1.1 Flashcards
What do gametes form from?
Diploid germ cells
When do germ cells arise and where?
3 weeks after conception
In epiblast
Why must germs cells separate from somatic cells early in development?
To protect them from the influence on hormones acting on the somatic cells.
Remain undifferentiated.
To where do the primordial germ cells migrate? What kind of tissue forms these?
Primordial gonads
Formed by somatic mesenchymal tissue.
Describe meiosis
-
How many female gametes are produced per year? Why is this? How long are they capable of fertilisation?
12-14 (400 over reproductive life span)
Necessity to nurture embryo and fetus limits the number produced.
Ova are capable of fertilisation by sperm for about 36 hours after they are released from the gonad.
Describe male fertility.
Males are continuously fertile to exploit intermittent female fertility.
Large numbers of sperm must be produced as only a tiny proportion survive the journey.
Give male secondary sexual characteristics.
Large body size Body composition and fat distribution Facial hair Male pattern baldness CNS effects Hair and skin Smell
Give female secondary sexual characteristics
Small body size Subcutaneous fat distribution Hair and skin Breast development CNS effects
What does the urogenital ridge give rise to? What tissue is it formed rom?
Intermediate mesoderm
Gonads and kidneys
What tissues are the gonads derived from
Intermediate mesoderm fromt eh urogenital ridge and primordial germ cells.
Where doe the primordial germ cells arise?
Where do they migrate to
Arise in the wall of the yolk sac near the allantois and migrate into the retroperitoneum along the dorsal mesentery.
What determines gonadal sex?
Presence of Y chromosome even if XXY
What gene leads to the development of the male and where is it located
SRY gene on the short arm of the Y chromosome
Do medullary cords develop in testis/ovary
Develop in testis, degenerate in ovary
Do cortical cords develop in testis//ovary
None in testis, develop in ovaties
Does the tunica albuginea develop in the testis or ovary
Testis
Give the 2 duct systems that develop in embryos.
Mesonephric (Wolffian) Duct
Paramesonephric (Mullerian) Duct
Where do the duct systems end
Cloaca
A blind pouch where the GI, urinary and repro tracts converge and end
Describe the function of the mesonephric system
Mesonephric tubules + Mesonephric duct serve as emrboynic kidney
What is the urogenital sinus? How is it formed?
The cloaca is split into the urogenital sinus and the anorectal canal in the division of the GI and urinary/repro tracts by the urorectal septum.
What is the urogenital sinus continuous with? How? What does this become in adults?
Continuous with umbilicus via the urachus that becomes the median umbilical ligament in adults, tethering the bladder to the anterior abdominal wall.
What develops from the urogenital sinus in males and females?
Under the influence of testosterone in males, the prostate develops from the urogenital sinus.
In females it forms the lower part of the vagina.
Describe the development of the duct system in the male.
- Mesonephric ducts reach the urogenital sinus.
- Ureteric bud sprouts from MD
- Smooth musculature appears and the UGS begins to expand
- Teststerone maintains the mesonephric duct.
- This leads to the development of prostate and prostatic urethra from UGS.
- Paramesonephric duct regresses in the presence of testis derived Mullerian Inhibiting Hormone
Describe the development of the duct system in the female
Mesonephric ducts regress in the absent of androgens.
Paramesonephric ducts draw together and fuse and the loss of the uterine septum leads to the formation forming the uterus and uterine tubes.
Describe the path of the paramesonephric ducts.
Cranially open into abdominal cavity
Runs down length of embryo
Meet at cloaca
What prevents the paramesonephric ducts from developing
Mullerian Inhibiting Substance.
What happens hormonally in an XY embryo?
Testis develop
Androgen secretion supports mesonephric duct
Testis secretes MIH causing paramesonephric duct ot degenerate