During labor, distension of the cervix and vagina triggers reflex contraction of the uterus and continued oxytocin release until delivery. What is the correct classification of this reflex arc?

• A A simple spinal reflex mediated entirely below the foramen magnum
• B An endocrine feedback loop mediated by placental CRH
• C A humoral reflex driven by falling progesterone levels alone
• D A neuroendocrine reflex requiring hypothalamic integration and posterior pituitary release ✓

Explanation

The Ferguson reflex is a positive-feedback neuroendocrine reflex. Afferent impulses from cervical stretch ascend to the hypothalamus, where they stimulate magnocellular neurons of the supraoptic and paraventricular nuclei to fire, releasing stored oxytocin from the posterior pituitary. Oxytocin strengthens uterine contractions, which further stretches the cervix, sustaining the loop until delivery removes the stimulus. It cannot be completed by spinal circuits alone because the efferent limb is hormonal, carried by blood-borne oxytocin.

Reference: Ganong's Review of Medical Physiology, 26th ed.

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Written and medically reviewed by the StethoPrep medical team.