Question

For each aspect of labour A–E, select the most appropriate option from the following list of muscle activities. 

1. Smooth muscle relaxation. 

2. Smooth muscle contraction. 

3. Skeletal muscle relaxation. 

4. Skeletal muscle contraction. 

A. The onset of the first stage of labour is when regular spasms of abdominal pain begin (labour pains). 

B. The onset of the second stage of labour is when the uterine cervix becomes fully dilated. 

C. During the second stage of labour the mother is encouraged to make powerful bearing down/pushing actions to help deliver the baby. 

D. After the third stage of labour which ends with the expulsion of the placenta, the mother may be given oxytocin, or encouraged to put the infant to the breast.

E. During the first stage of labour, the mother is encouraged to avoid bearing down actions and breath-holding so that the baby is not forced against an incompletely dilated cervix.

Answer 1

A. Option 2 Smooth muscle contraction. Labour begins when the state of uterine quiescence is replaced by regular, painful, contractions of the uterine smooth muscle. 

B. Option 1 Smooth muscle relaxation. Full relaxation of the smooth muscle in the uterine cervix sets the stage for passage of the baby; in the body generally, expulsion is achieved by contraction behind and relaxation in front of what is being expelled; in the heart expulsion of contents takes place on a very short time scale, in the bladder and rectum it is longer, and in the uterus the time scale is relatively very long. 

C. Option 4 Skeletal muscle contraction. This is a form of the Valsalva manoeuvre, where abdominal skeletal muscle contracts to favour expiration against a closed glottis; this manoeuvre helps expulsion of abdominal contents when the relevant orifice is open as well as in delivery of the baby, the maneouvre has a part is speeding micturition and defaecation, and in producing vomiting. 

D. Option 2 Smooth muscle contraction. Oxytocin favours powerful contraction of the uterine smooth muscle which helps to limit bleeding after delivery (post-partum haemorrhage); stimulation of the breast by the baby leads to release of endogenous oxytocin from the posterior pituitary. 

E. Option 3 Skeletal muscle relaxation. The mother cannot influence the uterine contractions, but can favour relaxation of the abdominal muscles by avoiding the Valsalva manoeuvre, usually expressed as ‘not pushing down’, but rather breathing shallowly.