BIO 241 1nd Edition Lecture 3 Outline of Last Lecture I. Erythrocytes II. Hemoglobin (Hb)III. Erythrocyte lifespanIV. Leukocytes V. Containment of pathogensVI. Thrombocytes Outline of Current Lecture II. Hemostasis (control of bleeding)III. Clot retraction (syneresis)IV. Fibrinolysis (clot dissolution)V. Blood typesCurrent LectureII. There are three basic mechanisms that begin immediately aftervascular injury. Vascular spasm occurs first and is when the blood vesseldecreases its diameter by contracting to limit the amount of blood flowto this area. Platelet plug formation occurs second and it also has threebasic mechanisms which are shown in the diagram to the side. Coagulation is the third basic mechanism and is when the blood cellsclot together. The first step in platelet plug formation is adhesion and is when plateletsstick to the wound site. The next step is the release reaction which is thedegranulation of the platelet, meaning it starts releasing clotting factors(thrombocytes are from the previous lecture). The final step of plateletplug formation is aggregation which is the continuation of plateletssticking to and around the wound site. III. Clot retraction is the cross-linking of fibrin which causes compactionof clot into wound site. IV. Fibrinolysis is the dissolution of clot, meaning the fibrin in the clot begins to break down.V. In humans, there are various blood types. Using the ABO system, there are four blood types: A, B, AB, and O. RBCs have membrane-bound agglutinogens on them. These agglutinogens are shaped differently for the four types. Within the blood (the components of blood are discussedin previous lecture and will help with this section), the plasma has antibodies on its surface called agglutinins that will destroy any RBC that does not have the correct agglutinogen. These agglutinins consist of anti-A and anti-B (no anti-O) and if paired with the wrong agglutinogen, can cause agglutination (the clumping of RBCs) and hemolysis (the rupture or destruction of redblood cells). The diagram below will significantly help with understanding which blood type and which plasma type are compatible. Notice that group O does not have any agglutinogens and AB has no agglutinins. AgglutinogensAgglutininsI know I have often heard that blood type O is the universal donor of blood and that AB is the universal receptor. Dr. Ballard clarified that this statement is actually incorrect. O blood is the universal donor of cells,not the blood in its entirety. As shown above, group O does not have any membrane-bound agglutinogens; therefore, it can give its cells to any type. This does not include the plasma because there are anti-A and anti-B which would lead to hemolysis. Type AB is the universal donor of plasma, meaning its plasma get be given to any blood type since there are no agglutinins. AB cannot give its cells to everyone because of the agglutinogens that have both
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