Gray's Anatomy Review - Embryology
A 32-year-old pregnant woman who is in the 30th week of her pregnancy visits her obstetrician for the first time (which is later in her pregnancy than usual). An ultrasound reveals that she is carrying twins. However, it is also revealed that one twin is surrounded by excessive amniotic fluid, while the other is surrounded by too little. A diagnosis of twin-to-twin transfusion syndrome is made. Which of the following types of pregnancy is most likely the cause of such a condition? A. Dichorionic, diamniotic twins B. Dichorionic, monoamniotic twins C. Monochorionic, monoamniotic twins D. Conjoined twins E. Monochorionic, diamniotic twins
E. In monochorionic diamniotic twins, the single placenta (due to as yet unknown factors) develops blood vessel connections between the umbilical vessels of the twins. These connections result in an unbalanced blood supply known as twin-twin transfusion syndrome (TTTS). In TTTS, the donor twin does not get enough blood and the recipient twin becomes volume overloaded. In an attempt to reduce its blood volume, the recipient twin increases urine production, eventually resulting in polyhydramnios. At the same time, the donor twin produces less than the usual amount of urine leading to oligohydramnios. As the disease progresses, the donor produces so little urine that its bladder may not be seen on ultrasound. The twin becomes wrapped up by its amniotic membrane (known as a "stuck" twin). Often the polyhydramnios of the recipient twin is the first thing noticed by the patient due to a sudden increase in the size of the uterus. This condition is only possible when twins share a single chorion but have separate amniotic sacks. See Moore KL, Persaud TVN, Torchia MG: Before We Are Born, ed 8, 2013, pp. 85-87*
An obstetrician has delivered a small-forgestational age baby boy who is born 4 weeks too early. His mother is a 20-year-old chronic smoker who smoked a pack of cigarettes every day during her pregnancy. What teratogen most likely contributed to the low birth rate and premature delivery? A. Heroin B. Warfarin C. Rubella D. Tetracycline E. Nicotine
E. Nicotine can cause premature delivery, low birth weight, and poor physical growth due to its constrictive effect on uterine blood vessels. It also causes conotruncal defects and urinary tract abnormalities. Tetracycline exposure can cause tooth and bone defects including yellow discoloration and hypoplasia. Heroin is a behavioral teratogen and presents with small birth weight, central nervous system dysfunction, and small head circumference. Congenital rubella syndrome presents with cataracts, cardiac defects, and deafness among other defects. 306
A male infant is born with cleft hand, also known as "lobster-claw hand." This abnormality is caused by the apical ectodermal ridge (AER) failing to properly develop. Which of the following best describes the principal function of the AER? A. Establishes the anteroposterior axis of the limb bud B. Stimulates blood vessel growth into the limb bud C. Stimulates cartilage differentiation in the limb bud D. Stimulates nerve growth into the limb bud E. Stimulates outgrowth of the limb bud
E. The AER secretes growth factor, which initiates outgrowth of the limb mesenchyme that initiates formation of the limb bud. 235, 239
A 24-year-old woman visits an obstetrician and complains of not being able to get pregnant for the last 4 years. History reveals that she has been experiencing hot flashes, irregular periods, night sweats, and vaginal dryness. A diagnosis of premature ovarian failure is made. Estrogen replacement therapy is prescribed. What is the organ responsible for secreting estrogen? A. Anterior pituitary B. Posterior pituitary C. Hypothalamus D. Adrenal cortex E. Ovary
E. The ovaries are almond-shaped reproductive glands located close to the lateral pelvic walls on each side of the uterus that produce oocytes. The ovaries also produce estrogen and progesterone, the hormones responsible for the development of secondary sex characteristics and regulation of pregnancy. Follicle stimulating hormone (FSH) is produced by the anterior pituitary gland, which stimulates the development of ovarian follicles and the production of estrogen by the follicular cells. Luteinizing hormone (LH) serves as the "trigger" for ovulation (release of secondary oocyte) and stimulates the follicular cells and corpus luteum to produce progesterone. Gonadotropin releasing hormone (GnRH) is secreted from the hypothalamus and stimulates the production and secretion of FSH and LH from the anterior pituitary. 10, 14-17
A 5-year-old boy is brought to a plastic surgeon's office. He has a small jaw, large mouth, flat cheekbones, and malformed pinna. He had a cleft palate at birth, which was surgically corrected shortly afterward. The parents complain that sometimes he does not respond when they talk to him. What correctly describes this boy's embryologic defect? A. Trisomy 13 B. Defect in FBN1 gene C. Failure of fusion of medial nasal prominences D. Failure of rostral neuropore to close E. Failure of neural crest migration into the first arch
E. Treacher Collins syndrome (craniofacial dysostosis) is an autosomal disorder characterized by malar hypoplasia, downward-slanting palpebral fissures, defects of the lower eyelids and external ears, and sometimes abnormalities of the middle and internal ears. This is a first arch syndrome due to failure of neural crest cells to migrate to the first arch during the fourth week of development. Trisomy 13, also called Patau syndrome, is a chromosomal condition associated with severe intellectual disability and physical abnormalities in many parts of the body including microphthalmia, cleft lip and palate, and brain and spinal cord anomalies. Defect in the fibrillin 1 (FBN1) gene leads to Marfan's syndrome. Failure of fusion of the medial nasal prominences leads only to cleft lip and palate, while failure of closure of the rostral neuropore leads to meroencephaly or anencephaly. 108
A 29-year-old pregnant woman in her first trimester complains of preeclampsia and spotting. Ultrasound examination reveals an enlarged uterus and chorionic villi. Laboratory tests show elevated hCG levels. The physician suspects a hydatidiform mole, a condition characterized by gross edema of the chorionic villi surrounded by trophoblastic cells. The trophoblastic cell normally gives rise to which two cell layers? A. Ectoderm and endoderm B. Endoderm and mesoderm C. Hypoblast and epiblast D. Neural crest and neural tube E. Syncytiotrophoblast and cytotrophoblast
E. Upon trophoblastic invasion of the endometrium, the trophoblastic cells produce two cell layers: the syncytiotrophoblast is the outer layer that is related to the endometrial wall while the cytotrophoblast is the inner layer, which usually gives rise to the chorionic villi. The ectoderm, endoderm, and mesoderm are body germ layers produced during gastrulation. Hypoblast and epiblast cells are derived from the inner cell mass of the blastocyst, and the epiblast will ultimately, under gastrulation, form the germ layers. Neural crest cells do not give rise to the syncytiotrophoblast and cytotrophoblast; the neural tube forms the central nervous system. 24-25, 45
The parents of a 2-week-old infant bring their child to the emergency department complaining of poor feeding, wheezing, coughing, and a hoarse cry in the child. Imaging confirms a double arched aorta resulting in a ring around the trachea and esophagus. What is the embryologic origin of this condition? A. Failure of the distal part of the right aorta to disappear B. Failure of the fifth aortic arch to disappear C. Failure of the first aortic arch to disappear D. Failure of the second aortic arch to disappear E. Failure of the sixth aortic arch to disappear
A. A double arch of the aorta is a rare cardiac anomaly. There is the formation of a right and left arch of the aorta, which occurs due to a persistence of the distal part of the right dorsal aorta. This creates a vascular ring around the trachea and esophagus with resulting compression of these structures. Babies present with wheezing aggravated by crying, feeding, and flexion of the neck. 211-214
