Embryology — Past Paper OmpathStudy

Embryology — Questions and Answers Complete review bank: 52 questions recovered from all 29 source pages. 1. A newborn male infant is examined. There is a palpable right testis, but no left testis, in the scrotal sac. The infant has no other abnormalities noted. Which of the following is the most likely abnormality involving the gonads of this infant? A. Agenesis B. Fusion C. Hypopituitarism D. Incomplete descent E. Leydig cell aplasia F. Venous atresia Answer: D. Cryptorchidism is one of the most common problems involving the testis. Descent may be delayed. It can sometimes be chemically induced. Surgical correction may be employed. If not corrected, the affected gonad will not have spermatogenesis, and there will be an increased risk for carcinoma. 2. Following ovulation and fertilization of an ovum, a blastocyst develops. Growth and differentiation occurs following implantation. Which of the following differentiated tissues will develop into the placenta? A. Epimere B. Neural plate C. Sclerotome D. Trophoblast E. Umbilical vesicle Answer: D. Early in development, cells in the blastocyst destined to become the placenta become trophoblasts that line a blastocystic cavity, with an inner cell mass composed of embryoblasts destined to become the fetus. Hence, the placenta is a fetal structure, not a maternal structure. 3. A 5-year-old child fatigues easily. On examination a machinery-like murmur is auscultated over his chest. Echocardiography shows shunting of blood from the aorta to the pulmonary artery. An abnormality involving which of the following persistent embryologic structures is most likely present in this boy? A. Ductus arteriosus B. Endocardial cushion C. Sinus venosus D. Third aortic arch E. Truncus arteriosus Answer: A. The ductus arteriosus is normally open in fetal life to provide a shunt of blood from the pulmonary circulation to the systemic circulation. It should close soon after birth. If it does not close, there is a left-to-right shunt. 4. A 3500 gm infant born at term is doing well and gaining weight normally until the fourth week of life. He then exhibits feeding difficulty with forceful vomiting. Now, on physical examination, no external anomalies are noted. However, there is a firm mass palpable in the upper mid abdominal region. Which of the following conditions is the infant most likely to have? A. Duodenal atresia B. Hepatoblastoma C. Hirschsprung disease D. Pyloric stenosis E. Tracheoesophageal fistula Answer: D. There is abnormal hypertrophy of the pyloric ring, leading to obstruction and projectile vomiting. It is more common in males than females. 5. An infant born at term is examined, and there is abnormal fusion of the 3rd, 4th, and 5th digits of the left hand. A radiograph of the left hand shows transformation of metacarpals I, II, III, and V to short, carpal-like bones. A mutation involving which of the following genes most likely led to these findings? A. CFTR B. FGFR3 C. HOXD13 D. SHH E. TBX5 Answer: C. This gene is in the homeobox family of genes producing transcription factors that control morphogenesis, including limb development. Mutations may lead to lack of separation (syndactyly). 6. An infant born at term has a radiograph taken. No congenital abnormalities are noted. The upper heart borders are not well visualized. Which of the following structures normally present is most likely to obscure the heart borders in this infant's radiograph? A. Esophagus B. Lymph node C. Stomach D. Thymus E. Vertebra Answer: D. The thymus is in the anterior mediastinum and is proportionately larger in a newborn than later in life, and is busily schooling T lymphocytes, so it has a soft tissue density similar to the heart that lies posterior to it. In adults, the thymus appears on radiographs as only a small fatty remnant. 7. A secondary oocyte is developing normally. At which of the following times does the second maturation division of meiosis become completed? A. In the ovarian cortex B. During ovulation C. At fertilization D. In the blastocyst E. Upon implantation Answer: C. When the sperm penetrates the ovum, the process of meiosis is completed, with expulsion of the last polar body. 8. During the 3rd week of embryonic development, splanchnic mesoderm differentiates into blood islands with angioblasts. In what developing tissue site does this process occur? A. Heart B. Liver C. Spleen D. Thymus E. Vertebra Answer: A. The first significant amount of red blood cell production occurs in paired heart tubes, but quickly moves to spleen, then liver for most of 2nd and 3rd trimester, then marrow in 3rd trimester and beyond. 9. An ovum is fertilized. After 3 weeks a blastocyst implanted on the endometrium has an inner embryoblast and an outer trophoblast. Which of the following is the next step in forming a 3-layered embryonic disk? A. Decidualization B. Gastrulation C. Lateralizaton D. Neurulation E. Placentation Answer: B. The 3 germ layers form in the process of gastrulation in the 3rd