1.When examining a histological section of a normal ovary, a technician notices an oocyte surrounded by several layers of follicular cells.

A small antrum is present. Which of the following is the correct term for the entire structure, composed of the oocyte, follicular cells, and antrum?

A. Corpus luteum

B. Graafian follicle

C. Primary follicle

D. Primordial follicle

E. Secondary follicle

The correct answer is E. Follicles in different stages of

maturation have different appearances.

The most primitive follicles, primordial follicles (choice D), are inactive reserve follicles that contain primary oocytes (arrested in prophase of first meiotic division) surrounded by a single layer of flattened follicular cells.

Primary follicles (choice C), the next stage, are slightly larger and contain a central oocyte surrounded by one or several cuboidal follicular cells.

When several small spaces in the follicular mass fuse to form the antrum (follicular cavity), the follicle is termed a secondary follicle (choice E).

The secondary follicles continue to enlarge, and develop a more complex structure that includes cumulus oophorus, corona radiata, theca interna, theca externa, and zona pellucida.

The Graafian follicle (choice B) is the mature form of the follicle,which extends through the entire cortex and bulges out at the ovarian surface. After it ruptures and releases the ovum, the corpus luteum (choice A)develops as the cells of the follicle and the theca interna cells enlarge, become epithelioid, and secrete estrogen.

The granulosa lutein cells contain yellow pigment and secrete progesterone. If pregnancy does not occur, the corpus luteum eventually degenerates; if pregnancy occurs, it is maintained throughout the pregnancy.

Zona pellucida

antrum

Granulosacells

Theca folliculi

follicles

2.The mother of a 7-year-old boy expresses concern to her pediatrician that her son has developed an irritated swelling on the side of his neck. Palpation reveals a small, mucus-secreting cyst along the anterior border of the sternocleidomastoid muscle. This branchial sinus, or external cervical fistula, is the result of incomplete obliteration of which of the following developmental structures?

A. First pharyngeal arch

B. First pharyngeal cleft

C. First pharyngeal pouch

D. Second pharyngeal arch

E. Second pharyngeal cleft

F. Second pharyngeal pouch

• The correct answer is E. • In normal development of the neck, the second

pharyngeal cleft grows inferiorly to fuse with the cardiac ridge, thereby obliterating clefts 2-4. The cervical sinus formed by the fusion of these tissue masses is normally a transient structure, but may persist as a cyst, external fistula, or internal fistula.

The first pharyngeal arch (choice A) gives rise to various bony, muscular and ligamentous structures: the

malleus and incus; the muscles of mastication, plus the tensor tympani, tensor veli palatini, mylohyoid and

anterior digastric; the sphenomandibular ligament and anterior malleolar ligament.

• The first pharyngeal cleft (choice B) is retained as the external auditory meatus and canal. The first pharyngeal pouch (choice C) gives rise to the tympanic cavity and auditory tube.

• The second pharyngeal arch (choice D), like the first, gives rise to bones, muscles and ligaments: the stapes and lesser horn and upper part of the body of the hyoid bone; the muscles of facial expression, plus the stapedius, stylohyoid and posterior digastric; the stylohyoid ligament.

The second pharyngeal pouch (choice F) becomes the tonsillar bed.

3.A newborn child has an abnormally formed mandible, ears, and palate. He is diagnosed with mandibulofacial dysostosis.

This syndrome is due to abnormal development of which of the following structures?

A. First pharyngeal arch

B. First pharyngeal cleft

C. Second pharyngeal arch

D. Second pharyngeal cleft

E. Third pharyngeal cleft

F. Third pharyngeal pouch

• Explanation:• The correct answer is A. The pharyngeal arches

are outpouchings of tissue visible on the external neck of the embryo. They are separated by the pharyngeal clefts (each one caudal to its arch).

• The pharyngeal pouches are the outpouchings of the pharynx visible inside the embryo that correspond to the arches.

• The defect described is due to abnormal development of the derivatives of the first pharyngeal arch.

• It is thought that the initial defect may be insufficient migration of neural crest cells.

