Embryology Practice Questions

Q: What is the pattern of inheritance in neural tube defects?

Multifactorial inheritance. ***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.

Q: The covering of an omphalocele is derived from which of the following layers?

Amnion. ***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.

Q: Identify the uterus shown in the image?

Bicornuate. ***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.

Q: 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?

Canalicular. ***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.

Q: 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?

Clitoris. ***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 1

What is the pattern of inheritance in neural tube defects?

Accepted Answer

Multifactorial inheritance

Answer

Autosomal recessive

Answer

X-linked dominant

Answer

Autosomal dominant

Answer

X-linked recessive

Question 2

The covering of an omphalocele is derived from which of the following layers?

Accepted Answer

Amnion

Answer

Chorion

Answer

Mesoderm

Answer

Endoderm

Answer

Ectoderm

Question 3

Identify the uterus shown in the image?

Accepted Answer

Bicornuate

Answer

Didelphys

Answer

Arcuate

Answer

Septate

Answer

Unicornuate

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?

Accepted Answer

Canalicular

Answer

Alveolar

Answer

Pseudoglandular

Answer

Saccular

Answer

Embryonic

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?

Accepted Answer

Clitoris

Answer

Labia minora

Answer

Labia majora

Answer

Vestibule

Answer

Bartholin glands

Embryology — MCQs

Embryology — MCQs

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