A 1-year-old female infant was brought to her pediatrician because of a small "strawberry" like swelling on her scalp that has been growing rapidly. A diagnosis of hemangioma is confirmed. Which of the following embryologic layers gives rise to this vascular tumor? A. Mesoderm B. Endoderm C. Ectoderm D. Trophoblast E. Syncytiotrophoblast
A. A hemangioma is a benign endothelial cell tumor. It is characterized by an increased number of normal or abnormal vessels filled with blood. Hemangiomas usually appear in the first weeks of life and grow most rapidly over the first 6 months. Hemangioblast is the common precursor for blood vessels and blood formation induced by vascular endothelial growth factor secreted by surrounding mesoderm. The endoderm forms the epithelial lining of the primitive gut, respiratory tract, tympanic cavity and auditory tube, and the allantois and vitelline duct. The ectoderm gives rise to the central nervous system, the peripheral nervous system, the sensory epithelium of the ear, nose, and eye, the epidermis, hair, and nails, the subcutaneous, mammary, and pituitary glands, and the enamel of the teeth. Trophoblast become cells that form the outer layer of a blastocyst and that provide nutrients to the embryo and later develop into a large part of the placenta. They are the first cells to differentiate from the fertilized egg. Syncytiotrophoblast is the epithelial lining of the placental villi, which will penetrate the walls of the uterus to establish maternofetal circulation. 285
18 A 20-year-old woman is trying to become pregnant. If she does, a blastocyst will form early in her pregnancy. Which of following statements accurately describes the formation of the blastocyst? A. Blastomere → morula → blastocyst B. Morula → zygote → blastocyst C. Blastomere → blastocyst D. Zygote → blastocyte → blastocyst E. Morula → blastocyte → blastocyst
A. After fertilization of the ovum, cleavage commences with the formation of blastomere and then a 16-cell morula. Fluid would then enter the cavity of the morula with the formation of a blastocyst. The blastocyst will then invade the endometrial wall. 21-24
Below are embryonic changes that occur during development of the upper limbs: 1. Separate fingers 2. Limb bud development 3. Webbed fingers 4. Digital rays. Which of the following most likely represents the correct order of developmental changes that occur in the upper limbs between weeks 5 and 8? A. 2-4-3-1 B. 3-4-2-1 C. 2-3-4-1 D. 4-2-3-1 E. 1-4-3-2
A. Development of the upper limb begins at 26 to 27 days after fertilization with the appearance of the upper limb buds; at 33 to 36 days the hand plates are formed and the digital rays are present; at 44 to 46 days notches form between digital rays, and at 49 to 51 days webbed fingers are distinct. Separate fingers appear at 52 to 53 days. 58-60
24 A pregnant mother is due in 2 weeks. Her body mass index (BMI) is in the overweight category and she has developed gestational diabetes. Pregnant women with gestational diabetes are more likely to have babies weighing 9 lb or more. During delivery, the obstetrician would be most concerned about which of the following for this expecting mother? A. Interspinous distance B. Distance of the pelvic inlet C. AP diameter D. Placenta previa E. Distance of the pelvic outlet
A. During embryogenesis, poorly controlled diabetes mellitus in the mother is associated with a 2- to 3-fold increase in the incidence of birth defects such as macrosomia, which is diagnosed as birth weight greater than 8 pounds 13 ounces (4000 grams), regardless of gestational age. Fetal macrosomia makes vaginal delivery difficult and puts the baby at risk of injury during birth. Therefore, cesarean section is recommended, during which epidural anesthesia is given. Hence, the interspinous distance is of concern. Other common anomalies with maternal diabetes mellitus include holoprosencephaly (failure of the forebrain to divide into hemispheres), meroencephaly (partial absence of the brain), sacral agenesis, congenital heart defects, and limb anomalies. 311
A 28-year-old woman visits an obstetrician for in vitro fertilization. FSH-analogs are injected to stimulate follicles. Then hCG is injected to induce the final oocyte maturation. Lastly, the oocyte is retrieved via a procedure called transvaginal oocyte retrieval. Knowing the anatomic relationship between the ovary and the vagina, the physician will insert the needle through which space of the vaginal wall to reach the ovary? A. Posterior fornix B. Lateral fornix C. Pouch of Morison D. Retropubic space of Retzius E. Extraperitoneal space
A. Each ovary is oval shaped, and is attached to the back of the broad ligament by the mesovarium. The position of the ovary is, however, extremely variable, and it is often found hanging down in the rectouterine pouch (pouch of Douglas). The posterior wall of the vagina is longer than the anterior wall and the posterior fornix is deeper than the other fornices. The posterior fornix is covered by peritoneum of the front of the rectouterine pouch (of Douglas) (GAS Fig. 5-58). 14-18
A 32-year-old woman visits an obstetrician complaining of significant bleeding in her first trimester and pain in the lower back. Ultrasound confirms the diagnosis of an abdominal pregnancy. Where is the most common place for an ectopic abdominal pregnancy? A. Pouch of Douglas B. Pouch of Morison C. Retropubic space D. Extraperitoneal space E. Retroperitoneal space
A. Ectopic pregnancy is the existence of a pregnancy outside the normal confines of the uterus or abnormally in the uterus. Although the uterine (fallopian) tube is the most common site of an ectopic pregnancy, it can also occur in the abdominal cavity, and when that is the case, the pouch of Douglas in the most common site. The pouch of Morison is the space between the liver and the right kidney and is not usually a site for ectopic pregnancy. The retropubic space is an extraperitoneal space between the pubic symphysis and the urinary bladder. It is a very unlikely site for ectopic pregnancy. Ectopic pregnancies rarely exist at the other sites listed (Fig. 8-1). 32-33
A cyanotic 9-year-old boy is brought to the emergency department, coughing up blood and complaining of severe chest pain. Examination by the physician reveals a heart arrhythmia and a heart murmur. Looking at the patient's history, the physician diagnoses the boy with Eisenmenger's syndrome, a left-to-right shunt converted into a right-to-left shunt secondary to elevated pulmonary artery pressure. Which of the following disorders could be the initial congenital defect (left-toright shunting) causing this syndrome? A. Ventricular septal defect B. Ebstein's anomaly C. Underdeveloped left ventricle (hypoplastic left heart syndrome) D. Common atrioventricular canal E. Large foramen secundum
A. Eisenmenger's syndrome or tardive cyanosis is the process in which a left-to-right shunt caused by a congenital heart defect causes increased flow through the pulmonary vasculature, causing pulmonary hypertension. This in turn causes increased pressure in the right side of the heart and reversal of the shunt into a right-to-left shunt. Eisenmenger's syndrome is a cyanotic heart defect characterized by a long-standing intracardiac shunt caused commonly by ventricular septal defects. In Ebstein's anomaly the septal leaflet of the tricuspid valve is displaced toward the apex of the right ventricle of the heart. There is subsequent atrialization of part of the right ventricle (which is now contiguous with the right atrium). This causes the right atrium to enlarge and the anatomic right ventricle to be small. Here there is an initial right-to-left shunt that results in a cyanotic baby. With the underdeveloped left ventricle, both the aorta and left ventricle are underdeveloped before birth, and the aortic and mitral valves are each too small to allow sufficient blood flow. As blood returns from the lungs to the left atrium, it must pass through an atrial septal defect to the right side of the heart. In this defect babies appear cyanotic. In the common atrioventricular canal defect the heart has one common chamber due to defects in the formation of its septae. Patients develop pulmonary hypertension by the second year of life. In a large foramen secundum (foramen ovale) the atrial septal defect (ASD) does lead to pulmonary hypertension but has a much slower progression. Symptoms usually appear after the third decade of life. 208, 211-212
