Repro System Development Flashcards
A Reproductive System has 3 Components:
- gonads
- duct system
- external genitalia
- Sex Determination occurs at ________
- Sex Differentiation occurs during ____________________ (influenced by genetic & epigenetic factors)
- Sex Determination occurs at fertilization
- Sex Differentiation occurs during embryonic and into the fetal period (influenced by genetic & epigenetic factors)
- Presence and action of ________________, appears to actively influence sexual differentiation in a male direction
- A second factor _____________________ is involved in promoting regression of the paramesonephric (müllerian) ducts
- Presence and action of androgens, appears to actively influence sexual differentiation in a male direction
- A second factor Mullerian Inhibiting Substance (MIS or MIF) is involved in promoting regression of the paramesonephric (müllerian) ducts
What are the two embryoinc precursor tissues for the reporductive system?
- Intermediate Mesoderm
- Endoderm
What happens during the indifferent stage (weeks 4-6)?
primordia of the organs of the reproductive system begin to form
The Indifferent Gonad Forms within the ___________ Aspect of the __________ _____
- What is the structure renamed once the gonad primordium appears?
The Indifferent Gonad Forms within the Ventromedial Aspect of the Nephrogenic Cord
- With appearance of gonad primordium, the ridge is renamed the UG Ridge
Cell Types Found in Forming Gonads (3):
- germ cells
- supporting cells
- interstitial cells
List the Primordial Germ Cells (PGC):
- What can generate a teratoma?
- Gamete progenitor cells
- Extra-gonadal origin
- Migrate to gonad
- Unique morphology
- Persistence of PGC’s outside the gonad may generate a teratoma
Describe the **development of the primordial germ cells: **
- What do they form?
- Where do they orginate from?
- What week are they first seen?
- When do they migrate?
- What happens once they reach the gonad?
- Form the stem cells for gamete production
- Extragonadal origin
- First seen in the yolk sac wall during week three
- During weeks 4-5 they migrate to the gonad
- Once in the gonad, they become associated with or surrounded by epithelial supporting cells derived from a proliferation of the coelomic epithelium
What is the fate of the cranial and caudal attachments of the primitve gonad?
-
Cranial
- Suspensory ligament
-
Caudal
- Gubernaculum
Note: UG ridge is attached to body wall dorsally by a mesentery
What two sets of ducts develop during the indifferent stage?
-
Mesonephric Duct (MD) (“The Wolffian System”)
- Associated with the mesonephric kidney
-
Paramesonephric Duct (“The Mullerian System”)
- Lateral to MD
- Invagination of coelomic epithelium
- Formation induced by MD
- Contacts the UG Sinus
What are the external swellings in the caudal region of the embryo?
*Progenitors of the External Genitalia*
-
Genital Tubercle
- A midline swelling
-
Urethral (Urogenital) Folds
- Surround the UG membrane
-
Labioscrotal Swellings
- Lateral to the urethral (urogenital) Folds
What is the first event that occurs after the indifferent stage?
Differentiation of the gonad
What gene results in the formation of the testes?
SRY gene on the Y chromosome
- Encodes for a DNA binding protein the Testicular Determining Factor (TDF)
What cells form in the testes as a result of the SRY gene?
-
Germ Cells
- PGC form spermatogonia
-
Sertoli Cells (supporting cells)
- Express Sox 9
- Form from coelomic epithelial cords
- Associate w/germ cells (seminiferous cords)
-
Leydig Cells (interstitial cells)
- Secrete testosterone [week 8]
What is the fibrous capsule that surrounds the testes?
tunica albuginea
In the absence of SRY gene expression, the indifferent gonad develops into an _____
In the absence of SRY gene expression, the indifferent gonad develops into an Ovary
- Note: Expression of 2 X chromosomes needed for ovarian development
What cells develop in the ovary?
-
Germ Cells
- PGC become oogonia
-
Follicle/Granulosa Cells (supporting cells)
- Associate w/oogonia forming primordial follicles
-
Interstitial Cells
- Can produce steroid hormones
- Where do the testes descend into?
- What happens if this fails?
- Where do the ovaries descend into?
-
Testis Descend into the Scrotum
- Failure of descent = Cryptorchidism
- Ovaries Descend into the Pelvis
In the presence of _________ (male embryo), the growth and differentiation of the mesonephric ducts are supported
In the presence of testosterone (male embryo), the growth and differentiation of the mesonephric ducts are supported
- Derivatives of the Mesonephric Duct:
- Derivatives of the Mesonephric Tubules:
-
Derivatives of the Mesonephric Duct:
- Duct of Epididymis
- Ductus (Vas) Deferens
- Ejaculatory Duct
- Seminal Vesicle
-
Derivatives of the Mesonephric Tubules:
- Efferent Ductules
- Note: In the male, there is a continuous duct system from seminiferous tubules to the urethra
- What supports the development of the prostate?
- Describe the development of the prostate:
- Induced and supported by androgens
- Prostate Gland may have a Dual Origin
- Both primordia begin as buds
- Most glands - form from buds of the endoderm lining of the pelvic part of UG sinus
- Central zone glands – form from buds from the mesoderm
- Budding is induced by UG sinus Mesenchyme
Presence of ___ in male embryos stimulates the regression of the paramesonephric ducts
Presence of MIS in male embryos stimulates the regression of the paramesonephric ducts
- Note: Part of the prostatic utricle is derived from the Paramesonephric Duct
In the absence of __________ (female embryo) the
development of the mesonephric ducts is not supported
In the absence of testosterone (female embryo) the
development of the mesonephric ducts is not supported
- Note: Cystic remnants of the mesonephric duct can be found within the broad ligament
In the female embryo, absence of ___ allows the growth and differentiation of the paramesonephric ducts
In the female embryo, absence of MIS allows the growth and differentiation of the paramesonephric ducts
Describe the growth and differentiation of the paramesonephric ducts:
- The caudal 1/3 Fuses, and becomes the uterus & part of the vagina
- The cranial 2/3 remains unfused, and becomes the oviduct
- The paramesonephric ducts & pelvic part of UG sinus interact with each other to form the vagina
How can abnormal development of the paramesonephric ducts present?
Range from total absence to complete duplication of uterus & vagina
Remodeling of the Definitive UG Sinus (during Indifferent Stage):
-
Pelvic Portion
- Male
- Female
-
Phallic Portion
- Male
- Female
-
Pelvic Portion
- Male
- Distal Prostatic & Membranous Urethra
- Female
- Part of Vagina
- Male
-
Phallic Portion
- Male
- Penile Urethra
- Female
- Vestibule
- Male
In the presence of ___, the genital tubercle and
urethral folds elongate
In the presence of DHT, the genital tubercle and
urethral folds elongate
- The lining of the penile urethra is derived from the _______ of the ______ part of the UG Sinus
- The portion of the penile urethra within the glans is formed by an ingrowth of _______
- The lining of the penile urethra is derived from the endoderm of the phallic part of the UG Sinus
- The portion of the penile urethra within the glans is formed by an ingrowth of ectoderm
What does normal development of the male reproductive ducts and external genitalia depend on (2)?
- Presence of androgens
- Conversion of testosterone to dihydrotestosterone by 5-α reductase in the accessory glands and external genitalia
What can abnormal formation of the male urethra result in?
-
Hypospadias
- Urethral opening proximal to tip of glans
-
Epispadias
- Urethra open dorsally
In the absence of ___, the primordia of the external genitalia develop in a female direction
In the absence of DHT, the primordia of the external genitalia develop in a female direction
- The genital tubercle forms the clitoris
- The urethral folds form the labia minora
- The labioscrotal swellings form the labia majora
