We present a numerical-experimental diffusion study in which we elucidate the spatial oxygen profile around and inside a zebra fish embryo in the pre-circulation stage (24-28 hpf). Lowest oxygen partial pressures are found in the head with a gradient of posteriorly increasing pressure along the midline of the embryo. Furthermore, this study shows the yolk mass to have a relatively high oxygen permeability as compared to the surrounding medium and the respiring tissue. The oxygen permeability of the respiring tissue in this stage is close to that of water. Knowledge of the details of the oxygen distribution are important for an understanding of vasculogenesis and angiogenesis, since oxygen levels influence the expression of endothelial growth factors.
The orientation and organisation of collagen fibrils play an important role in the mechanical functioning of the articular cartilage (AC) that covers the surfaces in the diarthrodial joints. In the adult animal, typically an arcade like 'Benninghoff structure' is found. Because the remodelling capacity of the collagen network in the adult animal is limited, this Benninghoff structure needs to develop before the animal reaches maturity, and it needs to develop correctly. The aim of this study is to use quantitative polarised light microscopy (qPLM) and scanning electron microscopy (SEM) techniques to investigate if this Benninghoff structure is already present in the young animal, and to quantitatively investigate possible differences in collagen structure in the equine distal metacarpus of the young and adult animal. In total, 21 forelimbs of 13 horses are used. In animals of age 10 months and older, we find an arcade like Benninghoff structure for the collagen fibril network in both the qPLM and SEM study. The qPLM study shows that the collagen's predominant orientation is parallel to the articular surface throughout the entire cartilage depth in two animals directly after birth. These findings are supported by SEM results on a foal. We conclude that structural remodelling of the collagen network in AC occurs in the first months after birth. Because animals start with collagen parallel to the articular surface and need to remodel this structure to a Benninghoff architecture, and because collagen structure is an important parameter for AC mechanics and mechanobiology, these results suggest implications for AC epigenetics.