Embrology of reproductive system Flashcards
Briefly describe the timeline of development
- at 5 weeks, primordial germ cells migrate from yolk sacs to the urogenital ridges – these will eventually form the gametes
- between 5-7 weeks the kidneys start to ascend
- at two months is the indifferent stage
- between 10-12 weeks the ‘switch’ begins: formation of seminiferous tubules and ovarian follicles ^[gonad formation guides tube formation]
- 3 months - external genitalia develop
- Between 8-9 months: testes descend into the scrotum
ovaries also descend but do not cover the same distance, end up in pelvis
What is the origin of the urogenital system?
by three weeks, the trilaminar germ disc has formed.
This consists of ectoderm, mesoderm and endoderm.
The urogenital system is derived from intermediate mesoderm.
What forms the beginnings of the urogenital system within the intermediate mesoderm?
The intermediate mesoderm migrates to form a ridge near or lateral to the hindgut. This forms the urogenital ridge – the beginnings of the urogenital system.
What are the key features of the undifferentiated stage?
- germ cells from yolk sac migrate into the intermediate mesoderm
- note that there are two connections from the embryo to yolk sac, one is the allantois: which is responsible for waste storage
- note also the cloacal membrane, just over the cloaca, which becomes the urethral and rectal openings
- Note the two ridges that form from the intermediate mesoderm: nephrogenic and genital ridges
- note also the mesonephric and paramesopheric ducts
- mesonephric duct and tubule formed from the condensation of germ cells
- this forms a primitive kidney, the mesonephros, the first functioning kidney ^[although second incarnation] and associated mesonephric ducts. Both are functional
- note the mesonephros is composed of glomerulus, Bowman’s capsule and mesonephric tubule – glomerulus comes from branches of dorsal aorta which is positioned medial to the mesonephros (R and L)
- mesonephric tubules connect to mesonephric duct
- paramesonephric duct forms from invagination of visceral peritoneum
- note also cloaca separates in urogenital sinus: source of paramesonephric and mesonephric ducts drainage
- genital ridge - site of gonad formation. Mesonephric tubule located between duct and gonad
All this occurs between week 5 and 6
What is the origin of the suspensory ligament in females?
the outgrowth above the gonads- this will become the suspensory ligament in females (containing ovarian artery, vein and nerve)
What are the progenitor structures of the prostate and bulbourethral glands?
The primordium of prostate or lesser vestibular glands also known as paraurethral glands or Skene’s glands
- Also primordium of bulbourethral or greater vestibular glands also known as Bartholin glands
Within urogenital sinus
What are the progenitor structures of the lesser and greater vestibular glands?
The primordium of prostate or lesser vestibular glands also known as paraurethral glands or Skene’s glands
- Also primordium of bulbourethral or greater vestibular glands also known as Bartholin glands
Within urogenital sinus
Describe the development of male development
From week 4: mesonephros and mesonephric ducts form
During weeks 5 and 6, indifferent gonads form, with primordial germ cells from yolk sac, epithelial cells and mesenchymal cells
SRY gene turned on from week 7 resulting in TDF expression and testes development
Medullary (testis) cord contains primitive germ cells develops in response to TDF, Sertoli (sustentacular cells) and Leydig or interstitial cells
- In males, most of action occurs in the medulla in the gonads
- Testicular cords developing from mesonephric tubule, branching further into seminiferous tubules
- Developing tunica albuginea
- Rete testis, efferent tubules and mesonephric ducts develop
- from mesonephric duct: epididymis, vas deferens, ejaculatory duct and seminal vesicles develop ^[seminal vesicles an outgrowth]
- Paramesonephric or Mullerian duct degenerates
Leydig cells derived from mesenchyme produce testosterone, resulting in development of male genital ducts, male external genitalia and accessory glands
- Interstitial or Leydig cells secrete testosterone, responsible for male development and maintenance of libido, outside the seminiferous tubules
