Which of the following sequences correctly represents the layers of the alimentary canal from the most visceral (deep) to the most superficial (surface)?

A. Urea: Urea is the major nitrogenous waste normally present in urine.
B. Albumin:Albumin in urine (albuminuria/proteinuria) is abnormal and suggests glomerular damage or increased filtration of plasma proteins.
C. Sodium: Sodium is a normal urinary electrolyte whose excretion varies with intake and hormonal control.
D. Creatinine:Creatinine is a normal waste product excreted in urine and used clinically to assess renal function.

A. Gallbladder: The gallbladder stores and releases bile into the duodenum via the common bile duct when stimulated (e.g., by CCK). It does release a secretion into the duodenum, but it primarily stores bile produced by the liver.
B. Liver: The liver produces bile, which drains via hepatic ducts into the common bile duct and empties into the duodenum -the liver is a primary secretor whose products reach the duodenum.
C. Spleen: The spleen is a lymphoid/hematologic organ (filters blood, immune functions) and does not release digestive secretions into the duodenum.
D. Gastric glands: Gastric glands secrete gastric juice into the stomach lumen (not the duodenum), so they do not release secretions into the duodenum.
E. Pancreas: The exocrine pancreas secretes digestive enzymes and bicarbonate into the duodenum via the pancreatic duct.
F. Intestinal glands: Intestinal glands (crypts of Lieberkühn) secrete intestinal juice directly into the intestinal lumen (including the duodenum), but the most commonly tested paired organs that "release secretions into the duodenum" are the liver (bile) and pancreas (pancreatic juice).