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==Introduction==

==Introduction==

The basic function of the [[Cervix - Anatomy & Physiology|cervix]] during pregnancy is to retain the foetus within the uterus and to maintain the internal environment of the uterus by preventing the external environment accessing the uterus. Therefore the cervix regulates the passage to and from the uterine cavity. This ensures that any micro-organisms within the external environment are unable to access the uterus. During pregnancy the [[Uterus - Anatomy & Physiology|uterine body]] becomes distended whilst stretch resistant tissues allow the cervix to be maintained in a closed state.  For the foetus to move out of the uterus, the cervix must soften or 'ripen'.

The basic function of the [[Cervix - Anatomy & Physiology|cervix]] during pregnancy is to retain the foetus within the uterus and to maintain the internal environment of the uterus by preventing the external environment accessing the uterus. Therefore the cervix regulates the passage to and from the uterine cavity. This ensures that any micro-organisms within the external environment are unable to enter the uterus. During pregnancy the [[Uterus - Anatomy & Physiology|uterine body]] becomes distended whilst stretch resistant tissues allow the cervix to be maintained in a closed state.  For the foetus to move out of the uterus, the cervix must soften or 'ripen'.

==Cervix Structure==

==Cervix Structure==

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The texture of the cervical tissues is influenced by the relative levels of oestogen and progesterone and therefore is changable dependant on the stage of the oestrous cycle. The mucous membrane of the cervix is highly folded and contains mucin producing cells. Mucin production increases under the influence of oestradiol and helps to lubricate the vagina in preparation for copulation. Mucin is also responsible for the transport of bacteria and foreign bodies away from the uterus. During the luteal phase and during pregnancy small levels of mucin are produced under the influence of progesterone to help form a 'cervical plug'. This plug ensures that the external environment is unable to penetrate the uterus.  

The texture of the cervical tissues is influenced by the relative levels of oestogen and progesterone and therefore are changable dependant on the stage of the oestrous cycle. The mucous membrane of the cervix is highly folded and contains mucin producing cells. Mucin production increases under the influence of oestradiol and helps to lubricate the vagina in preparation for copulation. Mucin is also responsible for the transport of bacteria and foreign bodies away from the uterus. During the luteal phase and during pregnancy small levels of mucin are produced under the influence of progesterone to help form a 'cervical plug'. This plug ensures that the external environment is unable to penetrate the uterus.  

===Cervical Species Differences===

===Cervical Species Differences===

In ruminants the cervical mucus is expelled from the vagina during oestrous and is known as 'bulling string'. Bulling string therefore indicates that animal is in oestrous and should be mated.

In ruminants the cervical mucus is expelled from the vagina during oestrous and is known as 'bulling string'. Bulling string therefore indicates that animal is in oestrous and should be mated.

==Cervical Softening==

==Cervical Softening==

A number of variables during pregnancy lead to the initiation of contractions of the myometrium including oxytocin, prostaglandins and neural inputs from the autonomic nervous system. These contractions of the myometrium lead to an increased pressure within the amniotic fluid. These contractions trigger a series of events that lead to the cervix becoming flexible and gradually beginning to dilate. As the force of the contractions increases, the cervix will open completely. Much of the activity related to the initiation of contractions is initiated by fetal stress resulting in an increased production of fetal cortisol. The effects listed below are all linked to the initial increase in fetal cortisol in some way.

A number of variables during pregnancy lead to the initiation of contractions of the myometrium including oxytocin, prostaglandins and neural inputs from the autonomic nervous system. These contractions of the myometrium lead to an increased pressure within the amniotic fluid. These contractions trigger a series of events that lead to the cervix becoming flexible and gradually beginning to dilate. As the force of the contractions increases, the cervix will open completely. Much of the activity related to the initiation of contractions is begun by fetal stress resulting in an increased production of fetal cortisol. The effects listed below are all linked to the initial increase in fetal cortisol in some way.

===Endocrinology===

===Endocrinology===

Immediately prior to birth, the pre-parturition cervix loses firmness. Cervical softening involves two changes in the intracellular matrix; firstly a reduction in the number of collagen fibres and secondly an increase in GAGs to decrease aggregation of the remaining collagen fibres.

Immediately prior to birth, the pre-parturition cervix loses firmness. Cervical softening involves two changes in the intracellular matrix; firstly a reduction in the number of collagen fibres and secondly an increase in GAGs to decrease aggregation of the remaining collagen fibres.

Relaxin is produced by the ovaries and the placenta and together with progesterone prevent uterine contractions throughout the pregnancy. However, relaxin also aids in the loosening of tissues in the cervix and pelvic ligaments to loosen pre-parturition. Relaxin and PGE2 work in combination on the cervix.  

Relaxin is produced by the ovaries and the placenta and together with progesterone prevent uterine contractions throughout the pregnancy. However, relaxin also aids in the loosening of tissues in the cervix and pelvic ligaments to loosen pre-parturition. Relaxin and PGE2 work in combination on the cervix.  

===Progesterone Production===

===Progesterone Production===

The initiation of myometrial contractions via fetal cortisol results in cells within the uterus and the placenta undergoing a degree of stretch. This stretching is thought to activate several systems within the cells resulting in the production of progesterone. Stretching can increase the avaliability of cyclo-oxygenase 2 or COX-2 which is part of a chain of reactions converting arachadonic acid to PGE2 and PGF2α resulting in an increased cellular output. Both of these types of prostaglandin potentiate oxytocin once outside the cell and this inturn potentiates an increase in the level of arachadonic acid, thus scaling up production in the entire system. Secondly the stretching the cell also results in increased expression of oxytocin receptors in the cell surface resulting in a greater impact on the cell for a given level of oxytocin, further upregulating the system.  

The initiation of myometrial contractions via fetal cortisol results in cells within the uterus and the placenta undergoing a degree of stretch. This stretching is thought to activate several systems within the cells resulting in the production of progesterone. Stretching can increase the avaliability of cyclo-oxygenase 2 or COX-2, which is part of a chain of reactions converting arachadonic acid to PGE2 and PGF2α resulting in an increased cellular output. Both of these types of prostaglandin potentiate oxytocin once outside the cell and this inturn potentiates an increase in the level of arachadonic acid, thus scaling up production in the entire system. Secondly the stretching within the cell also results in increased expression of oxytocin receptors in the cell surface resulting in a greater impact on the cell for a given level of oxytocin, further upregulating the system.  

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

[[Category:Parturition]][[Category:To Do - Review]]