Correct Answer: B

Section: Anatomy The palatoglossus muscle, which can be observed in the oral cavity to form the palatoglossal arch anterior to the palatine tonsil, lies in the same location as the embryonic oropharyngeal membrane. It lies at the junction line between the stomodeum and the foregut. The buccinator (choice A) is a muscle of the cheek and thus is located in the original stomodeum. The palatopharyngeus (choice C) is located posterior to the palatoglossus and palatine tonsil, forming the palatopharyngeal arch. The palatopharyngeus, stylopharyngeus (choice D), and superior constrictor (choice E) muscles are all pharyngeal muscles and thus are located in the original foregut.

Correct Answer: D

Section: Anatomy HMD is also known as respiratory distress syndrome, which is most often caused by the lack of lung surfactant, due to a premature birth. Lung surfactant production begins around 20 weeks after fertilization. But it is present only in small amounts until the last 2 weeks before birth when its amount increases significantly. Alveolar ducts (choice A) branch from the respiratory bronchioles during development. Type I alveolar cells (choice D) or pneumocytes are squamous epithelial cells, which participate in gas exchange. These epithelial cells line the terminal saccules (choice C). Type II alveolar cells (choice E) synthesize surfactant.

Correct Answer: C

Section: Anatomy The inferior laryngeal nerve is motor to the intrinsic muscles of the larynx except the cricothyroid muscle, and is sensory to the larynx below the level of the vocal fold. The external laryngeal nerve (choice A) is the branch of the superior laryngeal nerve that contains the motor fibers to the cricothyroid muscle and to the cricopharyngeus muscle. The glossopharyngeal nerve (choice B) does not supply either motor or sensory fibers to the larynx. The internal laryngeal nerve (choice D) is the branch of the superior laryngeal nerve that contains the sensory fibers to the laryngeal mucosa above the vocal fold. The superior laryngeal nerve (choice E) is sensory to the laryngeal mucosa above the vocal fold and also includes motor fibers to the cricothyroid muscle.

Correct Answer: C

Section: Biochemistry Severe hereditary galactosemia presents in the first few months of life with symptoms that include poor feeding and associated weight loss, vomiting, diarrhea, lethargy, and hypotonia. Clinical findings will include those presented in the case. The symptoms are aggravated by consumption of cow's milk and can be resolved provided proper diagnosis is made and treatment is started early. Alkaptonuria (choice A) results from the accumulation of homogentisic acid, a by-product of tyrosine catabolism, in the urine and tissues. Oxidation of homogentisate in the urine causes it to turn dark and in the tissues results in ochronosis, which refers to the ochre color of the deposits in connective tissue, bones, and other organs. Essential fructosuria (choice B) is a benign asymptomatic metabolic disorder manifesting with alimentary hyper- fructosemia and fructosuria. Menkes disease (choice D) results from a defect in intracellular copper transport and the symptoms of the disease are caused by loss of function of copper- dependent enzymes. Symptoms include abnormal (kinky) hair and pigmentation, cerebral degeneration, failure to thrive, and skin laxity. Symptoms of von Gierke disease (choice E) result from the excessive accumulation of glycogen in liver, kidney, and intestinal mucosa. Symptoms include growth retardation, hypoglycemia, heptomegaly, hyperlipidemia, lactic acidemia, and hyperuricemia.

Correct Answer: B

Section: Biochemistry Hemochromatosis is defined as a disorder in iron metabolism that is characterized by excess iron absorption, saturation of iron-binding proteins, and deposition of hemosiderin in the tissues. The primary affected tissues are the liver, pancreas, and skin. Iron deposition in the liver leads to cirrhosis and in the pancreas causes diabetes. The excess iron deposition leads to bronze pigmentation of the organs and skin. In fact, the bronze skin pigmentation seen in hemochromatosis, coupled with the resulatant diabetes lead to the designation of this condition as bronze diabetes. The primary cause of hemochromatosis is the inheritance of an autosomal recessive allele. The locus causing hemochromatosis has been designated HFE and is a major histocompatibility complex (MHC) class-1 gene. The gene encodes an alpha-chain protein with three immunoglobulinlike domains. This alpha- chain protein associates with beta-2microglobulin. Normal HFE has been shown to form a complex with the transferrin receptor and in so doing is thought to regulate the rate of iron transfer into cells. A mutation in HFE will therefore, lead to increased iron uptake and storage. The majority of hereditary hemochromatosis patients harbor a mutation in HFE that results in the substitution of Cys 282 for a Tyr. This mutation causes loss of conformation of one of the immunoglobulin domains in HFE. Another mutation found in HFE causes a change of His68 to Asp. DMT1 (choice A) is responsible for the intestinal absorption of dietary iron and thus, a deficiency in this protein would lead toreduced total body iron, not excess. Ferritin (choice C) is the intracellular iron binding and storage protein. A deficiency in ferritinwould lead to less iron deposition, not excess. Ferroportin (choice D) is the iron transport protein that moves dietary iron from within intestinal enterocytes across the basolateral membrane to the circulation, therefore, a deficiency in this protein would have consequences similar to deficiencies in DMT1. Transferrin (choice E) is the iron transport protein of the blood that binds to the trasferrin receptor on cell surfaces, allowing cellular uptake of circulating iron. A deficiency in this protein would lead to less iron deposition not more.

