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Age-related features of the small intestine
Medical expert of the article
Last reviewed: 06.07.2025
The small intestine of a newborn is 1.2-2.8 m long; at the age of 2-3 years, its length is on average 2.8 m. By the middle of the second childhood period, its length is equal to the length of the intestine of an adult (about 5-6 m). The width of the lumen of the small intestine by the end of the first year is 16 mm, and by 3 years - 23.2 mm.
The duodenum in a newborn has a ring-shaped form, its bends are formed later. Its beginning and end are located at the level of the 1st lumbar vertebra. At the age of over 5 months, the upper part of the duodenum is at the level of the 12th thoracic vertebra; by the age of 7, the descending part descends to the 2nd lumbar vertebra and even lower (by the age of 12). The duodenal glands in a newborn are small in size, they are less branched than in an adult. They develop most intensively in the first years of a child's life.
In a newborn, the arrangement of the jejunum and ileum loops is different - horizontal and vertical, which is associated with the position of the mesenteric root and the functional state of the intestine. The folds and villi of the mucous membrane are weakly expressed. The number of intestinal glands increases in the first year of life. Single and group lymphoid nodules (lymphoid plaques) in the thickness of the intestinal mucosa in a newborn are already present. The muscular membrane is poorly developed, especially its longitudinal layer.
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