Download Biology 392 - Chapter 38-2

• Dinner Is Served
• Remember the last time you sat
down to a dinner of your favorite
foods? Recall everything that
you did before you swallowed
your first bite.
1. Why do you cut up your food?
2. What role do your teeth play in eating?
3. Saliva is the fluid that is found in your mouth.
What role do you think it plays in eating?
Chapter
38.2
The Process of Digestion
Main Function
 Helps convert foods into simpler
molecules that can be absorbed and
used by the cells of the body

Built around a one-way tube
(alimentary canal) that runs through
the body
Organs of the Digestive System
The path that food travels:
 Mouth  pharynx  esophagus 
stomach  small intestine  large
intestine  rectum  anus
 Several major accessory structures
including the salivary glands, the
pancreas and the liver add secretions
to the digestive system.
Digestive System
Mouth
Pharynx
Salivary glands
Esophagus
Liver
Gallbladder
(behind liver)
Stomach
Pancreas (behind
stomach)
Large intestine
Small intestine
Rectum
The Mouth


Beginning of the digestive system
Mechanical digestion  physical breakdown
large pieces into smaller pieces


Chewing – Teeth: cut, tear, crush food
Purpose is to increase surface area of food so
that more enzymes can breakdown the
molecules
The Mouth (Cont’d)

Chemical Digestion  large food molecules
are broke down into smaller food molecules


Enzymes, acid
Salivary glands – produce saliva


Moistens food
Contains enzymes
 Amylase  breaks down starches and releases
sugars
 Lysozyme  fights infection
Swallowing

Food is pushed to the back of the throat

While chewing, the tongue pushes food up
and back
 Smashes food against the hard and soft
pallet

Clump of food  bolus
Epiglottis  flap of tissue that blocks off the
opening to the trachea, directing the food
down the esophagus
Esophagus

Food tube


Connects pharynx and
the stomach
Peristalsis 
contractions of the
smooth muscle squeeze
the food through the
esophagus into the
stomach

Fig. 38-11 page 980
Stomach

Large muscular sac



Site of chemical and mechanical digestion
Contracts to churn and mix stomach fluids
together
Cardiac sphincter –


Ring of muscle that lets food into the stomach
and prevents acid from entering the
esophagus
Heartburn  painful, burning sensation, that
results from the backflow of stomach acid
Stomach (cont’d)

Contains gastric glands



Produce mucus – protects the stomach
Produce hydrochloric acid - keeps stomach
pH acidic
Produce pepsin – digests proteins
 Works best in acidic conditions
Mixture of stomach fluids and food  chyme
Small Intestine

3 parts: duodenum, ileum, jejunum


Pyloric sphincter – separates stomach
and small intestine
Functions:


Complete chemical digestion
Absorb nutrients
Pancreas


Pancreas and gall bladder release
enzymes/fluids into small intestine
Pancreas



Produces hormones that regulate blood sugar
Produces enzymes that breakdown all the
macromolecules
Produces sodium bicarbonate – neutralizes
stomach acid and allows enzymes to function
properly
Gall Bladder


Gall bladder releases bile into the small
intestine
Bile



loaded with lipids and salts
Acts as a detergent to breakdown fats
Produced in the liver
Villi

Villi – fingerlike projections on the
inside lining of the small intestine



Covered by microvilli
Provides an enormous surface area for
the absorption of nutrient molecules
Once food is ready to leave it is
nutrient free
 Only cellulose, water, and other
indigestible substances remain
Large Intestine

3 parts: ascending colon, transverse
colon, descending colon

Contains bacteria that aids digestion

Functions:


Transports waste
Absorbs water
Enzymes in Digestion
Site
Enzyme
Mouth
Salivary amylase
Breaks down starches into
disaccharides
Stomach
Pepsin
Breaks down proteins into large
peptides
Small intestine
(from pancreas)
Amylase
Continues the breakdown of
starch
Trypsin
Continues the breakdown of
protein
Lipase
Breaks down fat
Maltase, sucrase, lactase
Breaks down remaining
disaccharides into
monosaccharides
Peptidase
Breaks down dipeptides into
amino acids.
Small intestine
Role in Digestion
Digestive System Disorders

Peptic ulcers



Diarrhea


Acids released by the stomach damage the
organ’s own lining, producing a hole
Caused by Helicobacter pylori – bacteria
Not enough water is absorbed
Constipation

Too much water is absorbed