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The cells in the respiratory epithelium are of five main types: a) ciliated cells, b) goblet cells, c) brush cells, d) airway basal cells, and e) small granule cells (NDES) [6] Goblet cells become increasingly fewer further down the respiratory tree until they are absent in the terminal bronchioles; club cells take over their role to some extent here. [7]
Goblet cells secrete the mucus layer which protects the epithelium from the luminal contents. Enteroendocrine cells secrete various gastrointestinal hormones including secretin, pancreozymin, enteroglucagon among others. Subsets of sensory intestinal epithelial cells synapse with nerves, [9] and are known as neuropod cells. [10]
The main role of goblet cells is to secrete mucus in order to protect the mucous membranes where they are found. Goblet cells accomplish this by secreting mucins, large glycoproteins formed mostly by carbohydrates. The gel-like properties of mucins are given by its glycans (bound carbohydrates) attracting relatively large quantities of water. [10]
In the large intestines, villi are absent and a flat surface with thousands of glands is observed. Underlying the epithelium is the lamina propria, which contains myofibroblasts, blood vessels, nerves, and several different immune cells, and the muscularis mucosa which is a layer of smooth muscle that aids in the action of continued peristalsis ...
The mucosa is composed of one or more layers of epithelial cells that secrete mucus, and an underlying lamina propria of loose connective tissue. [1] The type of cells and type of mucus secreted vary from organ to organ and each can differ along a given tract. [2] [3]
The mucus prevents large particles from contacting the epithelial cell layer while allowing small molecules to pass. The mucus also facilitates passage of the luminal contents along the length of the intestines, protects the epithelial cells from digestive enzymes , and prevents the direct contact of microorganisms with the epithelial layer.
The length of the human colon is, on average 160.5 cm (measured from the bottom of the cecum to the colorectal junction) with a range of 80 cm to 313 cm. [11] The average inner circumference of the colon is 6.2 cm. [10] Thus, the inner surface epithelial area of the human colon has an area, on average, of about 995 cm 2, which includes ...
The lungs are suspended within the pleural cavity of the thorax. The pleurae are two thin membranes, one cell layer thick, which surround the lungs. The inner (visceral pleura) covers the lungs and the outer (parietal pleura) lines the inner surface of the chest wall. This membrane secretes a small amount of fluid, allowing the lungs to move ...