Changes

== Exchange ==

== Exchange ==

In all types of placenta noted above, antibodies are able to cross the various layers between the maternal and fetal circulation. This allows the maternal blood to convey passive immunity against various infectious agents. However, there are some differences between the mechanisms used to facilitate exchange in different placentas. The names and main differences in exchange characteristics are noted below;  

In some types of placenta including the endotheliochorial, antibodies are able to cross the various layers between the maternal and fetal circulation. This allows the maternal blood to convey passive immunity against various infectious agents. However, in some species such as horses and farm species, there are some differences between the mechanisms used to facilitate exchange in different placentas. These species are not able to confer immunity via the placenta and instead rely on the passive transfer of antibodies via colostrum. This is the case for species with epitheliochorial placentas. The names and main differences in exchange characteristics are noted below;  

===Histotrophic Exchange===

===Histotrophic Exchange===

This type of exhange facilitates nourishment of the embryo prior to implantation, i.e. where no placenta exists. In ungulates, this type of exchnage is very important as there is a long period prior to implantation. For example, in the horse implantation can take up to 35 days, whilst in ruminants it can take between 15 to 20 days.  

This type of exhange facilitates nourishment of the embryo prior to implantation, i.e. where no placenta exists. In ungulates, this type of exchnage is very important as there is a long period prior to implantation. For example, in the horse implantation can take up to 35 days, whilst in ruminants it can take between 15 to 20 days.