1. Human Digestive System
Digestion is the breaking down of food in the body, into a form that can be absorbed and used or
excreted. It is also the process by which the body breaks down food into smaller components that can be
absorbed by the blood stream.
Human Digestive System -The Mouth + Saliva
The human digestive system is a complicated and impressive system. Understanding
how the digestive system works helps us to eat healthier. Stay healthy by what you
eat and keep your digestive system healthy.
When you eat food, the saliva mixes with the food. This is a very important process
in preparing the food for the stomach. The salivary juices and enzymes help break
down the food beginning the process of changing the food to the parts the body can
utilize –such as carbohydrates (disaccharides –maltose, etc), proteins, fats,
vitamins, minerals, etc.
Breakdown of Nutrients
When you take smaller bites and chew the food well before you swallow it, you help
make the job of the stomach a little less difficult. The stomach is an amazing place
where acids and enzymes work hard to kill bacteria, start the process of breaking
food down into small molecules -nutrients the body can actually process –such as
carbohydrates, fats, proteins, vitamins, etc.

2. The stomach’s digestive juices include saliva, mucous, hydrochloric acid (HCl),
enzymes, bicarbonate and bile. What ends up leaving the stomach and heads to the
small bowel is chyme –which is semi-digested food.
Human Digestive System -The Small Intestine
The body absorbs the molecules and nutrients that have been broken down, when it
goes through the ileum (~5-7 feet long), which is the last section of the small
intestine before it links to the large intestine. The villi lining the wall of the ileum
help give a large surface for absorption.
Nutrients are absorbed through various ways including active transport, endocytosis,
facilitative diffusion and passive diffusion.
For example:
Fatty acids, fat-soluble substances, monoglycerides and cholesterol are
absorbed through simple diffusion.
Amino acids are absorbed through active absorption.
Sugars like fructose are absorbed with the help of carrier protein molecules.
Water and water-soluble substances are absorbed through osmosis. Water
soluble nutrients leave the GI tract in the blood and travel through the portal
vein to the liver and then to the heart.
The Body's Fuel + Nutrition
The nutrients that come from the food we eat and get broken down are absorbed
into our body and then transported by the blood system and the lymph system to all
the cells and organs in our body. The cells use these nutrients on the molecular level
to give us the energy we need, the ability to heal, the fuel for our cells to do what
they are supposed to do: like your heart beating!
When you smell food or think of food, this triggers the hormones and nervous
system that coordinates digestion and absorption (like the brains behind it). If you
are stressed or sick this can slow the process of digestion down.
The Large Intestine -The Colon
At the end of the digestion process, the waste products leave the small intestines
with the help of fiber and enter the colon –the large intestine. The colon reabsorbs
water and the friendly bacteria helps process vitamins and nutrients. Any fiber or
undigested food that does not get broken down is excreted in the stool. That is how
the digestive system works in a nutshell!
You Are What You Eat!
There is so much more than we think about that goes into how food processes in the
human digestive system. The better we understand the process of how the digestive
system works, the more realize the value of eating healthy and eating a balanced
diet: vegetables, fruits, whole grains and fiber… such as flax seed!

3. Mouth and Esophagus
Digestion begins in the mouth with the grinding of food a mixture of saliva. The saliva breaks
down the chemicals in the food a bit, which helps make the food mushy and easy to swallow.
The tounge pushes the food to the back of the mouth and into the esophagus, or gullet.
The esophagus 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. Here peristalsis (constriction and relaxation of
muscles) begins that propels material through the digestive system.
(A special flap called the epiglottis covers the opening of your windpipe to make sure the food
enters the esophagus and not the windpipe.)
Stomach
The stomach is attached to the end of the esophagus. It is the biggest bulge in the digestive tract.
It has the following functions:
to store the food you've eaten.
to break down the food into a liquidy mixture.
to slowly empty that liquidy mixture into the small intestine.
The strong muscles in the walls of the stomach and the gastric juices that also come from the
stomach's walls helps in breaking the food into smaller and smaller pieces. Pepsin, the
predominant stomach enzyme is a potent digester of meats and other proteins.
Some points to note:
Virtually nothing is absorbed through the stomach walls except alcohol.
An ordinary meal leaves the stomach in three to five hours.
Watery substances leave the stomach quite rapidly while the fats remain considerably
longer.
Most of the process of digestion occurs beyond the stomach.
Small Intestine
It is a long tube, twenty-two feet long (see the above pic), where digestion is completed
and virtually all absorption of nutrients
(vitamins, minerals, proteins, carbohydrates and fats) occurs. It has an alkaline
environment which is necessary for the most important work of digestion and absorption.
The food may spend as long as 4 hours in the small intestine and will become a very thin, watery
mixture. The nutrients from the food pass from the intestine into the blood.
The nutrient-rich blood comes directly to the liver for processing.
Liver - the main storage organ for fat-soluble vitamins
The liver is the largest solid orgain of the body and weighs about four pounds. It acts as a blood
reservoir and a storage organ for vitamins such as A and D and for digested carbohydrate
(glycogen), which is released to sustain blood sugar levels. It manufactures enzymes,
cholesterol, proteins, vitamin A (from carotene), and blood coagulation factors.
One of the prime functions of the liver is to produce bile. Bile contains salts that promote efficient
digestion of fats.

4. 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.
Gallbladder
It is a saclike storage organ about three inches long. It holds bile, modifies it chemically, and
concentrates it ten-fold. Even the sight of food may empty the gallbladder. Constituents of
gallbladder fluids sometimes crystallize and form gallstones.
Pancreas
This gland is about six inches long and provides the body's most important enzymes. It
secretes:
Insulin, which accelerates the burning of sugar in the body.
Pancreatic juice, which contains some of the body's most important digestive enzymes -
lipases, which split fats;proteases, which split proteins; and amylases, which split
starches.
Large Intestine
The large intestine is almost the last stop on the digestive tract. The leftover waste - remnants
of the food that your body can't use - goes on to the large intestine. The body gets its last chance
to absorb the water and some minerals into the blood. The waste gets harder and harder as it
keeps moving along, until it becomes a solid. Then it is pushed into the rectum. The solid waste
stays here until you are ready to go to the bathroom.