Purpose of the Digestive System:
To break food down into nutrients.
These nutrients are then absorbed and transported to body
cells via the circulatory system.
Body cells need nutrients for growth, repair, maintenance
In humans, the digestive system is one long tube called the
GASTROINTESTINAL TRACT.
Four stages of Food Processing:
NAME OF STAGE
Ingestion
DESCRIPTION
Take in nutrients
LOCATION
Mouth
Digestion
Physical or chemical
breakdown of food
molecules
Digested molecules are
absorbed into cells of
digestive tract
waste materials are
removed from the body
Stomach
Small Intestine
Absorption
Egestion
Small Intestine
Large Intestine
Large Intestine
Digestion begins as soon as the food enters
the mouth.
Food enters the mouth where teeth hold,
tear and grind food.
The tongue is responsible for moving the
food around the mouth.
Chewing action stimulates the production
of Saliva (produced by salivary glands)
Saliva is made of water, mucus, and the enzyme amylase. It
chemically digests the food, turning in into a watery mixture
that can easily pass into the stomach.
The throat is a connecting tube between the mouth and the
esophagus, which in turn links to the stomach. Food is
carried along the esophagus by muscular contractions called
peristalsis.
Food is stored and digested in the stomach (J-shaped)
The cells that line the stomach secrete gastric juices
(hydrochloric acid and other important enzymes) which
chemically break down the food, releasing the nutrients.
The stomach lining is protected by mucus. Without mucus,
the gastric juices would break down the stomach lining,
causing ulcers.
Muscular contractions move the partially digested food
around the stomach.
Small amounts of water, some medicines (e.g. aspirins), and
alcohol
The small intestine connects the stomach to the large
intestine.
The small intestine is more than 20 feet long!
It has three parts: duodenum, jejunum, and ileum. These
parts are all connected:
Most chemical digestion takes place in the first 25m – called
DUODENUM
Partially digested food that enters the small intestine is called
CHYME (same consistency of porridge)
Liver secretes bile directly into the small Intestine
Produces the enzyme MALTASE which breaks maltose into
Glucose
Produces the enzyme PEPTIDASE which digests proteins
By the end of digestion, the macromolecules are
broken down into molecules small enough to be
absorbed from the intestine and into the bloodstream:
CARBOHYDRATES ---- GLUCOSE
PROTENS- ----- AMINO ACIDS
LIPIDS--- FATTY ACIDS AND GLYCEROL
These products are now ready to be absorbed into the
small intestine:
Accessory Organs (Liver, Gall Bladder and Pancreas)
The liver is essential in digestion
Mass: 1.5 Kg (or 3 pounds)
Produces bile continuously and is stored in the
Gallbladder until it is needed
Bile contains bile salts which break down fat molecules
Stores carbohydrates and vitamins
Detoxifies many harmful toxins such as
alcohol. Detoxifying means to convert harmful
substances into non harmful ones – BUT if consumed
in large amounts, toxins can destroy liver cells 
CIRRHOSIS
A flat, elongated gland in the abdomen
18-25 cm long - easy to recognize - looks like a finger
The pancreas produces digestive juices (enzymes) that
continue the process of breaking down foods, which begins in
the stomach. These juices are released into the small intestine
(duodenum)
The pancreas also produces hormones, most famously
insulin (which causes the muscles and other bodily tissues to
take up glucose from the blood to fuel their activity).
Also called COLON. It is approx. 1.5m long
FUNCTIONS:
I) Absorbs water
II) Harmless bacteria live in the walls of the large intestine –
these bacteria produce vitamin K and B.
III) Expels digestive waste products
Interesting Facts:
The average person eats about 1.5kg of food a day, and
produces about 0.4 Kg of waste in the form of feces.
Feces are composed mainly of undigested cellulose (fiber),
along with living and dead bacteria, and water.
Removal of feces is important because it eliminates toxic
wastes from the body, and decreases the risk of developing
colon cancer.
Girl inside small intestine