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Free STEP1 Exam Braindumps (page: 24)

Page 24 of 213
PDF with 845 Questions

Cilia are anchored to the apical portion of certain types of epithelial cells and they are mobile. Which of the following form the motile cytoskeletal component of the cilia?

  1. intermediate filaments
  2. microfilament
  3. microtubule
  4. neurofilament
  5. tonofilaments

Answer(s): C

Explanation:

Acilium is formed by a concentric array of nine microtubule doublets surrounding a central pair of microtubules (9 + 2 organization). Intermediate filaments (choice A) are intermediate in diameter size (10 nm) between the microtubules (25 nm) and the microfilaments (7 nm). They do not confer motility to the cilia. They instead participate in the cytoskeletal integrity of nerve cells, neurofilaments (choice D) or hemidesmosomes, tonofilaments (choice E). Microfilaments (choice B) are found in microvilli and stereocilia.



A 79-year-old female patient was admitted to the hospital, presenting with fever, vomiting, dehydration, and distension of the abdomen. An X-ray reveals ileus and exploratory surgery reveals occlusion of vasa recta of the jejunum. Which of the following arteries supply branches to the involved vasa recta?

  1. ileocolic artery
  2. inferior pancreaticoduodenal artery
  3. right colic artery
  4. right gastroepiploic artery
  5. superior mesenteric artery

Answer(s): E

Explanation:

Ileus is obstruction of the intestine, in this case due to paralysis resulting from ischemia. The jejunum receives its vascular supply from jejunal branches arising from the superior mesenteric artery. The ileocolic artery (choice A) supplies the ileum, ileocolic junction, and the appendix. The inferior pancreaticoduodenal artery (choice B) provides vascular innervations to the pancreas and duodenum, and forms the anastomosis between the foregut and midgut. The right colic artery (choice C) supplies the ascending colon and the right gastroepiploic artery (choice D) the greater curvature of the stomach and greater omentum.



Which of the following is directly involved with the descending modulation of pain transmission?

  1. dopamine
  2. MLF
  3. nucleus raphe magnus
  4. rubrospinal fibers
  5. ventral lateral thalamic nucleus

Answer(s): C

Explanation:

The nucleus raphe magnus receives input from the periaqueductal gray and gives rise to descending serotonergic fibers of the raphe spinal projection. The latter fibers activate enkephalinergic spinal cord interneurons that presynaptically inhibit incoming pain fibers at their initial synapse in the spinal cord dorsal horn. The neurotransmitter dopamine (choice A) has not been shown to be involved in the descending systems that modulate pain transmission. The MLF (choice B) is an ascending fiber system in the brainstem that is primarily involved in the control of eye movements. The rubrospinal system (choice D) is a descending fiber tract involved with the control of limb musculature. The ventral lateral nucleus of the thalamus (choice E) is primarily involved with motor function and does not contribute to descending pathways that influence pain transmission.



Which of the following vessels participate in the arterial circulation of the spleen?

  1. afferent arteriole
  2. efferent arteriole
  3. interlobar arteries
  4. interlobular arteries
  5. sheathed arteriole

Answer(s): E

Explanation:

The spleen receives its blood supply from the splenic artery, which branches off from the celiac trunk from the abdominal aorta. At the hilum of the spleen, the splenic artery branches off into trabecular arteries, which enter the spleen along the trabeculae and branch in the parenchyma as central arteries running in the white pulp. The central arteries branch into penicillar arterioles, which give rise to capillaries and sheathed arterioles. The capillaries feed the marginal sinuses as well as the red pulp sinuses. Afferent (choice A) and efferent (choice B) arterioles, and interlobar (choice C) and interlobular (choice D) arteries are vessels found in the kidney.



Page 24 of 213



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