An ultrasound of a 35-year-old pregnant woman reveals that she is carrying conjoined twins, a condition caused by incomplete division of embryonic discs. The most common location where conjoined twins (1/200 monozygotic conceptions) connects is: A. Thoracopagus B. Dicephalus C. Craniopagus D. Omphalopagus E. Rachipagus
A. Failure of complete division or fusion of adjacent embryonic discs leads to conjoined twins. These are always monozygotic and share a single chorion, placenta, and amniotic sac. The most common site of attachment is an anterior union of the thoracic regions called thoracopagus, with the second most common being omphalopagus, where the twins are joined at the anterior abdominal wall. The original "Siamese twins" were of this latter type. 87-88
A pediatrician examines a newborn baby and finds a smooth philtrum, thin vermilion border (upper lip), and small palpebral fissures. These craniofacial abnormalities are mostly associated with which teratogen that can cross the placenta in utero and mammary glands during breastfeeding? A. Alcohol B. Warfarin C. Heroin D. Rubella E. Tetracycline
A. Fetal alcohol syndrome (FAS) is associated with intrauterine growth restriction (IUGR), mental deficiency, microcephaly, ocular anomalies, joint abnormalities, and small palpebral fissures. Warfarin can be associated with nasal hypoplasia, stippled epiphyses, hypoplastic phalanges, eye anomalies, and mental deficiency. Tetracycline exposure can be associated with stained teeth and hypoplasia of enamel. Rubella virus is associated with various anomalies such as IUGR, postnatal growth retardation, cardiac and great vessel abnormalities, microcephaly, sensorineural deafness, cataract, microphthalmos (also referred to as microphthalmia), glaucoma, pigmented retinopathy, mental deficiency, neonate bleeding, hepatosplenomegaly, osteopathy, and tooth defects. Women who use heroin during pregnancy greatly increase their risk of serious pregnancy complications. These risks include poor fetal growth, premature rupture of membranes, premature birth, and stillbirth. 304-307
A couple hopes to start a family soon but the wife is currently taking medication for epilepsy. The obstetrician explains that exposure to this type of medication can cause serious birth defects, such as microcephaly, cleft palate, and congenital heart defects. Antiepileptic drug exposure during pregnancy will most likely cause which of the following? A. Fetal hydantoin syndrome B. Fetal alcohol syndrome C. Down's syndrome D. Treacher Collins syndrome E. DiGeorge's syndrome
A. Fetal hydantoin syndrome occurs in 5% to 10% of children born to mothers treated with phenytoin or hydantoin anticonvulsants. The usual pattern of defects consists of IUGR, microcephaly, mental deficiency, ridged frontal suture, inner epicanthal folds, eyelid ptosis, broad depressed nasal bridge, nail and/or distal phalangeal hypoplasia, and hernias. Fetal alcohol syndrome (FAS): intrauterine growth restriction (IUGR), mental deficiency, microcephaly, ocular anomalies, joint abnormalities, and short palpebral fissures. Trisomy 21 (Down's syndrome), the most common numerical abnormality resulting in birth defects (intellectual disability, abnormal facies, heart malformations), is usually caused by nondisjunction. The risk of meiotic nondisjunction increases with increasing maternal age. Treacher Collins syndrome is characterized by craniofacial deformities, such as absent cheekbones. Infants with DiGeorge syndrome are born without a thymus and parathyroid glands and have defects in their cardiac outflow tracts. 304-308
Oxygenated blood that reaches the heart in fetal circulation from the IVC passes through which of the following valves formed by a portion of the septum secundum? A. Foramen ovale B. Ductus arteriosus C. Foramen primum D. Ductus venosus E. Truncus arteriosus
A. In the fetal heart the left and right atria communicate with each other by an opening in the septum secundum, referred to as the foramen ovale. Ductus arteriosus is a vessel that connects the pulmonary artery and the aortic arch in the fetus. Foramen primum is the perforation in the inferior septum primum, which is closed off as it fuses to the endocardial cushion. Ductus venosus is the vessel that connects the left umbilical vein to the inferior vena cava. Truncus arteriosus will give rise to the aorta and pulmonary trunk (Fig. 8-5). 196-202
A 28-year-old woman who became pregnant 10 weeks ago has a house cat. She feeds the cat raw meat and handles the litter. Blood work reveals positive IgM for a zoonotic parasite. The fetus is susceptible to congenital deafness, low birth rate, inflammation of the retina, and jaundice. Which of the following teratogens can give rise to these findings? A. Toxoplasmosis B. Heroin C. Mercury poisoning D. Alcohol E. Tetracycline
A. Infectious teratogens include toxoplasmosis, which can result in jaundice, intracranial calcifications, chorioretinitis, microcephaly, microphthalmia, and hydrocephalus. Congenital syphilis can result in the formation of abnormal teeth and bones, congenital deafness, hydrocephalus, and mental retardation. Herpes simplex can also result in spasticity and mental retardation. Cytomegalovirus infection may result in cerebral palsy, mental retardation, intrauterine growth retardation, microphthalmia, blindness, deafness, and hepatosplenomegaly. Congenital rubella syndrome presents with cataracts, cardiac defects, and deafness among other defects. Alcohol exposure can result in fetal alcohol syndrome, which has a wide spectrum including mental and growth retardation plus morphogenetic disturbances. Cocaine use can cause microcephaly, neurobehavioral disturbances, spontaneous abortion, and urogenital disturbances. Streptomycin can cause vestibulocochlear (CN VIII) nerve defects. Methadone and heroin exposure can result in small birth weight, central nervous system dysfunction, and small head circumference. Tetracycline exposure can result in tooth and bone defects including yellow discoloration and hypoplasia. 304-305, 310
During weeks 3 to 8, the embryo is most susceptible to teratogens because major organs develop during this time. Which of the following exposures during this period would most likely result in congenital deafness, low birth rate, inflammation of the retina, and jaundice? A. Toxoplasmosis B. Heroin C. Mercury poisoning D. Alcohol E. Tetracycline
A. Infectious teratogens include toxoplasmosis, which causes jaundice, intracranial calcifications and chorioretinitis, microcephaly, microphthalmia, and hydrocephalus. Congenital syphilis can lead to abnormal teeth and bones, congenital deafness, hydrocephalus, and mental retardation. Herpes simplex exposure can result in microcephaly, microphthalmia, spasticity, and mental retardation. Cytomegalovirus infection may result in cerebral palsy, mental retardation, intrauterine growth retardation, microphthalmia, blindness, deafness, and hepatosplenomegaly. Congenital rubella syndrome presents with cataracts, cardiac defects, and deafness. Alcohol exposure can result in fetal alcohol syndrome, which has a wide spectrum including mental and growth retardation plus morphogenetic disturbances. Cocaine exposure can cause microcephaly, neurobehavioral disturbances, spon taneous abortion, and urogenital disturbances. Streptomycin causes vestibulocochlear nerve defects. Methadone and heroin are behavioral teratogens and present with small birth weight, central nervous system dysfunction, and small head circumference. Tetracycline causes tooth and bone defects including yellow discoloration and hypoplasia. 304-305, 310
