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THE DIGESTIVE
SYSTEM
IT’S INTESTINE TIME!!
bn
MAIN IDEA OF INTESTINES
 Small intestine 
where the major events of
DIGESTION &
almost all ABSORPTION occur
 Large intestine 
where WATER ABSORPTION,
vitamin production, and
FECES FORMATION occurs
intestine VALVES!
 Valve from stomach to small
intestine (S.I.)  pyloric sphincter
 Valve from the S.I. to L.I. 
ileocecal valve/sphincter
3 SECTIONS OF S.I.
1) **DUODENUM
2) JEJUNUM
3) ILEUM
MESENTERY
 Layer of membrane (peritoneum)
that holds the small intestine coiled
together as well as to
the posterior abdominal wall
3 IMPORTANT FEATURES OF
THE Small Intestine (S.I.):
1) CIRCULAR FOLDS  deep folds of
both the mucosa and submucosa of small
intestine
(like rugae of stomach)
*increase surface area
PEYER’S PATCHES –
collections of lymphatic tissue
in submucosa; there are
more at the end of S.I. because
undigested food contains bacteria
3 IMPORTANT FEATURES
OF THE S.I.
2) VILLI  finger-like projections of
mucosa that
increase surface area
Contain capillary beds and
lymphatic capillaries (LACTEALS)
3 IMPORTANT FEATURES
OF THE S.I.
3) MICROVILLI 
very tiny projections of membrane of
mucosa cells on the VILLI
** Both villi & microvilli absorb digested
foods through mucosa & submucosa
Small Intestine Note:
 ** Enzymes produced by the
PANCREAS and bile made by the
LIVER enter the DUODENUM!!
Chemical Digestion &
Absorption in the S.I.
 Chemical digestion is completed in the
small intestine due to bile as well as
enzymes in the pancreatic and intestinal
juices.
 Approx. 90% of all ABSORPTION takes
place in the S.I.! (other % in stomach & L.I.)
SMALL INTESTINE
labeled:
First Figure/19.11 LABEL (p.472):
 Duodenum
 Jejunum
 Ileum
 Stomach
 Large Intestine
SMALL INTESTINE
labeled:
Second Figure/19.12 LABEL (p 473):
 Mucosa
 Submucosa
 Muscularis externa
 Serosa
 Villus
 Blood capillary
 Lacteal
 Simple columnar epithelium
THE
LARGE
INTESTINE (L.I.)
LARGE INTESTINE
 *Is much larger in diameter but shorter
in length than the small intestine
 runs from the ileocecal valve to the
anus
LARGE INTESTINE (COLON)
MAIN FUNCTIONS:
 Dries out undigested food residue
*absorbs water & vitamins
 Eliminates residues from the body as
wastes (feces)
5 SECTIONS OF Large Intestine:
1) Cecum
2) Appendix
3) Colon (ascending colon, transverse
colon, descending colon, and
sigmoid colon)
4) Rectum
5) Anal Canal
ANUS – opening to exterior
LARGE INTESTINE (L.I.)
 The outer layer of the muscularis externa is
bundled into 3 bands called TENIA COLI
which bunch up the colon into pouches
called HAUSTRA
Tenia = flat band
Haustra = “drawer” puckered
appearance
2 valves in Anal Canal:
- External voluntary sphincter
(skeletal muscle)
- Internal involuntary sphincter
(smooth muscle)
Appendix
 Hangs from the
cecum (first section of L.I.)
 Sometimes bacteria can get into
appendix and it becomes inflamed =
appendicitis
 If it broke open it would empty its
contents into the abdominopelvic cavity
which could be fatal
Important Features of L.I.
 There are NO villi 
nutrient absorption into bloodstream
happened in S.I.
 LOTS of goblet cells in the simple
columnar epithelium produce mucus
(functions as lubricant)
BACTERIA
 Bacteria live in the L.I. and break
down some of the remaining
nutrients which produces
gas (flatulence)
 FECES contain indigestible food
materials, mucus, bacteria, and water
Digestion & Absorption in the L.I.
 MECHANICAL DIGESTION in the large
intestine includes:
 HAUSTRAL churning or contraction of
the haustra (pouches of colon) when the
walls of the colon fill with chyme
 PERISTALSIS (muscular contractions
that propel food
 MASS PERISTALSIS is a large
peristaltic contraction that moves fecal
material into RECTUM
DEFECATION REFLEX
 Mass peristalsis moves indigestible
materials from colon into the rectum:
 Stretch receptors in the mucosa of the
rectum are stimulated are the rectum is
emptied
 The internal involuntary sphincter opens
due to a combination of pressure and
parasympathetic nerve impulses
Chemical Digestion
& Absorption in L.I.
 The last small bit of digestion occurs
in the L.I. by bacteria which break
down any small carbohydrates,
amino acids, etc.
 Products of this breakdown include:
gas (flatulence) as well as some
vitamins
Chemical Digestion
& Absorption in L.I.
 L.I. absorbs mostly WATER and vitamins
 Remember almost all absorption
(including most water absorption
happens in S.I.)
 In the L.I. water is absorbed by osmosis
LARGE INTESTINE
labeled:
First Figure/19.14 LABEL (p 478):
 Haustra
 Tenia coli
 Cecum
 Ileocecal sphincter
 Ileum
 Ascending colon
 Transverse colon
 Descending colon
 Sigmoid colon
 Rectum
 Anal canal
 Anus
LARGE INTESTINE
LABELED:
Second Figure/19.15 LABEL (p 479):
 Mucosa
 Submucosa
 Muscularis externa
 Serosa
 Simple columnar epithelium
Accessory ORGANS Summary
PANCREAS  pancreatic enzymes that
break down all 4 organic molecule
groups are secreted into the duodenum
Accessory ORGANS Summary
LIVER 
 2 main lobes which
are broken up into lobules
 Produces bile which enters duodenum
through the common hepatic duct
 Bile breaks up fat molecules so that
enzymes can digest them
Accessory ORGANS Summary
GALLBLADDER 
 On inferior surface of liver
 Stores bile when food is not being
digested
Accessory ORGANS Summary
SALIVARY GLANDS 
 *Salivary amylase
And salivary lipase
TEETH 
 Mechanical digestion of food
 Deciduous: first teeth/baby teeth