What is the pattern of inheritance in neural tube defects?
Q2
The covering of an omphalocele is derived from which of the following layers?
Q3
Identify the uterus shown in the image?
Q4
Scientists are studying human lung development by trying to identify which proteins and signaling factors trigger lung bud division and bronchiole branching. Their main focus is particularly around the 20th week of gestation, during which terminal bronchioles branch into respiratory bronchioles and further into alveolar ducts. Which of the following phases of embryonic lung development is the stage in which the scientists are interested in studying?
Q5
During the obstetric clerkship, the doctor is observing a 3rd-year resident assist a delivery. The patient only had 1 prenatal ultrasound that reported a male fetus. The delivery progresses without complications. The pediatrician-in-charge of the newborn notices a short, broad, upturned penis with an orifice in its dorsal aspect, and both testicles are present in the scrotum. Both the attending and PGY-3 resident immediately recognize the condition. Which of the following female anatomical structures is derived from the embryonic structure affected in this patient?
Q6
A primigravid 28-year-old woman delivers a 38-week-old male infant via spontaneous vaginal delivery. She had no prenatal care during her pregnancy. At birth the infant has underdeveloped hands and radiograph reveals missing phalanges in the thumbs. Examination of the buttocks reveals a missing anus. Further work-up reveals flow between the two ventricles on echocardiography and a single kidney on preliminary abdominal ultrasound. The infant also has difficulty feeding that results in coughing and apnea. Which of the following tissues was most likely affected during embryologic development?
Q7
A 36-year-old man comes to the physician for a follow-up examination. Two weeks ago, he was diagnosed with an ischemic stroke of the right middle cerebral artery. He was treated with thrombolytics and does not have any residual symptoms. His pulse is 82/min and regular. Cardiovascular examination shows no abnormalities. Echocardiography shows a reproducible, transient, low-volume, right-to-left shunt through the atrial septum during coughing. Which of the following conditions is caused by failure of an embryologic process similar to that responsible for this patient's heart condition?
Q8
A newborn boy born vaginally to a healthy 37-year-old G3P1 from a pregnancy complicated by hydramnios fails to pass meconium after 24 hours of life. The vital signs are within normal limits for his age. The abdomen is distended, the anus is patent, and the rectal examination reveals pale mucous with non-pigmented meconium. Based on a barium enema, the boy is diagnosed with sigmoid colonic atresia. Disruption of which structure during fetal development could lead to this anomaly?
Q9
A research team is studying certain congenital anomalies of the respiratory tract. The method consists of marking a certain germinal layer with an isotope, following its development stages in chicken embryos, and finally analyzing the specimen. A given specimen of tissue is presented in the exhibit. Which of the following germinal structures most likely gave rise to the epithelial lining of this specimen?
Q10
A 26-year-old woman comes to the physician because she has not had a menstrual period for 5 weeks. Menarche was at the age of 14 years and menses occurred at regular 30-day intervals. She reports having unprotected sexual intercourse 3 weeks ago. A urine pregnancy test is positive. Which of the following best describes the stage of development of the embryo at this time?
Embryology US Medical PG Practice Questions and MCQs
Question 1: What is the pattern of inheritance in neural tube defects?
A. Multifactorial inheritance (Correct Answer)
B. Autosomal recessive
C. X-linked dominant
D. Autosomal dominant
E. X-linked recessive
Explanation: ***Multifactorial inheritance***
- Neural tube defects (NTDs) are a classic example of **multifactorial inheritance**, meaning they result from a combination of **genetic predispositions** and **environmental factors**.
- Risk is influenced by multiple genes, and environmental factors like **folate deficiency** play a significant role.
*Autosomal recessive*
- This pattern involves two copies of an altered gene to cause disease, typically resulting in a **25% recurrence risk** for siblings.
- While some rare isolated NTDs might have an autosomal recessive component, the general presentation of NTDs does not fit this classic mendelian pattern.
*X-linked dominant*
- Involves genes on the **X chromosome** where one altered copy is sufficient to cause disease; affected fathers pass it to all daughters, but no sons.
- This inheritance pattern is very rare for NTDs and would present with a distinct sex-linked pattern of affected individuals.
*Autosomal dominant*
- Requires only one copy of an altered gene to cause disease, leading to a **50% recurrence risk** for offspring.
- While some syndromes associated with NTDs can be autosomal dominant, the primary mechanism for isolated NTDs is not solely due to a single dominant gene.
*X-linked recessive*
- Involves genes on the **X chromosome** where two altered copies are needed in females, but only one in males; typically affects males predominantly.
