1 Anatomic Science

Anatomic Science 1. At which of the following ages does fetal movement first occur? A. 1 month B. 2 months C. 4 months D. 6 months E. 7 months The correct answer is B. Neuromuscular development is sufficient to allow fetal movement in the eighth week of life. Other features of Week 8 include the first appearance of a thin skin, a head as large as the rest of the body, forward-looking eyes, appearance of digits on the hands and feet, appearance of testes and ovaries (but not distinguishable external genitalia), and a crown-rump length of approximately 30 mm. By the end of the eighth week, nearly all adult structures have at least begun to develop, and the fetus "looks like a baby." 2. Most of the oocytes in the ovary of a prepubescent girl are in which meiotic stage? A. Anaphase of the second meiotic division B. Metaphase of the first meiotic division C. Metaphase of the second meiotic division D. Prophase of the first meiotic division E. Telophase of the first meiotic division The correct answer is D. The first meiotic division is the "reduction" meiotic division, in which the diploid complement of DNA is reduced to a haploid complement. The bulk of oocytes in premenopausal women, girls, and babies are arrested at prophase of the first meiotic division. Postmenopausal women have very few viable oocytes. It is important to note that ovulation occurs before the oocyte is completely mature. The secondary oocyte leaving the follicle is in metaphase of the second meiotic division (choice C). The cell's metabolic operations have been discontinued and the oocyte drifts in a state of "suspended animation," awaiting the necessary stimulus for further development. If fertilization does not occur, the oocyte disintegrates without completing meiosis. 3. An abrasion results in the total loss of epidermis over a large area of an arm, but one month later, the abrasion has healed, with regrowth of the epidermis. Which of the following mechanisms accounts for the restoration of the epidermis over the abraded area? A. Growth of epidermis from hair follicles and sweat glands in the dermis B. Migration of endothelial cells from newly grown capillaries C. Transformation of dermal fibroblasts into epidermal cells D. Transformation of macrophages into epidermal cells E. Transformation of melanocytes into epidermal cells The correct answer is A. The dermis contains skin appendages (e.g., hair follicles), which contain epithelial stem cells. In the process of healing a large area where the epidermis has been lost but the dermis is intact, re-epithelialization occurs by growth of epidermal cells from the underlying skin appendages, as well as from the intact epidermis along the wound edges. Physiologically, the dermis lies beneath the epidermis. It has two major components, a superficial papillary layer and a deeper reticular layer. The papillary layer contains the capillaries and the sensory neurons, which supply the surface of the skin. The reticular layer consists of an interwoven meshwork of dense irregular connective tissue. None of the other cell types are known to directly contribute to the regeneration of epidermis over abraded skin. 1 4. Hirschsprung's disease indicates a developmental abnormality in which of the following embryonic tissues? A. Ectoderm B. Endoderm C. Neural crest D. Neural ectoderm E. Splanchnic mesoderm The correct answer is C. The baby has Hirschsprung's disease, which is due to an absence of ganglion cells in the wall of the colon. Neural crest cells contribute to the formation of many adult structures. Among these are all of the postganglionic neurons of the autonomic nervous system and the sensory neurons of the peripheral nervous system. Ectoderm (choice A) forms the epidermis of the skin and the parenchymal cells of glands associated with the skin such as the sweat glands, sebaceous glands, and mammary glands. Endoderm (choice B) forms the epithelial lining of the gut tube and the parenchymal cells of glands associated with the gut tube, such as the liver and pancreas. Neural ectoderm (choice D) forms the central nervous system, the somatic motor neurons of the peripheral nervous system, and the preganglionic neurons of the autonomic nervous system. Splanchnic mesoderm (choice E) forms the visceral peritoneum, visceral pleura, visceral pericardium, and the stroma and muscle of the wall of the gut, among other structures. 