Final answer:
b.Oxytocin is the hormone responsible for the contractions during labor. It stimulates uterine contractions and dilation of the cervix.
Step-by-step explanation:
Oxytocin is the hormone primarily responsible for the contractions during labor. When fetal development is complete, oxytocin stimulates uterine contractions and dilation of the cervix. Throughout most of pregnancy, oxytocin hormone receptors are not expressed at high levels in the uterus. However, toward the end of pregnancy, the synthesis of oxytocin receptors in the uterus increases, and the smooth muscle cells of the uterus become more sensitive to its effects.
Oxytocin is continually released throughout childbirth through a positive feedback mechanism. It prompts uterine contractions that push the fetal head toward the cervix, and cervical stretching stimulates additional oxytocin synthesis and release. This increases the intensity and effectiveness of uterine contractions and prompts additional dilation of the cervix. The feedback loop continues until birth.
The hormone primarily responsible for stimulating uterine contractions during baby delivery is oxytocin. Oxytocin stimulates the smooth muscle cells of the uterus, causing them to contract. This process begins towards the end of the third trimester when estrogen stimulates the development of oxytocin receptors on the uterine wall.
As the fetus reorients and the cervix stretches, nerve impulses trigger the release of oxytocin from the posterior pituitary. This causes uterine contractions which, through a positive feedback mechanism, intensify and increase in force until the baby and placenta are expelled.