1.
The indifferent embryo begins phenotypic sexual differentiation during
Correct Answer
C. Week 7 of development
Explanation
The embryo during weeks 1-6 remains in an indifferent or undifferentiated stage. The
embryo begins phenotypic sexual differentiation during week 7.
2.
The indifferent embryo completes phenotypic sexual differentiation during
Correct Answer
E. Week 20 of development
Explanation
By week 12, female and male characteristics can be recognized. By week 20, phenotypic sexual differentiation is complete.
3.
After the sinovaginal bulbs have proliferated and fused, they form a solid core of endodermal
cells called the
Correct Answer
D. Vaginal plate
Explanation
The sinovaginal bulbs proliferate, fuse, and form the vaginal plate under the inductive
influence of the paramesonephric ducts. The vaginal plate then canalizes to form the inferior two
thirds of the vagina.
4.
A structure found within the adult female pelvis formed from the gubernaculum is the
Correct Answer
C. Round ligament of the uterus
Explanation
The round ligament of the uterus and the ovarian ligament both form from the gubernaculum.
5.
The labia minora arise embryologically from which of the following structures?
Correct Answer
D. Urogenital folds
Explanation
In the female, the urogenital folds remain unfused and form the labia minora.
6.
The uterine tubes of the adult female are derived embryologically from which of the following?
Correct Answer
C. ParamesonepHric duct
Explanation
The cranial portion of the paramesonephric ducts form the uterine tubes.
7.
MALE REPRODUCTIVE SYSTEM
One day a 9-year-old girl surprisingly announces to her mother, "Guess what,
mommy, I'm not a girl; I'm a boy." The mother is shocked but does not act on the comment.
During the next few years, the mother notices some tomboyish behavior and difficulty in
social adjustment at school. When the girl is 12 years old, puberty starts with a striking virilization of the external genitalia. The mother is extremely concerned and seeks medical attention. What is the most likely cause?
Correct Answer
A. Male pseudointersexuality
Explanation
Reduced levels of androgens during fetal development of a XY male fetus cause feminization of the male external genitalia such that the baby can be phenotypically mistaken for female. Parents raise the XY male baby as a girl until puberty or other medical problems bring the child to medical attention.
8.
The most common cause of female pseudointersexuality is
Correct Answer
D. Congenital adrenal hyperplasia
Explanation
Female pseudointersex individuals have a 46,XX genotype. This condition is most commonly caused by congenital adrenal hyperplasia, in which the fetus produces excessive amounts of androgens. The high androgen level masculinizes the female genitalia.
9.
The most common cause of male pseudointersexuality is
Correct Answer
C. Inadequate production of testosterone and MIF
Explanation
Male pseudointersex individuals have a 46,XY genotype. This condition is most commonly
caused by inadequate production of testosterone and MIF by the fetal testes. The low testosterone and MIF levels stunt the development of the male genitalia.
10.
The most common cause of testicular feminization syndrome is
Correct Answer
E. Lack of androgen receptors
Explanation
The most common cause of testicular feminization syndrome is the lack of androgen receptors in the urogenital folds and labioscrotal swellings. Because these tissues lack androgen receptors, they are blind or unresponsive to androgens. Consequently, these tissues develop into
female external genitalia even though the fetus has a 46,XY genotype.
11.
In the male, failure of the urethral folds to fuse completely results in
Correct Answer
A. Hypospadias
Explanation
Failure of the urethral folds to fuse completely results in the external urethral orifice opening onto the ventral surface of the penis, a condition known as hypospadias.
12.
The Y chromosome carries a gene on its short arm that codes for
Correct Answer
C. Testes-determining factor (TDF)
Explanation
The gene product that is coded on the short arm of the Y chromosome is called the testesdetermining factor (TDF).
13.
Bilateral cryptorchidism usually results in
Correct Answer
B. Sterility
Explanation
Sterility is a common result of bilateral cryptorchidism. When both testes fail to descend
into the scrotum, the increased temperature they are exposed to in the abdominal cavity inhibits
spermatogenesis.
14.
A 17-year-old girl presents with a complaint of amenorrhea. Physical examination reveals
good breast development and normal amount of pubic hair. A rudimentary vagina and a
mobile mass within both the right and left labia majora are found on pelvic examination.
Ultrasound reveals the absence of a uterus. What is the diagnosis?
Correct Answer
A. Testicular feminization syndrome
Explanation
This is a classic case of testicular feminization syndrome. A karyotype analysis would reveal that this normal-appearing 17-year-old girl actually has a 46,XY genotype. The mobile masses within the right and left labia majora are the testes and should be surgically removed because this tissue has a propensity toward malignant tumor formation. The most common cause of this syndrome is a lack of androgen receptors in the phallus, urogenital folds, and labioscrotal swellings.
15.
INTEGUMENTARY EMBRYOLOGY
Melanocytes are found in which epidermal layer?
Correct Answer
A. Stratum basale
Explanation
Melanocytes are found in the stratum basale, the deepest layer of the epidermis, at the dermoepidermal junction.
16.
A young black girl shows isolated patches of skin and hair that lack melanin pigment. In
addition, other skin lesions are observed that look suspiciously like a malignant melanoma.
What is the most likely diagnosis?
Correct Answer
C. Piebaldism
Explanation
Piebaldism is an autosomal dominant disorder and is basically a localized albinism.
17.
A young infant shows extremely stretchable and fragile skin, hypermobile joints, and cigarette-paper scars over the knees. What is the most likely diagnosis?
Correct Answer
A. Ehlers-Danlos syndrome
Explanation
Ehlers-Danlos syndrome is an autosomal dominant disorder involving the gene for peptidyl
lysine hydroxylase.
18.
A young infant shows skin blisters over the entire body with generalized skin erosion.
Pathology indicates a cleft between the epidermis and dermis. What is the most likely diagnosis?
Correct Answer
B. Junctional epidermolysis bullosa
Explanation
Junctional epidermolysis bullosa refers to a group of autosomal recessive disorders caused
by a mutation in the gene for laminin 5.
19.
The administration of which of the following agents may result in discoloration of both
deciduous and permanent teeth?
Correct Answer
E. Tetracycline
Explanation
Tetracyclines are bound to calcium in newly formed teeth both in utero and in young children. They may cause discoloration and enamel dysplasia