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Oestrous Cycle - Anatomy & Physiology (view source)
Revision as of 11:06, 11 September 2008
, 11:06, 11 September 2008→Cyclic Changes in the Ovaries
=== Cyclic Changes in the Ovaries ===
=== Cyclic Changes in the Ovaries ===
* The ovaries of a mature, cyclic sow are large and look like mullberries.
** Surface lobulations are due to elevations of large follicles and corpora lutea.
* When mature, follicles reach a diameter of 0.8-1cm.
* When mature, corpora lutea reach a diameter of 1-1.3 cm.
* It is difficult to study follicular dynamics in a sow because it is hard to identify a single follicle due to the large number present.
* Except during the follicular phase, there is continuous proliferation and atresia of follicles.
* There is normally a pool of about 50 follicles 2-5mm in diameter at any one time.
* Between day 14-16 of the cycle,there is follicular recruitment under the influence of gonadotrophins.
** This is possible due to a decline in progesterone, and subsequent withdrawal of negative feedback.
* A large number of these recruited follicles are destined for ovuation.
* At day 21-22 it is possible to identify the pre-ovulatory population.
* The growth of pre-ovulatory follicles during this follicular phase is associated with rapid atresia of small follicles. There is also a block to replacement of atretic follicles within the proliferating pool, so there must be some ovarian control mechanism. What exactly this mechanism is is currently unknown, but various substances have been proposed, including:
** Steroids
** Growth factors
** Growth factor binding proteins
** 'Follicle regulatory protein'
* The ripe follicle is a 'se-shell pink' colour. It has a fine network of surface blood vessels and one point which is very transparent. This transparent point indicates the site of imminent ovulation.
* Haemorrhagic follicles are common.
* After ovulation, a considerable number of follicles ~ 0.4cm remain on the ovary. Some of these enlarge gradually to 0.9cm by day 18.
* Immediately after ovulation, the ruptured follicle is seen as a congested depression on the ovary.
* Accumulation of blood clot soon gives the ruptured follicle a conical shape.
=== Endocrine Changes during the Oestrous Cycle ===
=== Endocrine Changes during the Oestrous Cycle ===