Question

Uterine smooth muscle cells are sensitive to the hormone oxytocin. When oxytocin binds to its receptors on the uterine cell surface, the cell produces second messengers that lead to contraction of uterine smooth muscle cells. During pregnancy, estrogen (a hormone made from cholesterol) levels continually rise, increasing production of oxytocin receptors on uterine cells. At the time of labor and birth, oxytocin is released in large amounts due to stretching of the uterine cervix. High levels of oxytocin promote strong enough uterine contractions to expel the baby out of the uterus.

For oxytocin, what causes its release?
a) Hormonal stimuli arriving in the hypophyseal portal system
b) Humoral stimuli from circulating levels of estrogen
c) Neural stimuli onto hypothalamic cells

Answer 1

Oxytocin is released during childbirth in response to neural stimuli from the stretching of the cervix, leading to the stronger contractions of the uterus in a positive feedback loop.

Step-by-step explanation:

The hormone oxytocin is released during childbirth largely in response to neural stimuli. Specifically, the stretching of the cervix as the baby moves through the birth canal activates stretch-sensitive nerve cells. These cells send signals to the brain, which then triggers the hypothalamus to signal the posterior pituitary to release oxytocin into the bloodstream. The released oxytocin then binds to receptors on the uterine smooth muscle cells, promoting stronger contractions. This forms a positive feedback loop, where the contractions cause further stretching of the cervix, leading to increased release of oxytocin, which in turn causes even stronger contractions. This cycle continues until the baby is born, ceasing the stretching of the cervix and thus the stimulus for oxytocin release.