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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.
- Winter '13