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Free STEP1 Exam Braindumps (page: 33)

Page 32 of 213
PDF with 845 Questions

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?

  1. adipose cells in the hypodermis
  2. basal cells of the epidermis
  3. fibrocytes of the dermis
  4. melanocytes of the epidermis
  5. upper differentiating cells of the epidermis

Answer(s): B

Explanation:

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.



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

  1. disintegrins
  2. integrins
  3. intercellular adhesion molecules (I-CAM)
  4. neural cell adhesion molecules (N-CAM)
  5. selectins

Answer(s): E

Explanation:

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.



After removal of cancerous lymph nodes from the lateral pelvic wall, a patient develops painful spasms of the adductor muscles and sensory deficits in the medial thigh region. The adductor muscles are innervated by which of the following nerves?

  1. femoral
  2. inferior gluteal
  3. obturator
  4. pudendal
  5. sciatic

Answer(s): C

Explanation:

The obturator nerve innervates the adductor muscles and the medial region of the thigh. The nerve originates from the lumbar plexus, runs on the lateral aspect of the pelvic wall, and exits through the obturator canal to reach the medial aspect of the thigh. Lying on the lateral pelvic wall, it may be injured by surgical mishap. The femoral nerve (choice A) innervates the anterior aspect of the thigh and the muscles contained within the sartorius and the quadriceps femoris. The inferior gluteal nerve (choice B) innervates the gluteus maximus muscle and is confined to the gluteal region. The pudendal nerve (choice D) is sensory to the genitalia, motor to the perineal muscles, the external urethral sphincter, and the external anal sphincter. The sciatic nerve (choice E) innervates the hamstring muscles in the posterior aspect of the thigh.



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?

  1. mesonephric duct
  2. metanephric diverticulum
  3. metanephric mass of intermediate mesoderm
  4. paramesonephric duct
  5. pronephric duct

Answer(s): B

Explanation:

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.






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