Changes

The foetus triggers the onset of parturition, by initiating a cascade of complex endocrine/biochemical events. The foetal '''hypothalamo-pituitary-adrenal axis''' is obligatory for the initiation of parturition.

The foetus triggers the onset of parturition by initiating a cascade of complex endocrine/biochemical events. The foetal hypothalamo-pituitary-adrenal axis is obligatory for the initiation of parturition.

== Regulation of Prostaglandins ==

== Regulation of Prostaglandins ==

 

The [[Uterus - Anatomy & Physiology|uterus]] is an important site of prostaglandin synthesis. During pregnancy, the presence of the foetus inhibits the production of prostaglandins in order to prevent luteolysis. At parturition, an increase in prostaglandin synthesis is required. Prostaglandins are synthesized from '''arachadonic acid''', which is derived from '''glycerophospholipids''' by the enzyme '''phospholipase A2''' (PLA2). '''Oestrogen''' liberates phospholipase A2 from lysosomes. '''Progesterone''' stabilises lysosomes, so phospholipase A2 cannot be liberated from lysosomes. An increase in '''oestrogen:progesterone ratio''' increases prostaglandin production. The increase in '''oestradiol''' (bioactive oestrogen) also increases expression of '''endometrial oxytocin receptors'''.

The [[Uterus - Anatomy & Physiology|uterus]] is an important site of prostaglandin synthesis. During pregnancy, the presence of the foetus inhibits the production of prostaglandins in order to prevent luteolysis. At parturition, an increase in prostaglandin synthesis is required.

 

* Prostaglandins are synthesized from '''arachadonic acid''', which is derived from '''glycerophospholipids''' by the enzyme '''phospholipase A2''' (PLA2).

** '''Oestrogen''' liberates phospholipase A2 from lysosomes.

** '''Progesterone''' stabilises lysosomes, so phospholipase A2 cannot be liberated from lysosomes.

* An increase in '''oestrogen:progesterone ratio''' increases prostaglandin production.

* The increase in '''oestradiol''' (bioactive oestrogen) also increases expression of '''endometrial oxytocin receptors'''.

== Regulation of Oxytocin ==

== Regulation of Oxytocin ==

Details of oxytocin synthesis and secretion may be found [[Pituitary_Gland_- Anatomy & Physiology#Oxytocin|here]].

 

Details of Oxytocin Synthesis and Secretion may be found [[Pituitary_Gland_- Anatomy & Physiology#Oxytocin|here]].

 

 

=== Furgesson Reflex ===

=== Furgesson Reflex ===

* Neuroendocrine reflex

The furgesson reflex is a neuroendocrine reflex. Oxytocin is released in response to cervical stimulation by the foetus, this causes further synthesis and secretion of oxytocin, thus exibiting positive feedback. Oxytocin concentrations continue to rise until the foetus is expelled, thus the cervical stimulation ceases.

* Oxytocin is released in response to cervical stimulation by the foetus.

* Oxytocin release causes further synthesis and secretion of oxytocin, thus exibiting positive feedback.

* Oxytocin concentrations continue to rise until the foetus is expelled, thus the cervical stimulation ceases.

 

=== Role of Relaxin ===

=== Role of Relaxin ===

* Glycoprotein hormone  

Relaxin is a glycoprotein hormone. It is produced by either the, corpus luteum or placenta depending on species. Its synthesis is stimulated by '''PGF2α'''. This causes softening of the connective tissue in the [[Cervix - Anatomy & Physiology|cervix]] and promotes elasticity of the pelvic ligaments. This prepares the birth canal, so that the passage of the foetus can occur with relative ease.

* Produced by either the corpus luteum or placenta depending on species.

* Synthesis is stimulated by '''PGF2α'''

* Causes softening of the connective tissue in the [[Cervix - Anatomy & Physiology|cervix]].

* Promotes elasticity of pelvic ligaments.

* Prepares the birth canal by loosening supportive tissues so that the passage of the foetus can occur with relative ease.

== Role of Oestrodiol Elevation prior to Parturition ==

== Role of Oestrodiol Elevation prior to Parturition ==

* Initiates secretory activity of the reproductive trace, particularly the [[Cervix - Anatomy & Physiology|cervix]].