Genetic analysis of a 20-year-old, 6-foot-tall man reveals a mutation in the FBN1 gene. He has unusually long and thin limbs, a hollowed chest, and severe nearsightedness (myopia). He is diagnosed with Marfan's syndrome. A computed tomography (CT) scan of the thorax revealed an unusual bulge anterior to the spinal cord and to the left of midline. Which condition will he be most susceptible to? A. Ruptured aorta B. Double inferior vena cava C. Portal hypertension D. Hydronephrosis E. Pyloric stenosis
A. Marfan syndrome affects the connective tissue supporting the body's joints and organs (e.g., heart, aorta, and eyes). Abnormalities in the connective tissue are due to mutations in a single protein building block (amino acid) in the fibrillin-1 protein. This leads to a severe reduction in the amount of fibrillin-1 available to form microfibrils, and elasticity in many tissues is decreased. In Marfan's syndrome elastic fibers are significantly reduced, eventually leading to aortic aneurysm and rupture. The thoracic aorta is contained in the posterior mediastinal cavity. It begins at the lower border of the fourth thoracic vertebra, where it is continuous with the aortic arch, and ends in front of the lower border of the twelfth thoracic vertebra at the aortic hiatus, where it becomes the abdominal aorta. 225-229
Ultrasound of a 20-year-old pregnant woman in the 20th week of pregnancy revealed abnormal limb development of her fetus, showing one arm to be shorter than the other. Which of the following most accurately describes this condition? A. Meromelia B. Central digit ray deformity C. Talipes equinovarus D. Polydactyly E. Syndactyly
A. Meromelia is the partial absence of a limb (amelia is total absence). Syndactyly refers to fused digits, and polydactyly is an excess in the number of digits. Central digit ray formation is the underlying mechanism for syndactyly, and talipes equinovarus is a malrotation of the foot, more commonly referred to as clubfoot. 245, 304
A 20-year-old pregnant woman in her third trimester visits an obstetrician complaining of periodic spotting. Ultrasound reveals implantation of the embryo near the internal os of the cervix. Despite periodic spotting, she experiences no pain during pregnancy. Which of the following describes this clinical symptom? A. Placenta previa B. Abruptio placentae C. Preeclampsia D. Leiomyoma E. Pelvic inflammatory disease
A. Placenta previa is defined as a placenta that has implanted into the lower segment of the uterus. It is now classified as either major, in which the placenta is covering the internal cervical os, or minor, when the placenta is sited within the lower segment of the uterus, but does not cover the cervical os. The mother will present with painless bleeding, often recurrent in the third trimester, and ultrasound scans will demonstrate the abnormal location of the placenta. The bleeding occurs due to separation of the placenta as the lower segment develops in the third trimester. A placental abruption is separation of a normally positioned placenta from the uterine wall. Preeclampsia is a serious disorder that occurs during pregnancy, usually after the 20th week of gestation. Maternal hypertension, proteinuria, and edema are essential features of this condition. Leiomyoma is a benign tumor of smooth muscle (fibroid). Pelvic inflammatory disease is characterized by inflammation and infection arising from the endocervix leading to endometritis, salpingitis, oophoritis, pelvic peritonitis and subsequently, formation of tubo-ovarian and pelvic abscesses. 81-82
A 24-year-old overweight woman visits an obstetrician and complains of not being able to get pregnant for the last 4 years. History reveals irregular menstrual periods, decreased breast size, and hair growth on the chest and belly. Transvaginal ultrasound most likely reveals a thick band around which of the following reproductive organs? A. Ovary B. Posterior wall of the uterus C. Fimbriae of the uterine (fallopian) tube D. Isthmus of the uterine (fallopian) tube E. Ampulla of the uterine (fallopian) tube
A. Polycystic ovary syndrome (PCOS) is a syndrome of ovarian dysfunction along with the cardinal features of hyperandrogenism and polycystic ovary morphology. Its clinical manifestations include menstrual irregularities, signs of androgen excess (e.g., hirsutism), and obesity. The ultrasound criteria for the diagnosis of a polycystic ovary are eight or more subcapsular follicular cysts <10 mm in diameter and increased ovarian stroma. 14-18
A 28-year-old woman visits an obstetrician for in vitro fertilization. FSH-analogs are injected to stimulate follicles. Then hCG is injected to induce final oocyte maturation. Lastly, the oocyte is retrieved via a procedure called transvaginal oocyte retrieval. The retrieved oocyte is arrested at what stage of development? A. Prophase of meiosis 1 B. Metaphase of meiosis 1 C. Prophase of meiosis 2 D. Metaphase of meiosis 2 E. Prophase of meiosis 2
A. Primary oocytes begin the first meiotic divisions before birth, but completion of prophase in meiosis 1 does not occur until adolescence. The follicular cells surrounding the primary oocytes secrete a substance, oocyte maturation inhibitor, which arrests the meiotic process of the oocyte. 14-19
44 A 3-day-old male infant was brought into the emergency department. The parents complained that their son cried constantly, especially hours after feeding. History revealed chronic diarrhea, fatigue, foul smelling stools, and inability to gain weight. The infant had not passed meconium and was also small for his age. Abdominal CT revealed obstruction of a small segment of the bowel due to the superior mesentery artery wrapping itself around the segment. A GI specialist diagnosed this intestinal deformity as a type IIIb intestinal atresia (also known as Christmas tree or apple peel deformity). Which of the following arteries is also affected? A. Middle colic/right colic/ileocecal artery B. Splenic artery C. Inferior mesenteric artery D. Left renal artery E. Left gastric artery
A. The superior mesenteric artery is closely related to the duodenum and gives rise to the middle colic, right colic, and ileocecal arteries. Therefore, any of these vessels may be affected. The splenic and left gastric arteries are branches of the celiac artery and lie superior to the intestines. The inferior mesenteric artery branches of the abdominal aorta are located too inferiorly. The left and right renal arteries branch from the aorta retroperitoneally and are not related to the intestinal tract. 141-159
A 47-year-old homeless man presents to the emergency department with a severe toothache. He has a large facial swelling that had previously been of painless until this admission. The physician diagnoses an ameloblastoma, a benign tumor of ameloblasts. During normal development, what develops from the ameloblasts? A. Enamel B. Alveolar bone C. Cementum D. Periodontal ligaments E. Pulp
A. Tooth development (odontogenesis) usually begins in the sixth to eighth week. This development occurs in three stages: bud stage, cap stage, and bell stage. The enamel usually develops in the advanced bell stage when cells of the inner enamel epithelium develop into ameloblasts, which produce and deposit enamel in the form of rods over the dentine. 288-289
A neonate with marked cyanosis in the lower extremities, cardiomegaly, harsh heart murmurs, and dyspnea is diagnosed with a patent ductus arteriosus. This condition is due to faulty migration of neural crest cells that leads to partial development of which of the following embryologic structures? A. Right subclavian artery B. Aorticopulmonary septum C. Tricuspid valve D. Inferior vena cava E. Left subclavian artery
B. Aorticopulmonary septum is the correct answer. The cardiac neural crest cells are involved in the development of the muscle and connective tissue walls of large arteries, parts of the cardiac septum, and parts of the thyroid, parathyroid, and thymus glands. The aorticopulmonary septum is derived specifically from the cardiac neural crest cells; once formed it separates the aorta and pulmonary arteries and fuses with the interventricular septum within the heart during development. The right subclavian artery takes its origin from the fourth pharyngeal arch. The tricuspid valve is formed from proliferation of tissue around the atrioventricular canal. The inferior vena cava takes its origin from the vitelline veins. 209, 211-212