- This inheritance pattern does not account for the observed familial clustering and environmental contribution seen in NTDs.
Question 2: The covering of an omphalocele is derived from which of the following layers?
A. Amnion (Correct Answer)
B. Chorion
C. Mesoderm
D. Endoderm
E. Ectoderm
Explanation: ***Amnion***
- An **omphalocele** is a congenital abdominal wall defect where abdominal contents protrude through the umbilical ring, covered by a sac derived from the **amnion** and peritoneum.
- The covering of an omphalocele defect is an intact peritoneal sac that is covered externally by **amnion**.
*Chorion*
- The **chorion** is the outermost membrane surrounding an embryo, providing protection and nourishment, but it does not form the covering of an omphalocele.
- It works in conjunction with the decidua to form the **placenta** and has finger-like projections called villi on its outer surface.
*Mesoderm*
- The **mesoderm** is one of the three primary germ layers in embryonic development, giving rise to connective tissue, muscle, and blood cells.
- **Fetal skin**, not the omphalocele covering, develops from the mesoderm and ectoderm.
*Endoderm*
- The **endoderm** is the innermost of the three primary germ layers, giving rise to the lining of the digestive tract and respiratory system.
- The omphalocele covering is derived from the amnion, not the endoderm, which is involved in forming internal organs.
*Ectoderm*
- The **ectoderm** is the outermost of the three primary germ layers, giving rise to the nervous system, skin epidermis, and sensory organs.
- While ectoderm contributes to skin development, the omphalocele sac is specifically covered by amnion, not ectodermal derivatives.
Question 3: Identify the uterus shown in the image?
A. Bicornuate (Correct Answer)
B. Didelphys
C. Arcuate
D. Septate
E. Unicornuate
Explanation: ***Bicornuate***
- The image displays a uterus with two distinct uterine horns that are partially fused at the fundus, creating a **heart-shaped external indentation**.
- This morphology is characteristic of a **bicornuate uterus**, which results from incomplete fusion of the paramesonephric (Müllerian) ducts.
*Didelphys*
- A **uterus didelphys** would show two completely separate uteri, each with its own cervix and often a separate vagina.
- The image clearly shows a single cervix and a single vaginal canal, with only the upper uterine body being divided.
*Arcuate*
- An **arcuate uterus** has a small, concave indentation at the fundus, but the overall shape is typically that of a normal uterus with a mild deformity.
- The image shows a much more significant division of the uterine cavity than seen in an arcuate uterus.
*Septate*
- A **septate uterus** has a normal external contour but contains an internal septum that divides the uterine cavity into two parts.
- The image demonstrates both internal and external division with a heart-shaped fundal indentation, which distinguishes bicornuate from septate uterus.
*Unicornuate*
- A **unicornuate uterus** results from failure of one Müllerian duct to develop, creating a single elongated uterine horn.
- The image shows two uterine horns, not a single horn, ruling out this diagnosis.
Question 4: Scientists are studying human lung development by trying to identify which proteins and signaling factors trigger lung bud division and bronchiole branching. Their main focus is particularly around the 20th week of gestation, during which terminal bronchioles branch into respiratory bronchioles and further into alveolar ducts. Which of the following phases of embryonic lung development is the stage in which the scientists are interested in studying?
A. Canalicular (Correct Answer)
B. Alveolar
C. Pseudoglandular
D. Saccular
E. Embryonic
Explanation: ***Canalicular***
- The **canalicular stage**, occurring from weeks 16 to 26, is characterized by the formation of **respiratory bronchioles**, alveolar ducts, and the beginning of vascularization.
- This stage is crucial for the development of blood-air barrier precursors, making it relevant for studying branching and differentiation into gas exchange structures.
*Alveolar*
- The **alveolar stage** begins much later (late fetal period, 32 weeks, continuing for several years postpartum) and primarily involves the maturation of **alveoli** and increase in their numbers.
- While essential for complete lung function, it does not describe the initial branching and differentiation of bronchioles that occurs around 20 weeks.
*Pseudoglandular*
- The **pseudoglandular stage**, from weeks 6 to 16, involves the formation of the major conducting airways (bronchi and terminal bronchioles) but not yet respiratory bronchioles or alveolar ducts.
- The description of terminal bronchioles branching into respiratory bronchioles places it beyond this stage.
*Saccular*
- The **saccular stage**, from weeks 26 to 32, is marked by the formation of saccules (primitive alveoli) and further thinning of the blood-air barrier.
- While it involves growth of the respiratory tree, the detailed branching into respiratory bronchioles and alveolar ducts is primarily a feature of the preceding canalicular stage.