- mesonephric duct develops into epididymis, vas deferens, ejaculatory duct and seminal vesicle
- mesonephric tubules develop into efferent ductules
- urogenital sinus develops into prostate and bulbourethral glands
Sertoli cells produce AMH resulting in paramesonephric duct degeneration
- Sertoli cells, within the seminiferous tubules, provide support to spermatogenic cells and secrete AMH
Describe the development of the testes
Medullary (testis) cord contains primitive germ cells develops in response to TDF, Sertoli (sustentacular cells) and Leydig or interstitial cells
- In males, most of action occurs in the medulla in the gonads
- Testicular cords developing from mesonephric tubule, branching further into seminiferous tubules
- Developing tunica albuginea
- Rete testis, efferent tubules and mesonephric ducts develop
- from mesonephric duct: epididymis, vas deferens, ejaculatory duct and seminal vesicles develop ^[seminal vesicles an outgrowth]
- Paramesonephric or Mullerian duct degenerates
Describe the role of Leydig cells
Leydig cells derived from mesenchyme produce testosterone, resulting in development of male genital ducts, male external genitalia and accessory glands
- Interstitial or Leydig cells secrete testosterone, responsible for male development and maintenance of libido, outside the seminiferous tubules
- mesonephric duct develops into epididymis, vas deferens, ejaculatory duct and seminal vesicle
- mesonephric tubules develop into efferent ductules
- urogenital sinus develops into prostate and bulbourethral glands
Describe the role of Sertoli cells
Sertoli cells produce AMH resulting in paramesonephric duct degeneration
- Sertoli cells, within the seminiferous tubules, provide support to spermatogenic cells and secrete AMH
Describe the process of testes descent
The testes and ovaries descends during the 8th and 9th months.
The gubernaculum guides the testes or ovaries down.
It moves anteriorly through the layers of the abdomen wall.
Invagination of parietal peritoneum assists testes and makes space.
This is why layers of the scrotum are continuous with the abdominal wall.
- transversalis fascia becomes the internal fascia of the scrotum
- internal oblique becomes cremaster muscle
- external oblique fascia becomes external fascia
A problem that occurs is undescended testes - high scrotal or higher in the inguinal canal or abdomen.
Another problem that can occur is hydrocele if invagination is not completely closed- can be non- or completely communicating hydrocele
Describe issues with testes descent
A problem that occurs is undescended testes - high scrotal or higher in the inguinal canal or abdomen.
Another problem that can occur is hydrocele if invagination is not completely closed- can be non- or completely communicating hydrocele
Describe development of female genitali
During week 4 the mesonephros and mesonephric ducts develop
Indifferent gonads, with migration of primordial germ cells from yolk sac and formation of Mullerian ducts (persistence of paramesonephric ducts)
Cells of ovary expand from cortex.
Primitive sex cords develop into cortical cords and ovarian follicles, containing oocytes and follicular cells.
From week 7 and onwards, SRY gene not present, therefore no TDF and development of ovaries
In the absence of a Y chromosome female development occurs.
Mesonephric tubule and duct i.e. Wolffian ducts degenerate.
Development of ovaries: primary cells include oocytes (primitive germ cells), and follicular cells which produce estrogen, stimulating the formation of female genitalia
A lack of testes means no testosterone or AMH, therefore uterine tubes, uterus and vagina develops
The paramesonephric ducts are progenitors of the upper female GT.
The two ducts come together and fuse to form the uterus and upper part of the vagina (at the caudal end). Unfused portions (at the cranial end) form the uterine tubes.
Describe the development of the upper female GT
A lack of testes means no testosterone or AMH, therefore uterine tubes, uterus and vagina develops
The paramesonephric ducts are progenitors of the upper female GT.
The two ducts come together and fuse to form the uterus and upper part of the vagina (at the caudal end). Unfused portions (at the cranial end) form the uterine tubes.