4.A neonate is found to have a sacrococcygeal teratoma that contains several different tissue types resulting from a persistence of the primitive streak. The primitive streak normally gives rise to which of the following structures?

A. Dorsal root ganglia

B. Lining of the gastrointestinal tract

C. Notochord

D. Spinal cord

E. Thyroid gland

• The correct answer is C. The primitive streak is the region of the epiblast through which the cells that give rise to the notochord and the mesoderm of the embryo pass. The only adult derivative of the notochord is the nucleus pulposus of the intervertebral disk.

• The mesoderm gives rise to many different tissue types including muscle, connective tissue, and blood.

• This accounts for the many different tissue types found in a sacrococcygeal teratoma.

• The dorsal root ganglia (choice A) are derived from neural crest cells. The neural crest develops at the time of neurulation, which is a process of infolding of the neural ectoderm that is induced by the notochord.

• The lining of the gastrointestinal tract (choice B) is derived from endoderm. The endoderm also gives rise to evaginations of the gastrointestinal tract, such as the liver and pancreas.

• The smooth muscle and connective tissue of the gastrointestinal tract are derived from mesoderm.

• The spinal cord (choice D) is derived from neural ectoderm, which invaginates during neurulation to form the neural tube. The caudal part of the neural tube forms the spinal cord, and the rostral part of the neural tube forms the brain.

• The thyroid gland (choice E) is derived from endoderm. The endoderm of the floor of the pharynx evaginates to form the thyroglossal duct, which descends to form the thyroid gland. The adult site of the evagination of the thyroglossal duct is marked by the foramen cecum on the tongue.

5.A 17-year-old male is examined by a physician, who notes a mass at the back of the young man's tongue.

The physician biopsies the mass, and the pathology report comes back with a diagnosis of normal thyroid tissue.

The occasional presence of such tissue at the back of the tongue is related to the embryonic origin of the thyroid near which of the following structures?

A. First pharyngeal pouch

B. Foramen cecum

C. Nasolacrimal duct

D. Second pharyngeal arch

E. Third pharyngeal pouch

• The correct answer is B. The thyroid gland originates as a mass of endodermal tissue near the foramen cecum, which is near the tuberculum impar (which becomes the central part of the tongue).

• During development, the thyroid descends in front of the pharynx, maintaining a connection to the tongue via the

thyroglossal duct. Usually, the thyroglossal duct disappears.

Uncommonly, residual ectopic thyroid tissue can be left anywhere along the path, including at the back of the tongue. (In rare patients, all of the thyroid tissue remains at this site, forming a mass that should not be excised, for obvious reasons!)

• The first pharyngeal pouch (choice A) develops into the middle ear and eustachian tube.

• The nasolacrimal ducts (choice C) connect the eyes to the mouth.

• The second pharyngeal arch (choice D) develops into many muscles of the face and styloid process of the temporal bone.

• The third pharyngeal pouch (choice E) develops into the thymus and inferior glands.

6.Which of the following is not a foregut derivative, but is supplied by an artery of the foregut?

A. Liver

B. Lungs

C. Pancreas

D. Salivary glands

E. Spleen

• Explanation:• The correct answer is E. Derivatives of the

foregut include all of the epithelial-lined organs that attach to or include the mouth, esophagus, stomach, and duodenum: oral cavity, pharynx, tongue, tonsils, salivary glands (choice D), lower respiratory system (choice B), esophagus, stomach, duodenum proximal to the opening of

the bile duct, liver (choice A), gallbladder, and pancreas (choice C). With the exception of the pharynx,

• respiratory tract, and most of the esophagus, these organs are supplied by the celiac artery.

• The celiac artery, via its splenic branch, also supplies the spleen, which is not classified as a foregut derivative, because

it develops from a mass of mesenchymal cells (with no foregut epithelium) located between the layers of the dorsal mesogastrium.

7.A newborn infant has some of its abdominal viscera protruding through a defect in the abdominal wall. Which of the following is the likely cause of this defect?

A. Failure of the intestinal loop to retract from the umbilical cord

B. Failure of the yolk stalk to degenerate C. Failure of peritoneal fusion D. Incomplete fusion of the lateral body

folds E. Umbilical herniation

• The correct answer is D.

