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Digestive System
Digestive System – Function
Also called the gastrointestinal system, the digestive system breaks
down eaten material into nutrient molecules, absorbs water and ions,
and eliminates undigested residue.
The digestive system is a continuous tube (the digestive tract or
alimentary canal). Areas along this tube are specialized to perform
different functions related to getting the nutrients from your food to the
cells that need them. Accessory organs add secretions into different
areas along the tube.
Your cells can’t use the pizza you had for lunch in pizza form. It needs to
be broken down into molecules that are small enough to be absorbed. As
the pizza travels along the digestive tract, each organ along the way
breaks it down further. Muscles in the walls of the digestive tract keep
things moving along, and glands in the tissues secrete digestive juices—
mostly enzymes and acids—that break up the larger substances in the
pizza into smaller molecules. Food is physically broken into smaller
pieces in a process termed mechanical digestion. These pieces are then
chemically broken down into smaller units in a process termed chemical
digestion. Proteins are broken down into amino acids. Carbohydrates
are broken down into simple sugars. Fats are broken down into
molecules like fatty acids and cholesterol. It is important that the large
particles are broken into their smallest units so they can be absorbed
from the digestive tract into the bloodstream. Therefore, the main
functions of the digestive system are to ingest, break down, and absorb
the nutrients from our food. It also eliminates the wastes (anything not
absorbed) as feces.
Digestive System - Organs
The specialized organs of the digestive tract extend in a roughly superior
to inferior direction from the mouth (where food goes in) to the anus
(where waste comes out) in the following order:
•
Mouth
•
Pharynx
•
Esophagus
•
•
•
Stomach
Small intestine (including the duodenum, jejunum, and ileum)
Large Intestine (including the cecum, colon, and rectum)
•
Anus
Accessory organs in the digestive system are connected to the digestive
tract and secrete additional digestive juices.
The salivary glands produce saliva-containing (among others) amylase,
an enzyme that breaks down carbohydrates.
The pancreas secretes a variety of enzymes that break down fats,
carbohydrates, and proteins, as well as bicarbonate ions that neutralize
stomach acids. It is important to note that this function corresponds to
the exocrine portion of the pancreas.
The liver produces bile, which aids in fat digestion and absorption.
The gall bladder stores and concentrates bile and secretes it into the
small intestine.
The stomach is a sort of muscular sac that can expand to hold a large
meal. Glands in the walls of the stomach secrete enzymes and acids that
break down food. Muscles in the walls of the stomach churn the food
and digestive juices together. Although the stomach can receive a large
amount of food at a time, it releases its contents gradually into the small
intestine, so that the intestine can better perform its function.
Digestion continues in the small intestine, with additional digestive juices
produced by the pancreas, liver, and the walls of the small intestine
itself. The walls of the small intestine have numerous tiny folds, which
increase its surface area, allowing for efficient absorption of nutrients
into the circulatory system, which in turn takes the nutrients to all the
cells of the body.
Excess water is reabsorbed in the large intestine, and the undigested
portion of your pizza leaves the body. Resident microbes of the large
intestine (gut micro biota) can digest substances that our cells cannot.
Digestive System - Anatomy and Direction
The digestive system is located primarily in the abdomen.