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The Mouth Starts Everything Moving
Your digestive system started working even before you took the first bite of your
pizza. And the digestive system will be busy at work on your chewed-up lunch for the
next few hours — or sometimes days, depending upon what you've eaten. This process,
called digestion, allows your body to nutrients and energy it needs from the food you
eat. So let's find out what's happening to that pizza.
Even before you eat, when you smell a tasty food, see it, or think about it, digestion
begins. Saliva (say: suh-LYE-vuh), or spit, begins to form in your mouth.
When you do eat, the saliva breaks down the chemicals in the food a bit, which helps
make the food mushy and easy to swallow. Your tongue helps out, pushing the food
around while you chew with your teeth. When you're ready to swallow, the tongue
pushes a tiny bit of mushed-up food called a bolus (say: BO-luss) toward the back of
your throat and into the opening of your esophagus, the second part of the digestive
tract.
MOUTH- The mouth is a cavity formed between the tongue at its base, cheeks at the side, hard
and soft palate in its roof, and teeth at the front. The teeth tear and grind food, which is then churned
through movements of the jaws and tongue. Breaking the food into smaller pieces creates a larger
surface area for the action of enzymes in saliva; these begin to digest the food.
SALIVARY GLANDS- These glands produce a mucus-rich fluid, saliva, that moistens food and
so helps form it into a ball, called a bolus, that is easily swallowed. Saliva also contains enzymes that
begin the digestive process. When food enters the mouth, the brain sends messages to the glands,
triggering a rush of saliva. Food must mix with saliva before it can stimulate the taste buds, which
check that the food is safe to eat.
TYPES OF TEETH- Teeth come in four main types: incisors, canines, premolars, and molars.
Each is shaped for a specific function.
On the Way Down
The esophagus (say: ih-SOF-eh-guss) is like a stretchy pipe that's about 10 inches (25
centimeters) long. It moves food from the back of your throat to your stomach. But also
at the back of your throat is your windpipe, which allows air to come in and out of your
body. When you swallow a small ball of mushed-up food or liquids, a special flap called
the epiglottis (say: ep-ih-GLOT-iss) flops down over the opening of your windpipe to
make sure the food enters the esophagus and not the windpipe.
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If you've ever drunk something too fast, started to cough, and heard someone say that
your drink "went down the wrong way," the person meant that it went down your
windpipe by mistake. This happens when the epiglottis doesn't have enough time to flop
down, and you cough involuntarily (without thinking about it) to clear your windpipe.
Once food has entered the esophagus, it doesn't just drop right into your stomach.
Instead, muscles in the walls of the esophagus move in a wavy way to slowly squeeze
the food through the esophagus. This takes about 2 or 3 seconds.
FUN FACTS
 The length of your entire digestive system from mouth to anus is
approximately 30 feet long.
 Our salivary glands produce around 1.5 liters of saliva each day!
 Once swallowed, bolus (food) travels down through the esophagus to the
stomach, taking about 7 seconds to get there.
 Saliva production through our salivary glands is the first step in digestion.
Saliva is predominantly made up of water, but does contain other
substances, and can be stimulated by just thinking about or smelling food.
Food breakdown begins in our mouths through the process of chewing,
and through enzymes present in saliva. Saliva both lubricates food for easy
passage into the esophagus, and coats the food to protect our teeth and
the lining of our mouth and esophagus.
 The esophagus is bound on each end by a sphincter muscle, which is
responsible for opening to allow the bolus to pass through. Heartburn can
occur when the lower sphincter fails to close completely, allowing
stomach acid to travel upward and irritate the tissue in the esophagus and
throat.
 It takes 5- 30 seconds to chew food.
 In an average person, it takes 8 seconds for food to travel down the food
pipe, 3-5 hours in small intestine and 3-4 days in the large intestine.
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See You in the Stomach
Your stomach, which is attached to the end of the esophagus, is a stretchy sack shaped
like the letter J. It has three important jobs:
1. to store the food you've eaten
2. to break down the food into a liquidy mixture
3. to slowly empty that liquidy mixture into the small intestine
The stomach is like a mixer, churning and mashing together all the small balls of food
that came down the esophagus into smaller and smaller pieces. It does this with help
from the strong muscles in the walls of the stomach and gastric (say: GAS-trik) juices
that also come from the stomach's walls. In addition to breaking down food, gastric
juices also help kill bacteria that might be in the eaten food.
Luckily, our stomachs are lined by a thick layer of mucus to protect us from the
acid and the enzyme pepsin that it produces. The mixing motion of the stomach,
along with the acid and the breakdown of protein by the pepsin, turns the bolus
into a liquid substance called chyme, which in turn is then slowly released into the
small intestine. For a full meal, this process takes approximately two to three
hours.
Only a few things are absorbed into the bloodstream at the level of the stomach,
and interestingly, these are the very things that can cause stomach irritation:
alcohol, aspirin and non-steroidal anti-inflammatory drugs (NSAIDs).
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FUN FACTS
 Your stomach produces hydrochloric acid, the same stuff that masons use to
clean bricks.
 For every 2 weeks, the human stomach produces a new layer of mucous
lining, otherwise the stomach will digest itself.
 The adult stomach has a very small volume when empty but can expand to
hold up to 1.5 litres of food when full.
 The human stomach contains about 35 million small digestive glands.
 The human stomach produces about 2.5 liters of gastric juice everyday.
 The human body takes 6 hours to digest a high fat meal and takes 2 hours for
a carbohydrate meal
 Stomach rumblings (borborygmi) are caused by wave-like muscular
contractions (peristalsis) at the walls of the stomach and small intestine.
