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Which of the following is secreted by the arrow-marked structure in the pancreatic histology section given below?
The correct answer is A. The endocrine-producing cells of the islets of Langerhans are embedded within the exocrine pancreas. The islets mainly produce glucagon (from alpha cells), insulin (beta cells), and somatostatin (delta cells).
Choices B, C and D: The pancreas is a branched tubuloacinar exocrine gland with acini. The acini are composed of secretory cells that produce multiple digestive enzymes including proteases (like trypsinogen), lipases, and amylases. Acinar cells are functionally polarized, with basophilic RER at their basal ends below the nucleus, and membrane-bound, enzyme-containing eosinophilic zymogen granules toward their apex.
The correct answer is D. Uracil is a pyrimidine base that is only found in RNA.
Choice A: Cytosine (C) is a pyrimidine that is present in both DNA and RNA.
Choice B: Thymine (T) is a pyrimidine that is usually found only in DNA.
Choice C: Adenine is a purine that is present in both DNA and RNA. The other well known purine is Guanine, which is also found in both DNA and RNA.
There are 2 types of nitrogen-containing bases commonly found in nucleotides: purines and pyrimidines. Purines usually contain 2 rings in their structure. Pyrimidines have only 1 ring in their structure.
Which of the following statements about malaria is incorrect?
The correct answer is D. P. falciparum infection is not treated with chloroquine. It is treated with mefloquine or atovaquone/proguanil. Mefloquine should be avoided in a patient with a history of neuropsychiatric illness. If severe, it is treated with artemisinin-based combination therapy.
Choice A: P. falciparum is the most pathogenic of all the Plasmodium species. Cerebral malaria is the most severe pathology caused by the malaria parasite. Rupture of the blood-brain barrier occurs and may lead to hemorrhages resulting in neurological alterations.
Choice B: There are several hematological manifestations of malaria. These include severe anemia, coagulation disturbances due to thrombocytopenia, leukocyte numerical or functional changes, and spleen involvement.
Choice C: P. vivax infection is associated with recurrent relapses, not P. falciparum, due to the presence of liver hypnozoites in its life cycle. P. falciparum infection is associated with recrudescence.
A 20-year-old young man presents with a lesion at the lower end of the femur. X-ray shows a typical sunburst appearance. What is the most likely diagnosis based on the x-ray finding?
The correct answer is A. Osteogenic sarcoma is the most common primary malignant bone tumor. It is seen in ages 10–25, usually around the knee (lower femur or upper tibia). A typical “sunburst” pattern is often described on x-rays.
Choice B: Multiple myeloma is seen in old men and presents with fatigue, anemia, and localized pain at specific places on several bones. X-rays are diagnostic and show multiple, punched-out lytic lesions. These patients also have Bence-Jones protein in the urine and abnormal immunoglobulins in the blood, which is best demonstrated by serum protein electrophoresis (SPEP). Treatment is mainly by chemotherapy; thalidomide can be used in cases where chemotherapy fails.
Choice C: Ewing’s sarcoma is the second most common tumor of bones. It affects younger children and typically involves ages 5–15 years. It grows in the diaphyses of long bones and typically shows an “onion skin” pattern on x-rays.
Choice D: Soft tissue sarcoma has relentless growth of soft tissue mass over several months. They are firm and typically fixed to surrounding structures. They can metastasize hematogenously to the lungs. MRI delineates the extent of the mass and invasion of local structures. Incisional biopsy is done to obtain tissue for diagnosis. Treatment includes wide local excision, radiation, and chemotherapy.
If the zygote cleaves 14 days after fertilization, which type of twins are formed?
The correct answer is A. Monozygotic twins arise from one zygote. Chorionicity and amnionicity vary according to the duration of time from fertilization to cleavage. After 12 days, conjoined twins result. Most often this condition is lethal.
Choice B: Up to 72 hours (separation up to the morula stage), the twins are dichorionic, diamniotic. There are two placentas and two sacs. This is the lowest risk of all monozygotic twins.
Choice C: If cleavage occurs between 4–8 days (separation at the blastocyst stage), the twins are monochorionic, diamniotic. There is one placenta and two sacs. A specific additional complication is twin–twin transfusion, which develops in 15% of mono-di twins. The twins share a single placenta but do so unequally. The donor twin gets less blood supply, resulting in growth restriction, oligohydramnios, and anemia. However, neonatal outcome is usually better. The recipient twin gets more blood supply, resulting in excessive growth, polyhydramnios, and polycythemia. Intrauterine fetal surgery is indicated to laser the vascular connections on the placental surface between the two fetuses. Neonatal course is often complicated.
Choice D: If cleavage occurs between 9–12 days (splitting of the embryonic disk), the twins are monochorionic, monoamniotic. There is only one placenta and one sac. Specific additional risks are twin–twin transfusion but particularly umbilical cord entanglement which can result in fetal death. This is the highest risk of all monozygotic twins.
|Dichorionic diamniotic||0-3 days
|Monochorionic diamniotic||4-8 days
|Monochorionic monoamniotic||9-12 days
A 30-year-old woman has a dilated pupil that reacts sluggishly to light. What is the diagnosis?