This elevation initiates the secretory activity of the reproductive tract, particularly the [[Cervix - Anatomy & Physiology|cervix]], resulting in the [[Cervix - Anatomy & Physiology|cervix]] and [[Vagina and Vestibule - Anatomy & Physiology|vagina]] producing mucus. This washes out the cervical seal of pregnancy and lubricates the cervical canal and vagina and reduces friction, enabling the foetus to exit the reproductive tract with relative ease.

* Causes the [[Cervix - Anatomy & Physiology|cervix]] and [[Vagina and Vestibule - Anatomy & Physiology|vagina]] to produce mucus.

** Washes out the cervical seal of pregnancy.

** Lubricates the cervical canal and vagina

** Reduces friction, enabling the foetus to exit the reproductive tract with relative ease.

== Onset of Parturition ==

== Onset of Parturition ==

=== Species that depend on the Corpus Luteum===

==Species that depend on the Corpus Luteum==

[[Image:Endocrine Control of Parturition 1.jpg|thumb|right|150px|The Onset of Parturition, Copyright RVC 2008]]

The goat, cow, sow and bitch depend on the corpus luteum.

[[Image:Endocrine Control of Parturition 3.jpg|thumb|right|150px|The Onset of Parturition, Copyright RVC 2008]]

[[Image:Endocrine Control of Parturition 1.jpg|thumb|right|250px|The Onset of Parturition, Copyright RVC 2008]]

* The foetus initiates parturition.

* For parturition to occur, progesterone production by the corpus luteum must be terminated.

 

* As the foetus grows in a restrictive environment it becomes stressed. Stress leads to a rise in foetal [[Pituitary_Gland_- Anatomy & Physiology#Hormones_of_the_Anterior_Pituitary_Gland|ACTH]]. The rise in ACTH causes production of Cortisol from the foetal [[Adrenal_Glands_- Anatomy & Physiology|adrenal Glands]].

The foetus initiates parturition. For parturition to occur, progesterone production by the corpus luteum must be terminated. As the foetus grows in a restrictive environment, it becomes stressed. Stress leads to a rise in foetal [[Pituitary_Gland_- Anatomy & Physiology#Hormones_of_the_Anterior_Pituitary_Gland|ACTH]]. The rise in ACTH causes production of cortisol from the foetal [[Adrenal_Glands_- Anatomy & Physiology|adrenal glands]]. The rise in foetal cortisol leads 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.

=== Species that depend on Placental Progesterone===

=== Species that depend on Placental Progesterone===

[[Image:Endocrine Control of Parturition 4.jpg|thumb|right|150px|The Onset of Parturition, Copyright RVC 2008]]

 

[[Image:Endocrine Control of Parturition 4.jpg|thumb|right|250px|The Onset of Parturition, Copyright RVC 2008]]

[[Image:Endocrine Control of Parturition 5.jpg|thumb|right|150px|The Onset of Parturition, Copyright RVC 2008]]

[[Image:Endocrine Control of Parturition 5.jpg|thumb|right|150px|The Onset of Parturition, Copyright RVC 2008]]

* As previously explained, parturition is dependent on a rise in foetal Cortisol. However, in this case, the rise in foetal cortisol leads to a decrease in '''maternal''' progesterone.

As previously explained, parturition is dependent on a rise in foetal cortisol. However, in this case, the rise in foetal cortisol leads to a decrease in '''maternal''' progesterone. Foetal cortisol causes upregulation of the enzymes, '''17α hydroxylase, C17-C20-lyase and aromatase''' in order to increase the oestrogen:progesterone ratio.

* Foetal cortisol causes upregulation of the enzymes '''17α hydroxylase, C17-C20-lyase and aromatase''' in order to increase the oestrogen:progesterone ratio.

[[Category:Parturition]]

[[Category:Parturition]]

[[Category:Endocrine System - Anatomy & Physiology]]

[[Category:Endocrine System - Anatomy & Physiology]]

[[Category:To Do - A&P]]

[[Category:To Do - AimeeHicks]]