-These actions follow each other continuously and push along the intestinal
-The waves of contraction ripple through the GI tract at varying rates and
intensities depending on the part of the GI tract and on whether food is present.
Digestion, Absorption, and Transport
-The digestive tract is the bodys ingenious way of getting the nutrients ready for
absorption, and it solves many problems for you without any conscious effort of
-Human beings breathe, eat, and dr
-From this point on, the chyme remains at the neutral or slightly alkaline pH at
which the enzymes of both the intestine and the pancreas work best.
-Bile also flows into the duodenum.
-The liver secretes bile continuously, and it is concentrate
Anatomy of the Absorptive System
-The small intestine is a tube about 20 feel long an inch or so across.
-Its inner surface looks smooth and slippery, but viewed through a microscope, it
turns out to be wrinkled into hundreds of folds.
-Each fold, in turn
Final Stage of Digestion
The Final Stage
-The story of how digestion prepares food for absorption is now nearly complete.
-The three energy-yielding nutrients are
-These have been disassembled to basic building blocks and are r
-Enzyme is a giant protein molecule that facilitates a chemical reaction.
-It makes molecules, breaks a molecule, or changes a molecule.
-In its role as a catalyst, the enzyme itself remains unchanged.
-The enzymes involved in digestion facilitate
-If the stomach acid chances to reflux into the esophagus, it causes the
sensation of heartburn.
-The stomach enzymes work most efficiently in a fluid of pH 2 or lower.
-The salivary enzymes swallowed with food do not work in acid this str
Small and Large Intestines
-The stomach retains the bolus for a while, adds juices to it, and grinds it to a
suspension of particles in liquid called chime.
-Then, bit-by-bit, the stomach releases the chime through the pyloric sphincter
into the small int
Muscles of Digestion
-The strong muscles of the rectum holds back this waste until it is time to
-Then the rectal muscles relax, and the last sphincter in the system, the anus,
opens to allow passage of the waste.
-Food enters the mouth and trav
Human Waste System
-The materials within the tract should be kept moving, slowly but steadily, at a
pace that permits all reactions to reach completion.
-The enzymes of the digestive tract are designed to digest carbohydrate, fat, and
-The intestines not only push, but also periodically squeeze, their contents, as if
you had put strings around the intestines as intervals along their length and
pulled them gently now and then.
-This motion, called segmentation, momentarily