Download Digestive System

Functions of the Digestive
System
• Digestion- mechanical and chemical
breakdown of foods for use by the body’s
cells
• Absorption- the passage of digested food
from the digestive tract into the circulatory
system
• Elimination- the expulsion of undigested
food or body waste
Digestive System
• A fresh-baked apple pie is
browning in the oven. Just
the sight and smell of it —
and the anticipation of eating
it — are enough to make you
start salivating and producing
stomach acids. So even
before you take a bite, your
digestive system has swung
into action. After the first
morsel enters your mouth,
the many organs of your
digestive tract kick into high
gear.
Mouth and salivary glands
• After you take your first bite of
pie, your salivary glands
produce enough digestive juices
(saliva) to begin breaking it
down chemically. Besides the
salivary glands in the lining of
your mouth, you have three
pairs of larger salivary glands.
Together they produce 1 to 3
pints (about .5 to 1.5 liters) of
saliva a day.
• Not all of the work is chemical,
though. As you savor the bite of
pie, your teeth work to grind the
pie while your tongue mixes it
with saliva (mechanical). This
action transforms it into a soft,
moist, rounded mass (bolus)
suitable for swallowing.
Esophagus
•
As you swallow the bite of pie,
muscles in your mouth and
throat propel it to your upper
esophagus, the tube that
connects your throat to your
stomach. Muscles in the wall of
your esophagus create
synchronized waves — one after
another — that propel the pie
into your stomach. In this
process, called peristalsis,
muscles behind the bolus of pie
contract, squeezing it forward,
while muscles ahead of it relax,
allowing it to advance without
resistance.
• When the bolus reaches the
lower end of your esophagus,
pressure from the food signals a
muscular valve — the lower
esophageal sphincter — to relax
and let the food enter your
stomach.
Stomach
•
After entering your stomach,
the pie is broken down further.
With its powerful muscles, the
stomach begins churning and
mixing the food into smaller and
smaller pieces. Gastric juices,
rich in acid and enzymes, flow
from glands that line your
stomach. The acid and enzymes
help break down food into a
thick, creamy fluid called chyme.
• Once the chyme is well mixed,
waves of muscle contractions
propel it through the pyloric
valve and into the first section of
your small intestine
(duodenum). The pyloric valve
releases less than an eighth of
an ounce (about 4 cubic
centimeters) of chyme at a time.
The rest is held back for more
mixing.
Pancreas, liver
and
gallbladder
•
In your duodenum, digestion
continues as chyme from the
stomach mixes with a variety of
digestive juices from your
pancreas, liver and gallbladder:
• Pancreas. The pancreas produces
digestive enzymes that help break
down proteins, carbohydrates and
fats. It also produces the hormones
insulin and glucagon, which help
regulate the level of sugar (glucose)
in your blood.
• Liver. The liver performs more than
500 functions, including storing
nutrients, filtering and processing
chemicals in food, and producing
bile, a solution that helps digest
fats and eliminate waste products.
• Gallbladder. The gallbladder stores
and concentrates bile. As fatty food
enters the upper portion of your
small intestine (the duodenum), the
gallbladder contracts and forces
bile into the small intestine through
the common bile duct.
Small
intestine
•
As bile and pancreatic digestive
juices mix with other juices
secreted by the wall of your small
intestine, digestion continues.
What was once apple pie is
propelled into the second portion
of your small intestine, the
jejunum. Here it's further broken
down into smaller molecules of
nutrients that can be absorbed.
Then it slides into the final and
longest portion of your small
intestine — the ileum — where
virtually all of the remaining
nutrients are absorbed through
the lining of the ileum's wall.
• What remains of the food when it
reaches the end of the ileum is a
combination of water, electrolytes
— such as sodium and chloride —
and waste products, such as plant
fiber and dead cells shed from the
lining of your digestive tract
Large intestine
• As this residue passes
through the colon, nearly all
of the water is absorbed,
leaving a usually soft but
formed substance called
stool. Muscles in the wall of
your colon separate the
waste into small segments
that are pushed into your
lower colon and rectum. As
the rectal walls are stretched,
they signal the need for a
bowel movement.
• When the sphincter muscles
in your anus relax, the rectal
walls contract to increase
pressure. These coordinated
muscle contractions expel
the stool.
How long does it take?
• Digestion time varies depending on the individual.
For healthy adults, it's usually between 24 and 72
hours. After you eat, it takes about six to eight
hours for food to pass through your stomach and
small intestine. Food then enters your large
intestine (colon) for further digestion and
absorption of water. Elimination of undigested food
residue through the large intestine usually begins
after 24 hours. Complete elimination from the body
may take several days.
What happens if I swallow gum?
• Although chewing gum is designed to be chewed
and not swallowed, it isn't harmful if swallowed.
Folklore suggests that swallowed gum sits in your
stomach for seven years before it can be digested.
But this isn't true. If you swallow gum, it's true that
your body can't digest it. But the gum doesn't sit in
your stomach. It progresses relatively intact through
your digestive system and is excreted in your stool.
• On rare occasions, large amounts of swallowed
gum combined with constipation have caused
intestinal blockage in children.
Problems of the Digestive System
• Indigestion- burning discomfort in the
upper abdomen caused by eating too
much, too fast, eating certain foods, or
stress
• Heartburn-