood doping:]** re-infusing packed RBCs to elevate hematocrit. - A dangerous practice used by some athletes. Erythropoiesis requires amino acids, iron, folic acid, and vitamins B12 and B6. **[Pernicious anemia:]** lack of vitamin B12. **Hemoglobin recycling** - Macrophages of spleen, liver, and red bone marrow... - Engulf aged RBCs. - Remove Hb molecules from hemolyzed RBCs. - Break Hb into components. - Only the iron of each heme unit is recycled. **[Hemoglobinuria:]** red or brown urine due to abnormally high hemolysis in bloodstream. **[Hematuria:]** whole RBCs in urine due to kidney or blood vessel damage. Iron is removed from each heme unit, forming green **[biliverdin]**. - Converted to orange-yellow **[bilirubin]**. - Bilirubin is excreted by liver in bile. **[Jaundice:]** caused by buildup of bilirubin. - Converted by intestinal bacteria and oxygen to urobilins and stercobilins. - Urobilins make urine yellow. - Stercobilins make feces brown. **Iron recycling** - Iron removed from heme. - Is bound and stored in phagocytic cell. - Or released into bloodstream. - In bloodstream, iron is bound to **[transferrin]**. - Developing RBCs in red bone marrow absorb transferrins and use them to synthesize Hb. - Excess transferrins are removed in liver and spleen, storing iron in **[ferritin]** and **[hemosiderin]**. 19-3 The ABO and Rh blood groups are based on antigen-antibody responses. **[Surface antigens:]** substances on plasma membranes that identify cells to immune system. - Normal cells are ignored and foreign cells are attacked. Blood type is determined by presence or absence of surface antigens on RBCs: A, B, and Rh (or D). **Four blood types** - **[Type A]** (surface antigen A) - **[Type B]** (surface antigen B) - **[Type AB]** (antigens A and B) - **[Type O]** (neither A nor B) **Rh blood group** Based on presence or absence of Rh antigen. - **[Rh positive (Rh+) ]** - Rh surface antigen is present (e.g., Type O+). - **[Rh negative (Rh--) ]** - Rh antigen is absent (e.g., Type O--). **[Agglutinogens:]** surface antigens on RBCs. - Screened by immune system. **[Agglutinins:]** antibodies in plasma. - Attack antigens on foreign RBCs. - Causing **[agglutination]** (clumping) of foreign cells. **Agglutinins** - Type A blood - Anti-B antibodies - Type B blood - Anti-A antibodies - Type O blood - Both anti-A and anti-B antibodies - Type AB blood - Neither anti-A nor anti-B antibodies - Only **sensitized** Rh-- blood has anti-Rh antibodies **[Cross-reaction (transfusion reaction)]** may occur in a transfusion of blood or plasma from one person to another. - Occurs if donor and recipient blood types are **NOT COMPATIBLE**. - Plasma antibody meets its specific surface antigen. - RBCs agglutinate and may hemolyze. **Compatibility testing** - Performed in advance of transfusions. **[Cross-match testing:]** reveals cross-reactions between donor's RBCs and recipient's plasma. **Type O- is the universal donor.** **Type AB+ is the universal recipient.** - But cross-reactions can still occur. - Because at least 48 surface antigens exist besides A and B. 19-4 The various types of white blood cells contribute to the body's defense. **[White blood cells (WBCs)]**, also called ***leukocytes***. - Have nuclei and other organelles. - Lack hemoglobin. **WBC functions** - Defending body against pathogens. - Removing toxins and wastes. - Attacking abnormal or damaged cells. **Most WBCs are in...