Reproductive System Development - Bolender Flashcards
Again, a reproductive system has what three major components?
- External genitalia
- Gonads
- Ducts
Establishment of sex is a 2-step process.
- When does sex determination occur?
- When does sex differentiation occur?
- At fertilization (chromosomes)
- Embryonic period and early fetal period
What is the unique intermediate phase that the developing reproductive organs pass through? Describe it.
Indifferent Stage
- Progenitors of the gonads, ducts, and external genitalia have formed but are **morphologically indistinct **with respect to sex
- Duration of this phase varies for each component of the reproductive system
- The primordial gonad is a morphologically distinct part of what other developmental structure?
- Once the gonad primordium appears, what is the surrounding area called?
- The nephrogenic cord
- The UG ridge
What three major cell types are found in the forming gonads?
- Germ cells
- Supporting cells
- Interstitial cells
What is notable concerning the origin of primordial germ cells?
What can the persistence of primordial germ cells outside the gonad cause?
Extra-gonadal origin - migrate to the gonad
Teratoma
During development, the primitive gonad develops cranial & caudal attachements.
What will the cranial attachment become?
What will the caudal attachment become?
Cranial: suspensory ligament
Caudal: gubernaculum
How is the UG ridge attached to the body wall?
Dorsally, by a mesentery
The mesonephric duct is associated with what other primordial structure?
mesonephric kidney
What other reproductive primordia does the mesonephric duct induce formation of?
Each mesonephric duct induces the formation of the ipsilateral paramesonephric duct, which lies lateral to the mesonephric duct.
(As you know, depending on the sex of the fetus, one set of these ducts will eventually degenerate)
Name three external swellings in the caudal region of the embryo that are progenitors of the external genitalia.
- Genital Tubercle
- Urethral (Urogenital) Folds
- Labioscrotal Swellings
Summary of Indifferent Stage:
During weeks (1.)_______ a sexually determined but sexually undifferentiated embryo has formed:
- A pair of ___________ gonads
- Two sets of ducts: __________ and ______________
- ________ and ______ around the opening of the UG sinus
- Weeks 4-6
- undifferentiated
- mesonephric & paramesonephric
- elevations & folds
What component of the early reproductive system differentiates (to one sex or the other) first?
The gonads
- What gene directs gonad differentiation in a male direction?
- What chromosome is this gene on?
- What product of the gene mediates the actual effects?
- SRY
- Y chromosome
- Testicular Determining Factor (TDF)
In a gonad with high SRY expression, what will the primordial germ cells develop into?
Spermatogonia
(Male gonad)
- What are the supporting cells in the male gonad?
- What gene do these cells express?
- What are two important functions of this gene regarding reproductive system development?
- Sertoli cells
- Sox9
- Functions:
- Helps organize the male gonad
- Inhibits WNT4 expression (the equivalent female gene)
What are the interstitial cells of the male gonad?
What do they produce, and how early do they start making it?
Leydig cells
Testosterone, Week 8
What fibrous layer forms a capsule around the testis?
Tunica albuginea
(Capsule of the ovary in the female goes by the same name)
In a gonad with high WNT4 expression, what will the primordial germ cells develop into?
Oogonia
(Female gonad)
What are the supporting cells of the female gonad?
What is their purpose?
Follicle/Granulosa cells
- Associate with oogonia to form (primordial) follicles
How would you tell a histological section of a developing testes from one of a developing ovary?
The developing testes will display cords of epithelial cells.
The developing ovary will display primordial follicles.
True or False: Both the male and female gonads descend from their area of origination during development.
True.
- Testes descend into the scrotum
- Ovaries remain internal but still descend - into the pelvis
What is the failure of descent of one or both testes called?
Cryptorchidism
In the male, there is a _________ duct system from the seminiferous tubules to the urethra
Continuous
What are the mesonephric tubules?
What do they differentiate into?
Genital ridges next to the mesonephros that grow over to the testes, penetrate it, and become connected to the seminiferous tubules.
The efferent ductules
What four reproductive structures are derivatives of the mesonephric ducts?
- Duct of epididymis
- Ductus (Vas) Deferens
- Ejaculatory Duct
- Seminal Vesicle
The prostate gland may have a dual origin.
What two areas are thought to give rise to prostate glands?
What do both primordia begin as?
- Most glands: Form from buds of the endoderm lining of the pelvic part of the UG sinus
- Central zone glands: Form from buds of the mesoderm
- Both primordia begin as buds
Budding of the primordial prostate glands is induced by what?
The UG sinus mesenchyme
Though the vast majority of the paramesonephric ducts regress in male embryos due to Mullerian Inhibiting Factor, what part of the male reproductive system is actually derived from the these ducts?
The prostatic utricle
(Fun fact: The utricle is a small, blind pouch in the wall of the prostatic urethra, thought to serve no purpose. It is essentially the male homologue of the female vagina and uterus)
What causes the mesonephric ducts to atrophy in a female embryo?
Where can cystic remnants of the mesonephric duct be found in the female body?
Absence of testosterone
Within the broad ligament
In the female:
What do the caudal 1/3 of the paramesonephric ducts become?
What do the cranial 2/3 of each duct become?
Caudal 1/3: Fuses & becomes the uterus & part of the vagina
Cranial 2/3: Remains unfused, becomes the oviduct
What two primoridal structures contribute to forming the vagina?
- Paramesonephric ducts
- Pelivc part of the UG sinus
How is the broad ligament formed?
As the two paramesonephric ducts “grow” medially from the mesonephros to fuse and become the uterus (& part of vagina), the intermediate mesoderm surrounding the ducts travels with it. When the ducts meet, the mesoderm has formed a supportive “bridge” across the body cavity, which will develop into the broad ligament.
How common is abnormal development of the paramesonehric ducts?
What can result?
- Common, but not always clinically significant
- Results range from total absence to complete duplication of uterus & vagina
What does the pelvic portion of the UG sinus form in the male?
Female?
- Male: Distal prostatic & membranous urethra
- Female: Part of vagina
What does the phallic portion of the UG sinus form in the male?
In the female?
- Male: Penile urethra
- Female: Vestibule
When do the urethral folds fuse in a male fetus?
What do the urethral folds form in the female fetus?
Month 3
Labia minora
What primordium is the glans of the penis derived from?
What is the homologous structure in the female anatomy?
Genital tubercle
Clitoris
- What germ layer is the penile urethra made up of?
- What about the portion of the penile urethra within the glans?
- Endoderm (of the phallic part of the UG sinus)
- An ingrowth of Ectoderm
Normal development of the male reproductive ducts and external genitalia depends on the conversion of testosterone to _________ by _________ in the accessory glands and external genitalia
DHT, 5a-reductase
Sex differentiation in the brain is determined in part by the release of gonadotrophic hormones.
- In females, this release of gonadotrophins occurs in a ___________ fashion
- In males, this release of gonadotrophins occurs in a ___________ fashion
- Females: Cyclic
- Male: Pulsatile (but not cyclic)
