Oogenesis Flashcards
What’s Oogenesis
It is the series transformation to change a diploid germ cell (non-functional 2n) into a haploid cell (functional gamete) in order to be fertilized
Location of oogenesis
It takes place in the ovaries and oviducts
Stages of oogenesis
It takes place by four stages: Multiplication- Growth- Maturation(meiosis)- differentiation
Multiplication
- During the fetal life, diploid germ cell 2n-s undergoes multiplication by mitosis.
- Happens during the first 4-5 months of embryonic life in the ovaries
Growth
During the fetal life, the diploid cell then undergoes growth by interphase to form oocyte I 2n-d which is arrested at Pro-1 at birth
Maturation
Oocyte II (2n-d) is arrested at Meta II in the oviduct. It degenerates if no fertilization occurred. Otherwise it resumes meiosis II after penetration of sperm cell n-s, to produce fertilized egg (ovum) 2n-d & 2nd polar body n-s
Differentiation
What happens to polar bodies?
Differentiation occurs only if fertilization takes place.
- The ootid(ovum n-s) with the 2nd polar body, by interphase, turn into zygote( 2n-d)
- After successive mitosis, embryo is produced
- Note that both polar bodies die later
Primordial Follicle
.1.
- It is made up of an oocyte 1 blocked at prophase 1
- surrounded by few follicular cells
Primary Follicle
.2.
- The no. of follicular cells increases
- we have oocyte 2 blocked at prophase 1
- surrounded by many follicular cells
Secondary Follicle
.3.
- The follicular cells form several layers composing granulosa
- The oocyte 1 is now surrounded by zona pelucida
Tertiary or Cavitary Follicle
.4.
- Granulosa presents many small cavities
- The follicle is now surrounded by a membrane called Theca
Mature or Graafian Follicle
.5.
- Granulosa presents 1 large cavity called atrium
- the follicle is now surrounded by 2 membranes ( theca internal and theca external)
What is folliculogenesis?
It is the maturation (development cycle) of the ovarian follicles (group of small cells surrounding & protecting the immature gamete)
- It starts during the fetal life
- pauses at birth
- resumes at puberty
Steps of folliculogenesis
1- Millions of primordial follicles are formed inside the ovary of the female fetus
2- Puberty
They start to transform into primary follicle then to secondary follicle then to tertiary/cavitary follicle
3- Menstruation
One of the tertiary follicles transforms into a mature graafian follicle
4- Ovulation
The empty graafian follicle transforms into yellow body ( corpus leteum) then into white body ( corpus albican) which degenerates at the end of the cycle.
Folliculogenesis vs. Oogenesis
- During fetal life:
Formation of millions of primordial follicles inside the ovary of the female fetus, where a diploid germ cell 2n-s undergoes multiplication by mitosis.
then undergoes growth by interphase to form oocyte 1 2n-d which is arrested at Pro-1 at birth - At Birth:
These follicles are arrested until puberty which is 4 months before the start of the first cycle - Puberty: 4 months before menstruation
They start to transform into primary follicles then to secondary follicles and then cavitary follicles - Menstruation: Cycle starts : Day 0: follicular phase:
One of the tertiary follicles transforms into a mature graafian follicle. Resumes Meiosis 1 to produce 1 polar body & oocyte II n-d 18 hours before. - Ovulation: Day 14: Luteal Phase
The empty graafian follicle transforms into yellow body (corpus leteum) then into white body (corpus albican) which degenerates at the end of the cycle. Oocyte II is arrested at Meta II in the oviduct. It degenerates if no fertilization occured. Otherwise, it resumes meiosis II after penetration of sperm cells n-s, to produce fertilized egg (ovum) 2n-s & 2nd polar body n-s - Day 28:
Degenerates as white body or karyogomy then interphase to form zygote 2n-d
