Oogenesis Flashcards
Corpus Luteum development - 1.
= empty follicle becomes corpus haemmorrhagicum
- central blood clot surrounded by granulosa cells
- undergoes changes and starts producing progesterone in granulosa
- now called luteal cells
Corpus luteum development - 2.
= corpus haemorrhagicum becomes corpus luteum
- CL developed
- maximum diameter = 65-80% of original follicle size
Corpus luteum development - 3.
= corpus luteum becomes corpus albicans
- end of diestrus CL regresses
- replaced by fibrous tissue ~ decreased vasculature and progesterone
What is the CL divided into and what happens to CL if pregnant
- Primary ~ from ovulation of dominant follicle of major primary waves at or near oestrus where oestrogen prevails
- Secondary ~ from ovulation of major secondary wave during dioestru or early preg where progesterone prevails
- Accessory ~ lutenised anovulatory follicles (esp during early preg)
(secondary and accessory = supplemental CLs)
if preg = primary CL persist until day 160 of gestation
What does oogenesis start with
= oogonium
- primordial gen cells (cortex)
- divide into oogonia which develop into primary oocytes (2N)
Primary oocytes
- produced from puberty to menopause
- pre-ovulatory stage
- 99% regress/atresia (breakdown)
- they are recruited from cortex
- migrate into medulla for development
- back to cortex for ovulation - ovulation fossa
Layers that surround oocytes
(see image in folder)
- Oocyte becomes surrounded by layer of granulosa cells (cumulus) attached to wall by clump of granulosa cells called hillock
- 2 layers of cells around oocyte
~ Inner cells = granulosa cells (avascular), produce oestrogen or progesterone
~ Outer cells = thecal cells (vascular), provide support to follicle, theca externa produces progesterone post ovulation
- Zona pellucida – membrane surrounding oocyst
Follicular development
- folicular waves
- primary oocytes grow
- Follicular waves
~ Synchronous emergence of group of follicles ≥ 5mm (diameter)
~ Recruited oocytes
~ Initiated by increase in FSH - Primary oocytes grow
~ One follicle (dominant follicle) reaches approx. 22mm in diameter and becomes pre-ovulatory follicle
~ Releases oestrogen
~ Rest regress (subordinate follicles)
Follicular development
- major and minor waves
- Minor waves occur when dominant follicle reaches 30mm and then regresses
- If dominant follicle reaches > 30mm this wave is known as major wave
- Major wave can be either:
~ Secondary (1st) follicular wave - precedes primary wave (emerges during late oestrus / early dioestrus)
~ Primary (2nd) follicular wave – emerge during mid-dioestrus and ovulates at next oestrus
Follicular development
- dominat folicle in 1st secondary wave either
~ Regresses
~ Becomes haemorrhagic without ovulation
~ Ovulates (where only one wave occurs)
- Spontaneous ovulation occurs when dominant follicle reaches approx. 40mm
- 85-90% of pre-ovulatory follicles soften just prior to ovulation
Folicular development
- final size depends on
- why do major and minor waves continue in early pregnacy in horse
- season
- breed/type of horse
~ quarter horses (43mm) larger than Arabians (40mm)
~ 3.1mm larger in thoroughbreds in australia than in england - follicular development in early pregnancy involves major and minor waves in succession where the dominant folicle of the major wave in anovulatory
- reduced circulation of LH = largest follicles fail to reach over 28mm = dominant folicles of major waves fail to ovulate
- endometrial cups form and eCG production begins 30 days after gestation
- dominant follicles of major waves are either ovulatory or anovulatory forming supplemental corpora lutea
Ovulation
- oocyte escapes surrounded by granulosa cells
~ First meiotic division – becomes secondary oocyte
~ Fluid escapes - Oocyte picked up by fimbrae
!!!Revision of oocyte divisions from primary oocyte to zygote!!!
