Uterine action
Each uterine contraction starts in the fundus near one of the cornua and spread across and downwards. The contraction lasts longest in the fundus wars. The contraction lasts longest in the fundus where it is also most intense, but the peak is reached simultaneously over the whole uterus and the contraction fades from all parts together. This pattern permits the cervix to dilate and the strongly contracting fundus to expel the fetus.
Contraction and retraction
During labour the contraction does not pass off entirely , but muscle fibres retain some of the shortening of contraction instead of becoming completely relaxed. This is termed retraction. The upper segment of the uterus becomes gradually shorter and thicker and its cavity diminishes.. uterine contractions may occur every 15-20min and may last for about 30s. By the end of the first stage , they occur at 2-3min intervals, last for 50-60sec and are very powerful.
-By the end of pregnancy, the body of uterus is described as having devided into two segments. When the labour begins the retracted longitudinal fibres in the upper segment causing it to stretch this is aided by the force applied by the descending presenting part.
-the retraction ring known as retraction or bandl’s ring which visible above the symphysis in mechanically obstructed labour when the lower segment thins abnormally. Physiologicl ring gradually rises as the upper uterine segment contracts and retracts and the lower uterine segment thinds out to accommodate the descending fetus
-The cervical canal widens at the level of the internal os, where as the condition of the external os remains unchanged.
-dilatation is the process of enlargement of the os uteri from a tightly closed aperture to an opening large enough to permit passage of the fetal mhead. Occurs as a result of uterine action s and the counterpressure applied by either the intact bag of membranes
-show as a result of the dilatation. Woman may see blood stained mucoid discharge a nfew hour before or within labour start