Digestion
Anatomy and Physiology
Why must we digest our food?
• To break down foods into small, useable
nutrients
• A chunk of hamburger is not useable to a
cell
• The process is both mechanical and
chemical
Major and Minor Players
• Alimentary canal
extends from mouth to
anus (9 meters long)
• Includes every part the
food material actually
passes through
• Accessory organs
supply enzymes to
help, but food does not
actually pass through
• Alimentary canal:
mouth, esophagus,
stomach, small
intestine, large
intestine, anal canal
• Accessory organs:
salivary glands, liver,
gallbladder, pancreas.
Peristalsis
• A wave- like motion
that moves food
through the alimentary
canal
• Smooth muscle action
Mouth
Mouth
• Mechanical digestion
begins here with
chewing
• 32 secondary teeth
• Structure is suited to
function
• Outer covering is
enamel, under it is
dentin
Mouth
• Three pairs of salivary
glands secrete saliva
• Parotid, sublingual,
and submandibular
• Saliva dissolves foods,
moistens for easier
swallowing, and
begins chemical
digestion
Mouth
• An enzyme called amylase is found in
saliva
• This enzyme splits starch into
disaccharides
Swallowing
• The pharynx is the
area behind the mouth
leading to the
esophagus
• Esophagus leads to the
stomach
• Soft palate raises so
food will not go into
nasal cavity
• Epiglottis closes off the
trachea
• Peristalsis forces food into
and on through the
esophagus
• Esophagus penetrates the
diaphragm
• Entrance is guarded by a
sphincter, which opens to
let food in, and closes to
prevent regurgitation
Swallowing
Stomach
• J shaped organ
• Holds about 1 liter
• Churns food and
mixes it with gastric
juices
• Begins protein
digestion
• Passes food into small
intestine
Stomach
• Gastric juices consist
of mucous, digestive
enzymes, and
hydrochloric acid
(HCl)
• Lining of stomach is
thick, has a coating to
protect it
• A hole in the lining is
an ulcer
Stomach
• Protein digestion
begins in stomach
with the enzyme
pepsin ( likes acid
conditions)
• Cells secrete
pepsinogen, which is
changed into pepsin
when it encounters the
HCl
Stomach
• Only protein is
chemically digested in
the stomach.
• The pH is very acidic,
and only pepsin can
function
Stomach
• Not much absorption
occurs from the
stomach into the
bloodstream
• Absorbs only small
amounts of water and
salts, alcohol, some
drugs
Small Intestine
• Two main jobs:
• Most digestion occurs
here; digestion is
finished here
• Nutrients are absorbed
into the bloodstream
• Neutralizes stomach
acid, so enzymes can
work
Small Intestine
• Consists of three
sections: duodenum,
jejunum, and ileum
• Receives secretions
from the liver and
pancreas, as well as
making its own
Small Intestine
• Peptidases: digest
proteins
• Sucrase, maltase,
lactase split
disaccharides into
monosaccharides
• Lipase splits lipids
into glyrcerol and fatty
acids
Small Intestine
• Inner wall is lined
with tiny projections
called villi
• Increases surface area
for more and better
absorption of nutrients
Large Intestine (colon)
• Begins in the lower
right side of abdomen
and extends up,
across, and down the
left side to the anus
• Sections are:
ascending colon,
transverse colon,
descending colon, and
sigmoid colon
Large Intestine (colon)
• No digestion takes
place here
• Absorbs water and
electrolytes into
bloodstream
• Stores feces
Colon Cancer
• Formation of
cancerous polyps
• Easy screening test
• High cure rate if
caught early
Accessory Organs
•
•
•
•
Salivary glands
Liver
Gall bladder
Pancreas
Liver
• Two large lobes
• Reddish brown color
• Important in
carbohydrate
metabolism (stores
glucose as glycogen)
• Also important in lipid
and protein
metabolism
• Liver also stores many
substances
• Helps destroy
damaged red blood
cells and pathogens
• Removes toxic
substances from blood
(such as alcohol)
Liver
• None of those
functions is important
to digestion.
• Secretion of bile is
important to digestion
• Bile aids digestive
enzymes by
emulsifying fats
Liver
• Emulsification is the
breaking of fat
globules into smaller
droplets
• Lipases can then work
better
Gall Bladder
• Stores the bile made
by the liver
• Attached to the
underside of the liver
• Releases bile into the
small intestine
Pancreas
• Both an endocrine and
a digestive organ
• Secretes pancreatic
juice (full of enzymes)
into small intestine
• Enzymes include:
pancreatic amylase,
pancreatic lipase,
trypsin and other
protein splitters
Pancreas