** - Connective tissue proper - Organs of lymphatic system A small fraction of WBCs circulates in blood about 5000 to 10,000 per microliter. **Characteristics of circulating WBCs** - All can migrate out of bloodstream. - All are capable of amoeboid movement. - **[Positive chemotaxis:]** all are attracted to specific chemical stimuli. - Some are phagocytic. **Types of WBCs** - Neutrophils - Eosinophils - Basophils - Monocytes - Lymphocytes The WBCs are grouped into 2 classes: granulocytes and agranulocytes. **Granulocytes** **Neutrophils** (neutral pH stain) - Also called ***polymorphonuclear leukocytes*** - 50--70% of circulating WBCs. - Pale cytoplasmic granules containing... - Lysosomal enzymes. - Bactericidal (bacteria-killing) compounds. - Very active, phagocytic cells. - Attack and digest bacteria. - **[Degranulation:]** reduction in number of cytoplasmic granules. - Occurs when vesicle containing pathogen fuses with lysosomes containing enzymes and defensins. - Release prostaglandins and leukotrienes. - Live in bloodstream for 10 hours or less. - Dead neutrophils contribute to pus. **Eosinophils** (acidic pH stains them reddish) - Also called ***acidophils*** - 2--4% of circulating WBCs. - Engulf bacteria, protozoa, and cellular debris. - Attack large parasites by releasing toxic compounds. - Nitric oxide. - Cytotoxic enzymes. - Sensitive to allergens. - Release enzymes that reduce inflammation caused by mast cells and neutrophils. **Basophils** (basic pH stains them blue-blackish) - Less than 1% of circulating WBCs. - Cross capillary endothelium and accumulate in damaged tissues. - Release... - **[Histamine:]** dilates blood vessels. - **[Heparin:]** prevents blood clotting. **Agranulocytes** **Monocytes** - Large, spherical cells. - 2--8% of circulating WBCs. - Remain in bloodstream for 24 hours. - Then enter peripheral tissues to become macrophages. - Aggressive phagocytes that engulf large pathogens. - Release chemicals that attract other phagocytic cells and fibroblasts to injured area. **Three Classes of Lymphocytes** **[T cells (T lymphocytes):]** cell-mediated immunity. - Attack foreign cells or control other lymphocytes. **[B cells (B lymphocytes):]** humoral immunity. - Differentiate into plasma cells, which synthesize antibodies. **[Natural killer (NK) cells:]** detect and destroy abnormal cells. **[Differential count]** of WBC population - Can detect infection, inflammation, and allergic reactions. **WBC Disorders** **[Leukopenia:]** low WBC count. **[Leukocytosis:]** high WBC count. **[Leukemia:]** cancer of WBCs indicated by extreme leukocytosis. **[Leukopoiesis:]** WBC production. - Hemocytoblasts produce myeloid stem cells and lymphoid stem cells. - Myeloid stem cells - Divide to produce **[progenitor cells.]** - Give rise to all formed elements ***except*** lymphocytes. **[Lymphocytopoiesis:]** production of lymphocytes from lymphoid stem cells. **WBC development** Some lymphoid stem cells remain in red bone marrow. - Differentiate into B cells or natural killer cells. Others migrate from red bone marrow to peripheral lymphatic tissues. - Thymus, spleen, and lymph nodes. - Produce lymphocytes. - T cells are produced in thymus. **[Colony-stimulating factors (CSFs):]** hormones that regulate WBC populations. - **[Multi-CSF:]** accelerates production of granulocytes, monocytes, platelets, and RBCs. - **[GM-CSF:]** stimulates granulocyte and monocyte production. - **[G-CSF:]** stimulates granulocyte production. - **[M-CSF:]** stimulates monocyte production. 