Question

Hormone oxytocin at the time to birth acts on uterus by

• A. Stimulating the smooth muscles to contract
• B. Reducing the lumen of uterus
• C. Increasing the movement of foetus
• D. Producing rhythmic movements in uterus

Answer 1

The correct option is A Stimulating the smooth muscles to contract

During birth, prostaglandins initiate the contraction in smooth muscles of uterine wall which makes option D incorrect. The pressure of fetus’s head against the cervix and send signals to make hypothalamus to trigger the release of oxytocin from posterior pituitary. Together, oxytocin (OT) and prostaglandins stimulate strong uterine muscle contraction forcing the fetus downwards. This makes option A correct. Options B and C are incorrect as fetus is expelled out of uterus by strong push of uterine wall contraction; not by reducing the lumen of uterus or by increasing its movement. Correct answer is A.