Unless fertilization occurs, the corpus luteum becomes scar tissue, which is known as the

A. Pancreatic duct: The pancreatic duct (duct of Wirsung) conveys pancreatic enzymes from the pancreas to the duodenum and typically joins the bile duct at the hepatopancreatic ampulla.
B. Common bile duct: The common bile duct is formed by the union of the common hepatic duct and cystic duct and carries bile from the liver/gallbladder to the duodenum.
C. Common hepatic duct: The common hepatic duct drains bile from the right and left hepatic ducts of the liver and joins the cystic duct to form the common bile duct.
D. Cystic duct: The cystic duct connects the gallbladder to the common bile duct and allows bile to flow into and out of the gallbladder for storage and release.

A. Type I pneumocytes: The respiratory membrane is formed by alveolar Type I (squamous) pneumocytes, their basement membrane fused with the capillary basement membrane, and capillary endothelial cells -allowing efficient gas diffusion.
B. Respiratory bronchioles: Respiratory bronchioles are airway structures leading to alveoli but are not the cellular layer that composes the thin respiratory membrane.
C. Segmental (tertiary) bronchi: These are larger conducting airways far upstream from the alveolar gas-exchange surface.
D. Type II pneumocytes: Type II cells produce surfactant and are present in alveoli, but the thin gas-exchange surface is primarily Type I pneumocytes (Type II are cuboidal and thicker).