Morphological Study Of Yak Placenta During Gestation

In order to clarify and reveal the morphological characteristics and relevant functions of yak placenta, the morphological characteristics of placentomes and their components during gestation, and the morphological characteristics of uterine glands of yak intercaruncular region during gestation, several experiments were conducted in this study. The results were showed as following.(1) Placental tissues, obtained from 151 to 180 days of pregnant yaks, were observed their morphological characteristics by use of the method of light microscopy, histochemistry, transmission electron microscopy and scanning electron microscopy. The results indicated that the characteristics of gross anatomy and histological structure of yak placenta were somewhat different from that in other cattles. The sessile, dome-shaped yak placentomes had interdigitating primary, secondary and tertiary chorion villous branches within complementary caruncular crypts. There was a straight maternal plate beneath the placentome. The trophoblast epithelium mainly consisted of mononuclear trophoblast cells and trophoblast giant cells. The trophoblast giant cells appeared with different types, could secrete extremely neutral and acid glycoconjugate. Their cytoplasm contained rough endoplasmic reticulum, advanced Golgi complex and specific secretory granules, and other cell organelles. There were glycoconjugate on basal lamina and microvilli junction of mononuclear trophoblast cells and crypt epithelial cells. Their cytoplasm contained mitochondria and secretory vesicles and other organelles, while glycoconjugate was not existed.(2) Thirty-one pregnant yaks were used to determine their anatomical and histological data of placentomes by morphometric method. The results indicated that there were no significant changes in the total number of yak placentomes during gestation, but remarkly fewer placentomes in the non-pregnant horn compared with the pregnant horn. The mean size of placentomes increased significantly from <61 days to 181～210 days and decreased in 211+ days. The development of placentomes in the pregnant horn were obviously different from that of the non-pregnant horn except <61 days, which were longer, wider and thicker. The volume density of fetal villi increased during gestation, with a concomitant reduction in the volume density of caruncular endometrium. However, there was no significant change in the surface density of fetal villi. The volume density of binucleate cell increased in prophase then decreased. No apparent changes in the volume densities of maternal and fetal pyknotic cell occurred throughout gestation. There was a significant increase in the average total volume of yak placentomes from 61～90 days to 181～210 days and a significant decrease in 211+ days. The same patterns were showed in the average total volumes of caruncular endometrium and binucleate cell as well as the mean total surface area of fetal villi. However, the mean total volumes of fetal villi, maternal and fetal pyknotic cell increased constantly with increasing gestation time. Three types of placentome shape were identified in yak.(3) Morphometric method was used to determine histological data of uterine glands of 31 yak intercaruncular region, and data were analyzed using statistical method. It was found that the height of glandular epithelium of yak intercaruncular region decreased significantly with increasing gestation age except 151～180 days. The perimeter and area of endometrial gland ducts increased significantly during gestation. There were significant differences in the volume densities of gland ducts at different stages of pregnancy, while no significant change occurred in the surface densities of gland ducts. The proportion of convoluted and tubular gland ducts became significantly larger or smaller with increasing gestation age, respectively. A significant change existed in the proportion of gland ducts containing luminal secretions. Gland ducts containing glandular invaginations (telescoping) could be found in the intercaruncular region.