Week 1.0 - development Flashcards
What composes the duct system in males?
- Epididymis
- Ductus deferens
- (urethra)
What composes the duct system in females?
- Fallopian tubes
- Uterus
- Cervix
- Vagina
What is the indifferent stage of development?
-The gonad and duct system at the point which it is the same regardless of sex
When does structural development of the genitalia occur and how does this differ from functional development and maturation?
- Structural development in utero
- Functional development and maturation continues after birth
What is meant by sexual maturation?
- Born physically immature
- Sexual maturation occurs as puberty and development of secondary sexual characteristics
State the secondary sexual characteristics which occur in males
- bigger body size (relative to female)
- Body composition and fat distribution
- Hair and skin
- Facial hair and male pattern baldness
- CNS effects
State the secondary sexual characteristics which occur in females
- Smaller body size (relative to males)
- Subcutaneous fat distribution
- Hair and skin
- Breast development
- CNS effects
What is the urogenital ridge?
-Region of intermediate mesoderm which gives rise to the embryonic kidney and the gonad
What tissues contribute to the gonad?
- Intermediate mesoderm
- Primordial germ cells (extragonadal)
What are primordial germ cells? How do they contribute to the gonad?
- Special population of cells identified from the yolk sac wall
- Migrate into the retroperitoneum along dorsal mesentery through umbilicus and arrive at gonad
- Populate mesodermal stroma
On a genetic level, what drives development of the male?
-Expression of SRY genes in primordial germ cells
Which structures do SRY genes affect?
- Gonads
- Duct system
- External genitalia
What affect does SRY have on the gonads?
-Causes differentiation into testis by development of medullary cords, no cortical cord development and thickening of the tunica albuginea
What determines the sex of an embryo?
-What chromosome the male gamete is carrying
How does the absence of a Y chromosome influence an indifferent gonad?
- Medullary cord degenerates
- Cortical cords develop
- No tunica aluginea
Why is it important that an ovary doesnt have a thick tunica albuginea?
Allows ova to be released
What are the names of the two duct systems involved in genital development?
- Mesonephric ducts (wolffian)
- Paramesonephric (mullarian)
Where do the mesonephric and paramesonephric ducts end?
-Cloaca
As well as gonadal function, what do the mesonephric ducts function to do?
-Embryonic kidney
What is the cloaca?
-The point at which the reproductive, gastrointestinal and urinary tracts end early in development
What is the urogenital sinus?
-Structure which forms from the hind gut by the urorectal septum and makes the future bladder and urethra (plus prostate in males and vagina in females)
Describe the development of the bladder and urethra from the urogenital sinus in the male
- Mesonephric ducts reach urogenital sinus
- Ureteric bud sprouts from mesonephric duct
- As MD makes contact with UGS, causes smooth muscle differentiation and trigone formation, bladder expansion
- UB and MDs make independent openings in UGS as it absorbs both ducts at separate points.
- Contact and development leads to formation of prostate
Describe the development of the bladder and urethra from the urogenital sinus in the female
- MDs reach UGS
- UBs sprout from MDs
- UGS begins to expand and SM appears as MDs make contact
- The absence of androgens causes MD to begin to regress and UB is absorbed by UGS
- Prostate is not formed due to absence of androgens
Where are the paramesonephric ducts and where do they come from?
-Appear from invaginations of the urogenital ridge and are lateral to the mesonephric ducts
What is the significance of the paramesonehric ducts opening into the peritoneal cavity at the cranial end?
-Future fallopian tubes open into peritoneal cavity
Describe how the mullarian ducts develop into the uterus and fallopian tubes
- As the paramesonephric ducts develop they grow towards each other, pulling the peritoneum with it
- They fuse in the midline and develop into the uterus and uterine tubes.
- As they fuse a septum is formed in the middle of the uterus, this regresses during development
What inductive event is caused by contact of paramesonephric ducts with UGS?
-Growth and extension of the UGS into vagina
From where is the vagina derived?
- Lower 2/3 UGS
- Upper 1/3 paramesonephric duct
What is the cause of a unicornate uterus?
-Failed regression of uterine septum
Why do the paramesonephric ducts not develop in the male?
-Testis produce mullarian inhibiting hormone causing degeneration of the ducts
What happens to the mesonephric duct in the female?
-After it has functioned as the embyonic kidney, the absence of androgens leads to its regression
What are the basic components of external genitalia at the indifferent stage?
- Genital tubercle
- Genital folds
- Genital swellings
Describe the formation of the external genitalia in the male
-Genital tubercle elongates and genital folds fuse on ventral surface to form spongy urethra under the influence of dihydrotestosterone
Describe the formation of the external genitalia in the female
-No testosterone means that genital tubercle does not elongate and the genital folds do not fuse, instead they open into the vestibule of the vagina
Describe the descent of the testis
- The testis begin high on the posterior abdominal wall as they are retroperitoneal structures from the urogenital ridge
- Evagination of processes vaginalis (derived from parietal peritoneum) on an oblique course through the anterior abdominal wall creates a pathway for the testis to pass though inguinal canal and into scrotum
- Processes vaginalis looses patency and closes up
Describe the descent of the ovary
- Ovary tethered to labioscrotal fold by gubernaculum
- Ovary drawn down from posterior abdominal wall but is physically stopped by the uterus and uterine tubes
- Round ligament of uterus remains in inguinal canal
What is hypospadias?
-Failed fusion of genital folds in the male
What is sexual dimorphism?
-Two different shapes of internal genitalia ie female and male
