KINETICS OF TISSUE PROLIFERATION IN COLORECTAL MUCOSA DURING POST‐NATAL GROWTH

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Abstract
The main developmental event in the colorectal mucosa during postnatal growth is a dramatic increase in the number of crypts of Lieberkuhn, resulting from a longitudinal fission of pre-existing crypts. The kinetic aspects of this process were analyzed, using extensive gland and cell counts involving the entire colon and rectum of 24 male BD IX rats distributed into 4 age groups. The number of crypts rose from an average 4652 to 423,800 between birth and adulthood; the corresponding ratios of bifurcating glands were 13.55 and 0.67%, respectively. Crypt production attained its maximum 18 days after birth with an hourly increment of 519 U. The time spent by replicating glands in the bifurcating stage (fission time) averaged 6.9-10.5 h. The mean number of epithelial cells/crypt rose from 249 in 4-day old rats to 635 in adults. The estimated total number of epithelial cells in the colon and rectum was 1 million in newborns and 248 million in adults. The increment in cell number peaked 3 wk after birth with a value of 310,000/h. During the 1st few days after birth, all cells produced in the epithelium were retained. Cell loss thereafter rapidly progressed, reaching 70% of the cell production in 3 wk old animals.