Placental Functions: Barrier, Transport, Endocrine, and Immune Roles

The placenta is a transient, fetomaternal organ essential for pregnancy maintenance and fetal development.

Core Functions

1. Selective Barrier & Transport: Syncytiotrophoblast separates maternal/fetal blood; permits passive/active transport of O₂, CO₂, nutrients (glucose, amino acids, fatty acids), waste (urea, creatinine), antibodies (IgG), but blocks most cells, large proteins, pathogens.
2. Gas Exchange: O₂ diffusion (maternal → fetal); CO₂ diffusion (fetal → maternal). Fetal Hb higher affinity ensures gradient.
3. Nutrient Transfer: Active transport (GLUT1 for glucose, System A for amino acids); lipoprotein lipase releases FFAs from maternal triglycerides.
4. Endocrine: hCG (rescues corpus luteum), progesterone, estrogen, hPL (lactogen), relaxin, kisspeptin. Modulate maternal physiology, fetal growth, parturition timing.
5. Immune Modulation: HLA-G, IDO, Tregs, cytokines create tolerance; prevent rejection of semi-allogeneic fetus.
6. Physical Support: Anchors umbilical cord, maintains amniotic cavity.

Clinical Significance

Placental insufficiency → IUGR, preeclampsia, stillbirth. Pathology exam guides recurrence risk counseling.