What is the primary function of enterocytes in the large intestine?
Secretion of digestive enzymes
Breakdown of food particles
Absorption of water, salts, and vitamins
Production of mucus
The Correct Answer is C
A. Secretion of digestive enzymes: The large intestine does not produce endogenous digestive enzymes. Any remaining chemical digestion in the colon is performed by the resident microbiota. The colonic mucosa is specialized for reclamation rather than catalytic secretion.
B. Breakdown of food particles: Mechanical and chemical breakdown is largely completed by the time chyme reaches the cecum. The large intestine focuses on consolidating waste rather than further degradation. Digestion is a function of the upper gastrointestinal tract.
C. Absorption of water, salts, and vitamins: Colonic enterocytes possess specialized ion transporters and water channels to desiccate fecal matter. They also absorb electrolytes and vitamins, such as Vitamin K, synthesized by bacterial flora. This maintains systemic fluid and electrolyte homeostasis.
D. Production of mucus: Mucus is synthesized and secreted by goblet cells, which are distinct from the absorptive enterocytes. While mucus is abundant in the colon to lubricate feces, it is not the product of the enterocytes. These two cell types have different roles.
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Correct Answer is C
Explanation
A. Lymphatic vessels:These vessels primarily transport chylomicrons and large lipid-soluble molecules from the intestinal mucosa. While some signaling molecules may enter lymph, enteroendocrine hormones are not specifically targeted here. They utilize the vascular route for systemic distribution.
B. Bloodstream:Hormones eventually reach the systemic circulation to exert their physiological effects on distant target organs. However, the immediate site of secretion from the basal membrane of the cell is not the vessel lumen. The bloodstream is the secondary destination.
C. Interstitial fluid:Enteroendocrine cells are basal secretors that release regulatory peptides into the surrounding extracellular space. From this fluid, the hormones diffuse into local fenestrated capillaries to enter the circulation. This is the primary site of hormonal release.
D. Gastric pits:These are invaginations of the gastric mucosa where exocrine cells, such as parietal and chief cells, discharge their secretions. Enteroendocrine cells do not secrete into the lumen. Their products are released basally to act as hormones.
Correct Answer is B
Explanation
A. It digests triglycerides with bile:Bile is synthesized by hepatocytes and secreted into the duodenum, not the stomach. Triglyceride emulsification occurs distal to the pyloric sphincter. The gastric environment is too acidic for biliary salts to function effectively.
B. It stores food and gases prior to chyme formation:The fundus is the superior, dome-shaped portion of the stomach that accommodates ingested boluses through receptive relaxation. It serves as a physiological reservoir for undigested food and accumulated digestive gases. It allows for gradual processing into chyme.
C. It produces intrinsic factor for protein absorption:While parietal cells in the fundus and body secrete intrinsic factor, this glycoprotein is specifically required for vitamin B12 absorption in the ileum. It is not involved in the proteolytic cleavage of proteins. Protein digestion requires pepsin.
D. It initiates absorption of nutrients:The gastric mucosa lacks the specialized villi and microvilli necessary for significant nutrient uptake. Absorption is almost exclusively a function of the small intestinal enterocytes. The fundus is primarily a site for storage and mechanical processing.
E. It absorbs vitamin B12 directly:Vitamin B12 cannot be absorbed in the stomach; it must first bind to intrinsic factor. The resulting complex travels to the terminal ileum for receptor-mediated endocytosis. Direct gastric absorption of this vitamin does not occur.
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