Anatomy and Physiology Answer Key

2 the vagus nerve provides the parasympathetic

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Unformatted text preview: s of the gut have specific pH optima (pH at which they operate most efficiently). Note: For pepsin (stomach) this optimum is acid pH 1.52.0, for the enzymes in the small intestine, the optimum is alkaline pH 7.5-8.2. (b) The enzymes are secreted as inactive precursors in order to prevent their activity in the site of production and release (where they would damage the tissue). Once in the gut lumen, they can be activated to digest the food (the gut lining itself is protected by mucus). 5. Alcohol is a small molecule and is absorbed directly from the stomach into the bloodstream. When the stomach is empty, the mucosa is more exposed than when the stomach is full of food and the absorption can take place much more rapidly. 6. Sphincters regulate the passage of food through the gut, allowing material to pass more quickly through the gut, or holding it back. Their activity depends on speed of digestion, food type, the influence of hormones, and the fullness of the gut. Note: Sphincter contraction partly or completely closes an orifice. The Liver's Role in Digestion (page 186) 1. (a) Bile provides the alkaline pH for the activity of the pancreatic enzymes (pH 7.5 -8.2). (b) Bile emulsifies fats (breaks them up) so that they are more accessible to the digestive enzymes and are more readily absorbed. 2. (a) It metabolizes fats, carbohydrates, and amino acids (especially with respect to converting glucose to glycogen and the metabolism of excess amino acids in the urea cycle). (b) It stores iron, copper, and vitamins (absorbed from the food but not necessarily required immediately). 3. The gallbladder stores the bile and releases it into the small intestine when it is required (in response to hormones released when there is food in the gut). 4. Bile acts as an emulsifier of fats in digestion and the bilirubin pigments present in bile are the metabolized breakdown products of spent red blood cells, which are excreted along with egested gut contents. 5. (a) Hormone 1: Secretin. Effect: Stimulates production of bile by liver cells. (b) Hormone 2: Cholecystokinin (...
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This document was uploaded on 01/28/2014.

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