Difference between revisions of "Parturition Endocrine Control - Anatomy & Physiology"

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'''''Regulation of Prostaglandins'''''
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== Introduction ==
 
  
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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.
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The [[Female_Reproductive_Tract_-The_Uterus|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.
  
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== Regulation of Prostaglandins ==
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* Prostaglandins are synthesized from '''Arachadonic Acid''', which is derived from '''Glycerophospholipids''' by the enzyme '''Phospholipase A2''' (PLA2).
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** '''Oestrogen''' liberates Phospholipase A2 from lysosomes.
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** '''Progesterone''' stabilises lysosomes, so Phospholipase A2 cannot be liberated from lysosomes.
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* An increase in '''Oestrogen:Progesterone ratio''' increases prostaglandin production.
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* The increase in '''Oestradiol''' (bioactive oestrogen) also increases expression of '''endometrial Oxytocin receptors'''.
  
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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 them. An increase in '''oestrogen:progesterone ratio''' increases prostaglandin production. The increase in '''oestradiol''' (bioactive oestrogen) also increases expression of '''endometrial oxytocin receptors'''.
 
  
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== Regulation of Oxytocin ==
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'''''Regulation of Oxytocin'''''
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[[Image:Parturition Cascade.jpg|thumb|right|250px|The Parturition Cascade, Copyright RVC 2008]]
 
  
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Details of oxytocin synthesis and secretion may be found in [[Pituitary_Gland_- Anatomy & Physiology#Oxytocin|pituitary gland]] page.
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Details of Oxytocin Synthesis and Secretion may be found [[Endocrine_System_-_Pituitary_Gland_-_Anatomy_%26_Physiology#Oxytocin|here]]
  
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Oxytocin acts to increase [[Uterine Contraction - Anatomy & Physiology|myometrial contraction]] (positive feedback) and prostaglandin release.
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* Oxytocin acts to:
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** Increase [[Parturition_-_Coordinated_Myometrial_Contraction_-_Anatomy_%26_Physiology|myometrial contraction]] (positive feedback)
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** Increase Prostaglandin release
  
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=== Ferguson Reflex ===
 
  
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The ferguson 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 exhibiting positive feedback. Oxytocin concentrations continue to rise until the foetus is expelled, thus the cervical stimulation ceases.
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'''Furgesson Reflex'''
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* Neuroendocrine reflex
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* Oxytocin is released in response to cervical stimulation by the foetus.
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* Oxytocin release causes further synthesis and secretion of oxytocin, thus exibiting positive feedback.
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* Oxytocin concentrations continue to rise until the foetus is expelled, thus the cervical stimulation ceases.
  
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=== Role of Relaxin ===
 
  
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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, thus preparing the birth canal so that the passage of the foetus can occur with relative ease.
 
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== Role of Oestrodiol Elevation prior to Parturition ==
 
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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 to reduce friction, enabling the foetus to exit the reproductive tract with relative ease.
 
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== Onset of Parturition ==
 
  
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'''''Onset of Parturition'''''
  
 
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{| style="width:75%; height:200px" border="1"
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''Species that depend on the Corpus Luteum to produce progesterone throughout pregnancy (Goat, Cow, Sow, Bitch)''
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* The foetus initiates parturition.
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* For parturition to occur, progesterone production by the Corpus Luteum must be terminated.
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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]].
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* 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 the Corpus Luteum==
 
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The goat, cow, sow and bitch depend on the corpus luteum.
 
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[[Image:Endocrine Control of Parturition 1.jpg|thumb|center|250px|The Onset of Parturition, Copyright RVC 2008]]
 
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[[Image:Endocrine Control of Parturition 3.jpg|thumb|center|250px|The Onset of Parturition, Copyright RVC 2008]]
 
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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.
 
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=== Species that depend on Placental Progesterone===
 
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In late pregnancy, the ewe, guinea pig, queen and mare depend on placental progesterone.
 
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[[Image:Endocrine Control of Parturition 4.jpg|thumb|center|250px|The Onset of Parturition, Copyright RVC 2008]]
 
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[[Image:Endocrine Control of Parturition 5.jpg|thumb|center|250px|The Onset of Parturition, Copyright RVC 2008]]
 
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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.
 
  
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{{OpenPages}}
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''Species that depend on Placental Progesterone in late pregnancy (Ewe,Guinea Pig,Queen,Mare)''
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[[Category:Parturition]]
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* 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.
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[[Category:Endocrine System - Anatomy & Physiology]]
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* Foetal Cortisol causes upregulation of the enzymes '''17α Hydroxylase, C17-C20-lyase and Aromatase''' in order to increase the Oestrogen:Progesterone ratio.
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[[Category:A&P Done]]
 

Revision as of 07:38, 8 July 2008

Regulation of Prostaglandins

The 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

Details of Oxytocin Synthesis and Secretion may be found here


Furgesson Reflex

  • Neuroendocrine reflex
  • 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.


Onset of Parturition

Species Ewe Horse Queen Goat Sow Cow
% of pregnancy when the Corpus Luteum is the principle source of Progesterone 37 61 79 100 100 100
% of pregnancy when the Placenta is the principle source of Progesterone 63 39 21 0 0 0


Species that depend on the Corpus Luteum to produce progesterone throughout pregnancy (Goat, Cow, Sow, Bitch)

  • 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 leades to a rise in foetal ACTH. The rise in ACTH causes production of Cortisol from the foetal 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.


Species that depend on Placental Progesterone in late pregnancy (Ewe,Guinea Pig,Queen,Mare)

  • 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.
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