Between 1966 and 1969, seven out of eight girls whose mothers had taken a certain agent during pregnancy were diagnosed with clear cell adenocarcinoma of the vagina. As a result, the researcher who identified the cause for the rise of this condition performed a case-controlled study. Which of the following teratogens is the most likely agent that pregnant mothers took to cause this condition in their daughters? A. Alcohol B. Diethylstilbestrol (DES) C. Lithium D. Nicotine E. Folic acid
B. Diethylstilbestrol (DES) is a synthetic nonsteroidal estrogen once commonly used in pregnant women to prevent breast engorgement, among many other uses. Prenatal exposure increases risk of multiple conditions including vaginal clear cell adenocarcinoma and reproductive tract malformations. It has since been proven to be toxic and teratogenic. Fetal alcohol syndrome from maternal alcoholism has a wide spectrum including mental and growth retardation plus morphogenetic disturbances. Lithium causes heart and great vessel abnormalities in utero. Nicotine causes premature delivery, conotruncal defects, and urinary tract abnormalities (Table 8-1). 304-305
A baby boy is born with a combination of congenital defects: atrial septal defect, patent ductus arteriosus, hypoplasia of the nasal bridge, and pectus carinatum (pigeon chest). The 35-year-old mother had not come in for any prenatal visits before parturition, and her medical history reveals that she had a heart surgery to repair a mitral valve defect secondary to rheumatic heart disease. She has been taking anticoagulant throughout her pregnancy. Which of the following teratogens will most likely explain the baby's congenital defects? A. Heroin B. Warfarin C. Rubella D. Tetracycline E. Nicotine
B. Fetal alcohol syndrome (FAS) is associated with intrauterine growth restriction (IUGR), mental deficiency, microcephaly, ocular anomalies, joint abnormalities, and short palpebral fissures. Warfarin is associated with nasal hypoplasia, stippled epiphyses, hypoplastic phalanges, eye anomalies, and mental deficiency. Tetracycline is associated with stained teeth and hypoplasia of enamel. Rubella virus is associated with various anomalies like IUGR, postnatal growth retardation, cardiac and great vessel abnormalities, microcephaly, sensorineural deafness, cataract, microphthalmos, glaucoma, pigmented retinopathy, mental deficiency, neonate bleeding, hepatosplenomegaly, osteopathy, and tooth defects. Women who use heroin during pregnancy greatly increase their risk of serious pregnancy complications. These risks include poor fetal growth, premature rupture of the membranes, premature birth, and stillbirth. 304-307
A 16-year-old boy visits the urologist with a lump in his left testis. Diagnosis of testicular teratocarcinoma is made. This tumor can be loosely referred to as "male pregnancy" because at an early stage the carcinoma contains all three primary germ layers: ectoderm, mesoderm, and endoderm. In normal embryologic development, which of the following processes give rise to these three primary germ layers? A. Morulation B. Gastrulation C. Cranio-caudal folding D. Cleavage E. Induction
B. Gastrulation occurs in early embryogenesis and is the process by which the blastula is reorganized into a three-layered structure, that is, ectoderm, mesoderm, and endoderm. Morulation involves the cleavage or division of the fertilized ovum usually into a 16-cell structure that resembles a ball. Cranio-caudal folding is a process that occurs with lateral folding of the embryo that transforms it from a flat disc into a three-dimensional tube within the body. Cleavage is the process of division of the fertilized ovum. Induction is the physiologic and chemical signal to stimulate cells to differentiate. 35-38
A woman in her first trimester visits her obstetrician for a routine ultrasound examination. Imaging reveals increased amniotic fluid surrounding the fetus. Which of the following is most likely to increase amniotic pressure? A. Renal hypoplasia B. Esophageal atresia C. Ureter obstruction D. Potter's syndrome E. Down's syndrome
B. Increase in amniotic fluid volume and pressure is called polyhydramnios. Esophageal atresia prevents the passage of excessive amniotic fluid into the stomach and intestines where it is absorbed. Fluid is eventually passed through the umbilical arteries into the placenta for removal into the maternal blood stream. This leads to a buildup of amniotic fluid and polyhydramnios. Renal hypoplasia and ureteric obstruction lead to a decrease in the amniotic fluid (oligohydramnios). Potter's and Down's syndromes have other associated anomalies. 84, 130, 138
A 27-year-old woman in a fishing town gives birth to an infant with severe neurologic symptoms of cerebral palsy including ataxia, numbness of hand and feet, and weakness of muscles. An evaluation of the infant reveals that he has Minamata disease. Which of the following teratogens/toxins consumed by the mother is the most likely cause of this congenital disorder? A. Lead B. Mercury C. Alcohol D. Cocaine E. Streptomycin
B. Minamata disease is a severe neurologic syndrome caused by methylmercury poisoning. It can be acquired or congenital, following maternal mercury ingestion as in this case. Accumulation of methyl mercury from maternal ingestion of fish and shellfish or pork (due to certain pesticide contamination) is the primary cause. Lead poisoning can cause permanent learning and behavioral disorders, and alcohol exposure can result in fetal alcohol syndrome, which has a wide spectrum including mental and growth retardation plus morphogenetic disturbances. Cocaine exposure can cause microcephaly, neurobehavioral disturbances, spontaneous abortion, and urogenital disturbances. Streptomycin exposure can result in vestibulocochlear (CN VIII) nerve defects. 309
A 32-year-old man presents to the emergency department with severe abdominal pain. Physical exam reveals rebound tenderness localized below the edge of the liver. Lab tests reveal a high white blood count, and CT scan shows an abnormal mass anterior to the right kidney. The physician suspects appendicitis due to an inflamed subhepatic appendix. Which of the following will cause the appendix to develop subhepatically? A. Rubella infection B. Malrotation of the midgut C. Failure of migration of the neural crest cells D. Meckel's diverticulum E. Failure of lateral folds to close
B. Misplacement of a normally formed appendix is due to malrotation of the midgut. Rubella infection leads to a myriad of birth defects including cataracts and cardiac problems but not GI problems. Neural crest cells do not directly contribute to the formation of the GI tract and failure of the lateral folds to close will form neural tube defects. Meckel's diverticulum is an outpouching of the ileum and may become infected, mimicking the symptoms of appendicitis, but would not be found subhepatically. 149
20 An obese 40-year-old woman is 33 weeks pregnant when she pays a visit to her obstetrician for her third trimester checkup. Physical exam reveals swollen hands. Her blood pressure (BP) is highly elevated, even though her BP throughout pregnancy has been normal. Laboratory tests reveal proteinuria. Because preeclampsia can develop into eclampsia (seizures) and put the baby and mother at risk, the physician immediately induces labor as treatment for the preeclampsia. Pain fibers from the uterus would follow which of the nerves below? A. Sympathetics (sympathetic pain line touching the peritoneum) B. Parasympathetics C. Somatic D. Somatic and sympathetics E. Sympathetics and parasympathetics
