platsenta

Platsenta is a temporary organ that develops during pregnancy in mammals, including humans. It connects the fetus to the uterine wall, enabling the exchange of nutrients, gases, and wastes, and it supports fetal endocrine and metabolic needs.

The placenta comprises fetal and maternal components. Fetal tissue includes the chorion, placental villi, and fetal blood vessels, while maternal tissue is the decidua basalis of the uterine lining. Blood from the mother flows into the intervillous space, where it bathes the villi and allows exchange with fetal blood in the villous capillaries. The placental barrier permits many small molecules to pass while restricting some pathogens and large molecules.

Development and function: the placenta forms as trophoblasts invade the endometrium early in pregnancy, with formation beginning around weeks 3–4 and maturation by the end of the first trimester. It produces hormones such as human chorionic gonadotropin (hCG), progesterone, estrogens, placental lactogen, relaxin, and corticoptropin-releasing hormone (CRH), helping regulate maternal physiology and maintain pregnancy. It also supports fetal growth by supplying oxygen and nutrients and removing waste products.

Clinical significance: placental disorders include placenta previa (low placental position), placental abruption (premature separation), and placenta accreta spectrum (invasion into the uterine wall). Placental insufficiency can contribute to fetal growth restriction and preterm birth. Abnormal placental pathology can be associated with maternal diseases or infections and is sometimes examined after delivery to understand neonatal outcomes.

Evolution and diversity: the placenta has evolved independently in several mammalian lineages. In humans it is typically hemochorial, with maternal blood in direct contact with fetal villi, reflecting adaptations to optimize exchange and immune interaction between mother and fetus.