During the fourth week of development, the lateral body folds move ventrally and fuse in the midline to form the anterior body wall.

Incomplete fusion results in a defect that allows abdominal viscera to protrude from the abdominal cavity, a condition known as gastroschisis.

• During development, the midgut normally herniates into the umbilical cord and then subsequently retracts into the abdominal cavity. Failure of the intestinal loop to retract from the umbilical cord (choice A) results in omphalocele.

Failure of the yolk stalk to degenerate (choice B) results in an ileal (Meckel's) diverticulum or a vitelline fistula or cyst. In the early embryo, the gut tube is connected to the yolk sac by a narrow connection known as the yolk stalk. Normally, this connection degenerates.

• During development, certain peritoneal organs fuse with the posterior abdominal wall to become secondarily retroperitoneal.

• Failure of this peritoneal fusion (choice C) will result in certain organs that are normally immobile being mobile (e.g., mobile cecum).

• Umbilical herniation (choice E) results from abdominal viscera protruding through a weakness in the abdominal wall after development.

• Such protrusions are covered by subcutaneous fascia and skin, distinguishing them from gastroschisis.

8.A 5-year-old child is brought to the emergency room with massive, painless bleeding from the rectum.Colonoscopy fails to demonstrate a lesion in the colon or anus. Upper endoscopy fails to demonstrate esophagitis, gastric ulcer, or duodenal ulcer. A [99mTc] technetium scan demonstrates an abnormality in the lower half of the abdomen. Failure of a normal developmental process involving which of the following structures is the most likely cause of this child's bleeding?

A. Appendix

B. Cecum

C. Duodenum

D. Ileu

E. Jejunum

• The correct answer is D.

• A Meckel's diverticulum is caused by failure of obliteration of the vitello-intestinal

duct.

It is classically located in the distal ileum within 30 cm of the ileocecal valve, and the structure is a true

diverticulum with mucosa, submucosa, and muscularis propria.

Many Meckel's diverticula contain ectopic pancreatic tissue or gastric mucosa, and the acid production from the gastric mucosa may be sufficient to produce a small peptic ulcer in adjacent intestinal mucosa.

Such small peptic ulcers are occasional sources of mysterious appendicitis-like pain or intestinal bleeding.

Peptic ulceration adjacent to a Meckel's diverticulum should be suspected in any child who presents with massive, painless rectal bleeding.

• Technetium [99mTc] concentrates in gastric mucosa, and the scan in this patient demonstrated a small amount of ectopic gastric mucosa located in the diverticulum.

• Acute appendicitis (choice A) is usually very painful and does not typically cause rectal bleeding.

• A lesion of the cecum (choice B) would have been revealed by thorough colonoscopy.

Failure of upper endoscopy to demonstrate a peptic ulcer of the duodenum (choice C) makes duodenal

disease unlikely.• Theoretically, the jejunum (choice E) could have been

the source of the problems, but jejunal bleeding is uncommon and a Meckel's diverticulum is a much more likely possibility.

9.A neonate with multiple congenital anomalies is found to have a complete absence of one kidney. Other genitourinary structures are intact. This is most likely the result of which of the following?

A. Absence of the ureteric bud

B. Complete division of the ureteric bud

C. Crossed renal ectopia

D. Double ureteric buds

E. Incomplete division of ureteric bud

• The correct answer is A. Unilateral renal agenesis is a common (1 in 1000 births) congenital anomaly that

may be completely asymptomatic, or may, as in this case, be identified during evaluation of other congenital

anomalies. A single umbilical artery may also be present, and may offer a clinical clue.

Unilateral renal agenesis is usually the result of a failure of the ureteric bud to develop.

Complete division of a ureteric bud (choice B) produces a bifid ureter with a double kidney on one side.

Crossed renal ectopia (choice C) produces fused kidneys on one side.

Double ureteric buds (choice D) produces a supernumerary kidney.

Incomplete division of a ureteric bud (choice E) produces a bifid ureter with a partially divided kidney.