Class 11 NEET Biology Structural Organisation in Animals

(a) : Intestine is lined by glandular epithelium which is secretory in function. The glands found in intestine are exocrine and may be unicellular or multicellular. When unicellular glands secrete mucus, they are called mucus cells or goblet cells and are common in the columnar epithelium of intestine. When unicellular glands secrete a clear watery fluid, they are called serous cells which are also present in intestinal glands. On the other hand, multicellular glands consist of a duct and secretory portion, both formed of epithelial cells. They are further of two types: tubular and saccular. In tubular glands secretory portion is tube like for example, Crypts of Lieberkuhn (a type of simple straight tubular glands found in intestine) and Brunner's gland (a type of simple branched tubular glands found in intestine).