Chapter 17 – Blood

Functions of blood Transportation/distribution Regulation/homeostasis Oxygen, carbon dioxide, nutrients, waste products, hormones Regulation/homeostasis Body temperature, pH, fluid volume Protection Clotting Fights infection

Blood Classified as connective tissue Color pH Volume Large extracellular matrix (plasma) approx 55% Formed elements approx 45% Color Due to hemoglobin in red blood cells Bright red = oxygen-rich; dark brick red = oxygen-poor pH Slightly alkaline 7.35 – 7.45 Volume Approx 8% of body weight Males – 5-6 L Females – 4-5 L

Whole blood composition

Formed elements Are created in red bone marrow (hematopoiesis or hemopoiesis) from stem cells Erythrocytes (red blood cells) Leukocytes (white blood cells) Only type that are true cells Thrombocytes (platelets)

Erythrocyte structure Biconcave discs Allows for rapid gas diffusion Anucleate and no organelles Packed with hemoglobin

Hemoglobin structure 4 polypeptide chains (2 alpha and 2 beta chains) Each chain has an associated heme group Each heme group has a central iron atom Serves as the binding site for oxygen molecule

Gas exchange In lungs In body tissues Oxygen diffuses from air sacs in lungs into blood and binds with iron in hemoglobin Oxyhemoglobin – bright red In body tissues Oxygen detaches from iron to diffuse out of bloodstream Deoxyhemoglobin – dark red Hemoglobin also carries about 20% of carbon dioxide Carbaminohemoglobin CO2 binds to amino acids of globin chains

Erythrocyte production Red bone marrow Large capillaries (blood sinusoids) Cells Immature blood cells Marcophages – consume debris/foreign cells Hemocytoblast Ability to become any bloodcell type Once ‘committed’ it can not change pathway Pathway Color of cell changes from blue to pink as hemoglobin accumulates Reticulocytes Speckled appearance due to clumped ribosomes In circulation approx 2 days before forming mature RBC 1 – 2% of RBC count; indicates rate of RBC production

Regulation of RBC production Erythropoietin (EPO) Hormone produced by (mainly) kidneys and liver Stimulates RBC production in response to low blood oxygen levels Also in response to testosterone Commerically available for kidney failure patients EPO increases hematocrit (measure of % of RBCs in whole blood) Has been abused by athletes

Blood Typing Antigens or agglutinogens Antibodies or agglutinins Glycoproteins on the surface of RBCs that serve as identification Antibodies or agglutinins Will attack foreign antigens Causes agglutination, or clumping Small vessels can become blocked Leads to cell destruction Free hemoglobin in kidneys can result in acute renal failure ABO and Rh can cause severe reactions if mismatched during a blood transfusion

ABO blood types

Rh factor + has the Rh antigen; - does not Rh – individuals do not have preformed antibodies against the Rh factor Must have an exposure to the antigen in order to form antibodies against it Rh- woman Risk of erythroblastosis fetalis Given Rogam during pregnancy

Erythroblastosis fetalis

Leukocytes Involved with immunity Diapedesis – WBCs can leave bloodstream and enter the lymphatic system and loose connective tissue Amoeboid movement Types Granulocytes – cytoplasm contains obvious granules Neutrophil Eosinophil Basophil Angranulocytes – cytoplasm does not contain granules Monocyte Lymphocyte

Granulocytes Neutrophil Eosinophil Basophil Nucleus is multilobed Also called polymorphonuclear leukocytes (PMNs) Phagocytize bacteria Eosinophil Fight parasites that are too large for phagocytosis Release enzymes that digest parasite Basophil Histamine – allergic reactions Vasodilator; attracts other WBCs Heparin – antocoagulant

Agranulocytes Monocytes Lymphocytes Enters tissues to become macrophages Fight viral infections, chronic infections, bacterial-infected cells Lymphocytes Most are located within the lymphatic system T cells Destroy infected cells and tumor cells B cells Plasma cells produce antibodies Fight ‘free’ infectious agents (haven’t entered a cell yet)

Leukocyte production Relative amount of WBCS “Never Let Mom Eat Beans” Lifespan = less than 10 days Stem cell lines Hemocytoblast differentiates into either: Lymphoid stem cell line Develops into lymphocytes Myeloid stem cell line Develops into all formed elements of blood except lymphocytes

Thrombocyte (platelet) production Stimulated by thrombopoietin (produced by kidneys) Megakaryocyte is formed by mitosis without cytokinesis Megakaryocyte presses against sinusoid wall and extends cytoplasmic branches through walls into bloodstream Break off to form platelets

Hemostasis Hemostasis – stopping of bleeding 3 stages Clot retraction Vascular Vascular spasm Endothelial damage exposes underlying collagen Smooth muscle contraction; endothelium becomes sticky Platelet Platelets adhere to endothelium and each other to form a plug Coagulation Clotting cascade ultimately forms fibers Clot retraction Platelets contract – brings damaged regions closer together for repair

Fibrinolysis Clot dissolution Plasminogen converts to plasmin Plasminogen trapped in clot Slow conversion Digests fibrin strands

Abnormal values Red blood cells White blood cells Platelets Anemia - low Iron insufficiency, blood loss, kidney disease, bone marrow disorder Polycythemia – elevated Bone marrow disorder, dehydration White blood cells Leukopenia – low Bone marrow disorder Leukocytosis – elevated Infection, inflammation, bone marrow disorder Platelets Thrombocytopenia – low Excessive destruction or inadequate production Thrombocytosis – elevated Infection, inflammation, cancer