Summary
Hormonal changes and contractions expel the baby, with oxytocin driving labour.
In depth
Oxytocin, prostaglandins and a positive feedback loop strengthen contractions; stages: dilation, delivery of the baby, delivery of the placenta. Cortisol from the fetus helps prepare lungs and initiate labour.
Fetal lung maturity and cortisol help trigger labour. After birth the first breath inflates lungs and circulation changes. Oxytocin also helps expel the placenta and contract the uterus to limit bleeding.
Example: skin-to-skin contact supports bonding and breastfeeding.
Birth (parturition) is controlled by a positive feedback loop. Pressure of the baby's head on the cervix sends nerve signals to the hypothalamus, causing the posterior pituitary to release oxytocin, which strengthens uterine contractions, which in turn increases pressure; the loop ends with delivery.
Late pregnancy changes include falling progesterone relative to oestrogen, more oxytocin receptors and prostaglandin release. Labour has three stages: dilation of the cervix, delivery of the baby and expulsion of the placenta. At birth, the baby's lungs inflate and fetal shunts close.
Example: synthetic oxytocin (Pitocin) can induce labour.
Frequently asked questions
What is Birth?
Hormonal changes and contractions expel the baby, with oxytocin driving labour.
Which area of biology covers Birth, and how advanced is it?
Birth is one of the 54 topics in Developmental Biology. It is rated Beginner, so it suits learners who are starting out in biology. Related topics in this area include Fetal Development, Placenta, Embryo.
Why does Birth matter?
It is a standard textbook example of positive feedback.
Can you give an example of Birth?
Synthetic oxytocin (Pitocin) can induce labour.
What should I learn before Birth?
Birth is a Beginner topic, so no earlier topic is required. Other Beginner topics in Developmental Biology that pair well with it include Fertilisation, Zygote, Embryo.
What topics are related to Birth?
The closest topics to Birth are Fetal Development, Placenta, Embryo, Ageing and Development. Comparing them side by side is a good way to see how the ideas connect.
How can I check that I understand Birth?
Read the summary and the in-depth section, then use the quick check on the interactive lesson for Birth. To practise the whole of Developmental Biology, use the Developmental Biology quiz.
How is Birth different from Fetal Development?
Birth: Hormonal changes and contractions expel the baby, with oxytocin driving labour. Fetal Development: In humans the embryo becomes a fetus after eight weeks, growing until birth around nine months. Read both side by side and note what each one explains.
How should I study Birth step by step?
First, read the summary and write the definition in your own words. Second, read the in-depth section and note any example. Third, compare it with Fetal Development and explain the difference aloud. Finally, take the Developmental Biology quiz and come back to this page for any question you miss.