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Digestive System:
The digestive system is a body system that breaks down food so that nutrients can be
absorbed by the cells in the body. (Figure 8-6) Food is the source of energy for the body so that
the body can function and be active. Digestion is the process by which food is chemically
changed to a form that can pass through the cell membranes. The main organs of the digestive
system form a continuous tube or tract through which food moves as the result of involuntary
muscle contractions called peristalsis.
Digestion starts in the mouth when food is chewed and mashed by the teeth and
moistened by saliva. Saliva is the watery, slightly alkaline fluid secreted into the mouth. Saliva
contains an enzyme that starts the chemical breakdown of carbohydrates. An enzyme is a
chemical that speeds up a chemical reaction. Other enzymes are produced in the stomach and
small intestine to complete the process of digestion as food moves through those organs.
Digestion is completed in the small intestine, which is a coiled tube measuring approximately
twenty-three feet in length. The digested food is absorbed through cell membranes in the lining
of the small intestine into blood vessels that are present around cells in the lining. Food that is
not digested passes into the large intestine, which is also called the colon. The colon is the major
part of the large intestine. The cells that form the lining of the colon absorb water from the
undigested material and return it to the body tissues. This is an important factor in maintaining
the body’s water balance. The remaining undigested material forms a semi-solid mass called
feces, which is a excreted through the anus.
The liver, gallbladder, and pancreas are other body organs that are involved in the process
of digestion. They are not parts of the continuous digestive tract. The liver is the largest gland in
the body and produces bile. Bile is a liquid secreted by the liver. Bile is essential in the digestion
of fat in foods because it breaks fat particles into smaller droplets that will pass through cell
membranes. Bile produced in the liver moves through a tube called hepatic ducts to the
gallbladder where it is stored. When food is present in the stomach, bile is released from the
gallbladder, moves through the common bile duct, and empties into the small intestine.
The pancreas is an elongated, tapered, gland that lies across the back of the abdomen..
The pancreas produces an important enzyme called insulin, which helps digest glucose (sugar).
These enzymes flow through a duct that empties into the common bile duct. Anything that upsets
the body’s ability to process food affects the entire body. It is important to get medical help for
any chronic or lasting ailments that affects digestive organs.
See back for diagram of Digestive System.