Lymph then passes into much larger lymph vessels known as lymph ducts. Cholangiocytes are the epithelial lining cells of the bile ducts. Urine then flows through the nephrons, through a system of converging tubules called collecting ducts. Postnatally, the mammary ducts elongate into the mammary fat pad. Ursodiol may be useful if the disease is due to blockage of the bile ducts. The gland has short, striated ducts and long, intercalated ducts. The biliary tract is derived from the branches of the bile ducts. Rarely are diseases of the bile ducts, such as primary sclerosing cholangitis, causes of cirrhosis. Alveoli are also sparsely present on the walls of the respiratory bronchioles and alveolar ducts. It then travels on through the ureters, which are consequently known as urinogenital ducts. Most other vertebrates have generally similar reproductive systems consisting of gonads, ducts, and openings. This can show both under developed (hypoplastic) lymphatic ducts and dilated ducts. Common utility ducts or utility tunnels carry two or more utility lines. Male accessory organs are derived from mesonephric (wolfian) ducts. As well as issues with the tear ducts, sinus problems can also occur.