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=== Cyclic Changes in the Vagina ===
 
=== Cyclic Changes in the Vagina ===
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The main variations are in the epithelial cells of the anterior vagina and in the secretory function of the cervical glands.
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* Oestrus: Anterior vaginal epithelium becomes greatly thickened due to cell division and the growth of the tall, columnar, mucus-secreting superficial cells.
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* Dioestrus: Cells of the cranial vaginal epithelium vary from flat to low columnar. Invasion of the vaginal mucosa by leucocytes is maximal 2-5 days after oestrus.
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* Copious secretion of mucus by the cervix and anterior vagina begins 1-2 days before oestrus. 
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* Secretions diminish to the 4th day after oestrus.
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* Mucus is transparent and flows readily.
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* Variations in cervical mucus:
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** During oestrus and for a few days after, crystals are disposed in a distinct aborisation pattern.
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** For the remainder of the cycle this pattern is absent.
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** This pattern, and the amount of cervical mucus depends on oestrogen concentration.
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* Postoestrous vaginal mucus:
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** Floccules of leucocytes
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** Blood is frequently present
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* Hyperaemia of vaginal and cervical mucosae is progressive during pro-oestrus and oestrus.
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* At this time, the protrusion of the cervix into the cranial vagina is relaxed, so that 1-2 fingers can be inserted into the cervical os.
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* During metoestrus, there is a rapid reduction in vascularity.
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* From day 3-5 postoestrus:
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** Mucosa of the cervix  is pale and quiescent. 
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** The external os is constricted.
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** Mucus becomes scanty, sticky and pale yellow/brown.
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* There are also cyclical changes in the vaginal pH:
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** pH falls from 7.0 to 6.72 one day before first signs of behavioural oestrus.
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** At the start of oestrus, pH falls again to 6.54.
    
=== Cyclic Changes in the  Uterus ===
 
=== Cyclic Changes in the  Uterus ===
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