CELL APICAL SURFACE-AREA IN ENTEROCYTES FROM CHICKEN SMALL AND LARGE-INTESTINE DURING DEVELOPMENT

The absorptive surface of epithelial cells from chicken small and larg e intestine was studied at the day of hatch (1 d group) and at 2 and 6 wk after hatch. The segments considered were duodenum, jejunum, ileum , cecum (proximal, medial, and distal regions), and rectum. The length , diameter, and density of microvilli as well as cell apical diameter were measured in tip-villous enterocytes by transmission electron micr oscopy. The results obtained showed that during development: 1) microv illus length remained constant in duodenum and jejunum and decreased i n the other segments; 2) microvillus diameter increased only in the je junum and the rectum; 3) microvillus density increased in duodenum, il eum, distal cecum, and rectum (especially from 1 d to 2 wk) and did no t change in the other segments; 4) cell apical diameter did not change ; 5) apical surface area increased both in the duodenum (2nd to 6th wk ) and in the jejunum (1 d to 2 wk) but did not change in the ileum. In the proximal-medial cecum and in the rectum there was a decrease in a pical surface, whereas no changes were observed in distal cecum. Resul ts indicated that microvillus length and density are the variables tha t best explain the changes observed in apical surface that occurred du ring development.