USMLE USMLE Certifications USMLE-STEP-1 Questions & Answers

• Question 721:

  A renal calculus (kidney stone) passing from the renal pelvis into the ureter causes excessive distention and severe ureteric colic. During development in the embryo, the ureter arose from which of the following?

  A. mesonephric duct

  B. metanephric diverticulum

  C. metanephric mass of intermediate mesoderm

  D. paramesonephric duct

  E. pronephric duct

  Correct Answer: B

  Section: Anatomy The metanephric diverticulum or ureteric bud gives rise to the ureter, renal pelvis, calices, and collecting tubules. The metanephric mass of intermediate mesoderm (choice C) gives rise to the nephrons in the kidney. The mesonephric and paramesonephric ducts (choices Aand D) play essential roles in the development of the male and female reproductive system, respectively. The pronephric duct (choice E) is derived from the transitory, nonfunctional first set of kidneys or pronephroi and does not contribute to the development of the ureter.

• Question 722:

  Cell adhesion molecules enable intercellular contacts in epithelial as well as nonepithelial cells. Which of the following cell adhesion molecules are calcium-dependent molecules?

  A. disintegrins

  B. integrins

  C. intercellular adhesion molecules (I-CAM)

  D. neural cell adhesion molecules (N-CAM)

  E. selectins

  Correct Answer: E

  Section: Anatomy Cell adhesion molecules are divided into two major classes on the basis of their dependence on calcium. Calcium-dependent cell adhesion molecules are the cadherins and the selectins. Calcium- independent cell adhesion molecules include members of the immunoglobulin superfamily, the I-CAM (choice C), and the N- CAM, as well as the integrins (choice B). Disintegrins (choice A) are found in snake venom and disrupt the integrin-mediated cell binding to extracellular matrix proteins such as laminin or fibronectin.

• Question 723:

  A newborn infant suffers from epidermolysis bullosa simplex, characterized by skin blistering soon after birth. The blisters appear at sites of pressure or rubbing such as the fingers. You explain to the distressed parents that this condition is a disease of intermediate filaments and results from mutant genes for keratins K5 and K14. Which cells of the skin normally produce keratins K5 and K14?

  A. adipose cells in the hypodermis

  B. basal cells of the epidermis

  C. fibrocytes of the dermis

  D. melanocytes of the epidermis E. upper differentiating cells of the epidermis

  Correct Answer: B

  Section: Anatomy Basal cells of the epidermis produces keratins K5 and K14. Adipose cells in the hypodermis (choice A), fibrocytes of the dermis (choice C), and melanocytes of the epidermis (choice D) do not synthesize keratins. Upper differentiating cells of the epidermis (choice E) produce keratins K1 and K10. A keratin K9 is also found in the palmar or plantar regions of the epidermis.

• Question 724:

  Climbing fibers provide excitation to the deep cerebellar nuclei and the Purkinje neurons. The climbing fibers originate from which of the following structures?

  A. inferior olivary nucleus

  B. pontine nuclei

  C. spinal cord

  D. superior olivary nucleus

  E. vestibular nuclei

  Correct Answer: A

  Section: Anatomy The inferior olivary nucleus in the medulla oblongata is the sole source of climbing fibers to the cerebellum. All other sources of fibers to the cerebellum such as the pontine nuclei (choice B), spinal cord (choice C), or vestibular nuclei (choice E) provide mossy fibers to the cerebellum. The superior olivary nucleus (choice D) receives auditory fibers from the cochlear nuclei and projects back to the cochlea by way of the olivocochlear bundle. It modifies the sensory input from the organ of Corti in the cochlea and is not involved with cerebellar circuitry.

• Question 725:

  Secretion of pulmonary surfactant is a function of which of the following?

  A. alveolar dust cells

  B. endothelial cells of capillaries in the alveolar septum

  C. small granule cells

  D. type I pneumocytes (squamous alveolar cells)

  E. type II pneumocytes (greater alveolar cells)

  Correct Answer: E

  Section: Anatomy All the listed cell types are components of the respiratory system. Type II pneumocytes are the source of pulmonary surfactant. Alveolar dust cells (choice A) are macrophages. Endothelial cells (choice B) and type I pneumocytes (choice D) are components of the blood-air barrier. Small granule cells (choice C), which are members of the diffuse neuroendocrine system, function in paracrine and endocrine signaling.

• Question 726:

  A newborn infant displays wheezing respiration, which is aggravated when she feeds, flexes her neck, and/ or cries. Radioimaging studies of her chest reveal a double aortic arch compressing her trachea and esophagus. This rare developmental defect results from persistence of the right dorsal aorta, which normally disappears. The arch of the aorta arises from which of the following structures?