B. Pain fibers from organs and structures above the pelvic pain line will follow the sympathetic nerve fibers. Recall that the uterine fundus and body are located above the most inferior part of the pelvic peritoneal reflection, which is known as the pelvic pain line. Pain fibers from structures below the pelvic pain line will follow the parasympathetic nerves: the uterus is above the pelvic pain line. The uterus is a visceral organ and as such will not have somatic innervations. Pain fibers from the uterus are visceral afferent fibers and will only run with sympathetic fibers. 9-10
A 29-year-old, woman in her 27th week of pregnancy visits her obstetrician for a follow-up appointment. Ultrasound from a previous visit revealed a 4-cm mass growing at the base of the spine. What is the most likely diagnosis? A. Incomplete closure of the embryonic neural tube (lumbosacral myelomeningocele) B. Remnants of the primitive streak (sacrococcygeal teratoma) C. Swelling or growth of the endothelial cells that line blood vessels (hemangioma) D. Neuroendocrine tumor arising from any neural crest element of the sympathetic nervous system (neuroblastoma) E. Benign nerve sheath tumor of the peripheral nervous system (neurofibroma)
B. Remnants of the primitive streak (a thick linear band of epiblast at the beginning of week 3) may persist and give rise to a large tumor known as a sacrococcygeal teratoma. Because it is derived from pluripotent primitive streak cells, the tumor contains tissues derived from all three germ layers in incomplete stages of differentiation. Sacrococcygeal teratomas are the most common tumors in newborn infants and have an incidence of approximately 1 in 27,000. These tumors are usually surgically excised promptly and the prognosis is good (Fig. 8-2). 45, 47
A 3-year-old girl is brought to the emergency department for the fourth time in a year. The doctor suspects child abuse. Before social services is called, a genetics test is ordered and reveals that the patient has a mutation in the COL1A1 gene. In addition to bone fragility and short stature, physical exam may discover which of the following? A. Pigeon chest B. Short limbs C. Yellow sclera D. Ruptured aorta E. Stiff joints
B. The COL1A1 gene produces a component of type I collagen called the pro-α1(I) chain. Mutation of the gene leads to reduced production of pro-α1(I) chains and future reduced type I collagen. A shortage of this critical protein underlies the bone fragility and other characteristic features of osteogenesis imperfecta. Osteogenesis imperfecta has 4 types (I, II, III, and IV). In addition to more severe bone problems (fractures), features of these conditions can include blue sclerae, hearing loss, short stature, respiratory problems, and a disorder of tooth development. Discoloration of the sclera gives the appearance of a blue or blue gray color. This is due to the thinning of the sclera caused by a defective type I collagen; as a result the choroidal veins are evident, giving the appearance of a blue color. 225-229
A 55-year-old man visits his primary care provider complaining that he can no longer go bike riding without getting breathless and having chest pains. Upon examination, the physician detects a heart murmur. Echocardiography confirms aortic stenosis. What is the embryologic origin of the aorta? A. Bulbus cordis B. Truncus arteriosus C. Sinus venosus D. Ductus arteriosus E. Ductus venosus
B. The arch of the aorta develops from the truncus arteriosus, which is the cranial part of the primitive heart tube. It also gives rise to the pulmonary trunk. The bulbus cordis develops into the conus arteriosus of the right ventricle. The sinus venosus has two horns: a right horn that develops into the smooth sinus venarum of the right atrium and a left horn that develops into the coronary sinus. The ductus arteriosus connects the fetal pulmonary trunk to the aorta allowing for blood to bypass the pulmonary circulation. The ductus venosus connects the umbilical vein to the inferior vena cava allowing blood to bypass the hepatic circulation in the fetus. 204-205, 211-214
A 63-year-old woman is admitted to the emergency department with severe pleuritic chest pain radiating to the bottom portion of her scapula. The pain is relieved by bending forward and worsened by lying down or during inspiration. During physical examination the patient exhibits a friction rub sound auscultated at the lower left sternal border. Which of the following embryonic structures will most likely give rise to the affected structure? A. Splanchnopleuric mesoderm B. Somatopleuric mesoderm C. Septum transversum D. Oropharyngeal membrane E. Coelomic cleft
B. The structure involved is likely the parietal pleura, a derivative of the somatopleuric mesoderm. The lateral plate mesoderm gives rise to somatopleuric mesoderm and splanchnopleuric mesoderm. The somatopleuric mesoderm is the dorsal layer that is associated with ectoderm, which forms the body wall lining and dermis. The splanchnopleuric mesoderm, the ventral layer of the lateral mesoderm, is associated with endoderm; this forms the viscera and heart. The septum transversum forms the central tendon of the diaphragm. The oropharyngeal membrane forms a septum between the primitive mouth and pharynx. The coelomic cleft is formed during the division of the coelomic cavity and does not relate to the development of the pleura (Fig. 8-4). 39, 41, 53
During an eye examination of a 6-year-old boy, an ophthalmologist sees a wormlike structure projecting from the optic disc. The diagnosis is the persistence of the distal portion of the hyaloid artery. What does the proximal portion of the hyaloid vessels eventually become? A. Optic artery and vein of the retina B. Optic artery and vein of the lens C. Central artery and vein of the retina D. Central artery and vein of the lens E. Supra-orbital vessels
C. In the area of the embryo that becomes the eyes, the optic cup (an invagination of the neuroectoderm) is formed. This is connected to the developing brain by the optic stalk. Linear grooves called retinal fissures develop in the optic cups and along the optic stalks. These fissures contain vascular mesenchyme, which develop into the hyaloid artery and vein. The hyaloid vessels supply the optic cup and lens. As the retinal fissures fuse, these vessels are enclosed within the primordial optic nerve. The distal portion usually degenerates but the proximal portion becomes the central artery and vein of the retina. 271-277
A researcher is studying the developmental origins of the arteries that supply blood to the brain. The investigation involves injecting contrast media into the hearts of fetal chicken eggs and studying the arteries that develop in the pharyngeal arches because blood vessels that develop bilaterally in several of these structures supply the cerebral arterial circle (of Willis). Which of the following pairs of pharyngeal arches most likely gives rise to arteries that contribute to the blood vessels in the circle of Willis? A. Pharyngeal arches 1 and 2 B. Pharyngeal arches 2 and 3 C. Pharyngeal arches 3 and 4 D. Pharyngeal arches 4 and 5 E. Pharyngeal arches 4 and 6
C. Pharyngeal arches 3 and 4 give rise to the common carotid artery, internal carotid artery, the aortic arch, and subclavian artery. The cerebral circle of Willis is formed by arteries that take their origin from these structures. Arches 1 and 2 give rise to the maxillary artery, external carotid artery, stapedial artery, and hyoid artery, which do not contribute to the cerebral circle of Willis. Although Arch 3 participates in the formation of the circle of Willis, second arch structures do not. Arch 5 is rudimentary (if present) and has no derivatives. Arch 6 gives rise to the aortic arches, pulmonary artery, and ductus arteriosus but does not contribute to the circle of Willis (Fig. 8-3). 104, 211-212
A 4-hour-old infant boy with respiratory distress is examined in the NICU. His symptoms are alleviated when placed in the prone position. Which of the following will most likely explain his symptoms? A. Down's syndrome B. Treacher Collins syndrome C. Pierre Robin sequence D. Patent ductus arteriosus E. Bronchopulmonary dysplasia
