Friday, 6 November 2015

Placentation in the ferret

Transverse section through the uterus of a ferret (Mustela putorius furo)
at 28 days of gestation. From Strahl and Ballmann 1915.
A, allantois; H, hemophagous organ; N. yolk sac
A recent paper discussed the domestic ferret as a model for perinatal brain injury. As  the ferret is an altricial species, events that occur during human pregnancy are deferred to the postnatal period. However, neurogenesis and neuronal migration start in pregnancy and the effects of hypoxia on these processes could be explored.

Electron micrograph of the interhemal region in a ferret placenta.
Courtest of Dr. Allen C. Enders
Like all carnivores (except hyenas), ferrets have an endotheliochorial placenta. The endothelium of the maternal capillaries is swollen as readily seen by comparing with the endothelium of fetal capillaries above.

The interhemal region of the ferret placenta.
Courtesy of Dr. Allen C. Enders
At low power it can be seen that the fetal capillaries indent the surrounding trophoblast so the diffusion distance from maternal to fetal blood is minimized. Thus oxygen should diffuse across this barrier almost as readily as in the human hemochorial placenta.

Hematoidin crystals in the hemophagous region of the ferret placenta.
From Strahl and Ballmann 1915
Like other carnivores, the ferret has a prominent hemophagous region (shown in the top figure). Here trophoblast takes up maternal red blood cells by phagocytosis and processes the contained hemoglobin to extract the iron. The hemoglobin breakdown product is hematoidin, which crystallizes out. We have described the same thing in tenrec placenta (here).

The most thorough study of ferret placenta was published a century ago (full reference here). The ultrastructure was later described by Lawn and Chiquoine (here). There are recent reviews of endotheliochorial placentation (here) and placentation in carnivores (here).

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