2011 (SBTE) 25th Annual Meeting Proceedings - International ...

R.C. Cheb
hebel.
el. 2011. Use of Applied Reproductive Technologies (FTAI, FTET) to Improve the Reproductive Efficiency in
Dairy Cattle. Acta Scientiae Veterinariae. 39(Suppl 1): s203 - s221.
Figure 13. Stereo micrographs of porcine embryos. (A) Day 15-16 embryo showing lens placode (LP), otic placode (OP), somites (S),
developing heart (H), yolk sac (YS), and allantois (Al). (B) Day 18-19 embryo showing pharyngeal arches (PA), developing heart with atrial
(At) and ventricular (Ve) compartments, forelimb bud (FB), hind limb bud (HB), and prominent mesonephros (Mn).
extra-embryonic mesoderm. The extra-embryonic
mesoderm is split into an outer component lining
trophectoderm and an inner component lining the
hypoblast, and the cavity between these two
components is referred to as the extra-embryonic
coelom (Figure 11). With the continued development
of the coelom, an intra-embryonic coelom similarly
divides the lateral plate mesoderm in such a way that
the so-called somatic mesoderm associates with the
surface ectoderm to constitute the somatopleura while
the so-called visceral mesoderm associates with the
endoderm to form the splanchnopleura. Between the
paraxial and lateral plate mesoderm, the intermediate
mesoderm is established.
6.3 Paraxial mesoderm
As a general rule, development proceeds in
an anterior to posterior direction (one exception to
this was the development of the primitive streak). Accordingly,
formation of somites progresses from the
occipital region posteriorly. Each somite subsequently
differentiates into three components: The ventromedial
part of the somite associates with the notochord
establishing the sclerotome which patterns formation
of the vertebral column. The dorso-lateral part of each
somite forms regionalized precursors of both dermal
and muscle tissue, the dermamyotome. From this
structure, a dorso-medially located cell population
forms the myotome and a dorso-laterally located
group becomes the dermatome. The myotome of each
somite contributes to muscles of the back and limbs,
while the dermatome disperses and forms the dermis
and subcutis of the skin. Later, each myotome and
dermatome will receive its own segmental nerve
component.
6.4 Intermediate mesoderm
The intermediate mesoderm, which connects
paraxial and lateral plate mesoderm, differentiates into
structures of both the urinary system and the gonads,
together referred to as the urogenital system. The N
urinary system is first developed as an abortive
anteriorly located paired pronephros, succeeded by
a very prominently developing paired mesonephros
(Figure 13B). The mesonephros develops excretory
ducts; the mesonephric ducts (Wollfian ducts). Finally,
the even further posteriorly located paired metanephos
develops and the persisting kidneys. The gonads
develop on the medial aspect of the mesonephros,
initially as the genital ridges which receive the primordial
germ cells. In the male, the mesonephric
ducts develops into the epididymal ducts and the
ductus deferens. In the female, however, another duct,
the paramesonephric duct (the Müllerian duct), forms
parallel to the mesonephric duct and develops into
the oviduct, the uterus, and the cranial portion of the
vagina.
6.5 Lateral plate mesoderm and body folding
Through anterior-posterior and lateral foldings,
the subdivision of the coelom into intra- and
extra-embryonic cavities becomes progressively
better defined and the embryonic body gradually assumes
the shape of a closed tube enclosing another
tube, the primitive gut. The somatopleura will form
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