Development of male genital system

Question

Answer

When does formation of the undifferentiated gonads begin?

Around the fifth week of development.

Which paired ducts are present during the indifferent stage of gonadal development?

The mesonephric ducts and paramesonephric ducts.

What is the sex-determining gene responsible for initiating male gonadal differentiation?

The Sex-determining Region Y (SRY) gene.

When does the gonadal or genital ridge form?

At approximately the fourth week of gestation.

Where does the gonadal ridge develop?

Next to the mesonephric system along the posterior body wall.

What is the urogenital ridge?

The region where the gonad and mesonephros are together; it is the common precursor of the urinary and genital systems.

Why is the close relationship between the gonad and mesonephros important in males?

Mesonephric tubules and ducts later contribute to the male sperm-conducting system.

Where are primordial germ cells initially formed?

In the endoderm of the yolk sac.

How do primordial germ cells reach the genital ridge?

They migrate along the hindgut, through the dorsal mesentery, and into the genital ridge.

When does primordial germ-cell migration begin and end?

It begins during the fourth week and reaches the genital ridge by the sixth week.

What may happen if germ cells fail to reach the genital ridge?

They may give rise to germ-cell tumors such as sacrococcygeal teratomas.

What is a sacrococcygeal teratoma?

A tumor thought to arise from germ cells that failed to migrate to the genital ridge.

How common are sacrococcygeal teratomas at birth?

They occur in up to approximately 1 in 10,000 births.

Which sex is more likely to develop a sacrococcygeal teratoma?

Female fetuses are approximately four times more likely than male fetuses.

Are most fetal sacrococcygeal teratomas malignant?

No. Most are not malignant.

What defines a Type I sacrococcygeal teratoma?

It is predominantly external or has only a minimal presacral component.

What defines a Type II sacrococcygeal teratoma?

It is externally visible but has significant intrapelvic extension.

What defines a Type III sacrococcygeal teratoma?

It appears externally but is predominantly a pelvic mass extending into the abdomen.

What defines a Type IV sacrococcygeal teratoma?

It is entirely presacral with no external presentation.

What surrounds the germ cells after they reach the genital ridge?

Epithelial cells derived from the surface lining of the genital ridge.

What do proliferating surface epithelial cells form inside the developing gonad?

Primitive sex cords.

What happens to the primitive sex cords in male development?

They lose their connection with the surface epithelium of the gonad.

What structure forms from the remaining surface epithelium of the male gonad?

The tunica albuginea.

What is the tunica albuginea?

A tough outer covering formed by thickening of the surface epithelium of the testis.

What happens to the primitive sex cords at puberty?

They canalize to form seminiferous tubules.

What is the shape of the primitive male sex cords before canalization?

They become horseshoe-shaped.

What is the embryological origin of Sertoli cells?

They are derived from the epithelium of the primitive sex cords.

What is the main supportive function of Sertoli cells?

They act as nurse cells for developing sperm.

Which hormone is produced by Sertoli cells during male development?

Antimüllerian hormone (AMH), also called müllerian-inhibiting substance.

What is the effect of antimüllerian hormone in the male embryo?

It causes the Müllerian ducts to regress.

What is the embryological origin of Leydig cells?

They arise from mesenchyme of the genital ridge.

What hormone is secreted by Leydig cells?

Testosterone.

What is the function of the rete testis?

It connects the seminiferous tubules with selected mesonephric tubules.

What do connected mesonephric tubules become?

Efferent ductules.

What is the function of the efferent ductules?

They conduct sperm from the rete testis toward the mesonephric duct.

What does the mesonephric duct become in the male reproductive system?

The ductus deferens.

What happens to mesonephric tubules that do not become efferent ductules?

They degenerate, leaving remnants called paragenital tubules.

What is the embryological origin of the appendix epididymis?

It is a remnant of the unused portion of the mesonephric duct.

What is the later name of the ductus deferens during late fetal development?

The vas deferens.

How does the seminal vesicle develop?

As a proliferating outpocketing of the duct epithelium near the prostate.

What portion of the duct forms the ejaculatory duct?

The segment from the seminal vesicle to its opening into the prostatic urethra.

How does the epididymis develop?

The proximal ductus deferens proliferates and becomes highly coiled.

What is the indifferent stage of external genital development?

An early stage in which the external genitalia are structurally similar in both sexes.

Is the indifferent stage dependent on sex hormones?

No. It is also called the hormone-independent or ambisexual stage.

Which enzyme converts testosterone into the hormone needed for male external-genital development?

5-alpha reductase converts testosterone into dihydrotestosterone.

Which hormone regulates development of the male external genitalia?

