Kensinger R S, Collier R J, Bazer F W
Dairy Science Department, University of Florida, Gainesville 92611.
J Anat. 1986 Apr;145:49-59.
Ultrastructural changes occurring in porcine mammary tissue were characterised between Day 90 of pregnancy and Day 4 of lactation. Porcine mammary tissue on Day 90 of pregnancy was composed of alveoli which contained negligible to moderate amounts of secretion. Epithelial cells of these alveoli were relatively undifferentiated. The appearance and distribution of cellular organelles suggested that mammary epithelial differentiation had been initiated by Day 105 of pregnancy in the pig. A further increase in intracellular lipid droplets and granular endoplasmic reticulum suggested that differentiation had progressed by Day 112. On the day of parturition, secretions within the alveolar lumina assumed the appearance of normal milk (as opposed to colostrum) and the epithelia displayed a distinct cellular polarity characteristic of lactating mammary tissue. By Day 4 of lactation, differentiation of epithelial cells appeared to be complete, with dilated cisternae of the granular endoplasmic reticulum and with numerous secretory vesicles. Elongated microvilli were present and numerous cells contained lipid droplets which were being extruded into the lumina. Data from this and previous studies indicate that lactogenesis in the pig occurs in two stages. Stage 1 occurs between Days 90 and 105 of pregnancy, and Stage 2 between Days 112 of pregnancy and early lactation when the predominant feature is active milk secretion.
对妊娠90天至泌乳第4天期间猪乳腺组织发生的超微结构变化进行了表征。妊娠90天时，猪乳腺组织由肺泡组成，肺泡内含有少量至中等量的分泌物。这些肺泡的上皮细胞相对未分化。细胞器的外观和分布表明，猪在妊娠105天时乳腺上皮分化已经开始。细胞内脂滴和颗粒内质网的进一步增加表明，到妊娠112天时分化已经进展。在分娩当天，肺泡腔内的分泌物呈现出正常乳汁（与初乳相反）的外观，上皮细胞表现出泌乳乳腺组织特有的明显细胞极性。到泌乳第4天时，上皮细胞的分化似乎已经完成，颗粒内质网的池扩张，有大量分泌小泡。存在细长的微绒毛，许多细胞含有正在被挤出到管腔中的脂滴。这项研究和以前研究的数据表明，猪的泌乳发生在两个阶段。第一阶段发生在妊娠90天至105天之间，第二阶段发生在妊娠112天至泌乳早期，此时的主要特征是活跃的乳汁分泌。