C. Pierre Robin sequence (also called Robin sequence) is an autosomal recessive congenital disorder due to failure of neural crest cells to migrate to the first arch. It is initiated by a hypoplastic mandible, which results in posterior displacement of the tongue and obstruction to the closure of the palatine plates leading to bilateral cleft palate. Respiratory symptoms are common in patients with Robin sequence particularly when the baby is placed on his/her back (supine). The small, recessed mandible (micrognathia) causes the tongue to fall backward and obstruct the airway when babies are placed in the prone position. Down's syndrome is a result of trisomy 21; patients present with slanted palpebral fissures, cardiac anomalies, and impaired cognitive function. Although Treacher Collins is also a first arch syndrome, it also includes other craniofacial anomalies, disfigured external ears, and impaired hearing. Patent ductus arteriosus is a cardiac anomaly due to failure of closure of the ductus arteriosus at birth that usually presents with a holosystolic murmur. Bronchopulmonary dysplasia is a respiratory syndrome seen in newborns and characterized by lung inflammation and scarring. Patients will have respiratory distress when lying in any position (Fig. 8-6). 108
A 9-month-old male infant previously diagnosed with Down's syndrome is brought to the pediatrician by his parents because they observe a noticeable lump in the back of his neck. The physician learns that the infant has just recovered from a respiratory infection. Further analysis reveals the presence of fluid and white blood cells, an indication of embryonic lymphatic fluid. A differential diagnosis by the pediatrician is that there has been a failure of the jugular lymph sacs to join the lymphatic system, thereby preventing lymph drainage. Which of the following embryonic conditions could explain this case? A. Hemangioma B. Thyroglossal cyst C. Lingual cyst D. Cystic hygroma E. Squamous cell carcinoma of the larynx
D. Cystic hygromas are large swellings that usually appear in the inferolateral part of the neck and consist of large, single or multilocular, fluid-filled cavities. Hygromas may be present at birth, but they often enlarge and become evident during later infancy. Hygromas are believed to arise from parts of a jugular lymph sac that are pinched off, or from lymphatic spaces that do not establish connections with the main lymphatic channels, whereas a thyroglossal cyst is a fibrous cyst that forms from a persistent thyroglossal duct. Lingual cysts in the tongue may be derived from remnants of the thyroglossal duct. They may enlarge and produce pharyngeal pain, dysphagia (difficulty in swallowing), or both. 222, 285
A 28-year-old pregnant woman in her third trimester visits her obstetrician's office with her husband. The husband is short, with short limbs, bow legs, lumbar lordosis, and a large head with frontal bossing. Ultrasound revealed the baby to have a short humerus. As a precaution, genetic testing is ordered. Assuming the genetic test comes back positive for a mutation in the FGF3 gene, what other features are more than likely to be present in their child? A. Pigeon chest (Marfan's syndrome) B. Brittle bones (osteogenesis imperfecta) C. Trident hand (achondroplasia) D. Cardiac abnormalities E. Mental retardation
C. The FGFR3 gene provides instructions for making a protein called fibroblast growth factor receptor 3. These proteins play a role in several important cellular processes, including regulation of cell growth and division, determination of cell type, formation of blood vessels, wound healing, and embryo development. Mutations in the FGFR3 gene cause more than 99% of cases of achondroplasia. In achondroplasia (autosomal dominant disorder) the problem is not in forming cartilage but in converting it to bone (endochondral ossification at the epiphysial cartilage plates), particularly in the long bones of the limbs. Other features include an average-size trunk, short arms and legs with particularly short upper arms and thighs, and limited range of motion at the elbows. The head is enlarged (macrocephaly) with a prominent forehead and a "scooped out" nose (flat nasal bone). Fingers are typically short and the ring finger and middle fingers may diverge, giving the hand a three-pronged (trident) appearance. Also, lordosis and kyphosis of the vertebral column may be present. 235, 236, 302
A 25-year-old woman in her 28th week of pregnancy visits her obstetrician for a routine check-up. Her doctor explains that her baby's lungs are starting to produce surfactant, a necessary component for respiration. Surfactant is produced during which of the following periods of lung development? A. Pseudoglandular period B. Canalicular period C. Terminal sac period D. Bronchiole period E. Alveolar period
C. The development of the lungs occurs in four stages: the pseudoglandular stage (6 to 16 weeks), where the lungs resemble exocrine lungs. The parts of the lung involved in gaseous exchange have not yet formed. The canalicular stage (16 to 26 weeks) involves maturation of the bronchioles and development of a few primordial alveoli. The terminal sac stage (26 weeks to birth) is when the alveoli begin maturing, the blood gas barrier is formed, and surfactant is secreted by type 2 pneumocytes. The final stage is the alveolar stage (32 weeks to 8 years); alveoli continue to develop as the lungs prepare for the transition to autonomous gas exchange (Fig. 8-7). 130-135
A 6-year-old child was brought into the emergency department with vomiting and abdominal pain. He complains that pain is radiating down his back and is worsened when he lays flat on his back. Physical exam reveals abdominal tenderness. Lab results show elevated serum pancreatic enzymes. Abdominal CT scan shows a pancreas containing two separate duct systems emptying into the duodenum. The main pancreatic duct is very short and drains only a small portion of the head of the pancreas, while the remainder of the pancreas is drained via the other duct. The GI specialist diagnosed the patient with pancreas divisum. Which of the following accurately describes the embryologic anomaly? A. Formation of a bifid ventral bud B. Formation of a bifid dorsal bud C. Failure of the dorsal and ventral buds to fuse D. Fusion of the dorsal and bifid ventral bud E. Nonrotation of the midgut
C. The dorsal and ventral buds normally fuse to form the adult pancreas, the ventral duct although smaller becomes the terminal portion of the main duct. A bifid ventral bud, when fusing to the dorsal bud, typically leads to annular pancreas, which is a band of pancreatic tissue that wraps around the duodenum. Nonrotation of the midgut would result in displacement of the entire pancreas. 144
A 40-year-old alcoholic man visits his physician's office for the fourth time this year complaining of abdominal and back pain. Abdominal CT scan shows a pancreas containing two separate duct systems emptying into the duodenum. The main pancreatic duct is very short and drains only a small portion of the head of the pancreas, while the remainder of the pancreas is drained via the other duct. The gastrointestinal (GI) specialist diagnosed the patient with pancreas divisum. Which of the following accurately describes the embryologic abnormality? A. Formation of a bifid ventral bud B. Formation of a bifid dorsal bud C. Failure of the dorsal and ventral buds to fuse D. Fusion of the dorsal and bifid ventral bud E. Nonrotation of the midgut
C. The dorsal and ventral buds normally fuse to form the adult pancreas. The ventral duct, although smaller, becomes the terminal portion of the main duct. A bifid ventral bud, when fusing to the dorsal bud, typically leads to the formation of an annular pancreas, which is a band of pancreatic tissue that wraps around the duodenum. Nonrotation of the midgut would result in displacement of the entire pancreas. 144
A 60-year-old man has been feeling "pins and needles" and some sharp pains over his right upper chest and back for several weeks. A rash of red erupted vesicles is seen at the right border of the sternum, a few centimeters above the nipple. Antiviral treatment is initiated to treat herpes zoster. The patient recovers, is free of pain, and his skin looks normal. Which of the following structures has the same embryologic origin as the location where the viral particles are still residing? A. Dorsal horn B. Ventral horn C. Dorsal root ganglion D. Conus medullaris E. Dura mater
