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Unlock This CourseThe placenta is one of the most amazing organs in the human body. It's temporary, lasting only during pregnancy, yet it performs vital functions that keep a developing baby alive and healthy. Think of it as a biological bridge between mother and baby, allowing essential materials to pass between them whilst keeping their blood supplies separate.
The placenta forms early in pregnancy and grows alongside the baby. By the time a baby is born, the placenta weighs about 500-600 grams and is roughly the size of a dinner plate. It's expelled from the mother's body shortly after birth, which is why it's sometimes called the "afterbirth".
Key Definitions:
The placenta begins forming about 6 days after fertilisation when the blastocyst implants into the uterine wall. The outer layer of the blastocyst, called the trophoblast, develops into the placenta. By week 12 of pregnancy, the placenta is fully formed and functional.
The placenta has a unique structure that allows it to perform its many functions effectively. It consists of both maternal and foetal tissues working together in perfect harmony.
The placenta is made up of several important parts, each with specific roles in supporting the developing baby.
These are tiny, finger-like projections that extend into the mother's blood supply. They massively increase the surface area for exchange between mother and baby - imagine them like the roots of a tree spreading out to absorb nutrients.
Maternal blood flows through spaces around the villi, bringing oxygen and nutrients close to the foetal blood vessels. The two blood supplies never actually mix - they're separated by thin membranes.
Contains two arteries and one vein that transport blood between the foetus and placenta. The vein carries oxygen-rich blood to the baby, whilst the arteries carry deoxygenated blood back to the placenta.
The total surface area of all the chorionic villi in a full-term placenta is approximately 11 square metres - that's about the size of half a tennis court! This enormous surface area ensures efficient exchange of materials between mother and baby.
The placenta is like a multi-purpose life support system for the developing baby. It performs several crucial functions that would normally be carried out by different organs in a fully developed human.
Just like your lungs exchange oxygen and carbon dioxide, the placenta does this job for the foetus. Oxygen from the mother's blood diffuses across the placental membrane into the foetal blood, whilst carbon dioxide moves in the opposite direction to be removed by the mother's lungs.
Oxygen-rich blood from the mother flows around the chorionic villi. The oxygen dissolves and passes through the thin placental membrane into the foetal blood vessels. This oxygenated blood then travels through the umbilical vein to nourish the baby's developing organs.
The placenta acts like a sophisticated filter and transport system, allowing beneficial substances to reach the baby whilst removing harmful waste products.
Glucose, amino acids, vitamins, minerals and water pass from mother to baby. These provide the building blocks and energy needed for rapid growth and development.
Urea, carbon dioxide and other metabolic waste products pass from the foetal blood into the maternal blood to be processed by the mother's kidneys and lungs.
The placenta prevents many harmful substances from reaching the baby, including most bacteria and some toxins. However, it's not perfect - alcohol, nicotine and some drugs can still cross over.
The placenta is also an important endocrine organ, producing several hormones that are essential for maintaining pregnancy and preparing the mother's body for childbirth and breastfeeding.
These hormones work together to ensure the pregnancy continues successfully and that both mother and baby are prepared for birth.
This hormone maintains the corpus luteum in early pregnancy, ensuring continued progesterone production. It's also the hormone detected by pregnancy tests. Levels peak around 8-10 weeks of pregnancy.
The placenta takes over production of these hormones from the ovaries. Progesterone maintains the uterine lining and prevents contractions, whilst oestrogen promotes growth of the uterus and mammary glands.
Sometimes the placenta doesn't develop or function properly. Placenta praevia occurs when the placenta covers the cervix, potentially causing bleeding. Placental abruption happens when the placenta separates from the uterine wall too early. Both conditions require medical attention and can affect the baby's oxygen and nutrient supply.
The placenta doesn't remain static during pregnancy - it continues to grow and adapt to meet the changing needs of the developing foetus.
Understanding how the placenta changes during pregnancy helps explain why certain complications might occur at different stages.
The placenta forms and establishes blood supply. By week 12, it's fully functional. The risk of miscarriage is highest during this period as the placenta is still developing.
The placenta grows rapidly to keep up with the baby's increasing needs. Blood flow increases significantly and hormone production reaches peak levels.
The placenta reaches maturity but may begin to show signs of ageing near term. This is why pregnancies that go significantly overdue may need medical intervention.
After the baby is born, the placenta's job is done. It's expelled from the uterus in the third stage of labour, usually within 30 minutes of birth. The umbilical cord is clamped and cut, permanently separating mother and baby's circulatory systems.
The placenta must be completely expelled to prevent bleeding and infection. Healthcare providers carefully examine it to ensure no pieces remain in the uterus. In some cultures, the placenta is considered sacred and may be buried or consumed.
The placenta is truly remarkable - a temporary organ that performs the functions of lungs, kidneys, liver and endocrine glands for the developing foetus. Its efficient design ensures that babies receive everything they need to grow and develop whilst being protected from many harmful substances. Understanding placental function helps us appreciate the complexity of human reproduction and the amazing adaptations that make pregnancy possible.