USMLE题库Endocrinology11-20.pptx

1、Endocrinology题库Q 11A 16-year-old Caucasian girl who aspires to be a fashion model presents for a routine examination.She wishes to modify her diet and exercise plans so that she can lose an additional 20 lbs(9 kg)because she believes she is currently too fat”to participate in a beauty pageant later

2、this year.She is frustrated that she cant seem to drop these extra pounds11 in spite of strict dietary limitations and vigorous exercise for two hours each day.Her menstrual history is significant for amenorrhea for the past four months.Her height is(165 cm)and her weight is 100 lbs(45.3 kg),resulti

3、ng in a BMI of 16.6 Kg/m2.On physical examination,she is pale and emaciated.Fine hair is noted on her trunk.Which of the following is the most likely mechanism of her amenorrhea?A.Primary ovarian failureB.Primary pituitary dysfunctionC.HypothyroidismD.HyperprolactinemiaE.Hypothalamic dysfunctionA 11

4、Correct answer:EAnorexia nervosa is an eating disorder characterized by an intense fear of eating,significant loss of body weight(to less than 85%of expected weight or BMI less than 17.5 kg/m2),inaccurate perception of ones own body shape and size,and amenorrhea.The amenorrhea results from loss of p

5、ulsatile GnRH release from the hypothalamus,which occurs when the level of body fat falls below a certain critical level.Loss of this cyclic gonadotropin release leads to a decrease in LH and FSH secretion from the pituitary,which in turn causes circulating estrogen levels to be low.Administration o

6、f pulsatile GnRH in individuals with anorexia nervosa allows for the normalization of estrogen levels and subsequent ovulation.Amenorrhea also often occurs in serious athletes with very low body fat(e g.long distance runners,ballet dancers)as well as in individuals with prolonged cachectic illnesses

7、,via the same mechanism.If left untreated,the low estrogen levels in these amenorrheic individuals could lead to osteoporosis.(Choices A and B)The amenorrhea in patients with anorexia nervosa stems from a deficiency in hypothalamic GnRH release,rather than a problem with the pituitary or ovaries.(Ch

8、oice C)While the decreased caloric intake associated with anorexia nervosa can cause thyroid dysfunction,these thyroid abnormalities play no role in the development of amenorrhea.Patients with anorexia nervosa can develop the abnormality of thyroid functioning termed,fsick euthyroid syndrome/or low

9、T3 syndrome.Early in the course of anorexia,T3 levels are low,and T4 and TSH levels are normal.However,in prolonged severe disease,both T3 and T4 levels are low.(Choice D)While hyperprolactinemia is a known cause of amenorrhea(and galactorrhea,as well),patients with anorexia nervosa do not typically

10、 have hyperprolactinemia.Q 12A 43-year-old nurse comes to the physician complaining of episodic confusion,blurred vision,tremors,and sweating.These episodes have increased in intensity over the past year.Her other medical problems include major depression.Serum laboratory results obtained during an

11、episode are as follows:Glucose 35 mg/dLInsulin 18pU/L (N:9 pU/L)Proinsulin 10 pU/L (N:20%of total insulin)C-peptide 4.01 ng/mL(N:0.8-1.9 ng/mL)Which of the following is the most likely cause of her hypoglycemia?A.Alpha-cell tumorB.Insulin administrationC.SomatostatinomaD.Sulfonylurea useE.VIP-secret

12、ing tumoA 12Correct answer:DThis patient is hypoglycemic due to excessive endogenous insulin secretion.The production of insulin begins with the synthesis of proinsulin in the endoplasmic reticulum,where it is folded and its disulfide bonds are oxidized.It is subsequently transported to the Golgi ap

13、paratus,where it is packaged into secretory vesicles and further processed by a series of proteases to form mature insulin and c-peptide.Insulin secretagogues such as sulfonylureas and meglitinides cause increased insulin production and secretion.These medications bind to ATP-dependent K+channels on

14、 the cell membrane of pancreatic beta cells,inhibiting the hyperpolarizing potassium current and causing depolarization.This opens voltage-gated Ca2+channels,resulting in increased exocytosis of secretory granules filled with mature insulin and c-peptide(as well as a small amount of proinsulin that

15、escapes cleavage).Consequently,there is a rise in serum insulin,c-peptide,and proinsulin levels.Insulin secretagogues and insulinoma can cause similar changes in insulin,c-peptide,and proinsulin levels.The only way to distinguish between insulinoma and sulfonylurea or meglitinide abuse is by testing

16、 the urine or blood for hypoglycemic agents.Factitious hypoglycemia occurs most commonly in diabetic patients and non-diabetics with health-related occupations.It is associated with depression and personality disorders.(Choice A)Glucagonoma is a rare tumor of pancreatic alpha cells that secretes excessive amounts of glucagon.This results in hyperglycemia,anemia,and necrolytic migratory erythema(a raised erythematous rash typically affecting the face,groin,and extremities).(Choice B)Exogenous ins