USMLE Embryology Questions
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Free USMLE Step 1 Embryology Questions

A 29-year-old female presents with palpitations, increased sweating, and unintentional weight loss despite a good appetite. She also reports difficult swallowing and voice changes. All the symptoms have been developing over the past 6 months. The patient has no concurrent illnesses and takes no medications. Her vital signs are as follows: blood pressure 125/80 mm Hg, heart rate 106/min, respiratory rate 15/min, and temperature 37.0℃ (98.6℉). Physical examination is significant for increased perspiration, fine digital tremors, and a small mass at the posterior aspect of the tongue which moves along with the tongue movements. There is no neck swelling. Laboratory thyroid workup shows the following results:

Triiodothyronine (T3)191 ng/dL (2.93 nmol/L)
Thyroxine (T4), total22 µg/dL (283.1 nmol/L)
Thyroid-stimulating hormone 0.2 µU/mL (0.2 mU/L)

A 99 mTc thyroid scan reveals hyperfunctional thyroid tissue at the base of the patient’s tongue. Which the following statements is correct?

  1. This patient is at increased risk of thyroid carcinoma development
  2. Most often in such condition, there is an additional thyroid tissue elsewhere in the neck
  3. There is a male predilection for this condition
  4. This is the rarest location for ectopic thyroid tissue
  5. This condition results from a failure of caudal migration of thyroid tissue
A 31-year-old man presents for his annual physical exam. The physician fails to palpate ductus deferens on the left side. An ultrasound confirms the absence of left ductus deferens and further reveals the absence of the left epididymis, seminal vesicle, and kidney. Spermogram and reproductive hormones panel are within normal limits. A left-sided agenesis of an embryonic anlage is suspected. Which two structures are connected by this anlage during the embryogenesis?
  1. Pronephros and celom
  2. Mesonephros and celom
  3. Pronephros and cloaca
  4. Metanephros and celom
  5. Mesonephros and cloaca

A 9-year-old boy presents with abdominal pain which started almost 6 hours ago. The pain is located in the periumbilical area and radiates to the right lower quadrant. There was no vomiting or stool passage since the pain onset. The patient reports that he passed stools with blood several times during the past month. The patient’s vital signs are as follows: blood pressure 110/70 mm Hg, heart rate 81/min, respiratory rate 16/min, and temperature 37.5℃ (99.5℉). Physical examination reveals abdominal tenderness and guarding in the periumbilical area. Abdominal ultrasound does not reveal any abnormality with appendix. The patient is taken for exploratory laparoscopy. On laparoscopy, a 2-cm wide inflamed diverticulum is found 40 cm proximally to the ileocecal valve. It is resected and sent for histological evaluation. The result is shown in the exhibit. Which of the following statements is true? 

  1. Most probably, it resulted from traction by embryonic peritoneal adhesions
  2. The most probable cause of this diverticulum is increased intraluminal pressure
  3. It is an unobliterated embryonic bile duct
  4. It is a remnant of embryonic omphalomesenteric duct
  5. It is a false diverticulum
Embryology USMLE Step 1 Practice Question

Image: By Patho, License: CC BY-SA 3.0

Fertilization begins when the sperm binds to the corona radiata of the egg. Once the sperm enters the cytoplasm, a cortical reaction occurs which prevents other sperm from entering the oocyte. The oocyte then undergoes an important reaction. What is the next reaction that is necessary for fertilization to continue?
  1. Release of a polar body
  2. Degeneration of the sperm tail
  3. Acrosomal reaction
  4. The second meiotic division
  5. Formation of the spindle apparatus

A healthy 37-year-old woman (gravida 3, para 1) who undergone in-vitro fertilization delivers vaginally a boy. On examination, he is found to have his urethral meatus opening placed on the ventral side of the penis just under its head. Which statement about the patient’s condition is correct?

  1. Younger age of the mother is a major risk factor for this condition.
  2. It results from failure of genital swellings fuse.
  3. Hypospadias repair before the age of 3 years is associated with increased incidence of urethrocutaneous fistula.
  4. Such anatomy is formed before the 12th week of intrauterine development.
  5. It results from failure of genital folds fuse.
A pediatrician is called to examine a recently born dysmorphic male neonate. His birth weight is 1600 grams. On physical examination of face and skull, the head is microcephalic with prominent occiput and narrow bifrontal diameter is noted. His jaw is comparatively small with short palpebral fissures. His nose is narrow and nasal ala are hypoplastic. Examination of upper limbs reveals closed fists with index fingers overlapping over 3rd and 5th finger overlapping over the 4th finger. His nails are hypoplastic and he has rocker bottom feet. Based on these details, you suspect a particular chromosomal anomaly in this neonate. Which of the following statements best describes this patient’s condition?
  1. This condition is associated with teenage mothers
  2. 95% of these patients die in the 1st year of life
  3. The condition is more common in males
  4. Thrombocytopenia is the least common hematological abnormality found in these patients
  5. The most common congenital heart disease seen in this condition is patent ductus arteriosus
Embryology USMLE Step 1 Practice Question
A 2-year-old boy presents to the emergency department with his mother for evaluation of severe abdominal pain that began one hour ago. On exam, the patient is afebrile and has positive rebound tenderness diffusely with acute tenderness to the left lower quadrant. Stool guaiac test is positive. A small bowel perforation is suspected. What is the embryologic structure that is the underlying cause of this patient’s presentation?
  1. Vermiform appendix
  2. Anal membrane
  3. Fibrous cord remnant
  4. Vitelline duct
  5. Cloaca
A 4-year-old boy presents to the office with his mother. She states that the patient has been complaining of pain in his right testicle with swelling as well as abdominal pain with nausea. On exam, the abdomen is soft and nontender to palpation. The right scrotal sac is swollen and tender without erythema. The testicle does not transilluminate when a penlight is applied. The patient is afebrile and all vital signs are stable. What is the most likely etiology of this patient’s presentation?
  1. Patent processus vaginalis
  2. Engorgement of the pampiniform plexus
  3. Collection of fluid in the tunica vaginalis
  4. Infection of the epididymis
  5. Neoplasm of the testicle
A 5-year-old Caucasian boy presents with painless testicular swelling. His mother tells that it became apparent when he was 1 year old and it has been progressively increasing in size since then. She denies the history of any infectious diseases besides the seasonal flu, trauma or any other major illness. He did not visit any tropical countries. The patient’s vaccinations are up to date. Vital signs are within normal limits for the patient’s age. Physical examination reveals bilateral non-tender fluctuating testicular swelling with positive translucency which decreases a bit in the supine position and has a positive cough impulse sign. Sonography is shown in the exhibit. Which of the following statements about the patient’s condition is correct?
  1. On puncture of this structure, blood is the most likely content to be obtained
  2. It is most likely a result of viral replication within testicular tissue
  3. Revealed structure does not communicate with the peritoneal cavity
  4. Impaired lymphatic drainage from the scrotum is the cause of the patient’s condition
  5. A similar condition in girls could be caused by presence of the canal of Nuck
Embryology USMLE Step 1 Practice Question

Image: By Nevit Dilmen, License: CC BY-SA 3.0

A 26-year-old G1P0 presents for a routine prenatal checkup at 16 weeks. The patient has no concerns but is excited to learn the sex of the baby. Genetic testing was performed that showed XY genotype. However, ultrasound does not reveal development of external male genitalia. What essential process has not occurred in this fetus?
  1. Formation of the genital ridge
  2. Formation of the paramesonephric duct
  3. Conversion of testosterone DHT
  4. Production of testis-determining factor (TDF)
  5. Production of Mullerian inhibiting factor

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