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Placenta - Anatomy & Physiology (view source)
Revision as of 13:05, 12 July 2011
, 13:05, 12 July 2011→Exchange
== 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;
===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.
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Nutrition is supplied by uterine secretions/debris, often referred to as 'uterine milk'. Uterine milk secretions are usually maintained by '''progesterone'''. Pinocytosis (cellular drinking) is the main exchange mechanism.
* '''Pig and horse''': pinocytosis persists via '''areolae'''
* '''Pig and horse''': pinocytosis persists via '''areolae'''
* '''Sheep,cow,dog and cat''': pinocytosis persists via '''haemophagous zones''' that break down and release iron to the placenta.
* '''Sheep,cow,dog and cat''': pinocytosis persists via '''haemophagous zones''' that break down and release iron to the placenta.
'''Haemotrophic'''
'''Haemotrophic'''
* Direct transfer of nutrients from the maternal to foetal blood via the placenta. By Simple Diffusion, Facillitated Diffusion, Active Transport and Complex Diffusion
* Direct transfer of nutrients from the maternal to foetal blood via the placenta. By Simple Diffusion, Facillitated Diffusion, Active Transport and Complex Diffusion
==Placental Blood Supply and Drainage==
==Placental Blood Supply and Drainage==