Vitamin and Mineral Digestion Taken For Granted
by Kristy Haugen  
role is to convert the food into substances that are capable of being absorbed. The
digestive system is comprised of the following structures: the mouth, pharynx,
esophagus, stomach, small intestine, large intestine, and the anus. The liver,
gallbladder, pancreas, and salivary glands also play a role in digestion but are not
considered part of the alimentary canal (primary digestive organs).

Digestion begins in the mouth when food is ingested. This is a mechanical process.
Through mastication, (the biting and chewing action of the teeth) the breakdown of
food from larger particles into smaller particles takes place. This process doe not
chemically alter the food, but increases the total surface area of the food. This in turn
increases the speed and efficiency of enzyme activity. An enzyme is a protein that
catalyzes, or speeds up, a chemical reaction. Enzymes are essential to sustain life
because most chemical reactions in the body would occur too slowly, or would lead
to different products without the assistance of enzymes.

For more information on enzymes and how enzymes work, go to http://www. and click on ‘Liquid Vitamins Contain
Enzymes Because?’ article link.

Saliva also plays an important part with digestion in the mouth. Saliva is secreted by
the salivary glands which lubricates the food to facilitate swallowing. The salivary
glands begin to produce saliva in response to food; whether stimulated by smell or
taste. Some may experience a mouth watering sensation in response to a big juicy
steak. Also, saliva initiates the digestion of carbohydrates. Amylase is the digestive
enzyme found in saliva that helps with carbohydrate digestion. Once the food has
been sufficiently chewed, the tongue rolls it into a ball (bolus) and pushes it into the
pharynx (the cavity that leads from the mouth to the esophagus). Swallowing
(deglutition) propels the bolus downward into the upper esophagus using a peristaltic
contraction (wavelike motion). At this time, the epiglottis blocks the trachea (airway)
to prevent food from entering the lungs and interfering with breathing. Peristaltic
contractions continue to move the bolus (food) downwards to the lower esophageal
sphincter. This is the ring of smooth muscle fibers at the junction of the esophagus
and stomach; it is also referred to as the cardiac sphincter. When food approaches,
the sphincter relaxes to allow food into the stomach. After the food has passed
through the sphincter, the muscle fibers contract to keep the food and digestive
juices from re-entering the esophagus. Heartburn results when the cardiac sphincter
relaxes and allows the digestive juices to re-enter the esophagus. When this happens
too often, the smooth muscle of the esophagus is eroded, which can cause bleeding
and persistent heartburn referred to as GERD (gastro-esophageal reflux disease). This
can become a serious condition.

The stomach is a large muscular organ; the walls are lined by a thick gastric mucosa.
The stomach is also lined by two types of glands: gastric and pyloric glands. These
glands contain mucous cells which secrete mucus that protects the stomach lining
from the harsh stomach acid (pH of 2). Chief cells located in the gastric glands
secrete pepsinogen, which is a zymogen. A zymogen is an inactive form of an
enzyme. The gastric glands also contain parietal cells which secrete hydrochloric acid.
This aides in the conversion of pepsinogen to the active enzyme pepsin, and secrete
intrinsic factor which helps to absorb vitamin B12. Hydrochloric acid is essential to kill
bacteria in the food, and to help breakdown the food into an absorbable form. The
pyloric glands contain peptic cells which also secrete the zymogen pepsinogen.
Gastrin cells are located in the pyloric glands. These cells secrete the hormone gastrin
for hydrochloric acid production in the parietal cells; and stimulate the churning of the
stomach to help produce the acidic, semi-fluid, partially digested mixture referred to
as chyme. Protein digestion is initiated in the stomach.

The chyme then empties into the small intestine by way of the pyloric sphincter. The
pyloric sphincter is the ring of smooth muscle fibers located at the joining of the
stomach and small intestine. The small intestine consists of three regions: the
duodenum, jejunum, and ileum. The bulk of digestion will be done in the duodenum.
The jejunum and ileum have a primary function of absorption.

The small intestine has the perfect anatomy for absorption. The extended length,
highly coiled structure, along with surface villi (small finger like projections), and
epithelial cells with a brush border microvilli allow for increased surface area for
absorption. Nutrients are absorbed across the epithelium villi and are carried to the
bloodstream through capillaries (small blood vessels) or lacteals (small lymph vessels
that serve as extensions of the lymphatic vessel in the villi). Goblet cells located in the
small intestine secrete mucus on the surface epithelium of the villi for protection from
the digestive juices.

The pancreas releases a pancreatic juice in response to the hormone secretin that is
secreted by the duodenum. This hormone cholecystokinin (CCK) is secreted in
response to the acidity of the chyme in the small intestine. The pancreatic juice that is
secreted has an alkaline pH to neutralize the acidity of the chyme. The pancreatic
juice contains many enzymes (inactive & active) that digest carbohydrates, proteins,
and lipids (fats).

The liver plays the role of secreting and synthesizing bile. Bile is a non-enzymatic
digestive fluid that is used to breakdown (emulsify) fats. The gallbladder simply stores
and concentrates the bile. Bile is made up of bile salts, bile pigments, and cholesterol.

Meals high in fat tend to spend a longer amount of time in the stomach since it takes
more time to digest. The hormone enterogastrone is released by the duodenum. This
hormone inhibits the peristalsis in the stomach, slowing the release of chyme into the
small intestine. This also gives more time for the bile to properly digest the fats.

The remaining food passes from the small intestine to the large intestine. The large
intestine consists of three parts: cecum, colon, and rectum. The large intestine plays
a smaller role of digestion, mainly to absorb any electrolytes and water that has not
already been absorbed. This process is done in the colon. Many normally harmless
bacteria colonize the large intestine, such as E. coli. E. coli is important because this
type of bacteria produces vitamin K as a byproduct. This is a good source of vitamin
K. Also, the amount of time spent in the large intestine determines the consistency of
the stool. If too little time is spent in the colon, diarrhea and dehydration result. If too
much time is spent in the colon, constipation will result.

Lastly, the stool passes into the rectum. The rectum stores the feces (stool), which
consist of unabsorbed digestive secretions (enzymes), water, undigested food
(cellulose and fiber, etc.). The anus is the opening through which wastes are
eliminated. The anus is separated from the rectum by two sphincters that regulate

The digestive process is just one extremely complex process that occurs without
question. It is often taken for granted. The complexity isn’t easy to understand. The
next time you eat a juicy steak, understand the journey the meal is sent on is much
farther than the trip to the restaurant.

Copyright 2005 Kristy Haugen

About The Author

Kristy Haugen is a mother working to finish her second bachelor degree in Chemical
Engineering. She is also a Licensed Practical Nurse with a current bachelor degree in
Biology and Chemistry. She writes to quench her thirst for knowledge. Read more
articles at
The body is a complex web of
systems. Most are not fully
aware of the complexity of the
digestive system. However,
most know of its opposite,
indigestion. Most do not realize
how amazing the body can be,
especially the digestive tract.
When the process of digestion is
described as fascinating, passing
gas isn’t going to be the major
focus (flatulence), but more so
the process of how gas is

The digestive system’s primary
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