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USMLE STEP1 Exam (page: 7)
USMLE Step1
Updated on: 25-Dec-2025

Viewing Page 7 of 171
STEP1 PDF 845 Questions

An elderly resident of a nursing home fell down the front steps and subsequently became disoriented and lethargic. He is brought to the emergency room where an emergency MRI reveals that he has developed hydrocephalus due to a small hemorrhage obstructing the foramina of Monro. The foramina of Monro allow for communication between which of the following?

  1. fourth ventricle and cerebral aqueduct
  2. fourth ventricle and subarachnoid space
  3. lateral ventricles and third ventricle
  4. third ventricle and cerebral aqueduct
  5. third ventricle and fourth ventricle

Answer(s): C

Explanation:

The foramina of Monro form the communication between the lateral ventricles and the third ventricle. The cerebral aqueduct of Sylvius flows caudally into the fourth ventricle (choice A). The lateral foramina of Luschka and the median foramen of Magendie allow for communication between the fourth ventricle and the subarachnoid space. The third ventricle communicates posteriorly with the cerebral aqueduct of Sylvius (choice D). Thus, the third and fourth ventricle communicate by way of this cerebral aqueduct.



Which of the following is the correct sequence of erythroid differentiation?

  1. proerythroblast, basophilic erythroblast, polychromatophilic erythroblast, normoblast, reticulocyte, mature erythrocyte
  2. proerythroblast, normoblast, reticulocyte, polychromatophilic erythroblast, basophilic erythroblast, mature erythrocyte
  3. proerythroblast, polychromatophilic erythroblast, basophilic erythroblast, reticulocyte, normoblast, mature erythrocyte
  4. proerythroblast, reticulocyte, normoblast, polychromatophilic erythroblast, basophilic erythroblast, mature erythrocyte
  5. proerythroblast, reticulocyte, polychromatophilic erythroblast, normoblast, basophilic erythroblast, mature erythrocyte

Answer(s): A

Explanation:

The correct sequence of erythroid differentiation is indicated by choice A. Erythrocyte differentiation in the adult occurs exclusively in the bone marrow and consists of several cellular changes. The cell size decreases: proerythroblast 1419 m in diameter; basophilic erythroblast 1316 m; polychromatophilic erythroblast 1215 m; normoblast, reticulocyte, and mature erythrocyte 810 m. Condensation of the nuclear chromatin and decrease in nuclear diameter occur from the proerythroblast to the normoblast stage with ejection of the nucleus. Subsequent ejection of remaining organelles occurs in the reticulocyte to give rise to the mature erythrocyte. The maturing cells change their staining affinity because the increased hemoglobin in the cytoplasm results in increased acidophilia, whereas the decrease in the ribosome numbers in the cytoplasm results in decreased basophilia.
Choices B, C, D, and E are incorrect sequences.



In emphysema, which of the following components of the bronchioles is affected?

  1. ciliated cuboidal epithelial cells
  2. Clara cells
  3. elastic fibers
  4. goblet cells
  5. squamous type I alveolar epithelial cells

Answer(s): C

Explanation:

Elastic fibers are destroyed in emphysema by elastase. This protease is released by neutrophils recruited by macrophages under abnormal stimulus such as cigarette smoke. The loss of elasticity in the bronchioles and alveolar walls gives rise to emphysema, characterized by chronic airway obstruction. Ciliated cuboidal epithelial (choice A) and Clara (choice B) cells line the terminal bronchioles. Goblet cells (choice D) may be found at the beginning of the bronchioles and squamous type I alveolar epithelial cells line the respiratory bronchioles.



During development, the notochord grows in a cranial direction until it reaches the prechordal plate. This plate is the primordium of the oropharyngeal (or buccopharyngeal) membrane, which, in the embryo, will separate the stomodeum from the foregut. At 26 days of gestation, the oropharyngeal membrane will break down, allowing communication of the foregut with the oral cavity. Of the following structures in the adult, which one lies at the same location as the embryonic oropharyngeal membrane?

  1. buccinators
  2. palatoglossus
  3. palatopharyngeus
  4. stylopharyngeus
  5. superior constrictor

Answer(s): B

Explanation:

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.



Referring to following figure, arrow 2 indicates which of the following structures?

  1. intercalated disk
  2. motor end-plate
  3. sarcoplasmic reticulum
  4. tendinous junction
  5. transverse tubule or T tubule

Answer(s): A

Explanation:

The intercalated disks are specialized junctional complexes found only in cardiac muscle and they appear as dark lines between the muscle fibers. The motor end-plate (choice B) is a specialized group of synapses between the axon terminals of a motor neuron and the sarcolemma of a skeletal muscle fiber. It is not seen in cardiac muscle. The sarcoplasmic reticulum (choice C) is a specialized modification of the smooth endoplasmic reticulum for sequestering calcium ions. The transverse tubule or T tubule (choice E) is an invagination of the sarcolemma, which penetrates the muscle fiber and overlies the surface of the myofibrils. The sarcoplasmic reticulum and T tubule can only be seen in electron micrographs. There is no tendinous junction (choice D) in cardiac muscle.



Viewing Page 7 of 171



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