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Digestive System
Study Guide
Vocabulary
Esophagus - The passage between the mouth and the stomach, a muscular tube that uses
peristalsis to move food to the stomach.
Stomach - Large muscular sac that continues the mechanical
and chemical digestion of food.
Large Intestine - The last section of the digestive system, where
water is absorbed from food and the remaining material is
eliminated from the body.
Small Intestine - The part of the digestive system responsible for
most chemical digestion and absorption of nutrients.
Appendix - A small, finger-like extension of the large intestine,
but has no function in the digestive system.
Pancreas - A gland located behind the stomach that secretes
pancreatic juice into the small intestine, where it mixes with bile to
digest food.
Gallbladder - An organ that stores bile produced by the liver until
it is needed in the small intestine.
Liver - Large organ just above the stomach that makes bile to
break down fats; also filters poisons and drugs out of the blood.
Larynx - The area of the throat that contains the vocal cords and
produces vocal sounds.
Trachea - The windpipe; a passage through which air moves in
the respiratory system.
Epiglottis - A flap of tissue that seals off the windpipe and
prevents food from entering.
Rectum - A short tube at the end of the large intestine where
waste material is compressed into a solid form before being
eliminated.
The human digestive system breaks down the food you consume, using as much of the
nutrients as possible to fuel the body. After the energy is extracted from food through digestion
and metabolism, the remainder is excreted, or removed.
The digestive process
Imagine biting into a big, juicy cheeseburger. The enzyme in your saliva —salivary amylase —
is there to start digesting the carbohydrates, most likely those in the bun. Chewing allows teeth
to start breaking down some of that food. Swallowing is when the food bolus is squeezed down
your esophagus into your stomach. That action is called peristalsis, and it occurs throughout
your entire digestive tract.
Once the cheeseburger bits are in your stomach, they are referred to as a bolus. The bolus is
drowned in gastric juice, which is made up of the enzyme pepsin and hydrochloric acid (HCl).
If you eat too much, your stomach produces more acid, and the contents of your overly
full stomach can be forced back up into the esophagus, which runs in front of the heart,
giving you heartburn.
The enzyme and acid act to break down the food and release the nutrients. The carbohydrates,
protein, and fat in foods you consume all are important for proper nutrition. This final stage in
digestion occurs in the small intestine.
Digested food from the stomach is pumped into the small intestine, which gets flooded with
fluid and enzymes from the liver (bile) and the pancreas. Those chemicals help to break the
molecules of the digesting food into its smallest peices. The smallest form of carbohydrate is
glucose, which is a sugar molecule. Proteins can be reduced to amino acids; fats can be
reduced to fatty acids. The smallest forms of the nutrients pass through the walls of the small
intestine and are absorbed into the bloodstream.
The scoop on poop
The useable nutrients are absorbed into the bloodstream from the small intestine. The
leftover material continues on to the large intestine, where fecal matter (feces, or “poop”) is
created. The large intestine absorbs water and some electrolytes from the leftover material,
and that water is returned to the body to prevent dehydration. If too much water is absorbed,
constipation occurs; if too little water is absorbed, diarrhea occurs.
Once the feces are created, they pass to the colon, where they are stored. When the colon is
full, a signal is sent to your brain telling you that you need to relax your anal sphincter and
release the feces.
Back to the bloodstream
Important, useful molecules pass through the walls of the small intestine into the bloodstream.
The bloodstream carries those molecules throughout the entire body. Every nook and cranny is
supplied by blood capillaries, so every nook and cranny receive nutrients from the food you
digested.
The nutrients gained from digested food move through the capillary walls, and are absorbed by
the cells. At the same time, waste produced by the cells moves out of the cell, and into the
capillary, where it can be carried to the kidney for excretion or removal.