*Embryonic*
- The **embryonic stage**, from weeks 3 to 6, is the earliest phase where the lung bud emerges from the foregut and begins to divide into main bronchi.
- This stage is too early for the significant branching described, which involves terminal and respiratory bronchioles.
Question 5: During the obstetric clerkship, the doctor is observing a 3rd-year resident assist a delivery. The patient only had 1 prenatal ultrasound that reported a male fetus. The delivery progresses without complications. The pediatrician-in-charge of the newborn notices a short, broad, upturned penis with an orifice in its dorsal aspect, and both testicles are present in the scrotum. Both the attending and PGY-3 resident immediately recognize the condition. Which of the following female anatomical structures is derived from the embryonic structure affected in this patient?
A. Clitoris (Correct Answer)
B. Labia minora
C. Labia majora
D. Vestibule
E. Bartholin glands
Explanation: ***Clitoris***
The newborn has **epispadias**, a congenital malformation characterized by the urethral opening on the dorsal (upper) surface of the penis. This condition results from abnormal development of the **genital tubercle**, which forms during weeks 4-7 of embryonic development. In males, the genital tubercle normally differentiates into the glans and shaft of the penis. In females, this same embryonic structure gives rise to the **clitoris**. Since the affected structure in this patient is the genital tubercle, the corresponding female anatomical structure is the clitoris.
*Labia minora*
This structure is derived from the **urogenital folds**, not the genital tubercle. In males, the urogenital folds fuse to form the ventral aspect of the penis and enclose the penile urethra. The patient's epispadias affects the genital tubercle, not the urogenital folds.
*Labia majora*
This structure is derived from the **labioscrotal swellings**, which in males form the scrotum. The question states both testicles are present in the scrotum, indicating normal labioscrotal development. The malformation involves the genital tubercle, not the labioscrotal swellings.
*Vestibule*
The vestibule is derived from the **urogenital sinus**, not the genital tubercle. In males, the urogenital sinus contributes to the prostatic and membranous urethra, as well as the bulbourethral glands. The dorsal penile defect in epispadias specifically affects genital tubercle development.
*Bartholin glands*
These greater vestibular glands are derived from the **urogenital sinus**, which in males gives rise to the bulbourethral (Cowper's) glands. The patient's condition involves the genital tubercle, not structures derived from the urogenital sinus.
Question 6: A primigravid 28-year-old woman delivers a 38-week-old male infant via spontaneous vaginal delivery. She had no prenatal care during her pregnancy. At birth the infant has underdeveloped hands and radiograph reveals missing phalanges in the thumbs. Examination of the buttocks reveals a missing anus. Further work-up reveals flow between the two ventricles on echocardiography and a single kidney on preliminary abdominal ultrasound. The infant also has difficulty feeding that results in coughing and apnea. Which of the following tissues was most likely affected during embryologic development?
A. Neuroectoderm
B. Mesoderm (Correct Answer)
C. Endoderm
D. Neural crest
E. Surface ectoderm
Explanation: ***Mesoderm***
- The presented constellation of anomalies is consistent with **VACTERL association** (Vertebral defects, Anal atresia, Cardiac defects, Tracheo-Esophageal fistula, Renal anomalies, and Limb abnormalities).
- While VACTERL affects multiple germ layers, the **predominant tissue involved is mesoderm**, which gives rise to the cardiovascular system (ventricular septal defect), urogenital system (single kidney), skeletal system (limb and vertebral abnormalities), and connective tissue components of the GI tract (anal atresia musculature).
- The **majority of the defects** in this case—cardiac (VSD), renal (single kidney), and limb (missing phalanges)—are primarily **mesodermal derivatives**, making mesoderm the most likely affected tissue.
*Endoderm*
- The endoderm forms the **epithelial lining of the gastrointestinal and respiratory tracts**, including the esophagus, trachea, and anal canal lining.
- While the **tracheoesophageal fistula** and the epithelial component of **imperforate anus** do involve endodermal structures, the question asks for the **most likely** affected tissue, and the predominant pattern of defects points to mesoderm.
- Endodermal involvement alone would not explain the cardiac, renal, and limb defects.
*Neuroectoderm*
- The neuroectoderm gives rise to the **central nervous system (brain and spinal cord)**, retina, posterior pituitary, and pineal gland.
- While vertebral defects in VACTERL can be associated with neural tube defects, the primary anomalies described (cardiac, renal, limb, anal, TEF) are not primarily neuroectodermal in origin.
*Neural crest*
- Neural crest cells contribute to the **peripheral nervous system**, autonomic ganglia, melanocytes, craniofacial cartilage and bone, and parts of the heart (conotruncal septum and outflow tract).
