== Species that depend on the Corpus Luteum to produce progesterone throughout pregnancy (Goat, Cow, Sow, Bitch) ==
== Species that depend on the Corpus Luteum to produce progesterone throughout pregnancy (Goat, Cow, Sow, Bitch) ==
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[[Image:Endocrine Control of Parturition 1.jpg|thumb|right|150px|The Onset of Parturition, Copyright RVC 2008]]
* The foetus initiates parturition.
* The foetus initiates parturition.
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* As the foetus grows in a restrictive environment it becomes stressed. Stress leades to a rise in foetal [[Endocrine_System_-_Pituitary_Gland_-_Anatomy_%26_Physiology#Hormones_of_the_Anterior_Pituitary_Gland|ACTH]]. The rise in ACTH causes production of Cortisol from the foetal [[Endocrine_System_-_Adrenal_Glands_-_Anatomy_%26_Physiology|Adrenal Glands]].
* As the foetus grows in a restrictive environment it becomes stressed. Stress leades to a rise in foetal [[Endocrine_System_-_Pituitary_Gland_-_Anatomy_%26_Physiology#Hormones_of_the_Anterior_Pituitary_Gland|ACTH]]. The rise in ACTH causes production of Cortisol from the foetal [[Endocrine_System_-_Adrenal_Glands_-_Anatomy_%26_Physiology|Adrenal Glands]].
* The rise in foetal cortisol leased to an increased Oestrogen:Progesterone ratio by upregulating '''Aromatase''' enzymes which convert Androgens to Oestrogens. Cortisol also reduces Progesterone production.
* The rise in foetal cortisol leased to an increased Oestrogen:Progesterone ratio by upregulating '''Aromatase''' enzymes which convert Androgens to Oestrogens. Cortisol also reduces Progesterone production.
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== Species that depend on Placental Progesterone in late pregnancy (Ewe,Guinea Pig,Queen,Mare) ==
== Species that depend on Placental Progesterone in late pregnancy (Ewe,Guinea Pig,Queen,Mare) ==