Definition of guano. : a fertilizer containing the accumulated excrement of seabirds or bats; broadly : excrement especially of seabirds or bats.
This is a cross section through the small intestine. The tall, vertical cells seen at the top of the tissue are columnar cells (one is shown - red arrow), which make up simple columnar epithelium (the cells at the bottom of the image are connective tissue, which will be discussed later). Since columnar cells are quite thick, they do not readily allow passive diffusion.
Functions include secretion and absorption (located in small ducts of glands and kidney tubules). Simple columnar epithelium â is a single layer of tall, closely packed cells that line the digestive tract from the stomach to the rectum. Functions include absorption and secretion.pithelial tissue is a sheet of cells that covers a body surface or lines a body cavity.