Pregnancy, placenta, parturition and lactation
Chorionic villi and uterine tissue form the placenta, which feeds the foetus and makes hormones. After about 9 months, oxytocin drives birth, and mammary glands make milk.
The placenta
- After implantation, finger-like chorionic villi grow out of the trophoblast. They are surrounded by uterine tissue and maternal blood.
- The villi and uterine tissue interlock to form the placenta, a structural and functional unit between the foetus and the mother.
- It supplies oxygen and nutrients to the embryo and removes carbon dioxide and excretory wastes.
- The umbilical cord joins the placenta to the embryo and carries substances to and from it.
- The placenta is also an endocrine tissue. It makes hCG (human chorionic gonadotropin), hPL (human placental lactogen), estrogens and progestogens. Late in pregnancy, the ovary also secretes relaxin.
- Levels of estrogens, progestogens, cortisol, prolactin and thyroxine also rise several times in the mother's blood. This supports foetal growth and keeps the pregnancy going.
Germ layers and stem cells
Soon after implantation, the inner cell mass forms an outer ectoderm and an inner endoderm. A mesoderm then appears between them. These three germ layers give rise to all the tissues and organs of the adult. The inner cell mass also holds stem cells, which can give rise to all tissues and organs.
Month by month: development of the foetus
| Time | Milestone |
|---|---|
| After 1 month | The embryo's heart forms. Your textbook notes that hearing the heart sound with a stethoscope is the first sign of the growing foetus |
| End of 2nd month | Limbs and digits develop |
| End of 12 weeks (first trimester) | Most major organ systems are formed; limbs and external genital organs are well developed |
| 5th month | First movements of the foetus; hair appears on the head |
| End of about 24 weeks (second trimester) | Body covered with fine hair; eyelids separate; eyelashes form |
| End of 9 months | The foetus is fully developed and ready for delivery |
Parturition (childbirth)
- 1At the end of about 9 months (the gestation period), signals from the fully developed foetus and the placenta start mild uterine contractions. This is the foetal ejection reflex.
- 2The reflex triggers release of oxytocin from the mother's pituitary.
- 3Oxytocin acts on the uterine muscle and causes stronger contractions.This is why doctors may give oxytocin to induce delivery
- 4★Stronger contractions cause more oxytocin to be released. This loop repeats, making the contractions stronger and stronger.
- 5The baby is pushed out of the uterus through the birth canal. Soon after, the placenta is also expelled.
★ key step
Lactation
- The mammary glands differentiate during pregnancy and start making milk towards its end. Milk production is called lactation.
- The milk of the first few days is colostrum. It contains several antibodies that help the newborn resist infection.
- Doctors recommend breastfeeding during the early months to bring up a healthy baby.
Doctors advise giving the newborn colostrum, the thick yellowish first milk, soon after birth. Some families throw it away out of old custom, but its antibodies are the baby's first protection against infection.
3 marks: “What is the placenta? Write its functions, including the hormones it makes.” Structural and functional unit between foetus and mother, formed by chorionic villi and uterine tissue. Supplies oxygen and nutrients, removes carbon dioxide and wastes; endocrine tissue making hCG, hPL, estrogens and progestogens.
2 marks: “What is the foetal ejection reflex? What is the role of oxytocin in parturition?” Mild uterine contractions started by signals from the mature foetus and placenta. They trigger oxytocin release; oxytocin causes stronger contractions, which release more oxytocin, until the baby is delivered.
1 marks: “Why is colostrum important for a newborn baby?” It contains antibodies that help the baby resist infections.
C-P-R keeps a pregnancy going: hCG, hPL and Relaxin, made only during pregnancy.