Transcript The Human Digestion System

Chapter 38
Functions of the Digestive System
 To ingest food
 Digest food
 Force food along digestive tract
 Absorbs nutrients from the digested food
 Eliminates undigested foods from your body
The Mouth
 In the mouth the tongue and teeth begin the first part of
food digestion by chewing. Chewing is a part of
mechanical digestion.
 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
effective.
 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
disaccharides.
 Although swallowing happens quickly amylase still
acts on starches for 30 minutes inside the stomach.
Swallowing Food
 Swallowing is a voluntary action in which your tongue
helps push the food from the mouth to the
esophagus.
 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
during swallowing
The Stomach
 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
mechanical digestion.
Stomach Cont’d
 Chemical digestion also occurs in the stomach, the
wall of the stomach is full of glands that secrete
gastric juice.
 Gastric Juice: combination of Hydrochloric acid
and Pepsin.
 Pepsin: digestive enzyme that begins the chemical
digestion of proteins, only works in acidic
environments.
 In such an acidic environment why doesn’t the
stomach digest itself?
Stomach Cont’d
 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
villi.
 Villus: projection on the lining of the small
intestine that helps aid in the absorption of
nutrients.
The Large Intestine
 The undigested food will pass into the large
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intestine.
Large Intestine: a muscular tube also referred to as the
colon.
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.
Vocabulary Words
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Mechanical Digestion
Chemical Digestion
Salivary Glands
Saliva
Amylase
Esophagus
Peristalsis
Epiglottis
Stomach
Gastric Juice
Pepsin
Small Intestine
Duodenum
Liver
Pancreas
Bile
Gall bladder
Villus
Large intestine
Rectum