5. Injury at the lower border of a rib will most likely damage which structure? A. intercostal artery B. intercostal nerve C. intercostal vein D. internal intercostal muscle The correct answer is B. The three structures in the intercostal space are, from superior to inferior, the intercostal vein, artery, and nerve. The proper site for insertion of an intercostal drain is superior to a rib, not directly at the level of the superior border but slightly higher to avoid the collateral branches of the nerve, artery, and vein. The nerve is the most inferior structure and thus most likely to be damaged by the drain (producing an anesthetic dermatome). In addition, the nerve is the least protected by the costal groove. The intercostal artery (choice A) is the middle structure and thus is not the most likely to be damaged. The intercostal vein (choice C) is the most superior structure and is thus the least likely to be damaged. In addition, the vein is the structure best protected by the costal groove (the further superior the structure, the more protected by the costal groove). The internal intercostal fibers (choice D) will tend to be separated by the drain. In addition, the internal intercostal muscle is membranous (internal intercostal membrane) posteriorly, from the neck of the rib to its angle; therefore, many drains, when inserted, will not even pass through a layer of internal intercostal muscle. 6. Following the healing of a tibial fracture, a patient forms a small, new piece of viable bone near the joint (heterotopic ossification), which is interfering with joint mobility. Which of the following is the source of the osteoblasts that formed this bone? A. Cancellous bone near the fracture 2 B. Circulating stem cells C. Compact bone near the fracture D. Marrow E. Periosteum The correct answer is E. The source of bone-forming cells following a fracture is the damaged periosteum. Occasionally, some of these cells become "lost" and can form small pieces of inappropriately located bone that impair joint movement. Except in joint cavities, where they are covered by a layer of hyaline cartilage, bone surfaces are covered by the periosteum. The periosteum is composed of an outer fibrous and inner cellular layer. The periosteum assists in the attachment of a bone to surrounding tissues and associated tendons and ligaments. Surprisingly, neither the cancellous (choice A) nor the compact (choice C) bone near the fracture is the source of the bone-forming cells. Circulating stem cells (choice B) can repopulate damaged bone marrow (choice D), but neither the bone marrow nor the circulating stem cells is the source of the bone-forming cells. 7. A patient has a severe headache, and is unable to move his right leg. There is no higher cortical function loss, but deep deep tendon reflexes and Babinski's sign are absent. The medial aspect of the cerebral hemispheres is most affected. Which artery is most likely involved? A. left anterior cerebral artery B. left middle cerebral artery C. left posterior cerebral artery D. right anterior cerebral artery E. right posterior cerebral artery The correct answer is A. The medial aspect of the cerebral hemispheres is supplied by the anterior cerebral arteries. The small portion of primary motor cortex located here sends fibers to spinal-cord segments innervating the lower limbs. Because the corticospinal tracts cross over to the opposite side in the medulla oblongata, the left cerebral hemisphere controls the right side of the body. Hence, paralysis of the right leg results from loss of blood flow to the portion of the left hemisphere supplied by the left anterior cerebral artery. The middle cerebral artery (choice B) supplies the lateral convexity of the brain. Primary motor cortices on the lateral aspects of the hemispheres send fibers to the brainstem (innervating the face) and to spinal-cord segments innervating the upper limbs, the trunk, and the proximal part of the lower extremities. As with the anterior cerebral artery territories, the right hemisphere innervates the left body, and the left hemisphere innervates the right body. The posterior cerebral artery (choices C and E) supplies the occipital cortex; interruption of blood flow through this artery would probably produce visual deficits rather than paralysis. The right anterior cerebral artery (choice D) supplies blood to the medial aspect of the right cerebral hemisphere, which controls the left leg. This patient has paralysis of the right leg. 8. An infant is born with an abnormally developed falciform ligament. The hepatogastric and hepatoduodenal ligaments are also malformed. These developmental anomalies are most likely due to abnormal development of the A. dorsal mesoduodenum B. dorsal mesogastrium C. pericardioperitoneal canal D. pleuropericardial membranes E. ventral mesentery 3 The correct answer is E. The ventral mesentery forms the falciform ligament, ligamentum teres, and lesser omentum, which can be divided into the hepatogastric and hepatoduodenal ligament. The dorsal mesoduodenum (choice A) is the mesentery of the developing duodenum, which later disappears so that the duodenum and pancreas lie retroperitoneally. Both omental bursa and the greater omentum are derived from the dorsal mesogastrium (choice B), which is the mesentery of the stomach region.The pericardioperitoneal canal (choice C) embryologically connects the thoracic and peritoneal canals.The pleuropericardial membranes (choice D) become the pericardium and contribute to the diaphragm. 9. Which of the following structures is lined with epithelium derived from mesoderm of the ureteric bud? A.

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