Yes, rhesus monkeys do have a placenta, an organ that develops during pregnancy to provide oxygen and nutrients to the growing fetus. Rhesus monkeys (Macaca mulatta) are Old World primates frequently utilized in biological and medical studies due to their genetic and physiological similarities to humans. Understanding the rhesus monkey placenta offers valuable insights into primate reproductive biology and aids in advancing scientific knowledge related to pregnancy and development.
The Rhesus Monkey Placenta: Structure and Function
The rhesus monkey placenta is discoid and hemochorial. In a hemochorial placenta, fetal trophoblasts are in direct contact with the maternal blood. While human placentas typically have a single disc, most rhesus monkey placentas are bidiscoid, featuring two distinct discs. Approximately 80% of rhesus monkey gestations exhibit a bidiscoid placenta, with the remaining 20% having a single disc, a variation that does not appear to affect fetal growth or survival.
This organ performs several functions throughout pregnancy. It transfers oxygen and nutrients from the mother to the fetus and removes waste products. The placenta also serves as an endocrine organ, producing hormones that maintain pregnancy. It also regulates fetal cortisol levels, influencing endocrine and immune responses.
Key Similarities to the Human Placenta
The rhesus monkey placenta shares significant anatomical and functional parallels with the human placenta, making it a relevant model for comparative studies. Both species possess a hemochorial placenta, where fetal trophoblast cells are bathed directly in maternal blood, facilitating efficient exchange.
Structurally, both placentas are discoid, although the rhesus placenta commonly has two lobes or discs compared to the human’s single disc. Despite this difference, the fundamental organization, including the villous tree structure and the presence of an intervillous space, is quite similar.
The cellular composition and layers within the placenta are also comparable between rhesus monkeys and humans. Both feature a syncytial trophoblast layer, a multinucleated outer layer in direct contact with maternal blood, and extravillous trophoblasts that invade the maternal endometrium.
These similarities extend to their analogous roles in transferring nutrients and producing hormones essential for pregnancy maintenance and fetal development. While minor differences in gene expression and the extent of trophoblast invasion exist, the overall structural and functional design is remarkably conserved.
Role in Medical Research
The close similarities between rhesus monkey and human placentas make rhesus monkeys invaluable models for studying various aspects of human pregnancy and related health issues. Their placentation, long gestational period, and similar fetal growth trajectories provide a strong translational research system. This allows researchers to investigate complex processes and conditions that are difficult to study directly in human pregnancies due to ethical and technical limitations.
Rhesus monkeys have been instrumental in understanding Rh factor incompatibility, a condition affecting human pregnancies. The Rh blood group system was, in fact, named after these monkeys, where it was first identified. Research using rhesus monkeys has also advanced knowledge of viral transmission during pregnancy, including studies on Zika virus and its impact on placental function and fetal development.
Furthermore, they serve as models for studying the effects of maternal conditions or exposures, such as maternal immune activation, on fetal development and potential long-term health outcomes. Current research even explores gene therapy approaches in rhesus monkeys to improve placental function and support healthier pregnancies, with potential implications for human clinical trials.