- While neural crest cells contribute to cardiac outflow tract development, a **ventricular septal defect** is primarily a mesodermal defect of the ventricular septum formation.
- The constellation of renal, limb, and anal defects points away from primary neural crest involvement.
*Surface ectoderm*
- The surface ectoderm forms the **epidermis**, hair, nails, lens of the eye, tooth enamel, and anterior pituitary.
- The described anomalies do not involve these surface structures and are not consistent with surface ectodermal defects.
Question 7: A 36-year-old man comes to the physician for a follow-up examination. Two weeks ago, he was diagnosed with an ischemic stroke of the right middle cerebral artery. He was treated with thrombolytics and does not have any residual symptoms. His pulse is 82/min and regular. Cardiovascular examination shows no abnormalities. Echocardiography shows a reproducible, transient, low-volume, right-to-left shunt through the atrial septum during coughing. Which of the following conditions is caused by failure of an embryologic process similar to that responsible for this patient's heart condition?
A. Transposition of the great vessels
B. Hirschsprung disease
C. Midgut volvulus
D. Thyroglossal duct cyst
E. Hypospadias (Correct Answer)
Explanation: ***Hypospadias***
- The patient's presentation with a **transient right-to-left shunt** through the atrial septum during coughing, especially after an ischemic stroke, suggests a **patent foramen ovale (PFO)**. A PFO results from the failed fusion of the **septum primum** and **septum secundum** postnatally.
- Hypospadias is a developmental anomaly where the urethral opening is on the ventral side of the penis, resulting from the **incomplete fusion of the urethral folds** during embryogenesis. Both PFO and hypospadias arise from failures of fusion of embryonic structures.
*Transposition of the great vessels*
- This condition is caused by a failure of the **aorticopulmonary septum** to spiral during septation of the truncus arteriosus, leading to the aorta originating from the right ventricle and the pulmonary artery from the left ventricle.
- This is a defect in **septation and spiraling**, not a failure of fusion of distinct embryonic structures.
*Hirschsprung disease*
- This is characterized by the **absence of ganglion cells** (Meissner and Auerbach plexuses) in the distal colon, due to the failure of **neural crest cell migration** to the affected bowel segments.
- This condition is a defect in cell migration, distinct from a failure of embryonic structure fusion.
*Midgut volvulus*
- This occurs due to **malrotation of the intestines** during embryonic development, leading to an abnormally positioned small bowel that is prone to twisting around the superior mesenteric artery.
- This is a defect in **intestinal rotation and fixation**, rather than a failure of fusion.
*Thyroglossal duct cyst*
- This results from the **failure of complete obliteration of the thyroglossal duct**, an embryonic remnant formed during the descent of the thyroid gland from the tongue base to its final position in the neck.
- While it involves an embryonic remnant, it is a failure of **obliteration**, not fusion, of two separate structures.
Question 8: A newborn boy born vaginally to a healthy 37-year-old G3P1 from a pregnancy complicated by hydramnios fails to pass meconium after 24 hours of life. The vital signs are within normal limits for his age. The abdomen is distended, the anus is patent, and the rectal examination reveals pale mucous with non-pigmented meconium. Based on a barium enema, the boy is diagnosed with sigmoid colonic atresia. Disruption of which structure during fetal development could lead to this anomaly?
A. Inferior mesenteric artery (Correct Answer)
B. Superior mesenteric artery
C. Vitelline duct
D. Cloaca
E. Celiac artery
Explanation: ***Inferior mesenteric artery***
- **Sigmoid colonic atresia**, as observed in this case, results from an ischemic event affecting the segment of the bowel supplied by the **inferior mesenteric artery** during fetal development.
- Interruption of blood flow to this region can lead to subsequent **atresia** as the affected part of the intestine necroses and is reabsorbed.
*Superior mesenteric artery*
- The **superior mesenteric artery** primarily supplies the midgut structures, including the small intestine and parts of the large intestine up to the transverse colon.
- Disruption of the superior mesenteric artery would typically lead to atresias higher up in the **gastrointestinal tract**, such as jejunal or ileal atresias, not sigmoid colonic atresia.
*Vitelline duct*
- The **vitelline duct** (also known as the omphalomesenteric duct) connects the midgut to the yolk sac during early fetal development.
- Persistent patency or partial obliteration of the vitelline duct can lead to anomalies like **Meckel's diverticulum** or vitelline cysts, which are distinct from colonic atresia.
*Cloaca*
- The **cloaca** is a common cavity for the digestive, urinary, and reproductive tracts during early embryonic development.
