Placenta Structure and Functions

Labour and Birth

• 2-3 weeks prior to birth, the foetus moves into position, with the head pointing down towards the cervix
• High levels of oestrogen in the mother's body cause the pituitary gland to secrete oxytocin, promoting uterine contractions
• Stage 1 of labour: dilation of the cervix; myometrium starts contracting, becoming more frequent and intense, causing the cervix to dilate up to 10cm
• At 10cm, the amniotic fluid is released, and the cervix is fully dilated
• Stage 2: delivery of the baby; powerful contractions of the uterus and abdominal muscles push the baby out through the vagina, usually head first
• Stage 3: expulsion of the placenta, which usually occurs within 20 minutes after birth and lasts for around 15 minutes

Birth Options

• Vaginal birth: natural or assisted with medication
• Caesarean section: surgical delivery, usually performed if there are complications and the mother and/or foetus are at risk

Mammary Glands

• Produce milk; contain milk-secreting glands
• Lactation: milk production stimulated by oestrogen and progesterone, which develop milk glands and ducts
• Oxytocin promotes milk letdown

Placenta

• Develops from chorion and villi that penetrate the endometrium
• Villi provide a large surface area for exchange of substances with maternal blood supply
• Functions:
  • Oxygen and dissolved nutrients pass from mother to foetal blood
  • Waste products pass from foetus to mother for excretion
  • Maternal antibodies pass to foetus, providing passive immunity
  • Acts as a barrier, preventing harmful substances from entering the foetus
  • Produces progesterone and oestrogen, maintaining uterine changes during pregnancy
  • Later in pregnancy, secretes relaxin, which relaxes joints and ligaments for delivery

Amnion and Amniotic Fluid

• Amnion: membrane surrounding the embryo and foetus
• Amniotic fluid: surrounds the foetus, protecting it from external injury and providing a medium for breathing and swallowing movements
• Functions:
  • Supports foetal development
  • Cushions and protects the foetus
  • Holds urine released by the foetus
  • Regulates temperature and prevents dehydration

Umbilical Cord

• Flexible cord connecting the foetus to the placenta
• Contains two umbilical arteries and one umbilical vein
• Umbilical arteries: carry waste from the foetus to the mother's bloodstream
• Umbilical vein: carries oxygenated blood and nutrients from the mother to the foetus

Human Reproduction: Pregnancy and Birth

Copulation and Fertilization

• Copulation: sexual intercourse, transferring sperm into the vagina
• Fertilization: fusion of the sperm nucleus with the egg nucleus, forming a diploid zygote

Gestation (Pregnancy)

• Time between conception and birth (280 days or 40 weeks)
• Embryo and foetus develop in the uterus

Early Development (0-2 months)

• Fertilization: fusion of sperm and egg nuclei
• Blastocyst formation: morula develops into a hollow fluid-filled ball of cells
• Implantation: blastocyst sinks into the endometrium

Early Development (3rd-8th week)

• Formation of embryo and amnion
• Yolk sac forms part of the umbilical cord
• Trophoblast develops into the chorion, forming villi that penetrate the endometrium to form the placenta
• Embryo develops into three layers: ectoderm, endoderm, and mesoderm

Later Development (Foetal period)

• From week 9 to birth, the foetus grows rapidly
• Bones ossify, subcutaneous tissue forms, and antibodies enter the foetus via the placenta
• Foetus turns, with the head pointing towards the cervix