Introduction
The placenta is a vital organ that develops in the uterus during pregnancy. It serves as the critical interface between the mother and the developing fetus, providing essential functions for the baby’s growth and health.
Where is the placenta?
The placenta connects the developing fetus to the wall of the mother’s uterus during pregnancy. It grows in the uterus wall and is attached to the fetus within the uterine cavity by the umbilical cord. The placenta is formed by cells originating from the fetus and is therefore the first of the fetal organs to develop.
What does the placenta do?
Nutrient and Oxygen Supply:
The placenta allows nutrients (such as glucose, amino acids, vitamins, and minerals) and oxygen from the mother’s blood to pass to the fetus. This is essential for the baby’s development and growth throughout pregnancy.
Waste Removal:
It also helps remove waste products, such as carbon dioxide and metabolic byproducts, from the fetus’ blood, returning them to the mother’s bloodstream to be excreted.
Hormone Production:
It produces hormones essential for pregnancy, including:
- hCG (Human Chorionic Gonadotropin): hCG is the first hormone produced by the placenta, detectable in the mother’s blood and urine as early as 10 days after conception (it’s what pregnancy tests detect). It helps maintain the corpus luteum (a temporary gland in the ovary) in the early stages of pregnancy, ensuring the continued making of progesterone, which is vital for maintaining the uterine lining.
- Progesterone: Placenta takes over progesterone production after the corpus luteum’s role diminishes, around the 8th to 10th week of pregnancy. Progesterone is essential for maintaining the uterine lining (endometrium), preventing early contractions, and supporting the growth of blood vessels in the placenta.
- Estrogen: Placenta produces estrogen, primarily in the form of estriol during pregnancy. Estrogen helps regulate the development of the fetus and promotes the growth of the uterus, the development of the mammary glands, and increased blood flow to the uterus and placenta.
Barrier Function:
The placenta acts as a selective barrier, allowing necessary nutrients to pass while excluding many harmful substances and pathogens. However, it’s not foolproof; some substances (like alcohol, drugs, and certain viruses) can cross the placental barrier.
Immune Protection:
The placenta helps transfer antibodies from the mother to the baby, providing immune protection during pregnancy and after birth (this is known as passive immunity).
Development and Structure of the Placenta
The formation of the placenta begins shortly after the fertilized egg implants into the uterine wall. By the end of the first trimester, it is fully formed and takes over the role of supporting the fetus.
It typically attaches to the wall of the uterus, usually near the top. In some cases, it may attach lower (placenta previa), which can cause complications during delivery.
It consists of maternal and fetal parts. The fetal part is formed from the chorion (the outer membrane surrounding the embryo), while the maternal part is made of uterine tissue. It is connected to the baby via the umbilical cord.
What hormones does the placenta produce?
Placenta produces two steroid hormones – estrogen and progesterone. Progesterone acts to maintain pregnancy by supporting the lining of the uterus (womb), which provides the environment for the fetus and the placenta to grow.
Progesterone prevents the shedding of this lining (similar to that which occurs at the end of a menstrual cycle), since this would result in pregnancy loss. Progesterone also suppresses the ability of the muscular layer of the uterine wall to contract, which is important in preventing labor from occurring before the end of pregnancy
Estrogen acts to stimulate the growth of the uterus to accommodate the growing fetus and allows the uterus to contract by countering the effect of progesterone.
Human Placental Lactogen (hPL) or Human Chorionic Somatomammotropin (hCS)
hPL/hCS is important for regulating maternal metabolism during pregnancy. It modifies the mother’s insulin sensitivity and carbohydrate metabolism, ensuring an adequate supply of glucose and nutrients to the growing fetus.
Corticotropin-releasing hormone (CRH)
Placental CRH plays a role in regulating the timing of birth and is thought to influence fetal development, particularly the maturation of the lungs. CRH levels increase dramatically in the third trimester, and it may help trigger labor.
Relaxin
Relaxin helps relax the mother’s ligaments, especially in the pelvic area, to prepare for childbirth. It also helps soften the cervix in preparation for labor
Prolactin
Though primarily produced by the pituitary gland, the placenta also produces prolactin, which plays a vital role in preparing the breasts for milk production.
Leptin
Placental leptin helps regulate the mother’s appetite and metabolism during pregnancy. It plays a vital role in fetal growth by influencing energy balance and nutrient partitioning between the mother and fetus.
Complications Related to the Placenta:
Placenta Previa: When the placenta covers the cervix, it can cause bleeding and complications during delivery, often requiring a cesarean section.
Placental Abruption: A condition where the placenta detaches from the uterine wall before delivery. This can deprive the baby of oxygen and nutrients and may lead to preterm birth or stillbirth.
Placenta Accreta: This occurs when the placenta attaches too deeply into the uterine wall, causing complications during labor or delivery. It may require surgical intervention, including a possible hysterectomy.
Insufficient Placenta: In some cases, the placenta may not function adequately, resulting in fetal growth restriction or other pregnancy complications.
Baby’s Birth
After the baby is born, the placenta is delivered in the third stage of labor. This usually happens within 5 to 30 minutes after childbirth. Medical professionals examine the placenta to ensure it has been fully expelled, as retained placental tissue can cause complications like bleeding or infection.