- Defects in cloacal development lead to complex malformations involving these systems, such as **imperforate anus** or persistent cloaca, rather than isolated colonic atresia with a patent anus.
*Celiac artery*
- The **celiac artery** supplies the foregut structures, including the stomach, duodenum, liver, and spleen.
- Disruption of the celiac artery during fetal development would result in malformations of these upper gastrointestinal organs, not the sigmoid colon.
Question 9: A research team is studying certain congenital anomalies of the respiratory tract. The method consists of marking a certain germinal layer with an isotope, following its development stages in chicken embryos, and finally analyzing the specimen. A given specimen of tissue is presented in the exhibit. Which of the following germinal structures most likely gave rise to the epithelial lining of this specimen?
A. Ectoderm
B. Neural crest
C. Mesoderm
D. Endoderm (Correct Answer)
E. Surface ectoderm
Explanation: ***Endoderm***
- The **epithelial lining** of the entire respiratory tract, including the larynx, trachea, bronchi, and lungs, is derived from the **endoderm**.
- The **laryngotracheal groove** develops from the ventral wall of the primitive foregut, which is endodermal in origin, further differentiating into the respiratory tree.
*Ectoderm*
- The **ectoderm** primarily forms the epidermis, hair, nails, and the nervous system (brain and spinal cord).
- It does not contribute to the internal epithelial lining of the respiratory tract.
*Neural crest*
- **Neural crest cells** contribute to a wide variety of structures, including components of the peripheral nervous system, head mesenchyme, and melanocytes.
- They are not involved in forming the epithelial lining of the respiratory system.
*Mesoderm*
- The **mesoderm** forms the connective tissue, cartilage, and muscle components of the respiratory tract, such as the smooth muscle and cartilage rings of the trachea and bronchi, and the visceral pleura.
- However, it does not form the epithelial lining itself.
*Surface ectoderm*
- **Surface ectoderm** specifically gives rise to the epidermis, hair, nails, and glands of the skin, as well as the oral cavity epithelium.
- It does not contribute to the internal epithelial structures of the respiratory tract.
Question 10: A 26-year-old woman comes to the physician because she has not had a menstrual period for 5 weeks. Menarche was at the age of 14 years and menses occurred at regular 30-day intervals. She reports having unprotected sexual intercourse 3 weeks ago. A urine pregnancy test is positive. Which of the following best describes the stage of development of the embryo at this time?
A. Fetal heart is beating, but cardiac activity is not yet visible on ultrasound
B. Limb buds have formed, but fetal movements have not begun
C. Sexual differentiation has begun, but fetal movement has not started
D. Neural crest has formed, but limb buds have not yet formed (Correct Answer)
E. Implantation has occurred, but notochord has not yet formed
Explanation: ***Neural crest has formed, but limb buds have not yet formed***
- At **5 weeks gestational age (3 weeks post-fertilization)**, neurulation is completing or recently completed
- **Neural crest cells** migrate from the neural folds during weeks 3-4 post-fertilization and are definitely present by this time
- **Limb buds** appear later, around week 4-5 post-fertilization (week 6-7 gestational age), making this the most accurate description for the current developmental stage
*Fetal heart is beating, but cardiac activity is not yet visible on ultrasound*
- The primitive heart tube begins contracting around day 22-23 post-fertilization (early week 4)
- At 3 weeks post-fertilization (5 weeks gestational age), the heart may just be starting to beat, but this timing is less precise
- Cardiac activity becomes visible on transvaginal ultrasound around 5.5-6 weeks gestational age, so this option is close but less precise than the correct answer
*Limb buds have formed, but fetal movements have not begun*
- **Limb buds** typically appear around week 4-5 post-fertilization (week 6-7 gestational age)
- This is **too advanced** for 3 weeks post-fertilization
- While fetal movements aren't perceptible to the mother until 16-20 weeks, they begin much later than the current stage
*Sexual differentiation has begun, but fetal movement has not started*
- **Sexual differentiation** of the gonads begins around week 7 post-fertilization (week 9 gestational age)
- External genitalia differentiation occurs even later (weeks 9-12 post-fertilization)
- This stage is **far too advanced** for the current 3-week post-fertilization timeframe
*Implantation has occurred, but notochord has not yet formed*
- **Implantation** occurs 6-12 days after fertilization, which is approximately 2-3 weeks before a positive pregnancy test
- The **notochord** forms during gastrulation in the **3rd week post-fertilization** (5th week gestational age)
- By the time of this positive pregnancy test (5 weeks gestational age), the notochord has **already formed**, making this statement incorrect
