Placenta

Definition

The placenta is an organ that develops during pregnancy in mammals, serving as the interface between the mother and the developing fetus. It facilitates the exchange of nutrients, gases, and waste products, playing a crucial role in the survival and development of the offspring. This unique structure not only supports fetal growth but also influences maternal physiology and has evolved significantly among different mammalian lineages.

5 Must Know Facts For Your Next Test

1. The placenta is made up of both maternal and fetal tissues, specifically derived from the chorion, which originates from the embryo, and the uterine lining of the mother.
2. This organ is responsible for producing hormones that maintain pregnancy and regulate various physiological processes in the mother.
3. There are different types of placentas found in mammals, including diffuse, cotyledonary, zonary, and discoidal types, each reflecting adaptations to their reproductive strategies.
4. In addition to nutrient transfer, the placenta acts as a barrier protecting the fetus from certain pathogens and harmful substances while allowing some antibodies from the mother to pass through.
5. The evolution of the placenta is believed to have provided mammals with a significant reproductive advantage by enhancing offspring survival rates compared to egg-laying species.

Review Questions

• How does the structure of the placenta contribute to its function in nutrient exchange between the mother and fetus?
  • The placenta's structure is highly specialized for efficient nutrient exchange due to its large surface area created by villi that project into maternal blood pools. These projections increase contact with maternal blood, allowing for effective diffusion of nutrients and gases while facilitating waste removal. The close proximity of maternal and fetal blood supplies ensures that essential substances can be transferred quickly and efficiently while also providing a protective barrier.
• Discuss how different types of placentas reflect adaptations to various mammalian reproductive strategies.
  • Different mammalian species exhibit diverse placental structures such as diffuse, cotyledonary, zonary, and discoidal types, each adapted to their specific reproductive needs. For instance, ruminants have cotyledonary placentas that facilitate localized nutrient transfer where contact points develop between maternal and fetal tissues. In contrast, humans possess a discoidal placenta that allows for deeper embedding into the uterine wall, maximizing maternal-fetal interaction for nutrient uptake. These adaptations highlight how evolutionary pressures have shaped reproductive strategies across mammalian taxa.
• Evaluate the evolutionary significance of the placenta in mammals compared to other reproductive strategies like oviparity.
  • The evolution of the placenta represents a significant adaptive advantage for mammals over oviparous (egg-laying) species by providing a stable environment for developing embryos. The placenta allows for extended gestation periods, resulting in more developed young at birth compared to those born from eggs. This protection from environmental stresses and direct nourishment leads to higher survival rates of offspring in mammals. Furthermore, it supports complex social structures and parental investment, enhancing reproductive success in varied ecological niches.

Related terms

Viviparity: The reproductive mode where embryos develop inside the mother's body, resulting in live births, as seen in most mammals.

Gestation: The period of development of the fetus within the womb from conception to birth.

Chorioallantoic membrane: A structure formed from the fusion of the chorion and allantois, playing a key role in nutrient and gas exchange during fetal development in some reptiles and mammals.