19-5 Platelets, disc-shaped cell fragments, function in the clotting process. **[Platelets (*thrombocytes*):]** cell fragments involved in clotting system. - Circulate for 9--12 days. - Removed by phagocytes, mainly in spleen. - 150,000 to 500,000 per microliter of blood. - One-third of platelets in body are stored in vascular organs like the spleen. - Mobilized during a circulatory crisis. **Functions of Platelets** - Release important clotting chemicals. - Temporarily patch damaged vessel walls. - Reduce size of break in vessel wall. **[Thrombocytopoiesis:]** platelet production. - Occurs in red bone marrow. **[Megakaryocytes:]** giant cells in red bone marrow. - Produce platelets by shedding membrane-enclosed packets of cytoplasm. **Hormonal Control of Platelet Production** - Thrombopoietin (TPO) - Interleukin-6 (IL-6) - Multi-CSF 19-6 The process of blood clotting, or hemostasis, stops blood loss. **[Hemostasis:]** cessation of bleeding. Hemostasis has three phases... - Vascular phase - Platelet phase - Coagulation phase **Vascular Phase** - A cut triggers **[vascular spasm]**. - Contraction of smooth muscle fibers of vessel wall. - Lasts about 30 minutes. - Changes in endothelium during vascular phase. - Endothelial cells contract and expose basement membrane to bloodstream. - Endothelial cells release chemical factors and local hormones. - ADP, tissue factor, and prostacyclin. - **[Endothelins]** (peptide hormones). - Cause smooth muscle contraction and cell division. - Endothelial plasma membranes become "sticky". - Seal off tear and prevent blood flow. **Platelet Phase** - **[Platelet adhesion:]** platelets attach to exposed surfaces. - **[Platelet aggregation:]** platelets stick to each other. - Begins within 15 seconds after injury. - Forms **platelet plug** that closes small breaks. - Activated platelets release clotting compounds including... - Adenosine diphosphate (ADP) - Thromboxane A2 and serotonin - Clotting factors - Platelet-derived growth factor (PDGF) - Calcium ions **Factors that Limit Growth of Platelet Plug** - Prostacyclin inhibits platelet aggregation. - Inhibitory compounds released by WBCs. - Circulating enzymes break down ADP. - Negative feedback from serotonin, etc. - Blood clot isolates area from general circulation. **Coagulation Phase** (blood clotting) - Begins 30 seconds or more after injury. - Depends on **[clotting factors]** **(*procoagulants*)**. - Ca2+ and 11 different proteins. - **[Proenzymes:]** inactive enzymes. - Converted to active enzymes that direct reactions in clotting response. - Involves chain reactions of three pathways... - Extrinsic pathway - Intrinsic pathway - Common pathway **Extrinsic pathway** - Damaged endothelial cells or peripheral tissues release **[Factor III]** (tissue factor). - Enzyme complex activates **[Factor X]**. **Intrinsic pathway** - Begins with activation of proenzymes exposed to collagen fibers at injury site. - Platelets release **[PF-3]**. - Enzyme complex activates **[Factor X]**. **Common pathway** - Begins with activation of Factor X. - Factor X activates prothrombin activator. - Converts **[prothrombin]** (proenzyme) to **[thrombin]**. - Thrombin converts **[fibrinogen]** to insoluble **[fibrin]**. - Producing a **[blood clot]**. Thrombin generated in common pathway... - Stimulates formation of tissue factor. - Stimulates release of PF-3 by platelets. Forms **positive feedback loop** that accelerates clotting process. **Feedback control of blood clotting** - Anticoagulants (enzymes that inhibit clotting) - Antithrombin-III - Heparin - Accelerates activation of antithrombin-III. - Thrombomodulin - Activates protein C, which inactivates clotting factors and stimulates formation of plasmin. - Prostacyclin - Inhibits platelet aggregation and opposes factors. **Calcium ions and vitamin K** - Essential to clotting process. - All three pathways require Ca2+. - Vitamin K is required for synthesis of four clotting factors. **Bleeding and clotting extremes** - Thrombocytopenia - Hemophilia - Thrombophilia - Deep vein thrombosis (DVT) **[Clot retraction:]** pulls torn edges of vessel closer together. - Reduces residual bleeding. - Stabilizes injury site. - Reduces size of damaged area. - Making it easier for fibroblasts, smooth muscle cells, and endothelial cells to complete repairs.