Milk Protein Digestion Essay

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The first phase of digestion is the cephalic phase. Neurogenic signals from the cerebral cortex are transmitted through the vagus nerve to the stomach and stimulate gastric secretion. The cephalic phase occurs from smelling, seeing, thinking about and tasting food, prior to further digestion of food in the stomach.
Break down of milk begins in the mouth where salivary glands secrete salivary amylase and lipase. Salivary amylase initiates the hydrolysis of long carbohydrate chains to disaccharides and polysaccharides. Salivary lipase begins the hydrolysis of triglycerides to glycerides and free fatty acids. Milk moves through the esophagus by peristalsis. Enzymes are not secreted in the esophagus and digestion does not take place here. Milk then enters the stomach milk protein digestion begins and lipid digestion continues. Very little digestion of milk sugars continues in the stomach, however resumes in the small intestine.
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In the stomach, milk proteins casein and whey mix with HCL and pepsinogen. HCL is secreted by parietal cells which line the walls of the stomach. Pepsinogen is secreted by gastric chief cells, becoming active when contacting HCL. HCL causes proteins to denature. Casein and whey are now accessible to pepsin (the active form of pepsinogen) to be broken down into peptides for easier digestion in the small intestine. Casein represents about 80% of milk protein and functions to form a clot in the stomach for efficient digestion. The globular proteins of milk whey are beta-lactoglobin, alpha-lactalbumin, bovine serum albumin and immunoglobulins, and are more water soluble than caseins (Haug,

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