Embryology Flashcards
What is the first thing created when the sperm and egg fuse together?
Blastocyst (week 1 and 2)
What occurs during gastrulation?
The epiblast gives rise to the 3-layered embryo (week 3)
- ectoderm
- mesoderm
- endoderm
What does the ectoderm become?
The skin and neural tube (brain and spine)
What does the endoderm become?
the gut tube
What does the mesoderm become?
- paraxial -> somites -> vertebral bodies and limbs
- intermediate - urogenital system and reproductive system
lateral - body cavities (pleural cavities, peritoneal cavities)
Where does the urinary and reproductive system originate from?
The intermediate plate of the mesoderm
What are the 3 sets of kidneys which develop?
- pronephros (degenerate as soon as they’re formed)
- mesonephros (briefly functional)
- metanephros (the definitive kidney)
The metanephros forms from the branches of the mesonephros.
What is it that forms the gonads?
The mesonephros, after they are no longer functioning as the kidney.
What happens to create the indifferent gonad?
The mesonephros thickens
Primordial sex Cells are imported from the yolk sac to become the germ cells.
Which cells form the sperm or ovum?
Primordial sex cells which migrate from the yolk sac.
What ate the two tubes around the gonads?
- mesonephric duct
- paramesonephric duct
What is the name of the mesonephric duct?
Wolffian Duct
What is the name of the paramesonephric duct?
Mullerian Duct
How is the male gonad formed?
The indifferent gonad develops into the testis
the mesonephric duct develops into the vas deferens, epididymis, seminal vesicles
the paramesophrenic duct disappears
How is the female gonad formed?
the indifferent gonad develops into the testis
the paramesonephric duct forms the Fallopian tube, uterus, cervix of vagina
the mesonephric duct disappears.
Which gonad is always made unless instructed otherwise?
ovary.
Which gene is expressed on the Y chromosome and what does it code for? (male gonad)
The SRY gene encodes for the TDF (testis determining factor) protein
Which cells express the SRY gene?
The primordial cells
What action does the SRY gene have?
- It codes for TDF to make the indifferent gonad into a testis.
- it is expressed by the primordial supporting cells and it turns them into Sertoli cells
What do the Sertoli cells do?
secrete MIS (Mullerian Inhibiting substance)
What is MIS?
Mullerian Inhibiting substance
- it causes the paramesonephric duct to degenerate
- It also transforms mesenchymal cells to form leading cells
What is the action of leydig cells?
They produce testosterone which causes the production of the male external genitalia from the mesonephric duct.
Where does the prostate originate from?
outgrowth of urethra
where do the seminal vesicles originate from?
Mesonephric duct
What does the paramesonephric duct become in females?
- fallopian tube
- cervix
- upper part of vagina
How does the ovary develop?
the primary sex cords degenerate and secondary sex cords develop.
the primordial sex cells become incorporated in the secondary sex cords
primordial germ cells then bud off with a single layer of the cortical cord to form primordial follicles
the primordial follicles then do active mitosis
When are all follicles formed?
Month 7
When do oocytes enter meiosis?
By month 7, they complete stage 1 where they stay until puberty
How many primordial follicles are there at birth?
2 million - each one has an oocyte.
many follicles atrophy before puberty
How many follicles develop in each 28 day cycle?
12-15 develop after puberty
only ONE follicle reaches maturity and ovulation
This continues until menopause
Which part of the paramesonephric duct becomes what?
cranial end - ovary
caudal - uterus and superior vagina
What creates the inferior part of the vagina?
Urogenital sinus
What happens in the descent of the testes?
Week 7 - level T10
week 12 - deep inguinal ring (until 7 months)
Just prior to birth - enters scrotum
Which region are the gonads originally in?
The thoraco-lumbar region.
What happens in the descent of the ovary?
Week 7 - level T10
week 12 - broad ligament
round ligament drawn through inguinal canal
Which fibrous cord causes the descent of the gonads?
The gubernaculum.
What is a cause of indirect inguinal hernias?
When the processes vaginallis doesn’t lose its connection with the inguinal canal.
What does the gubernaculum become in females?
Both the ovarian ligament and round ligament.
What happens to the gubernaculum in males?
It becomes the scrotal ligament, and anchors the testis to the most inferior part of the scrotum.
