Changes

'''Parturition''' is the act of giving birth to a baby. It consists of many different stages which interact to provide delivery of child and the [[placenta]]. Childbirth usually occurs after 38 weeks of gestation (in clinical terms 40 weeks since last menstrual period), although children can be born after 24 weeks with some hope of survival (this is known as a preterm birth). Parturition tends to last between 8 hours (in multiparti mothers) to 14 hours (in primipari mothers), although longer labours are not unusual.

'''Parturition''' is the act of giving birth to a baby. It consists of many different stages which interact to provide delivery of child and the [[placenta]]. Childbirth usually occurs after 38 weeks of gestation (in clinical terms 40 weeks since amenorrhea). Parturition tends to last between 8 hours (in multiparti mothers) to 14 hours (in primipari mothers), although longer labours are not unusual.

==Organs Involved==

==Organs Involved==

The primary organ involved is the [[uterus]]. This contains a layer known as the myometrium which contains bundles of non-striated (smooth) muscle as well as connective tissue (collagen), nerves and blood vessels. The muscles of the inner wall of the myometrium are circular, whereas the muscles on the outer wall are longitudinal. During pregnancy this layer increases in mass approximately 20 fold, with hypertrophy increasing from 50um to 500um, hyperplasia increasing and glycogen deposits increasing.  

The primary organ involved is the [[uterus]]. This contains a layer known as the myometrium which contains bundles of non-striated (smooth) muscle as well as connective tissue (collagen), nerves and blood vessels. The muscles of the inner wall of the myometrium are circular, whereas the muscles on the outer wall are longitudinal. During pregnancy this layer increases in mass approximately 20 fold, with hypertrophy increasing from 50 um to 500 um, hyperplasia increasing and glycogen deposits increasing.  

The muscle cells act as a syncytium, in which spontaneous depolarising pacemaker potentials occur. If these are above a certain threshold (known as the action potential) then a wave of calcium is released and a contraction occurs.

The muscle cells act as a syncytium, in which spontaneous depolarising pacemaker potentials occur. If these are above a certain threshold (known as the action potential) then a wave of calcium is released and a contraction occurs.

==Labour==

==Labour==

Labour is the clinical process of parturition. A mother tends to become aware of labour with either 2-4 rapid contractions within a 10 minute period or the breaking of the amniotic membranes (the "water breaking").

Labour is the clinical process of parturition. A mother tends to become aware of labour with either 2-4 rapid contractions within a 10-minute period or the breaking of the amniotic membranes (the "water breaking").

===Regulation===

===Regulation===

===Stages===

===Stages===

'''Stage One''' is associated with the start of painful contractions and the dilating of the cervix. Contractions are initially slow until the cervix reaches a diametre of 3cm, then the increase in speed until the end of stage one, at which point the cervix is at a diametre of approximately 10cm. Each muscle cell does not completely relax, and therefore shortens with each contraction. The retraction ring gradually moves upwards.  

'''Stage One''' is associated with the start of painful contractions and the dilating of the cervix. Contractions are initially slow until the cervix reaches a diametre of 3 cm, then the increase in speed until the end of stage one, at which point the cervix is at a diametre of approximately 10 cm. Each muscle cell does not completely relax, and therefore shortens with each contraction. The retraction ring gradually moves upwards.  

'''Stage Two''' is associated with the delivery of the foetus. As the foetus moves down it is rotated due to the dimensions of the pelvis (ellipsoid laterally at the pelvic inlet, circular in the middle and ellipsoid medially at the pelvic outlet). This generally results in the baby's head facing the mother's rectum. Abdominal contractions assist with the expulsion of the child.

'''Stage Two''' is associated with the delivery of the foetus. As the foetus moves down it is rotated due to the dimensions of the pelvis (ellipsoid laterally at the pelvic inlet, circular in the middle and ellipsoid medially at the pelvic outlet). This generally results in the baby's head facing the mother's rectum. Abdominal contractions assist with the expulsion of the child. A breach birth occurs if the baby is delivered feet first.

'''Stage Three''' is associated with the delivery of the placenta. Because of the importance of completely removing the entire placenta (abandoned villi can result in maternal haemorrhage) this stage is usually assisted with steady traction on the umbilical cord and doses of oxytocin.

'''Stage Three''' is associated with the delivery of the placenta. Because of the importance of completely removing the entire placenta (abandoned villi can result in maternal haemorrhage) this stage is usually assisted with steady traction on the umbilical cord and doses of oxytocin.