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Blood & Blood Spatter Chapter 8 Composition of Blood • Three components – Red blood cells (erythrocytes) – White blood cells (leukocytes) – Platelets (thrombocytes) • Suspended in liquid called plasma – Carries antibodies, hormones, clotting factors, nutrients (glucose, amino acids, salts, minerals) Composition of Blood Blood Cells • RBC – carry respiratory gases (oxygen & carbon dioxide) – Hemoglobin – iron-containing protein that transports oxygen • Responsible for red color of blood • WBC – fight disease and foreign elements • Platelets – involved in blood clotting and repairing damaged blood vessels Leukocytes (WBC) • Only blood cells with a nucleus & DNA – Used for DNA profiling • Some are phagocytes (engulf foreign cells) and some release antibodies (proteins that “label” foreign cells for destruction) • Basophils, eosinophils, neutrophils, lymphocytes (B&T cells), monocytes Types of WBC Elements of Blood Blood Typing • Class evidence – Excludes a person as a suspect – Largely replaced by STR analysis using DNA from WBCs (why?) • Blood from one person does not always freely mix with blood from another – Agglutination occurs when mixing some blood types (clumping that leads to death) – Antigens on RBC identify a blood type – “name tags” that cause an immune response when foreign to the body A & B Antigens • A & B antigens determine ABO blood group – Act as nametags on RBC for identification – Antibodies bind to foreign antigens • Type A: RBC have A antigens • Type B: RBC have B antigens • Type AB: RBC have both A & B antigens • Type O: RBC have no antigens Antigens & Blood Types Rh Antigens • Additional protein antigen on RBCs – Presence or absence determines Rh blood group • Rh antigen present: Rh+ blood type • Rh antigen absent: Rh- blood type Antigen-Antibody Response • B-lymphocytes are WBC that secrete antibodies – Y-shaped protein molecules that bind to specific antigens, fitting together like a puzzle piece – Bind to foreign substances (viruses, bacteria, RBC of a foreign blood type) Agglutination • Y-shaped antibody arm fits with the foreign antigen of a RBC, second arm can fit with another antigen on another RBC – Causes clumping – If occurs in a blood transfusion, clumping can cause blood to cease flow due to obstruction, resulting in death • used to test blood to determine blood types – Mix antibodies with unknown blood to determine when agglutination does and does not occur Agglutination Agglutination No Agglutination Agglutination Blood Typing Tests Probability Type Percent Fraction A 42% 42/100 B 12% 12/100 AB 3% 3/100 O 43% 43/100 Rh+ 85% 85/100 Rh- 15% 15/100 Multiply to get the probability of A+, A-, B+, B-, etc. Example: A+ (.42 x .85 = .357 or 35.7%)