The correct answer is C. Adie pupil is a dilated pupil that reacts sluggishly to light, but better to accommodation. It is often seen in women and associated with loss of knee jerks. It is thought to be the result of a viral or bacterial infection that causes damage to the ciliary ganglion.
Choice A: Argyll Robertson pupil is characterized by pupillary light-near dissociation. There is no direct or consensual light reflex, whereas accommodation-convergence is intact. It occurs in patients with neurosyphilis and diabetes.
Choice B: Relative afferent (Marcus Gunn) pupil is caused by a lesion of the afferent limb of the pupillary light reflex. Diagnosis is made by the swinging flashlight test. On shining light in the Marcus Gunn pupil, both pupils do not constrict fully. On shining light in the normal eye, both pupils constrict fully. On shining light immediately again in the affected eye, there is apparent dilation of both pupils because the stimulus carried through that CN II is weaker. It is seen in multiple sclerosis.
Choice D: Horner syndrome is caused by a lesion of the oculosympathetic pathway. The syndrome consists of miosis, ptosis, apparent enophthalmos, and hemianhidrosis.
A 1-year-old boy was brought to the pediatrician for a white reflex in the eyes. On examination, he has microcephaly, cataracts, hearing loss, and patent ductus arteriosus. Which of the following congenital infections results in these features?
The correct answer is B. Features of congenital rubella include blueberry muffin spots (due to extramedullary hematopoiesis), thrombocytopenia, patent ductus arteriosus, peripheral pulmonary artery stenosis, cataracts, congenital hearing loss, hepatosplenomegaly, microcephaly, and mental and motor retardation.
Choice A: Infants with congenital toxoplasmosis have jaundice, hepatosplenomegaly, thrombocytopenia, anemia, microcephaly, chorioretinitis, hydrocephalus, intracranial calcifications, and seizures.
Choice C: Cytomegalovirus infection causes hepatosplenomegaly, jaundice, periventricular calcifications, intrauterine growth retardation, chorioretinitis, microcephaly, and sensorineural hearing loss.
Choice D: Findings of congenital syphilis may be classified as early (birth to 2 years) or late (>2 years). Early congenital syphilis is characterized by snuffles, a maculopapular rash, jaundice, periostitis, osteochondritis, chorioretinitis, and congenital nephrosis. Late congenital syphilis results in Hutchinson teeth, Clutton joints, saber shins, saddle nose, osteochondritis, and rhagades (thickening and fissures of the corners of the mouth).
Which of the following anti-hyperlipidemic drugs acts by decreasing LDL receptors on hepatocytes?
The correct answer is D. Alirocumab is a PCSK9 inhibitor. It is a hepatic protease that promotes the destruction of LDL receptors. Inhibition of PCSK9 can lower LDL 50-60% above that achieved by statin therapy alone.
Choice A:Nicotinic acid inhibits VLDL synthesis, which results in decreased plasma VLDL, decreased plasma LDL, and increased plasma HDL.
Choice B: Gemfibrozil binds to the PPARα receptor and increases expression of lipoprotein Lipase enzymes, resulting in decreased triglycerides, VLDL, and LDL. It is used in hypertriglyceridemia.
Choice C: Ezetimibe prevents intestinal absorption of cholesterol and reduces LDL levels. The most prominent side effect is gastrointestinal distress.
The resting membrane potential is closest to the isoelectric potential of:
The correct answer is B. In general, all excitable cell membranes at rest are maximally permeable to K+, and thus the resting membrane potential (RMP) is close to the equilibrium potential of K+ ion (around -90 mV).
The RMP is a potential difference seen due to the separation of positive and negative charges across the cell membrane. The diffusion of the K+ ion is the major factor in the genesis of the RMP. Other contributors are the Na-K ATPase pump and the Donnan effect.
Choices A, C, and D: The equilibrium potentials of sodium, chloride, and magnesium ions are not in a range close to -90 mV, and therefore are not the value of the resting membrane potential of the cell.
One must also have an idea of the isoelectric potential of the ions given below to come to the conclusion of the above answer:
|ION||EQUILIBRIUM POTENTIAL (mV)|
|Na+||+63 to +65|
|K+||-96 to -94|
|Cl-||-70 to -64|
|Ca2+||+132 to +137|
A study sample is determined by selecting every fourth student in a class. This type of sampling is an example of:
The correct answer is B. Systematic random sampling is a type of probability sampling method in which sample members from a larger population are selected according to a random starting point, but with a fixed, periodic interval. This interval, called the sampling interval, is calculated by dividing the population size by the desired sample size.
- Example: Every 10th person from all patients admitted in the hospital on June 4th.
Choice A:In simple random sampling, samples are drawn in such a way that every element in a population has an equal chance of being included.
- Example: Picking 7 random cards from a bag full of cards.
Choice C: Stratified random sampling involves dividing the entire population into homogeneous groups called strata (singular is stratum). Random samples are then selected from each stratum.
- Example: Dividing the population into men, women, and children, then picking a sample from each group.
Choice D: In cluster random sampling, the population is divided into internally heterogeneous groups, then a simple random sampling is done in that cluster.
- Example: Checking the immunization status in the community.
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