Initial vascularisation in the pig placenta: II. Demonstration of gland and areola‐gland subunits by histology and corrosion casts

Abstract

Tissues from 10 pregnant pigs between 9 1/2 and 43 days post coitum (p.c.) were prepared for histology and vascular corrosion casts to examine the vascularisation of the gland and areola-gland subunits of the early pig placenta. The endometrial vascular networks shown by casts were equal in both glandular and interglandular fields from days 9 1/2 to 14-15 p.c. This represents a cyclic stage uninfluenced by the early implanting embryo on day 13 p.c. By day 15 p.c., the first areola formation was observed both histologically and on casts. The maternal areolar and glandular capillary network developed into a widely meshed loose type, in contrast to the interareolar type which had a dense and parallel architecture. In some cases extremely large, crooked, and highly anastomosed maternal capillaries developed between these two networks. This specialized transition is thought to form the base for the ring-like seal formation (RSF) of the areolar periphery. A firm materno-fetal anchor therefore "seals" the areola and its glandular secretory contents from its interareolar surroundings. Therefore, the glandular and maternal areolar vasculatures are clearly discernable from that of the fetal areolar vasculature. The former are associated with the known maternao-fetal substance transfer of the porcine areolar-gland subunit. This association, however, seems to remain unspecialized in early placentation, as only the regular roundish areola--not the irregular areola--can be distinctly detected.

Microvasculature of regular and irregular areolae of the areola-gland subunit of the porcine placenta: structural and functional aspects

“…The periglandular capillary network is continuous with, and denser than, that of the areola (compare also with Fig. 4c in Leiser and Dantzer 1993). On the fetal regular areola (Fig.…”

“…This creates the sealing of the areolar cavity and, when irrigated with blood -as mimicked by the combined casts -provides a differentiated materno-fetal anchoring system. Leiser and Dantzer (1993) described this system as a ring-link seal formation (RSF) in a study of early porcine placentation.…”

“…Areolae normally develop into regular areolae. However, they may "fuse" to form an irregular areola, when several glands, by chance, are too close to each other, thus hampering an orderly seal formation (compare also Leiser and Dantzer 1993).…”

“…the maternal subepithelial capillaries (Keys and King 1988) and the fetal capillaries show a highly fenestrated endothelium (Friess et al 1981). Leiser and Dantzer (1993) investigated the development o f the blood vasculature o f the areola-gland subunit at the preplacental and early placental stages. They showed how the maternal and fetal subepithelial capillary systems changed with respect to architecture and microstructure during initial placentation.…”

Fetomaternal Attachment and Anchorage inthe Early Diffuse Epithel iochorial Placenta of the Camel <i>(Camelus dromedarius)</i>

“…This is consistent with Hasselager's [1986] observations, describing an 'asymmetry of the microvillous interdigitation' in the pig. Areolae in the camel, like in the pig [Dantzer, 1986;Leiser and Dantzer, 1994], are relatively large in early placentation and might therefore add to the 'looseness' of the connection.…”