  A. fifth pair of aortic arches

  B. fourth pair of aortic arches

  C. second pair of aortic arches

  D. sixth pair of aortic arches

  E. third pair of aortic arches

  Correct Answer: B

  Section: Anatomy The arch of the aorta is formed from the left fourth aortic arch. Part of the right fourth aortic arch becomes the proximal portion of the right subclavian artery, whereas the rest of the fourth arch disappears. However, if it persists, a right aortic arch is formed passing posterior to the trachea and esophagus. With the formation of the normally occurring left aortic arch, which runs anterior to the trachea and esophagus, a double aortic arch is created. This defect clamps the trachea and esophagus resulting in the respiratory symptoms. The second pair of aortic arches (choice C) partially form the stapedial arteries in the middle ear of the embryo. The third pair of aortic arches (choice E) form the common carotid arteries and contribute to the internal carotid arteries. The fifth pair of aortic arches (choice A) either does not develop or form primitive vessels, which disappear eventually. The sixth pair of aortic arches (choice D) contribute to the formation of the pulmonary arteries and ductus arteriosus.

• Question 727:

  After recovery from the surgical removal of the thyroid gland, the quality of the voice in a patient changed to a monotone. It was discovered that the cricothyroid muscle in this patient was paralyzed. The cricothyroid muscle is innervated by which of the following?

  A. accessory nerve

  B. ansa cervicalis

  C. external laryngeal nerve

  D. hypoglossal nerve

  E. internal laryngeal nerve

  Correct Answer: C

  Section: Anatomy The external laryngeal nerve, a branch of the superior laryngeal nerve from the vagus, innervates the cricothyroid muscle. Normally, the cricothyroid muscle varies the length and tension of the vocal cord, and in its absence, the voice acquires a monotonous quality. The accessory nerve (XI, choice A) only innervates the sternocleidomastoid and the trapezius muscles in the neck. The ansa cervicalis (choice B) supplies motor branches to the infrahyoid muscles. The hypoglossal nerve (XII, choice D) innervates intrinsic and extrinsic muscle fibers of the tongue. The internal laryngeal nerve (choice E) provides sensory innervation to the interior of the larynx.

• Question 728:

  A 14-year-old female patient complains of a severe sore throat and you use a cotton swab to obtain specimens for a culture. As you lightly touch the pharyngeal wall with the cotton swab, the patient gags. What is the location of neuronal cell bodies innervating pharyngeal constrictor muscles involved in the gag reflex?

  A. abducens nucleus

  B. ambiguus nucleus

  C. dorsal motor nucleus of the vagus

  D. facial nucleus

  E. hypoglossal nucleus

  Correct Answer: B

  Section: Anatomy Motor innervation of the pharyngeal constrictor muscles is derived from the ambiguous nucleus in the medulla oblongata. These motor fibers reach the constrictor muscles via the vagus nerve. The abducens nucleus (choice A) provides motor innervation to the lateral rectus muscle of the eye. The dorsal motor nucleus of the vagus (choice C) provides preganglionic parasympathetic innervation for the organs of the thorax and abdomen. The facial nucleus (choice D) sends motor innervation to the muscles of facial expression and the stapedius. The hypoglossal nucleus (choice E) innervates the muscles of the tongue.

• Question 729:

  You are concerned that your patient may have compromised function of the mitral valve. The sound of the mitral valve is best heard at which of the following locations?

  A. at the apex in the left fifth intercostals space in the midclavicular line

  B. at the xiphisternal junction

  C. in the fifth intercostal space to the right of the sternum

  D. in the second intercostal space to the left of the sternum

  E. in the second intercostal space to the right of the sternum

  Correct Answer: A

  Section: Anatomy There is only one point of the heart that can be directly identified on the precordium: the apex. A cardiac impulse may be visible at the apex, and palpation over it confirms the presence of the apex beat. The apex is located in the left fifth intercostal space just medial to the midclavicular line, and is the point where the mitral valve is best heard. None of the heart sounds are best heard at the xiphisternal junction (choice B). The tricuspid valve is best heard in the fifth intercostal space to the right of the sternum (choice C). The pulmonary valve is best heard in the second intercostal space to the left of the sternum (choice D). The aortic valve is best heard in the second intercostals space to the right of the sternum (choice E).

• Question 730:

  Corneal abrasions produce eye pain and excessive lacrimation. Which cranial nerve innervates the cornea?

  A. fifth (trigeminal)

  B. fourth (trochlea)

  C. second (optic)

  D. sixth (abducens)

  E. third (oculomotor)

  Correct Answer: A

  Section: Anatomy The ophthalmic division of cranial nerve V (trigeminal) provides general sensory innervations to the eyeball, including the cornea. Cranial nerve II (optic, choice C) carries the visual function of the retina of the eye. Cranial nerves IV (trochlea, choice B) and VI (abducens, choice D) innervate the superior oblique and lateral rectus muscles, respectively. The innervation of all other extraocular muscles is performed by cranial nerve III (oculomotor, choice E).