The Human Digestion System
Transcript The Human Digestion System
Functions of the Digestive System
To ingest food
Force food along digestive tract
Absorbs nutrients from the digested food
Eliminates undigested foods from your body
In the mouth the tongue and teeth begin the first part of
food digestion by chewing. Chewing is a part of
Mechanical Digestion: the physical process of
breaking food into smaller pieces
Mechanical digestion increases the surface are of food
particles which allows chemical digestion to be more
Chemical Digestion: process of structurally changing
food molecules through action of enzymes
The Mouth Cont’d
As you chew your salivary glands release saliva,
which is a mixture of water and the enzyme amylase.
Amylase breaks down the starch in food which are
generally in polysaccharide form into
Although swallowing happens quickly amylase still
acts on starches for 30 minutes inside the stomach.
Swallowing is a voluntary action in which your tongue
helps push the food from the mouth to the
Esophagus: muscular tube that connects the
mouth to the stomach
Food gets moved through the esophagus very quickly
(5-8 sec) by peristalsis.
Peristalsis: involuntary muscle contractions
along the walls of the digestive tract.
Swallowing Food Cont’d
Have you ever had food “go down the wrong tube?”
As you swallow food passes over the windpipe which
leads to your lungs, the epiglottis temporarily closes
when swallowing preventing food from going down
the wrong direction. Breathing is temporarily stopped
but if you talk or laugh while swallowing food can get
into the wrong place.
Epiglottis: flap of skin covering the windpipe
Food enters the stomach through a valve at the
bottom of the esophagus.
Stomach: is a muscular, pouch-like enlargement
of the digestive tract.
Made up of three layers of muscles lying across one
another. When these muscles contract they churn or
mix the food inside your stomach, another form of
Chemical digestion also occurs in the stomach, the
wall of the stomach is full of glands that secrete
Gastric Juice: combination of Hydrochloric acid
Pepsin: digestive enzyme that begins the chemical
digestion of proteins, only works in acidic
In such an acidic environment why doesn’t the
stomach digest itself?
To fight against the acidic environment the stomach
secretes a mucus that helps line the stomach and
create a protective layer.
Ulcers form from holes in this protective layer.
Food remains in the stomach for 2-4 hours until it is
passed into the small intestine.
When it finally passes food is in a liquid form with the
consistency of tomato soup.
The Small Intestine
Small intestine: muscular tube about 6m long
and 2.5cm in diameter.
Digestion is completed inside the small intestine.
Mechanical and Chemical digestion take place on
proteins and carbohydrates.
Duodenum: is the first 25 cm of the small intestine
The wall of the duodenum secrete enzymes that chemically
breakdown food but most of them enter through a duct
from the pancreas and liver.
Both of these organs play major roles in digestion although
food never passes through them.
Small Intestine Cont’d
Pancreas: is a soft, flattened gland that secretes
both digestive enzymes and hormones.
Enzymes from the pancreas break down
carbohydrates, fats, and proteins
Also sodium hydrogen carbonate is secreted which
makes the pancreatic juice alkaline. Meaning it
neutralizes the acidic stomach acid stopping pepsin
from continuing to work.
Small Intestine Cont’d
Liver: is a complex gland that secretes bile.
Bile: is a chemical that breaks fats into small
droplets and also neutralizes stomach acids.
Gallbladder: stores bile made from the liver.
Liquid food will stay in the small intestine for 3-5
hours allowing for absorption. Food is slowly moved
along by peristalsis. This pushes food over millions of
Villus: projection on the lining of the small
intestine that helps aid in the absorption of
The Large Intestine
The undigested food will pass into the large
Large Intestine: a muscular tube also referred to as the
1.5 m long and 6.5 cm in diameter
Water is absorbed through the walls of the large
intestine from the undigested food, leaving behind a
more solid material.
Anaerobic bacteria residing in the large intestine will
digest most of the material and synthesize some
vitamin B and K needed by the body.
Large Intestine Cont’d
After 18 to 24 hours in the large intestine, the
remaining undigested food will have reached the
rectum in the form of feces.
Rectum: The last section of the digestive system.
Feces is eliminated from the rectum through the anus.
The entire process from beginning of digestion to end
takes 24-33 hours.