mucous cell

**Definition:** Mucous cells are specialized secretory epithelial cells that produce mucins (heavily glycosylated proteins, e.g., MUC5AC, MUC6, MUC2). Mucins hydrate to form mucus, a viscous gel that lubricates and protects epithelial surfaces.

**Histology:** Mucous cells have a basal, flattened nucleus and apical cytoplasm filled with mucin granules. Mucin is water-soluble and is lost in routine H&E processing, so the cytoplasm looks pale, foamy, or "empty." Mucin stains with PAS (periodic acid-Schiff) and mucicarmine, and with Alcian blue for acidic mucins. Cells have abundant rough ER and a prominent Golgi apparatus, where mucins are glycosylated.

**Locations and types:** - **Stomach:** Surface mucous (foveolar) cells line the surface and gastric pits. They secrete thick, visible, alkaline mucus (MUC5AC) plus bicarbonate. Mucous neck cells sit in the gland necks and secrete a thinner, soluble mucus (MUC6). They are also thought to act as stem or progenitor cells. - **Intestines:** Goblet cells secrete MUC2. Their number increases from duodenum to distal colon. - **Respiratory tract:** Goblet cells and submucosal gland mucous cells trap particles, which the mucociliary escalator then clears. - **Salivary glands:** Mucous acini (e.g., sublingual, which is predominantly mucous) produce viscous saliva. The submandibular gland is mixed, and the parotid is serous. - **Others:** Brunner glands of the duodenum (alkaline mucus), esophageal glands, and the endocervix.

**Gastric mucosal barrier (high-yield):** The protective layer has three parts: a mucus gel layer, bicarbonate trapped in the mucus to keep the surface pH near neutral, and tight junctions between epithelial cells. Prostaglandins (PGE2 and PGI2) stimulate mucus and bicarbonate secretion and also increase mucosal blood flow. Inhibiting them removes this protection.

**Clinical significance:** - **NSAIDs** inhibit COX-1, which reduces prostaglandins. This causes gastric and duodenal ulcers. Misoprostol (a PGE1 analog) restores protection. - ***H. pylori*** disrupts the mucus layer and causes gastritis and peptic ulcers. - **Ménétrier disease:** Foveolar (surface mucous) cell hyperplasia causes giant rugal folds, protein-losing enteropathy, and hypoalbuminemia. Parietal cells are decreased, so acid is low. It is associated with TGF-α overexpression. - **Signet ring cell carcinoma and mucinous adenocarcinoma:** Tumor cells contain abundant intracellular mucin, which pushes the nucleus peripherally. This is classic for diffuse-type gastric cancer (E-cadherin/CDH1 loss) and also appears in colon cancer. Krukenberg tumors are ovarian metastases of signet ring gastric cancer. - **Cystic fibrosis:** Defective CFTR dehydrates airway mucus, so it becomes thick and impairs mucociliary clearance, leading to recurrent infections and bronchiectasis. - **Chronic bronchitis:** Hypertrophy of mucous glands increases the Reid index (above 50%) and causes a productive cough. - **Asthma:** Goblet cell hyperplasia and mucus plugging. - **Mucoceles:** Salivary mucus extravasation or retention cysts. Mucoepidermoid carcinoma is the most common malignant salivary gland tumor and contains mucus-secreting cells. - **Ulcerative colitis:** Goblet cell depletion in active disease. - **Celiac disease and Whipple disease:** Villous atrophy and other changes. Goblet cells are preserved in celiac disease. - **Mucinous (pseudomyxoma peritonei):** Mucin-secreting appendiceal tumors cause "jelly belly."

**Contrast with other gastric cells:** - Parietal cells secrete HCl and intrinsic factor. - Chief cells secrete pepsinogen and gastric lipase. - G cells secrete gastrin. - ECL cells secrete histamine. - D cells secrete somatostatin.

**Mnemonic:** Mucus + bicarbonate + prostaglandins = the stomach's defense against itself.