Poistokanavat

Poistokanavat, known in English as excretory ducts, are channels that carry secretions produced by glands or secretory cells to a destination such as a body surface or a lumen. They are essential components of the exocrine system, enabling the controlled discharge of substances including enzymes, mucus, sweat, bile, and tears. Ducts vary from simple single passages to complex, branched networks that connect with multiple secretory units.

Anatomy and histology: Ducts can be simple or compound. The lining epithelium changes along the duct, ranging from simple cuboidal in small ducts to taller columnar cells in larger ducts, with some sections near the surface showing stratified epithelia. Surrounding glandular regions may include myoepithelial cells and, in larger ducts, smooth muscle that helps propel secretions.

Examples: In the skin, eccrine and apocrine sweat glands drain through ducts to the skin surface. The pancreas and liver employ ducts such as the pancreatic duct and bile ducts to convey digestive fluids to the gastrointestinal tract. Salivary glands contain intercalated and striated ducts that modify saliva before it enters the oral cavity. Lacrimal glands use ducts to drain tears into the conjunctival sac.

Clinical relevance: Obstruction, inflammation, or injury of a duct can impair gland function and cause swelling or dysfunction. Common conditions include sialolithiasis (salivary duct stones), biliary obstruction, and pancreatitis arising from ductal blockage.

See also: Exocrine gland, duct system, histology.