Correct Answer: B

Section: Microbiology/Immunology

B. pertussis is a small gram-negative rod that produces a number of virulence factors that are involved in the pathogenesis of whooping cough (pertussis). The organism has a capsule that inhibits phagocytosis and is susceptible to several antibiotics. The pertussis vaccines (containing 15 antigens) provide excellent active immune protection. B. pertussis can be isolated and identified using Bordet- Gengou (choice B) medium. Blood agar (choice A) is a general enriched medium but is insufficient to isolate B. pertussis. MacConkey agar (choice C) is routinely used to isolate and identify lactose- positive and lactose-negative enteric bacteria. Thayer Martin agar (choice D) is used for the isolation of pathogenic neisseria species. Tryptic Soy agar (choice E) is a general medium that will support many species of normal flora bacteria.

Correct Answer: A

Section: Pathology and Path physiology Pemphigus vulgaris is an autoimmune disorder. The autoantibodies are directed against keratinocyte antigens with subsequent dyshesion and fluid-filled blister formation. Bacterial infections (choice B), dietary deficiencies (choice C), chemical toxins (choice D), and local ischemia (choice E) are not thought to be the causative agent of pemphigus vulgaris.

Correct Answer: E

Section: Pathology and Path physiology Thrombotic thrombocytopenic purpura is an acute microangiopathic hemolytic anemia. The clinical picture usually includes mental alterations, anuria, mucosal bleeding, and purpura. An abnormal platelet-aggregating substance is the likely initiating event. Acute idiopathic thrombocytopenia (choice A) does not have a hemolytic component, lacks renal failure, and does not display thrombi in the skin biopsy. Bernard-Soulier syndrome (choice B) and Glanzmann thrombasthenia (choice C) are hereditary disorders of platelet aggregation. Clinical symptoms of a coagulopathy usually occur in infancy. MayHegglin anomaly (choice D) is an inherited condition with thrombocytopenia and morphologically abnormal WBCs. Hemolysis, acute onset, and mental aberrations do not typify this disorder.

Correct Answer: D

Section: Pathology and Path physiology In thymic hypoplasia, the congenital developmental failure of the thymus leads to a lack of T- lymphocytes in the blood as well as in appropriate areas of lymph nodes (paracortical area). Deficient T-cell immunity will thus lead to severe, recurrent viral, mycobacterial, fungal, or protozoal infections during infancy. Thymic hypoplasia is best described in association with DiGeorge syndrome, in which defective embryological development of the third and fourth pharyngeal pouches results in developmental failure of thymus and parathyroid formation, congenital heart defects, and severe hypocalcemia, secondary to hyperparathyroidism. An associated, but less well-defined, entity is Nezelof syndrome, in which there is hypoplasia of the thymus, retention of normal parathyroid function, and possible varying degrees of humoral immunodeficiency. Bruton congenital agammaglobulinemia (choice A) is an Xlinked recessive disorder characterized by the failure of B-cell precursors to differentiate into mature B-lymphocytes, which are absent in the peripheral blood, lymph nodes, tonsils, and spleen. Serum immunoglobulin levels are decreased; however, the thymus and Tlymphocyte development are normal and cell-mediated immunity is intact. Chronic granulomatous disease of childhood (choice B) refers to a group of X-linked or autosomal recessive disorders characterized by different enzyme deficiencies of neutrophils and macrophages that lead to inhibition of hydrogen peroxide formation. Although still capable of bacterial phagocytosis, neutrophils and macrophages cannot kill bacteria, particularly the catalase-positive species such as Staphylococcus, Serratia, and Salmonella, which destroy their own endogenous hydrogen peroxide by virtue of catalase production. The disease occurs chiefly in males who present with recurrent bacterial infections of the skin, lymph nodes, lungs, and bones; widespread abscesses and granulomas are present. Severe combined immunodeficiency disease (choice C) is one of the most dramatic forms of congenital immunodeficiency in which a defect of lymphoid stem cells leads to failure of development of both Band T-lymphocytes. Although probably an embodiment of several different inherited diseases, most patients with severe combined immunodeficiency have the autosomal recessive form, and greater than half of these lack the enzyme adenosine deaminase, resulting in the accumulation of lymphotoxic metabolites. Failure of both cellular and humoral immunity causes a variety of severe viral, bacterial, fungal, and protozoal infections early in life, with death usually occurring within the first year. Wiskott-Aldrich syndrome (choice E) is an X-linked recessive disease characterized by thrombocytopenia, eczema, and immunodeficiency; both cellular and humoral immunity is impaired. Progressive T-cell deficiency occurs despite a morphologically normal thymus, and serum IgM levels are low, although IgG levels are usually normal. Recurrent bacterial, viral, and fungal infections occur, particularly with S. pneumonia and Haemophilus influenzae as these organisms have polysaccharide antigens that mainly elicit IgM antibody response. Thrombocytopenia may be severe and approximately one-third of patients die from hemorrhage. Patients are prone to developing lymphoma.

Correct Answer: A

Section: Anatomy Arrow 2 points to the central vein which defines the center of each hepatic lobule (choice B). Arrows 1 and 3 point to portal tracts (choice C), which are located at the angles of the margins of the hepatic lobule. The sinusoids (choice D) originate from the margins of the lobules and converge to the central vein by running between the plates of hepatocytes. The space of Disse (choice E) is found between the sinusoid lining cells and the surfaces of the hepatocytes. It is best seen in electron micrographs and not in a photomicrograph.