These are normal digestion movements, however the process is louder and
more noticeable when the stomach is empty as the sound is not muffled.
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22 Feet Isn't Small at All
The small intestine breaks down the food mixture even more so your body can absorb all
the vitamins, minerals, proteins, carbohydrates, and fats. The grilled chicken on your
pizza is full of proteins — and a little fat — and the small intestine can help extract them
with a little help from three friends: the pancreas (say: PAN-kree-uss), liver, and
gallbladder.
Those organs send different juices to the first part of the small intestine. These juices
help to digest food and allow the body to absorb nutrients. The pancreas makes juices
that help the body digest fats and protein. A juice from the liver called bile helps to
absorb fats into the bloodstream. And the gallbladder serves as a warehouse for bile,
storing it until the body needs it.
Your food may spend as long as 4 hours in the small intestine and will become a very
thin, watery mixture. It's time well spent because, at the end of the journey, the
nutrients from your pizza can pass from the intestine into the blood. Once in the blood,
your body is closer to benefiting from the complex carbohydrates in the pizza crust, the
protein in the chicken, and the calcium in your milk.
The small intestine (say: in-TESS-tin) is a long tube that's about 1½ inches to 2 inches
(about 3.5 to 5 centimeters) around, and it's packed inside you beneath your stomach.
If you stretched out an adult's small intestine, it would be about 22 feet long (6.7
meters) — that's like 22 notebooks lined up end to end, all in a row!
The lining of the small intestine has a huge surface area due to the folds in its lining as well as villi,
tiny fingerlike structures that project from the lining. Once digested, nutrients are absorbed into tiny
blood vessels within the villi. They are then carried in the blood to the liver for processing. Food can
remain in the small intestine for up to five hours.
Love Your Liver
The nutrient-rich blood comes directly to the liver for processing. The liver filters out
harmful substances or wastes, turning some of the waste into more bile. The liver even
helps figure out how many nutrients will go to the rest of the body, and how many will
stay behind in storage. For example, the liver stores certain vitamins and a type of
sugar your body uses for energy.
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Pancreas
The pancreas secretes digestive enzymes into the duodenum, the first segment of the
small intestine. These enzymes break down protein, fats, and carbohydrates. The
pancreas also makes insulin, secreting it directly into the bloodstream. Insulin is the
chief hormone for metabolizing sugar.
Gallbladder
The gallbladder stores and concentrates bile, and then releases it into the duodenum
to help absorb and digest fats.
FUN FACTS
 Absorption of nutrients is conducted by microscopic projections along the lining
of the small intestine called villi. Celiac disease is a disorder in which the
ingestion of gluten results in damage to the villi, which in turn can lead to health
problems stemming from the lack of absorption of vital nutrients.
 On average, the human adult male's small intestine is 6.9 m (22 ft 6 in) long,
and the female's 7.1 m (23 ft 4 in).
 Each day the pancreas releases about 1.5 litres (2 1/2 pints) of enzymecontaining juice into the tract. The liver produces about 1 litre (1 3/4 pints) of
bile, which is stored temporarily in the gall bladder.
 Liver is the largest and heaviest internal organ of the body and weighs about
1.6km
 The Liver is the only organ of the body, which has the capacity to regenerate
itself completely even after being removed almost completely
 A healthy liver processes 720 liters of blood per day.
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That's One Large Intestine
At 3 or 4 inches around (about 7 to 10 centimeters), the large intestine is
fatter than the small intestine and it's almost the last stop on the digestive
tract. Like the small intestine, it is packed into the body, and would
measure 5 feet (about 1.5 meters) long if you spread it out.
The large intestine has a tiny tube with a closed end coming off it called the
appendix (say: uh-PEN-dix). It's part of the digestive tract, but it doesn't
seem to do anything, though it can cause big problems because it
sometimes gets infected and needs to be removed.
Like we mentioned, after most of the nutrients are removed from the food
mixture there is waste left over — stuff your body can't use. This stuff
needs to be passed out of the body. Can you guess where it ends up? Well,
here's a hint: It goes out with a flush.
Before it goes, it passes through the part of the large intestine called the
colon, which is where the body gets its last chance to absorb the water and
some minerals into the blood. As the water leaves the waste product,
what's left gets harder and harder as it keeps moving along, until it
becomes a solid. Yep, it's poop (also called stool or a bowel movement).
The large intestine pushes the poop into the rectum (say: REK-tum), the
very last stop on the digestive tract. The solid waste stays here until you
are ready to go to the bathroom. When you go to the bathroom, you are
getting rid of this solid waste by pushing it through the anus (say: AY-nus).
There's the flush we were talking about!
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FUN FACTS
 Your large intestine receives about one quart of liquid a day from the small
intestine.
 Although there's great variation in frequency, the stool is in general moved once
or twice a day into the rectum in preparation for a bowel movement.
 The intestines are home to more than 500 species of bacteria, which they need
to function effectively. Some of these bacteria are thought to protect the
intestines from disease. Certain bacteria in the large intestine make vitamin K,
which the body needs for blood clotting
 We are not born with any bacteria in our digestive systems, but develop a
significant population within the first month, most of which can be found in our
large intestine. Recognition of the role that bacteria play in digestive health has
stimulated booming sales of products containing probiotics, often labeled as
"friendly bacteria." Bacteria fight off disease-carrying organisms, play a role in
absorbing nutrients that slip past the small intestine through fermentation, and
help to support our immune systems. You're most acutely aware of the work of
bacteria when its process of fermentation causes you to experience intestinal
gas.
 For every 24 hours, in a healthy adult, more than a gallon of water containing
over an ounce of salt is absorbed from the intestine.