Gametogenesis, fertilization and the blastocyst Flashcards
Once eggs are released from ovary, where do they go through and what do they go to
Go through fimbrae to fallopian tube
What are the parts of the Fallopian tube starting from the fimbrae
1) infundibulum
2) Ampulla
3) Isthmus
4) interstitial
Where does fertilization happen
Ampulla
What is the first entity that is present in female gametogenesis
Primary follicle
What is the primary follicle
Primary oocyte is surrounded by a single layer of follicular cells
What do primary follicles begin to develop into
-when does this happen
5-12 primary follicles develop and become growing follicles
-happens at the beginning of each monthly cycle
What happens to the primary follicles after they become growing follicles
Follicular cells multiply and become several layered
-Also become separated from the ovum by a layer called the Septum Pellucidum
What is the septum pellucidum
Layer that separates follicular cells from the ovum
What do all but one of the growing follicles degenerate to become
Corpus atreticum/scar
After all but one of the growing follicles becomes a corpus attreticum, what happens
The follicular cells of the remaining growing follicle secrete a fluid which produces a fluid-filled Antrum within the follicle
What is the thecal layer of the growing follicle made from?
Made from the ovarian non-gamete cells surrounding the follicle
What is the thecal layer divided into
- Vascular theca interna
- Avascular inactive theca externa
What does the theca interna do
Produce oestrogen
What is the mature follicle callled
Graafian follicle
In the graafian follicle (mature follicle), what do the majority of the follicular cells form
Stratum granulosum
What does the stratum granulosum produce
Progesterone
What do the remaining of the follicular cells do
Remainder surround oocyte as the cumulus oophorus
What is a secondary oocyte
- majority of the follicular cells have now formed the stratum granulosum
- The remainder of the follicular cells surround the oocyte as the cumulus oophorus
What is formed after a graafian follicle
Secondary oocyte
What happens after a secondary oocyte is produced
Mature follicle ruptures and releases an ovum
What does the released ovum still have
Retains a covering of follicular cells which form the corona radiata
What happens to the septum pellucidum after ovum is released
Septum pellucidum expands to become the zone pellucida
What forms the corpus luteum
Cells of the theca interna and the stratum granulosum enlarge and become yellowish to form the corpus luteum
What does the corpus luteum do?
-what did it do before ovulation
Secretes a large amount of progesterone
-THe follicle produced mainly oestrogen
What is the life span of the corpus luteum is fertilization does not occur
12 days
What degenerates if fertilization does not occur
Corpus luteum degenerates into the corpus albicans
- the cessation of its hormonal output leads to menstruation
What happens if fertilization does occur
The corpus luteum is sustained by the HCG produced bu the conceptus and form a large corpus luteum of pregnancy
What does a corpus luteum of pregnancy eventually form
Corpus albican
In a sperm, what does the head consist of
Largely of a nucleus with a sparse cytoplasmic covering
What is the acrosomal cap derived from
Golgi
What does the acrosomal cap do
contain enzymes which help in the penetration of the ovum
Main difference between spermatogenesis and oogenesis
spermatogenesis has mitosis followed by meiosis
-oogenesis has meiosis in ovaries and no mitosis
What is the cytoplasmic:nuclear ratio in spermatogenesis vs in oogenesis
Spermatogenesis
Low cytoplasmic:nuclear ratio
Oogenesis
High cytoplasmic:nuclear ratio
How is the abdominal cavity different in males and females
Abdominal cavity is closed in males but it communicates with the exterior in females
(vagina->Fallopian tube->abdominal cavity)
After being in the cervix, where does the sperm go and what happens to it
sperm reaches the isthmus and becomes less motile
What makes the sperm motile again? Where are these released from
Chemoattractants released from cumulus cells
What does sperm require in the female reproductive tract
Requires capacitation
-during which acrosomal region loses glycoprotein coat
What is fertilization 1
Shed secondary oocyte halted part way through 2nd meiotic division
What is fertilization 2
Mature ovum- penetration by spermatozoon prompts completion of 2nd meiotic division
What do acrosomal enzymes do
Help disperse corona radiata and aid penetration of zone pellucida. Plasma membranes of gametes fuse and male nucleus is ‘injected’
What is fertilization 3
Fertilized ovum is diploid again and the permeability of the zone pellucida is altered to prevent further penetration
What is done to stop more sperm entering fertilized ovum?
Zona reaction- permeability of zone pellucida is altered to prevent further penetration
Where are enzymes released from to digest sperm receptor proteins on ovum so they can no longer bind sperm
Enzymes released by cortical granules
What is the circumvitelline space
Ovum has shrunk and there is a ‘gap’ between the zona pellucida and the ovum
How are blastomeres formed
Mitosis
What happens when there is further cleavage
-what is DNA and protein synthesis like
Cells continue to cleave to form progressively smaller blastomeres. There is DNA synthesis but virtually no protein made
What is a morula
New solid balls of cells. Cytoplasmic:nuclear ration is now normal
What is the zone pellucida like in a morula and why
Still persists to stop implantation
What do morula cells undergo
-What happens to the zone pellucida
COmpaction- establishment of tight junctions between surface cells
-the zone pellucida starts to split
When does the blastocyst form
5 days after fertilization
What does a blastocyst look like
Has an inner cell mass and a trophoblast
When are 2 daughter cells (blastomeres) formed by mitosis
30h post fertilisation
