Embryology - Genital System

Front 1

When do male and female morphological characteristics begin to develop?

Back 1

7th week.

Front 2

What are the gonads derived from?

Back 2

1) Mesothelium (mesodermal epithelium) lining the posterior abdominal wall
2) Underlying mesenchyme (embryonic connective tissue)
3) Primordial germ cells

Front 3

What is the initial stage of gonadal development?

Back 3

During the 5th week, a thickened area of mesothelium develops on the medial side of the mesonephros

Front 4

What is the gonadal ridge? Gonadal cords?

Back 4

Proliferation of mesothelium (mesodermal epithelium) and the underlying mesenchyme produces a bulge on the medial side of the mesonephros called the gonadal ridge.
Gonadal cords are fingerlike epithelial cords that grow into the underlying mesenchyme.

Front 5

How do indifferent gonads differentiate depending on sex chromosomes?

Back 5

XX: Cortex of the gonad differentiates into an ovary and the medulla regresses.
XY: Medulla differentiates into a testis and the cortex regresses, except for the vestigial remnants.

Front 6

When are the primordial germ cells visible?

Back 6

Early in the 4th week among the endodermal cells of the yolk sac near the origin of the allantois. By the 6th week, they can be found incorporated in the gonadal cords.

Front 7

What causes the transformation of gonadal cords into seminiferous cords?

Back 7

The SRY gene on the Y chromosome has a testis-determining factor that has an effect on the medulla of the indifferent gonad.

Front 8

What forms when the testis-determining factor induces the gonadal cords to condense and extend into the medulla?

Back 8

The rete testis is formed.

Front 9

What causes the lost connection between the seminiferous cords and the surface epithelium?

Back 9

The development of the dense tunica albuginea, a thick fibrous capsule.

Front 10

What is the mesorchium?

Back 10

The testis' own mesentery. The mesorchium suspends the enlarging testis as it separates from the degenerating mesonephros.

Front 11

What role do the interstitial cells of Leydig play?

Back 11

The cells begin to secrete testosterone and androstenedione by 8th week. These androgenic hormones induce masculine differentiation of the mesonephric ducts and the external genitalia.

Front 12

What role do the sustenatacular cells of Sertoli play?

Back 12

They secrete a glycoprotein called antimullerian hormone, which suppresses the development of the paramesonephric (mullerian) ducts, which form the uterus and uterine tubes.

Front 13

What fate do the gonadal cords have in ovary development?

Back 13

Gonadal cords extend into the medulla, degenerate, and disappear.

Front 14

What extends from the surface epithelium of the developing ovary into the underlying mesenchyme?

Back 14

Cortical cords. As they increase in size, primordial germ cells are incorporated in them.

Front 15

What is the mesovarium?

Back 15

The mesovarium is a mesentery that suspends the ovary after it separates from the regressing mesonephros.

Front 16

What are the two duct systems?

Back 16

The mesonephric ducts (wolffian ducts) develop in males.
The paramesonephric ducts (mullerian ducts) develop in females.

Front 17

What arises from the mesonephric ducts under the influence of testosterone?

Back 17

The proximal part of the mesonephric duct becomes highly convoluted to form the epididymis. The remainder of this duct forms the ductus deferens and ejaculatory duct.

Front 18

What path do the paramesonephric ducts take?

Back 18

The paramesonephric ducts form on each side of the mesothelium on the lateral aspects of the mesonephroi. The edge of the paramesonephric grooves approach each other and fuse to form the paramesonephric ducts. These ducts pass caudally, parallel to the mesonephric ducts, until they reach the future pelvic region. Here they cross ventral to the mesonephric ducts, approach each other in the median plane, and fuse to form a Y-shaped uterovaginal primordium.

Front 19

What structure develops into the efferent ductules? The duct of the epididymis? The ductus deferens?

Back 19

As the mesonephros degenerates, some mesonephric tubules persist and are transformed into efferent ductules.
These ductules open into the mesonephric ducts, which has transformed into the duct of the epididymis. Distal to the epididymis, the mesonephric duct acquires a thick investment of smooth muscle and becomes the ductus deferens.

Front 20

How does the seminal gland form?

Back 20

A lateral outgrowth from the caudal end of each mesonephric duct gives rise to the seminal gland.

Front 21

How is the prostate formed?

Back 21

Multiple endodermal outgrowths arise from the prostatic part of the urethra and grow into the surrounding mesenchyme. The glandular epithelium of the prostate differentiates from these endodermal cells, and the associated mesenchyme differentiates into the dense stroma and smooth muscle of the prostate.

Front 22

How are the bulbourethral glands formed?

Back 22

These structures develop from paired outgrowths from the spongy part of the urethra. The adjacent mesenchyme differentiates into the smooth muscle fibers and the stroma.

Front 23

What is derived from the splanchnic mesenchyme in female genital development?

Back 23

Endometrial stroma and myometrium are derived from splanchnic mesenchyme.

Front 24

What forms the vagina?

Back 24

The vaginal epithelium is derived from the endoderm of the urogenital sinus and the fibromuscular wall of the vagina develops from the surrounding mesenchyme.

Front 25

What are the sinovaginal bulbs and how are they formed?

Back 25

Contact of the uterovaginal primordium with the urogenital sinus forms the sinus tubercle, which induces the formation of paired endodermal outgrowths, the sinovaginal bulbs. These bulbs extend from the urogenital sinus to the caudal ends of the uterovaginal primordium, and then fuse to form the vaginal plate. The central cells of this plate break down and form the lumen of the vagina.

Front 26

How is the hymen formed?

Back 26

The hymen is formed by invagination of the posterior wall of the urogenital sinus, resulting from expansion of the caudal end of the vagina.

Front 27

What are the initial stages of external genitalia development?

Back 27

Early in the 4th week, proliferating mesenchyme produces a genital tubercle in both sexes at the cranial end of the cloacal membrane. Labioscrotal swellings and urogenital folds soon develop on each side of the cloacal membrane. The genital tubercle soon elongates to form the primordial phallus. When the urorectal sinus fuses with the cloacal membrane at the end of the 6th week, it divides the cloacal membrane into a anal membrane and urogenital membrane.

Front 28

What is the urethral plate?

Back 28

The urethral plate is a proliferation of endodermal cells which extends from the phallic portion of the urogenital sinus. The urethral plate lines the urethral groove.

Front 29

How is the spongy urethra formed?

Back 29

The urogenital folds fuse with each other along the ventral surface of the penis.

Front 30

What do the corpora cavernosa and corpus spongiosum develop from?

Back 30

They develop from the mesenchyme in the phallus.

Front 31

What structures fuse to form the scrotum?

Back 31

Labioscrotal swellings.

Front 32

What is the processus vaginalis?

Back 32

It is an evagination of peritoneum, develops ventral to the gubernaculum and herniates through the abdominal wall along the path formed by the gubernaculum.