Which tissue is a primary target of oxytocin to induce labor?

• A. Uterus
• B. Kidney
• C. Lung
• D. Skin

Answer: (A)

Oxytocin’s main job in inducing labor is to stimulate the uterus, specifically the myometrium, the smooth muscle layer of the uterus. As labor nears, the uterus increases its expression of oxytocin receptors, making it more responsive to circulating oxytocin. When oxytocin binds to these receptors, it activates signaling that raises intracellular calcium in the myometrium, causing rhythmic contractions. These contractions help to dilate the cervix and push the baby downward.

The effect is amplified by the production of prostaglandins and by the formation of gap junctions between myometrial cells, which makes contractions more coordinated and stronger. This creates a positive feedback loop: stronger contractions promote more oxytocin release, driving labor forward.

The other tissues listed don’t mediate labor contractions in a direct, primary way. Oxytocin can play a role in milk ejection from the mammary glands, but when it comes to initiating labor itself, the uterus is the key target.