Physiology of normal labour complete into two steps -
1. Uterine contraction.
2. Retraction.
Uterine contraction -
During contraction, uterus becomes hard and somewhat pushed anteriorly
to make the long axis of the uterus in the line with that of pelvic axis.
Simultaneously, the patient experiences pain which is situated more on the
hypogastric region, often radiating to the thighs.
Probable cause of pain are -
- Myometrial hypoxia during contractions.
- Stretching of the peritoneum over the fundus.
- Stretching of the cervix during dilatation.
- Compression of the nerve ganglion.
The pain of uterine contractions is distributed along the cutaneous nerve
distribution of T10 to L1.
Intensity - The intensity of uterine contractions describes the degree of uterine
systole. The intensity gradually increases with advancement of labour until it
becomes maximum in the second stage during delivery of the baby. Intrauterine
pressure is raised to 40-50 mm Hg during first stage and about 100-120 mm Hg
in the second stage of labour during contractions.
Duration - In the first stage, the contractions last for about 30 second initially but
gradually increases in duration with the progress of labour. Thus in the second stage,
the contractions last longer than in the first stage.
Frequency - In the early stage of labour, the contractions come at intervals of ten to
fifteen minutes. The intervals gradually shorten with advancement of labour until in
the second stage, when it comes every two or three minutes.
Retraction -
Retraction is a phenomenon of the uterus in labour in which the muscle fibers are
permanently shortened. Unlike any other muscle of the body, the uterine muscles
have this property to become shortened once and for all. Contraction is a temporary
reduction in length of the fibers, which attain their full length during relaxation. In contrast,
retraction results in permanent shortening and the fibers are shortened once and for all.
The net effect of retraction on normal labour are -
- Essential property in the formation of lower uterine segment and dilatation and
effacement up of the cervix.
- To maintain the advancement of the presenting part made by the uterine contractions
and to help in ultimate expulsion of the fetus.
- To reduce the surface area of the uterus favouring separation of placenta.
- Effective haemostasis after the separation of the placenta.
2. Retraction.
Uterine contraction -
During contraction, uterus becomes hard and somewhat pushed anteriorly
to make the long axis of the uterus in the line with that of pelvic axis.
Simultaneously, the patient experiences pain which is situated more on the
hypogastric region, often radiating to the thighs.
Probable cause of pain are -
- Myometrial hypoxia during contractions.
- Stretching of the peritoneum over the fundus.
- Stretching of the cervix during dilatation.
- Compression of the nerve ganglion.
The pain of uterine contractions is distributed along the cutaneous nerve
distribution of T10 to L1.
Intensity - The intensity of uterine contractions describes the degree of uterine
systole. The intensity gradually increases with advancement of labour until it
becomes maximum in the second stage during delivery of the baby. Intrauterine
pressure is raised to 40-50 mm Hg during first stage and about 100-120 mm Hg
in the second stage of labour during contractions.
Duration - In the first stage, the contractions last for about 30 second initially but
gradually increases in duration with the progress of labour. Thus in the second stage,
the contractions last longer than in the first stage.
Frequency - In the early stage of labour, the contractions come at intervals of ten to
fifteen minutes. The intervals gradually shorten with advancement of labour until in
the second stage, when it comes every two or three minutes.
Retraction -
Retraction is a phenomenon of the uterus in labour in which the muscle fibers are
permanently shortened. Unlike any other muscle of the body, the uterine muscles
have this property to become shortened once and for all. Contraction is a temporary
reduction in length of the fibers, which attain their full length during relaxation. In contrast,
retraction results in permanent shortening and the fibers are shortened once and for all.
The net effect of retraction on normal labour are -
- Essential property in the formation of lower uterine segment and dilatation and
effacement up of the cervix.
- To maintain the advancement of the presenting part made by the uterine contractions
and to help in ultimate expulsion of the fetus.
- To reduce the surface area of the uterus favouring separation of placenta.
- Effective haemostasis after the separation of the placenta.
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