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Oestrous Cycle - Anatomy & Physiology (view source)
Revision as of 13:36, 10 September 2008
, 13:36, 10 September 2008→Follicular Growth and Development
==== Follicular Growth and Development ====
==== Follicular Growth and Development ====
* There is follicular growth and atresia throughout the oestrous cycle.
* There are normally two waves of follicular growth, but 3 waves also commonly occur:
** One begins on day 3-4
** The second begins on day 12-14
* A normal follicle of 9-13mm is present between day 5-11 before becoming atretic.
* In the second wave, an ovulatory follicle develops, measuring 9-13mm between day 15-20.
* Ovulatory follicle is selected ~3 days prior to ovulation.
* Follicular growth is under the influence of FSH.
* One follicle normally obtains dominance and subsequently ovulates.
* Dominance does not involve inhibin. It is probably due to an intra-ovarian mechanism which does not suppress FSH secretion. Other hormones such as IGF-1 (Insulin-like growth factor-1) may also be involved in follicular growth patterns.
* During dioestrus, there are several large follicles on the ovary. These range in size 0.7-1.5cm in diameter. These follicles do not alter the contours of the ovaries, but cause variation in size.
* During Pro-oestrus and oestrus, the dominant follicle enlarged and ovulation occurs once it is at least 1.9cm.
* The ripening follicle is detectable by rectal palpation during heat.
** It can be felt as a soft, bulging area on the surface of one ovary.
* Ovulation can occur from anywhere on the ovarian surface.
* The shape of the ovary when the corpus luteum develops will depend on the site of ovulation.
* The point of ovulation is usually an avascular area of the follicular wall. Therefore, haemorrage is not seen with ovulation in the cow. However, after ovulation there is congestion around the point of follicular rupture and sometimes there is a small blood clot in the centre of the new corpus luteum.
==== Crpus Luteum of the Oestrous Cycle ====
==== Crpus Luteum of the Oestrous Cycle ====