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ACCESS TO SURGERY: 500 SINGLE BEST ANSWER QUESTIONS IN GENERAL AND SYSTEMIC PHYSIOLOGY1.13Answer: AA positiveAccording to the ABO blood typing system there are four differentkinds of blood types: A, B, AB or O.general• Blood group A - If you belong to the blood group A,you have A antigens on the surface of your red bloodcells and B antibodies in your blood plasma.• Blood group B - If you belong to the blood group B,you have B antigens on the surface of your red bloodcells and A antibodies in your blood plasma.• Blood group AB - If you belong to the blood group AB,you have both A and B antigens on the surface of yourred blood cells and no A or B antibodies at all in yourblood plasma.• Blood group O - If you belong to the blood groupO, you have neither A nor B antigens on the surfaceof your red blood cells but you have both A and Bantibodies in your blood plasma.Many people also have a so-called Rh factor on the red blood cell’ssurface. This is also an antigen and those who have it are calledRh+. Those who have not are called Rh–. A person with Rh– blooddoes not have Rh antibodies naturally in the blood plasma (as onecan have A or B antibodies, for instance) but they can develop Rhantibodies in the blood plasma if they receive blood from a personwith Rh+ blood, whose Rh antigens can trigger the production ofRh antibodies. A person with Rh+ blood can receive blood from aperson with Rh– blood without any problems. So, in this vignettethe patient’s blood group is A positive as he has antigen A, antibodyB and Rh antigens.210
ANSWERS1.14Answer: CIt is the largest immunoglobin moleculeIgM forms polymers where multiple immunoglobulins are covalentlylinked together with disulphide bonds, normally as a pentameror occasionally as a hexamer. It has a large molecular mass ofapproximately 900 kDa (in its pentamer form). The J chain is attachedto most pentamers, while hexamers do not possess the J chain dueto space constraints in the complex. Because each monomer hastwo antigen binding sites, an IgM has 10 of them; however, it cannotbind 10 antigens at the same time because they hinder each other.Because it is a large molecule, it cannot diffuse well and is found inthe interstitium only in very low quantities. IgM is primarily foundin serum; however, because of the J chain, it is also important as asecretory immunoglobulin.generalDue to its polymeric nature, IgM possesses high avidity and isparticularly effective at complement activation. It is sometimescalled a ‘natural antibody’, but it is likely that the antibodies arisedue to sensitisation in the very young to antigens that are naturallyoccurring in nature. For example anti-A and anti-B IgM antibodiescan be formed in early life as a result of exposure to anti-A- andanti-B-like substances that are present on bacteria or perhaps alsoon plant materials. In germ-line cells, the gene segment encodingthe µ constant region of the heavy chain is positioned first amongother constant-region gene segments. For this reason, IgM is thefirst immunoglobulin expressed by mature B cells.IgM is also by far the physically largest antibody in the circulation. IgMantibodies are mainly responsible for the clumping (agglutination)of red blood cells if the recipient of a blood transfusion receivesblood that is not compatible with his/her blood type. IgM antibodiesappear early in the course of an infection and usually do not reappearafter further exposure. IgM antibodies do not pass across the humanplacenta. These two biological properties of IgM make it useful inthe diagnosis of infectious diseases. Demonstrating IgM antibodiesin a patient’s serum indicates recent infection or, in serum from aneonate, indicates intrauterine infection such as congenital rubella.211
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Page 17 and 18: ANSWERS1.9Answer: AUse anaerobic me
Page 19: ANSWERS1.11Answer: AErythropoietinE
Page 23 and 24: ANSWERSis known to affect humans an
Page 25 and 26: ANSWERS1.19Answer: BDecrease the ra

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