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?
D Incomplete descent
E Leydig cell aplasia
F Venous atresia
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Following ovulation and fertilization of an ovum, a blastocyst develops. Growth and differentiation occurs following implantation. Which of the following will develop into the placenta?
B Neural plate
E Yolk sac
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 structures is most likely present in this boy?
A Ductus arteriosus
B Endocardial cushion
C Sinus venosus
D Third aortic arch
E Truncus arteriosus
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
C Hirschsprung disease
D Pyloric stenosis
E Tracheoesophageal fistula
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?
An infant born at term has a radiograph taken. No congenital abnormalities are noted. The upper heart borders are not visualized. Which of the following structures is most likely to obscure the heart borders in this infant's radiograph?
B Lymph node
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
During the 3rd week of embryonic development, splanchnic mesoderm differentiates into blood islands with angioblasts. In what developing tissue site does this process occur?
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 55-year-old man has noted sharp pain in his right lower extremity for the past 2 months. MR imaging of his spine shows impingement on a spinal nerve root by a herniated structure located between L5 and S1. From which of the following embryonic derivatives does this herniated structure most likely arise?
C Lateral plate mesoderm
D Neural crest
In the developing embryo, pharyngeal arches are formed. The second (branchial) arch gives rise to the stapedius, orbicularis oris, and posterior belly of the digastric muscles. Which of the following cranial nerves is also derived from this arch?
An infant born at 30 weeks gestation develops respiratory distress soon after birth. the infant is intubated and upon mechanical ventilation there are breath sounds auscultated over the right chest, but not over the left. An abnormality involving a derivative from which of the following embryonic structures is most likely present in this infant?
B Neural crest
In the normally developing embryo, aortic arches are apparent by the end of the fourth week. Which of the following arteries is derived from the third pair of aortic arches?
A 19-year-old primigravida gives birth at term following an uncomplicated pregnancy to a 3000 gm male infant. He has not passed any stool by day 2 of life. On physical examination his abdomen is distended. An ultrasound scan shows a dilated colon. Laboratory studies show a normal sweat chloride test. A mutation involving which of the following genes is most likely to be present in this infant?
A fetus at 18 weeks gestation is normally formed and appropriately sized. No fetal or placental anomalies are present. Which of the following parts of the fetal vasculature is most likely to have the greatest oxygen concentration?
B Ductus arteriosus
C Pulmonary vein
D Right atrium
E Umbilical vein
An embryonic eye is developing normally. A retina is present on the posterior aspect of the globe. What is the embryologic origin of the portion of retina containing nerve cell bodies?
D Pharyngeal arch
E Surface ectoderm
A newborn examination is performed. The tympanic membranes are visualized bilaterally. What is the embryologic origin of the structure that forms the canal connecting the external ear to the tympanic membrane?
A Bony labyrinth
B First pharyngeal cleft
C Endolymphatic duct
D Otic pit
E Otic vesicle
A 2-year-old child has difficulty eating and drinking. On examination, there is a lateral cleft that involves the right upper lip. This defect is most likely due to failure in development and fusion of which of the following?
A Mandibular prominences and medial nasal prominences
B Mandibular prominences and secondary palate
C Maxillary prominences and mandibular prominences
D Maxillary prominences and secondary palate
E Medial nasal prominences and maxillary prominences
F Medial nasal prominences and secondary palate
A 20-year-old woman is unable to conceive and undergoes an infertility workup. A pelvic ultrasound reveals a bicornuate uterus. Which of the following is the most likely explanation for her anomalous uterus?
A Excess circulating maternal androgens while in utero
B Failure of primordial germ cell migration
C Failure of the paramesonephric ducts to fuse
D Failure of the urorectal septum to reach the perineum
E Low circulating levels of fetal estrogens
A newborn boy is noted to be dribbling urine. On examination he has a urethral opening on the ventral-midpoint of his penis. Abnormal development of which of the following structures is most likely responsible for his urinary problem?
A Anal pit
B Labioscrotal swellings
C Mesonephric ducts
D Prostatic urethra
E Urethral fold
F Urogenital sinus
In a developing embryo, neural crest cells form adjacent to the neural tube. These neural crest cells then undergo migration. Which of the following structures is derived from these migrating cells?
A Dorsal root ganglion
B Dura mater
C Epidermis covering the back
D Intervertebral disk
E Paravertebral muscle
A newborn infant boy is noted to have an abnormality involving his perineum and scrotum. There is failure of midline fusion in the urogenital region. Chromosome analysis shows his karyotype is 46, XY. Which of the following is most likely responsible for his condition?
A Abnormal androgen levels in utero
B Failure of mesonephric ducts to reach the urogenital sinus
C Failure of the urorectal septum to reach the perineum
D Formation of a cloaca
E Persistence of the allantois
A neonate undergoes a check of health status. On examination a faint cardiac murmur is auscultated. Echocardiography is performed and shunting of blood is noted from the left atrium to the right atrium. An abnormality in embryonic development of which of the following structures has most likely occurred in this neonate?
C Fourth aortic arch
D Sinus venosus
The two superior and two inferior parathyroid glands are found adjacent to the posterior aspect of the thyroid gland. From which of the following are these parathyroid glands derived in embryologic development?
A Foramen cecum
B Mandibular swellings
C Maxillary processes
D Pharyngeal pouches
E Thyroglossal duct
A 29-year-old woman describes mild discomfort with sexual intercourse for the past month. A pelvic examination reveals no vaginal discharge, and the cervix appears normal. On examination she has a small, slightly tender 2 cm mass in the lateral wall of her vagina. The excised mass is cystic, fluid filled, and lined by a cuboidal epithelium. This mass is most likely to be a remnant of which embryologic structure?
B Labioscrotal swelling
C Mesonephric duct
An infant is noted to have respiratory distress soon after birth. Physical examination reveals no external anomalies. A chest radiograph shows a left lung mass. A CT scan shows a peripheral, posterior left lower lobe lung posteriorly, with both cystic and solid components. Thoracic surgery is performed and the left lower lobe is removed without difficulty. There are no adhesions or abnormal vascular connections. Which of the following conditions is most likely to produce these findings?
A Congenital pulmonary airway malformation
B Diaphragmatic hernia with pulmonary hypoplasia
C Extralobar pulmonary sequestration
D Kartagener syndrome
E Tracheoesophageal fistula with atresia
A 31-year-old woman has noted no fetal movement by 16 weeks gestation. A fetal ultrasound shows the fetal head contains a brain with thin cortex, single enlarged ventricle, and fused thalami. Which of the following developing regions of the brain is most likely abnormal in this fetus?
A Cranial vault
During normal embryonic development, anterior-posterior differentiation occurs. By the end of the fifth week, dorsomedial somitic cells give rise to myotomes forming the epimere. Which of the following muscles is most likely derived from these cells?
A Erector spinae
B Lateral pterygoid
C Latissimus dorsi
D Psoas major
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