Repro System Development

Question 1

A Reproductive System has 3 Components:

Answer 1

1. gonads
2. duct system
3. external genitalia

Question 2

1. Sex Determination occurs at ________
2. Sex Differentiation occurs during ____________________ (influenced by genetic & epigenetic factors)

Answer 2

1. Sex Determination occurs at fertilization
2. Sex Differentiation occurs during embryonic and into the fetal period (influenced by genetic & epigenetic factors)

Question 3

1. Presence and action of ________________, appears to actively influence sexual differentiation in a male direction
2. A second factor _____________________ is involved in promoting regression of the paramesonephric (müllerian) ducts

Answer 3

1. Presence and action of androgens, appears to actively influence sexual differentiation in a male direction
2. A second factor Mullerian Inhibiting Substance (MIS or MIF) is involved in promoting regression of the paramesonephric (müllerian) ducts

Question 4

What are the two embryoinc precursor tissues for the reporductive system?

Answer 4

1. Intermediate Mesoderm
2. Endoderm

Question 5

What happens during the indifferent stage (weeks 4-6)?

Answer 5

primordia of the organs of the reproductive system begin to form

Question 6

The Indifferent Gonad Forms within the ___________ Aspect of the __________ _____

• What is the structure renamed once the gonad primordium appears?

Answer 6

The Indifferent Gonad Forms within the Ventromedial Aspect of the Nephrogenic Cord

• With appearance of gonad primordium, the ridge is renamed the UG Ridge

Question 7

Cell Types Found in Forming Gonads (3):

Answer 7

1. germ cells
2. supporting cells
3. interstitial cells

Question 8

List the Primordial Germ Cells (PGC):

• What can generate a teratoma?

Answer 8

1. Gamete progenitor cells
2. Extra-gonadal origin
3. Migrate to gonad
4. Unique morphology

• Persistence of PGC’s outside the gonad may generate a teratoma

Question 9

Describe the **development of the primordial germ cells: **

1. What do they form?
2. Where do they orginate from?
3. What week are they first seen?
4. When do they migrate?
5. What happens once they reach the gonad?

Answer 9

1. Form the stem cells for gamete production
2. Extragonadal origin
3. First seen in the yolk sac wall during week three
4. During weeks 4-5 they migrate to the gonad
5. Once in the gonad, they become associated with or surrounded by epithelial supporting cells derived from a proliferation of the coelomic epithelium

Question 10

What is the fate of the cranial and caudal attachments of the primitve gonad?

Answer 10

• Cranial
  
  • Suspensory ligament
• Caudal
  
  • Gubernaculum

Note: UG ridge is attached to body wall dorsally by a mesentery

Question 11

What two sets of ducts develop during the indifferent stage?

Answer 11

• 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

Question 12

What are the external swellings in the caudal region of the embryo?

Answer 12

*Progenitors of the External Genitalia*

1. Genital Tubercle
   
   • A midline swelling
2. Urethral (Urogenital) Folds
   
   • Surround the UG membrane
3. Labioscrotal Swellings
   
   • Lateral to the urethral (urogenital) Folds

Question 13

What is the first event that occurs after the indifferent stage?

Answer 13

Differentiation of the gonad

Question 14

What gene results in the formation of the testes?

Answer 14

SRY gene on the Y chromosome

• Encodes for a DNA binding protein the Testicular Determining Factor (TDF)

Question 15

What cells form in the testes as a result of the SRY gene?

Answer 15

• 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]

Question 16

What is the fibrous capsule that surrounds the testes?

Answer 16

tunica albuginea

Question 17

In the absence of SRY gene expression, the indifferent gonad develops into an _____

Answer 17

In the absence of SRY gene expression, the indifferent gonad develops into an Ovary

• Note: Expression of 2 X chromosomes needed for ovarian development

Question 18

What cells develop in the ovary?

Answer 18

• Germ Cells
  
  • PGC become oogonia
• Follicle/Granulosa Cells (supporting cells)
  
  • Associate w/oogonia forming primordial follicles
• Interstitial Cells
  
  • Can produce steroid hormones

Question 19

1. Where do the testes descend into?
   
   • What happens if this fails?
2. Where do the ovaries descend into?

Answer 19

1. Testis Descend into the Scrotum
   
   • Failure of descent = Cryptorchidism
2. Ovaries Descend into the Pelvis

Question 20

In the presence of _________ (male embryo), the growth and differentiation of the mesonephric ducts are supported

Answer 20

In the presence of testosterone (male embryo), the growth and differentiation of the mesonephric ducts are supported

Question 21

1. Derivatives of the Mesonephric Duct:
2. Derivatives of the Mesonephric Tubules:

Answer 21

1. Derivatives of the Mesonephric Duct:
   
   • Duct of Epididymis
   • Ductus (Vas) Deferens
   • Ejaculatory Duct
   • Seminal Vesicle
2. Derivatives of the Mesonephric Tubules:
   
   • Efferent Ductules

• Note: In the male, there is a continuous duct system from seminiferous tubules to the urethra

Question 22

• What supports the development of the prostate?
• Describe the development of the prostate:

Answer 22

• 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

Question 23

Presence of ___ in male embryos stimulates the regression of the paramesonephric ducts

Answer 23

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

Question 24

In the absence of __________ (female embryo) the
development of the mesonephric ducts is not supported

Answer 24

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

Question 25

In the female embryo, absence of \_\_\_ allows the growth and differentiation of the paramesonephric ducts

Answer 25

In the female embryo, absence of **MIS** allows the growth and differentiation of the paramesonephric ducts

Question 26

Describe the growth and differentiation of the paramesonephric ducts:

Answer 26

* 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

Question 27

How can **abnormal development of the paramesonephric ducts** present?

Answer 27

Range from **total absence to complete duplication** of uterus & vagina

Question 28

**Remodeling of the Definitive UG Sinus** (during Indifferent Stage)**:** 1. **Pelvic Portion** * Male * Female 2. **Phallic Portion** * Male * Female

Answer 28

1. **Pelvic Portion** * Male * Distal Prostatic & Membranous Urethra * Female * Part of Vagina 2. **Phallic Portion** * Male * Penile Urethra * Female * Vestibule

Question 29

In the presence of \_\_\_, the genital tubercle and urethral folds elongate

Answer 29

In the presence of **DHT**, the genital tubercle and urethral folds elongate

Question 30

* 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 \_\_\_\_\_\_\_

Answer 30

* 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**

Question 31

What does normal development of the male reproductive ducts and external genitalia depend on (2)?

Answer 31

1. Presence of **androgens** 2. Conversion of testosterone to dihydrotestosterone by **5-α reductase** in the accessory glands and external genitalia

Question 32

What can **abnormal formation of the male urethra** result in?

Answer 32

* **Hypospadias** * Urethral opening **proximal** to tip of glans * **Epispadias** * Urethra open **dorsally**

Question 33

In the absence of \_\_\_, the primordia of the _external genitalia develop in a female direction_

Answer 33

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_