On the question of whether the placental barrier is an effective barrier to the transmission of drugs, the functional cell of the placenta is referred to as syncytiotrophoblast ( Griffiths & Campbell, 2014). The primary function of the cells as stated is to enhance the exchange of gases, nutrients, and drugs between the mother and the fetus. To understand the syncytiotrophoblast cells, their anatomical structure is described. They are said to have a polarized plasma membrane that has brush borders and a border membrane on the maternal and fetal side respectively. Further described are the factors that regulate the transportation of drugs across the placental membrane. The factors include molecular weight of the drug, amount of drug that is protein bond, lipid solubility, and ionization. Drugs that are lipid soluble can cross the placental barrier with ease as compared to those which are insoluble. When drugs are highly polarized, they find it difficult to cross the placental barrier. Also, drugs with a low molecular weight and those that are not protein bond also experience relative ease while crossing the placental wall. The text also appreciates the presence of active efflux transporters in the placenta. Their role is to prevent substances such as drugs, substrates, and chemicals from infiltrating into the fetal circulatory system. The text claims that the role and the dynamics of the efflux transporters are not fully understood but are believed to work similarly to those found in the blood-brain barrier.
On the question of the transport mechanism used in the transportation of drugs, simple diffusion has been suggested as the main transport mechanism. It is majorly used for drugs that exhibit characteristics such as lipophilic, low molecular weight, non-protein bond, and non-polar. The text describes the process of passive diffusion as the movement of the drug from a high to a low concentration region. Energy is not required in the process, but movement is along the concentration gradient from the mother’s circulation, across the placental barrier, into the fetal circulation ( Feghali, Venkataramanan, and Caritis, 2015). The text further analyzes a factor that might play a role in increases the passive diffusion. As blood flow and surface area of the placenta increases as gestation proceeds, there is increased passive diffusion into the fetus. The size of the placenta is an important factor in passive diffusion. The thinner the placenta, the higher the diffusion rate. To summarize all the factors affecting passive diffusion, the text suggests a formula known as the Fick’s law of diffusion. The formula comprises the mathematical integration of the factors including concentration gradient, membrane thickness, and surface area to determine the ease of diffusion.
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Thirdly on the question of teratogenesis, the text begins by describing what teratogens are. They are substances that can lead to abnormalities in the fetus or embryo. The abnormalities are said to be either in the form of anomalies, malformations, or defects ( Tantibanchachai, (2014).
The text further goes ahead to describe the new rule known as the ‘'Pregnancy and Lactation Labeling Rule'' (PLLR) that has replaced the FDA ratings that were used in the classification of drugs with regards to pregnancy. The PLLR method has several subheadings that contain information on the effects, risks, and risk-benefit counseling of drugs that are prescribed to the expectant women. The information found in the new rule can also be used to determine the risks the drugs might pose on the breastfeeding child by analyzing the active metabolites. There is also a part of the new rule that provides vital information concerning testing for pregnancy as a result of adverse effects of drugs. The text, however, appreciates that the OTC drugs will not be affected by the said rules ( FDA, 2016).
References
FDA. (2016). Pregnancy and lactation labeling (drugs) final rule. Retrieved from https://www.fda.gov/drugs/developmentapprovalprocess/developmentresources/labeling/ucm093307.htm
Feghali, M., Venkataramanan, R., & Caritis, S. (2015). Pharmacokinetics of drugs in pregnancy.
Griffiths, S. K., & Campbell, J. P. (2014). Placental structure, function and drug transfer.
Tantibanchachai, C. (2014). Teratogens. Retrieved from https://embryo.asu.edu/pages/teratogens
