nbme 2003 embryo Flashcards
a PSA level is drawn from a 54-year-old man as part of a routine health exam. What embryonic structure gives rise to the organ being screened for carcinoma?
Urogenital sinus
the greater omentum is derived from this embryonic structure
dorsal mesoGAStrium.
A newborn baby has projectile vomiting shortly after each feeding. It is determined that there is obstruction of the digestive tract as a result of an annular pancreas. Annular pancreas is a result of an abnormality of which process?
Rotation of the ventral pancreatic bud around the second part of the duodenum
A newborn infant has some of its abdominal viscera protruding through a defect in the abdominal wall. What is the likely cause of this defect?
Incomplete fusion of the lateral body folds. (during the 4th week, lateral body folds move ventrally and fuse in the midline to form the anterior body wall - incomplete fusion results in abdominal viscera protruding from the abdominal cavity (gastroschisis).)
Autopsy of a baby who died minutes after birth demonstrates intestines within the thoracic cavity. What most probably accounts for these findings?
Partial absence of the diaphragm.
During development, the formation of the kidney is induced by what structure?
Metanephric duct. (the metanephric duct (a.k.a. ureteric bud) is a diverticulum of the mesonephric duct. it grown to the metanephric mass of the urogenital ridge. it induces the development of the metanephrons, which will give rise to the excretory units of the definitive kidney.)
What developmental abnormality might account for unexplained small intestinal bleeding?
Gastric heterotopia. (heterotopic rests are small areas of normal tissue in abnormal sites. in gastric heterotopia, which occurs typically in the small intestine can produce enough acid to cause a peptic ulcer in adjacent mucosa. the ulcer may be a source of gastrointestinal bleeding.)
When examining a histological section of a normal ovary, you notice an oocyte surrounded by several layers of follicular cells. A small antrum is present. What is the correct term for the entire structure, composed of the oocyte, follicular cells, and antrum?
Secondary follicle.
What cell types is derived from neuroepithelial cells?
Astrocytes. (astrocytes and oligodendrocytes are both derived from glioblasts, which in turn, are derived from neuroepithelial cells.)
What embryonic structure gives rise to the adrenal cortex?
Mesoderm.
A neuroscientist is investigating the development of the nervous system. In an experiment, he microinjects a dye into the embryo of an animal subject in vivo. After birth, he performs histological studies to determine the destination of the dye. In one animal subject, he locates the dye in the dorsal horn of the spinal cord. What location in the embryo was the most likely site of the injection?
Alar plate
A newborn boy does not pass meconium until 48 hours after his birth. Two weeks later his mother reports that he has not been passing stool regularly. Anorectal manometry reveals increased internal anal sphincter pressure on rectal distention with a balloon. Radiographic studies reveal massive dilation of the colon proximal to the rectum. This indicates a developmental abnormality in which embryonic tissue?
Neural crest. (the baby has Hirschsprung’s disease, 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 the postganglionic neurons of the autonomic nervous system and the sensory neurons of the peripheral nervous system.)
Physical exam of a young boy reveals discharge of urine from the umbilicus. The physician concludes that the urachus has failed to fuse. What structure is the normal adult remnant of the fused urachus?
Median umbilical ligament.
A male infant presents with flattened facial features, low set ears, and deformities of the feet. The lungs are underdeveloped. The pregnancy was complicated by severe oligohydramnios. The most likely cause of this condition is a malformation of the…?
ureteric buds. (this infant suffers from Potter syndrome, caused by an absence of both kidneys, often caused by a failure of the ureteric buds to develop.)
A 47-year-old male presents to his neurologist with an unsteady broad-based gait and slow, slurred speech. Neurological exam reveals dysdiadochokinesis, intention tremor, hypotonia, and nystagmus. The patients lesion is in a brain structure that derives from what embryonic structure?
Metencephalon
Evaluation of an infant with a variety of congenital abnormalities reveals hypocalcemia due to a lack of parathyroid hormone. On x-ray, the thymic shadow is absent. A failure of development and differentiation of what embryonic structure would most likely be responsible for the observed presentation?
Third pharyngeal pouch. (the third pharyngeal pouch normally gives rise to the inferior parathyroid glands and the thymus.)
The heart of an embryo first begins beating at which age?
4 weeks. (while the third week embryo is a primitive trilaminar plate, in the fourth week the heart begins to form and begins beating almost immediately.)
A 17-year-old male is examined by a physician, who notes a mass at the back of the young man’s tongue. The physician biopsies the mass, and the pathology report comes back with a diagnosis of normal thyroid tissue. The occasional presence of such tissue at the back of the tongue is related to the embryonic origin of the thyroid near what structure?
Foramen cecum. (the thyroid gland originates as a mass of endodermal tissue near the foramen cecum, which is near the tuberculum impar (which becomes the central part of the tongue), during development, thyroid descends in front of the pharynx, maintaining a connection to the tongue via the thyroglossal duct.)
A 2-year-old boy is brought to the pediatrician by his mother because he has had several episodes of rectal bleeding. Evaluation with a technetium-99m perfusion scan reveals a 3-cm ileal outpouching located 60 cm from the ileocecal valve. This structure likely contains what type of ectopic tissue?
Gastric.
