USMLE题库Endocrinology11-20.pptx

USMLE题库Endocrinology11-20.pptx

《USMLE题库Endocrinology11-20.pptx》由会员分享，可在线阅读，更多相关《USMLE题库Endocrinology11-20.pptx（22页珍藏版）》请在冰豆网上搜索。

Endocrinology题库Q11A16-year-oldCaucasiangirlwhoaspirestobeafashionmodelpresentsforaroutineexamination.Shewishestomodifyherdietandexerciseplanssothatshecanloseanadditional20lbs（9kg）becauseshebelievessheiscurrentlytoofat”toparticipateinabeautypageantlaterthisyear.Sheisfrustratedthatshecantseemtodroptheseextrapounds11inspiteofstrictdietarylimitationsandvigorousexercisefortwohourseachday.Hermenstrualhistoryissignificantforamenorrheaforthepastfourmonths.Herheightis（165cm）andherweightis100lbs（45.3kg）,resultinginaBMIof16.6Kg/m2.Onphysicalexamination,sheispaleandemaciated.Finehairisnotedonhertrunk.Whichofthefollowingisthemostlikelymechanismofheramenorrhea?

A.PrimaryovarianfailureB.PrimarypituitarydysfunctionC.HypothyroidismD.HyperprolactinemiaE.HypothalamicdysfunctionA11Correctanswer:

EAnorexianervosaisaneatingdisordercharacterizedbyanintensefearofeating,significantlossofbodyweight（tolessthan85%ofexpectedweightorBMIlessthan17.5kg/m2）,inaccurateperceptionofonesownbodyshapeandsize,andamenorrhea.TheamenorrhearesultsfromlossofpulsatileGnRHreleasefromthehypothalamus,whichoccurswhenthelevelofbodyfatfallsbelowacertaincriticallevel.LossofthiscyclicgonadotropinreleaseleadstoadecreaseinLHandFSHsecretionfromthepituitary,whichinturncausescirculatingestrogenlevelstobelow.AdministrationofpulsatileGnRHinindividualswithanorexianervosaallowsforthenormalizationofestrogenlevelsandsubsequentovulation.Amenorrheaalsooftenoccursinseriousathleteswithverylowbodyfat（eg.longdistancerunners,balletdancers）aswellasinindividualswithprolongedcachecticillnesses,viathesamemechanism.Ifleftuntreated,thelowestrogenlevelsintheseamenorrheicindividualscouldleadtoosteoporosis.（ChoicesAandB）TheamenorrheainpatientswithanorexianervosastemsfromadeficiencyinhypothalamicGnRHrelease,ratherthanaproblemwiththepituitaryorovaries.（ChoiceC）Whilethedecreasedcaloricintakeassociatedwithanorexianervosacancausethyroiddysfunction,thesethyroidabnormalitiesplaynoroleinthedevelopmentofamenorrhea.Patientswithanorexianervosacandeveloptheabnormalityofthyroidfunctioningtermed,fsickeuthyroidsyndrome/orlowT3syndrome.Earlyinthecourseofanorexia,T3levelsarelow,andT4andTSHlevelsarenormal.However,inprolongedseveredisease,bothT3andT4levelsarelow.（ChoiceD）Whilehyperprolactinemiaisaknowncauseofamenorrhea（andgalactorrhea,aswell）,patientswithanorexianervosadonottypicallyhavehyperprolactinemia.Q12A43-year-oldnursecomestothephysiciancomplainingofepisodicconfusion,blurredvision,tremors,andsweating.Theseepisodeshaveincreasedinintensityoverthepastyear.Herothermedicalproblemsincludemajordepression.Serumlaboratoryresultsobtainedduringanepisodeareasfollows:

Glucose35mg/dLInsulin18pU/L（N:

9pU/L）Proinsulin10pU/L（N:

20%oftotalinsulin）C-peptide4.01ng/mL（N:

0.8-1.9ng/mL）Whichofthefollowingisthemostlikelycauseofherhypoglycemia?

A.Alpha-celltumorB.InsulinadministrationC.SomatostatinomaD.SulfonylureauseE.VIP-secretingtumoA12Correctanswer:

DThispatientishypoglycemicduetoexcessiveendogenousinsulinsecretion.Theproductionofinsulinbeginswiththesynthesisofproinsulinintheendoplasmicreticulum,whereitisfoldedanditsdisulfidebondsareoxidized.ItissubsequentlytransportedtotheGolgiapparatus,whereitispackagedintosecretoryvesiclesandfurtherprocessedbyaseriesofproteasestoformmatureinsulinandc-peptide.Insulinsecretagoguessuchassulfonylureasandmeglitinidescauseincreasedinsulinproductionandsecretion.ThesemedicationsbindtoATP-dependentK+channelsonthecellmembraneofpancreaticbetacells,inhibitingthehyperpolarizingpotassiumcurrentandcausingdepolarization.Thisopensvoltage-gatedCa2+channels,resultinginincreasedexocytosisofsecretorygranulesfilledwithmatureinsulinandc-peptide（aswellasasmallamountofproinsulinthatescapescleavage）.Consequently,thereisariseinseruminsulin,c-peptide,andproinsulinlevels.Insulinsecretagoguesandinsulinomacancausesimilarchangesininsulin,c-peptide,andproinsulinlevels.Theonlywaytodistinguishbetweeninsulinomaandsulfonylureaormeglitinideabuseisbytestingtheurineorbloodforhypoglycemicagents.Factitioushypoglycemiaoccursmostcommonlyindiabeticpatientsandnon-diabeticswithhealth-relatedoccupations.Itisassociatedwithdepressionandpersonalitydisorders.（ChoiceA）Glucagonomaisararetumorofpancreaticalphacellsthatsecretesexcessiveamountsofglucagon.Thisresultsinhyperglycemia,anemia,andnecrolyticmigratoryerythema（araisederythematousrashtypicallyaffectingtheface,groin,andextremities）.（ChoiceB）Exogenousins