Correct Answer: D

Section: Anatomy

The falx cerebri is the dural partition separating the hemispheres of the brain, above the corpus callosum.

It has in its superior edge the superior sagittal sinus and in its inferior border, the inferior sagittal sinus. The cavernous sinus (choice A) is a dural pocket in the middle cranial fossa and is located on either side of the sella turcica. It is unusual because it contains the internal carotid artery and cranial nerves III, IV, V1, V2, and VI. The sigmoid sinus (choice C) is located in the posterior cranial fossa, below the level of the tentorium cerebelli, which contains in its posterior border the transverse sinus (choice E).

Correct Answer: D

Correct Answer: A

Section: Microbiology/Immunology Prevention of varicella and disseminated zoster rests on the administration of acyclovir. Killed varicellazoster virus (VZV) vaccine has not been shown to be effective. Furthermore, if the immunological system has been compromised the immune responses will be very weak and of questionable value (choice C). Live attenuated VZV vaccines cannot be given to immunocompromised individuals because vaccination can be lethal (choice D). Subunit VZV vaccines are not available, and will be of little value to persons with suppressed immunological responses (choice E). Indinavir is a protease inhibitor used for the treatment of AIDS, not for varicella or zoster (choice B).

Correct Answer: A

Section: Microbiology/Immunology The most likely diagnosis of the patient's illness is acute amoebic dysentery, because the classical symptomatology of acute amoebic dysentery is lower abdominal pain, cramping, colitis, tenesmus, flatulence, and bloody diarrhea. Malaria is characterized by periodic fever, fatal cerebral episodes, lysis of red blood cells, and nephritis due to immune complex formation, and is transmitted by mosquito bites (choice B). Trypanosomiasis is transmitted by bites of the tsetse fly and the trypanosomes initially cause chancres at the site of the bite. Then the trypanosomes reach the central nervous system, and the patient has lassitude, develops sleeping episodes, and tissue wasting or even death can occur (choice E). Trichomoniasis is limited to the vagina and is associated with a watery, foul smelling, abundant greenishgray discharge (choice D). Toxoplasmosis is a mild influenza-like disease with possible lymph node enlargement, and may be severe in immunocompromised patients. Congenital infections can damage the eyes or brain and may be fatal (choice C).

Correct Answer: E

Section: Microbiology/Immunology Streptococcal infections in chronic granulomatous disease are rare, because the defective myeloperoxidase-hydrogen peroxide-halide system can use hydrogen peroxide accumulated by phagocytized streptococci, which are catalase negative and cannot convert hydrogen peroxide to water and oxygen. Administration of pooled gamma globulin (choice C) or antistreptolysin (choice A) is likely to provide only brief, but not chronic, protection against streptococci. C-reactive protein (CRP) is a beta serum globulin which reacts with the C carbohydrate of the cell wall of S. pneumoniae. It is not an antibody and thus will not provide even brief protection against streptococci (choice B). Phagocytosis plays a major, not a minor, role in the killing of streptococci (choice D).

Correct Answer: C

Section: Pathology and Path physiology Figure displays interweaving bundles of smooth muscle cells, which, as a discrete myometrial nodule, define a leiomyoma. These are common tumors that may be asymptomatic or produce menorrhagia. Gross appearance is that of a solid white nodule. Adenomyosis (choice A) may clinically and grossly mimic leiomyomas. Adenomyosis, however, has a triphasic microscopic appearance consisting of benign endometrial glands, benign endometrial stroma, and smooth muscle hypertrophy. AKrukenberg tumor (choice B) is replacement of the ovary by metastatic GI adenocarcinoma. The diagnosis of metastatic malignancy (choice D) is not supported by the photomicrograph of a benign process. Ovarian ectopia (choice E) is exceedingly rare and is incompatible with the histology of the photomicrograph.

Correct Answer: B

Section: Pathology and Path physiology Hemophilia A is a genetic disorder characterized by very low levels of factor VIII, elevated partial thromboplastin time, normal prothrombin time, normal platelet aggregation with ristocetin, and spontaneous hemorrhages into joints, soft tissues, and mucosal surfaces. Christmas disease (choice A) is an alternative term for hemophilia B. Hemophilia B (choice C) is a hereditary coagulopathy due to a very low level of factor IX. Rosenthal syndrome (choice D) defines a deficiency of factor XI. von Willebrand disease (choice E) is characterized by a mild hereditary bleeding diathesis and abnormal platelet aggregation with ristocetin.

Correct Answer: E

Section: Pharmacology Vasodilators act by one of three mechanisms: increasing cyclic GMP (cGMP) levels in vascular smooth muscle cells; opening potassium channels; or blocking calcium channels. The organic nitrates and nitroprusside (nitrovasodilators) increase cGMP synthesis by generating nitric oxide (NO), which subsequently activates a soluble form of guanylyl cyclase. Activation of muscarinic receptors on vascular endothelial cells results in formation of NO (earlier identified as endothelium-derived relaxing factor) that diffuses to smooth muscle cells and relaxes them through increased cGMP levels. Erection of the penis involves neuronally regulated formation of NO, increased cGMP levels in the corpus cavernosum, and relaxation of cavernosal and vascular smooth muscle in erectile tissue. Rather than stimulating guanylyl cyclase, sildenafil (Viagra) acts as a selective inhibitor of cGMP phosphodiesterase type 5 to increase the half-life of cGMP in the tissues. The fact that sildenafil acts downstream of NO stimulation of guanylyl cyclase accounts for the toxic interactions between it and nitrovasodilators. The mechanism for relaxation of vascular smooth muscle by hydralazine (choice A) is unknown, but may involve NO. Minoxidil (choice B) is metabolized to minoxidil sulfate, which activates an ATP-sensitive potassium channel in smooth muscle. Nitroprusside (choice C) is a nitrovasodilator that spontaneously releases NO by a mechanism distinct from that of the organic nitrates. Prazosin (choice D) produces vasodilation by inhibiting alpha-1adrenoreceptors on arteriolar smooth muscle.

Correct Answer: B

Correct Answer: D

Section: Physiology It represents the estrogen estradiol, which is produced from androgen by granulosa cells of the ovaries and released into the capillaries. A woman's estradiol serum concentration roughly reflects the activities of her ovaries. Estradiol levels rise during the follicular phase of the menstrual cycle (days 0 13). They reach peak levels shortly before ovulation on day 1314, and drop back during the luteal phase (days 1428). They reach menstrual/follicular levels at the end of the luteal phase unless there is a pregnancy. After menopause, the ovaries atrophy and estradiol levels become very low. During reproductive cycles, androgens are the main substrate for estrogen synthesis in the granulosa cells. The androgen-estrogen conversion is under the influence of FSH (choice E). FSH concentrations are high after menopause compared to their premenopausal concentrations. The source of androgens is theca cells. They produce it from cholesterol under the influence of LH (choice B). LH concentrations, like FSH, are high postmenopausal. Both, FSH and LH levels are used as a diagnostic tool to determine menopause. Granulosa cells also produce progesterone (choice C) from cholesterol. Progesterone serum levels are low during follicular phase of the menstrual cycle and high during the luteal phase of the menstrual cycle. The transition of cholesterol to progesterone is under the influence of LH (choice A).