Dihydrotestosterone.

What regulates development of the female external genitalia?

The absence of testosterone together with the presence of estrogens.

What are the cloacal folds?

Mesodermal swellings that form around the cloacal membrane.

When do the cloacal folds first form?

At approximately the fourth week.

What do the cloacal folds form when they unite anteriorly?

The genital tubercle.

What develops lateral to the cloacal folds?

The genital swellings.

What is the cloaca?

The blind caudal end of the hindgut.

What is the allantois?

A ventral diverticulum of the cloaca that extends along the anterior body wall toward the umbilical cord.

What is the function of the urorectal septum?

It grows caudally to divide the cloaca into hindgut and urogenital sinus components.

By when has the urorectal septum separated the hindgut from the urogenital sinus?

By the end of the sixth week.

What do the cloacal folds become after cloacal separation?

They divide into anterior urethral folds and posterior anal folds.

What does the genital tubercle become in the male?

The penis.

What happens to the urethral folds during male development?

They move toward the midline and fuse to form the penile urethra.

What do the genital swellings become in the male?

The scrotal swellings.

How does the scrotum form?

The scrotal swellings enlarge, migrate caudally, and fuse in the midline.

What is the scrotal raphe?

The external line marking fusion of the two scrotal swellings.

How is the opening at the tip of the glans formed?

Ectoderm proliferates inward, meets the urethra, and then hollows to create the opening.

What is the urethral groove?

A groove on the ventral surface of the developing genital tubercle bounded by the urethral folds.

How far does the urethral groove extend during the indifferent stage?

It initially extends about halfway distally along the ventral genital tubercle.

What is the urethral plate?

A solid epithelial plate at the distal end of the urethral groove that extends toward the glans.

How does the urethral groove extend to the glans?

The solid urethral plate undergoes canalization.

How is the tubular penile urethra formed?

The urethral folds grow toward the midline and fuse.

What happens to the epithelial seam after the urethral folds fuse?

The seam is removed.

What is hypospadias?

A defect caused by incomplete closure of the fusing regions of the urethra or scrotum.

What clinical problem can result from hypospadias?

An abnormally located opening that may allow urine to leak.

What are the two hypospadias patterns shown in the slides?

Glandular hypospadias and urethral hypospadias.

Where do the testes initially develop?

In a retroperitoneal position in the lumbar region.

Why must the testes descend?

They must migrate to the scrotum and pass through the layers of the abdominal wall.

What happens to the abdominal-wall layers during testicular descent?

Each layer contributes a covering layer surrounding the testis.

What forms when the urogenital ridge becomes thinner caudally?

The caudal genital ligament.

What is the gubernaculum?

A condensed mass of matrix material associated with the caudal genital ligament that guides testicular descent.

Where does the gubernaculum extend?

From the caudal pole of the testis toward the scrotum through the inguinal canal.

What is the role of the gubernaculum?

It helps direct and pull the testis toward the scrotal sac.

What is the processus vaginalis?

An outpocketing of peritoneum that precedes the testis through the inguinal canal.

What does the processus vaginalis become around the descended testis?

It forms the visceral tunica vaginalis and the parietal layer lining the inner scrotum.

When should the testes reach the inguinal canal?

By approximately the seventh month.

When should the testes normally be present in the scrotum?

At birth.

Where are the testes located around week 7?

Within the abdominal cavity, deep to the peritoneum in a retroperitoneal position.

What is the attachment pattern of the gubernaculum around week 7?

It anchors the inferior pole of the testis to the scrotal swelling.

What happens around week 12 during testicular descent?

The peritoneum begins to evaginate, forming the processus vaginalis.

How does the processus vaginalis contribute to inguinal-canal formation?

It pushes through the abdominal-wall layers and creates a cavity that becomes the inguinal canal.

What remains after the testes reach the scrotum?

The gubernaculum persists as an anchor, while the caudal genital ligament regresses.

Which hormones regulate the gubernaculum during testicular descent?

Testosterone and antimüllerian hormone.

What mechanical changes may assist testicular descent?

Shortening of the gubernaculum and growth of the abdominal organs, which increases intra-abdominal pressure.

How many infants have testes that descend late but normally by about three months?

Approximately 3% of infants.

What is cryptorchidism?

Persistent undescended testis or testes.

Approximately what percentage of infants have persistent cryptorchidism?

Approximately 1%.

Why are the testes located in the scrotum rather than the abdominal cavity?

Sperm production requires a temperature lower than core body temperature.

How much lower than body temperature is the scrotal temperature maintained?

Approximately 2-3 degrees Celsius lower.