C. The herpes zoster virus after initial infection can remain latent in the dorsal root ganglion until the body becomes immunocompromised or stressed, and then reappears as a vesicular rash along one of the dermatomes, in this condition called shingles. The dorsal root ganglion sensory neurons are derivative of neural crest cells. Other neural crest cell derivatives include the pia mater, chromaffin cells of the adrenal medulla, thyroid parafollicular cells, Schwann cells, melanocytes, cranial nerves, connective tissue, and some bones of the skull and face. There are usually 21 pairs of denticulate ligaments, which take their origin from the pia mater and attach to the dura mater. As the pia mater is derived from neural crest cells the denticulate ligaments take their origin from the pia mater, which dictates that they share the same embryologic origin. The dorsal horn, ventral horn, and conus medullaris are all part of the spinal cord and are notochord derivatives. The dura mater is of mesenchymal origin. 252-253, 266
Nuchal translucency is used to screen for congenital defects during the 11th through 14th weeks of pregnancy. This procedure is recommended by an obstetrician for a 35-year-old pregnant woman who previously had a child with Down's syndrome (trisomy 21). Which of the following would be common to see in addition to a larger than normal accumulation of fluid at the back of the baby's head, indicating the possibility of another baby with Down's syndrome? A. Meromelia B. Hydrocephalus C. Anencephaly D. Atrioventricular septal defect E. Plagiocephaly
D. Down's syndrome is a congenital abnormality involving a triplication of chromosome 21. It is more common in children of women who become pregnant at 35 years or older (advanced maternal age is a risk factor). Down's syndrome is associated with various abnormalities including congenital heart defects. The most common congenital heart defect in Down's syndrome is endocardiac cushion type of atrial septal defect (40%) followed by ventricular septal defects (35%). 68, 298, 329
A 25-year-old woman trying to have her first child has a spontaneous abortion due to failure of implantation. Under normal circumstances, at what stage of embryonic development will an embryo most likely implant into the endometrium of the uterus? A. Trilaminar embryo B. Zygote C. Morula D. Blastocyst E. Bilaminar embryo
D. Implantation of the blastocyst begins at the end of the first embryonic week and normally occurs in the endometrium of the uterus, usually superiorly in the body of the uterus and slightly more often on the posterior than on the anterior wall. The blastocyst begins to implant on approximately the 6th day of the luteal phase. 29
A 42-year-old woman gave birth to an 8 lb baby girl with two additional toes to the right of her left big toe. Which of the following best describes this limb anomaly? A. Amelia B. Cleft foot C. Club foot D. Polydactyly E. Syndactyly
D. Polydactyly describes the presence of supernumerary digits of the hands and feet. Cleft foot occurs when one or more digital rays fail to develop, causing absence of the central digits. Clubfoot is a malrotation of the foot around the axis, and amelia is complete absence of a limb. Syndactyly is absence of digits either due to failure of digital rays to form or incomplete apoptosis. 244
A 14-month-old boy is brought to the ophthalmologist's office. His parents noticed that when photos of their child were taken, his eyes appeared white instead of red from the camera flash. Eye exam revealed poor vision in the right eye and CT scan showed calcifications within the right intraorbital mass. The boy is diagnosed with retinoblastoma. Which of the following structures share the same embryologic origin as the retina? A. CN II B. Lens C. Sclera D. Sphincter pupillae muscle of the iris E. Vitreous body
D. Retinoblastoma is a malignant carcinoma of the retina. The retina develops from the inner and outer layers of the optic cup, which is an invagination of the neuroectoderm. The outer thin layer becomes the inner pigment epithelium of the retina, while the inner layer becomes the light sensitive neural retina. The sphincter pupillae muscle of the iris develops from the neuroectoderm of the optic cup. CNII develops from the optic stalk. The lens develops from surface ectoderm. The sclera and the vitreous body develop from the mesoderm. 272-273
A young mother brings her 3-year-old daughter to the pediatrician with concerns of developmental delay. The pediatrician orders a CT scan, which shows partial atresia of the cerebellum. What is the embryologic origin of the cerebellum? A. Telencephalon B. Diencephalon C. Mesencephalon D. Metencephalon E. Myelencephalon
D. The brain develops from the neural tube. By the 28th week the caudal and rostral neuropores close, leading to the development of three primary brain vesicles: prosencephalon (forebrain), mesencephalon (midbrain), and rhombencephalon (hindbrain). By the fifth week, the forebrain subdivides into the telencephalon, which becomes the cerebral hemispheres, and a diencephalon, which becomes the thalamus, hypothalamus and epithalamus. The midbrain remains as the midbrain. The hindbrain subdivides into a metencephalon, which becomes the pons and cerebellum, and the myelencephalon, which becomes the medulla oblongata. 38, 254
A 55-year-old man with severe mitral regurgitation is scheduled for minimally invasive mitral valve repair. A percutaneous coronary sinus catheter is placed to deliver retrograde cardioplegia. During the procedure, the catheter stuck in an enlarged thebesian valve. Which of the following embryonic structures gives rise to the coronary sinus? A. Primitive ventricle B. Bulbus cordis C. Truncus arteriosus D. Left horn of the sinus venosus-left common cardinal vein E. Primitive atria
D. The left horn of the sinus venosus gives rise to the coronary sinus. The primitive atria and ventricles will give rise to the atria and ventricles, respectively. Bulbus cordis and truncus arteriosus gives rise to the smooth parts of the right and left ventricles and their corresponding arteries. 190-194
A 51-year-old man visits the emergency department with high fever, left lower quadrant pain, and blood in his urine (hematuria) for the past 3 days. A CT scan reveals the presence of a thrombus in the left inferior vena cava (IVC). Which of the following structures is most likely responsible for the presence of a left IVC? A. Right anterior cardinal vein B. Right vitelline vein C. Left vitelline vein D. Left supracardinal vein E. Left anterior cardinal vein
D. The left inferior vena cava results from regression of the right supracardinal vein while the left supracardinal vein persists. The right anterior cardinal vein and left cardinal veins contribute to the formation of the internal jugular veins and superior vena cava (with the common cardinal veins). The vitelline veins, during development, drain the yolk sac; they contribute to the formation of the hepatic veins, portal vein, and distal part of the inferior vena cava. 147, 192
A 6-hour-old female newborn is assessed in the neonatal intensive care unit (NICU). Medical records show cyanosis, an APGAR score of 0, pulmonary edema on radiograph, and a tetralogy of Fallot confirmed by echocardiography. Which of the following conditions is most likely associated with this clinical picture? A. Pulmonary edema B. Hepatosplenomegaly C. Cardiomegaly D. Anal atresia E. Meckel's diverticulum
D. VACTERL syndrome is a cooccurrence of birth defects. It commonly occurs in mothers who are 13 to 19 years of age who have taken progesteroneestrogen birth control pills during the critical stage of development. The acronym stands for Vertebral, Anal, Cardiac, Tracheal, Esophageal, Renal, and Limb anomalies. Tetralogy of Fallot is a common heart defect seen with the VACTERL association, as in anal atresia. 307
