Stomach
• Temporary “storage tank”
• Chemical breakdown of proteins begins and
food is converted to chyme
• Chyme: creamy paste
• ~ 6-10 inches long
• Empty  volume of 50 mL
• Full  can hold up to 4L (1 gallon) of food and
may extend nearly all the way to the pelvis!
Stomach
• Circular, longitudinal, and oblique smooth
muscle layers 
– allows for stomach to churn, mix, pummel food
 physically breaking it down
– Move food along the digestive tract
Stomach –
Regions
• Cardiac region
– Cardia  “near the
heart”
– Surrounds the
cardiac sphincter
• Fundus
– Dome-shaped part,
tucked beneath the
diaphragm
– Superior bulge
• Body
– midportion
Stomach –
Regions
• Pyloric region
– Funnel shaped
region near the
pyloric sphincter
• Pyloric sphincter
– Exit of the
stomach to the
small intestine
Stomach –
Regions
• Rugae (wrinkle, fold)
– seen when stomach
is empty  inward
collapse to form
large, longitudinal
folds
• Greater curvature
– Convex, lateral
surface
• Lesser curvature
– Concave, medial surface
Stomach - Regions
• Lesser omentum –
– Helps to keep the
stomach connected to
other digestive organs
and the body wall
– Runs from liver to
lesser curvature
Stomach - Regions
• Greater omentum –
– Helps to keep the
stomach connected to
other digestive organs
and the body wall
– Runs from greater
curvature to cover the
small intestine, spleen,
and large intestine
– Riddled with fat deposits
(oment = fatty skin)
Stomach
• Lining is simple columnar tissue with goblet
cells 
• produce a protective coat of mucus
• Also dotted with gastric pits (small openings)
which produce gastric juice 
• hydrochloric acid and pepsinogen (inactive)
– Release gastric juice = pepsinogen + HCl 
– pepsin (enzyme)
• Pepsin + proteins  digestion!
Stomach
• Mucous coats the inside of the stomach to
protect it from HCl and pepsinogen.
• Churning of food and mixing makes chyme
– Contains fats, sugars, starches, vitamins, minerals,
proteins, and amino acids.
Stomach
• The secreted HCl (hydrochloric
acid) makes the stomach very
acidic
• (pH 1.5 – 3.5)
– Necessary for activation and
optimal activity of pepsin which
digests proteins
– Aids in food digestion  denatures
proteins, breaks down cell walls of
plant foods, kills many of the
bacteria that are ingested with
foods
Ulcers
• When the mucus barrier is breached and underlying
tissue is damaged 
• erosion of the stomach wall
• Very painful. Usually starts 1-3 hours after eating.
Relieved by eating again.
• Danger  if ulcer perforates the stomach wall and
stomach contents leak into the abdominal cavity
• Thought to be caused by taking aspirin, ibuprofen,
smoking, spicy foods, alcohol, coffee, stress
• Most recurrent ulcers are caused by Helicobacter pylori
bacteria, but it is hard to prove this because it is found
in most healthy people
Stomach
• Food is forced out of the stomach by
peristalsis through the pyloric sphincter and
into the duodenum.
Small Intestine
• The body’s major digestive organ
• Digestion is completed and virtually
all absorption occurs.
• Starts at the pyloric sphincter and extends to the
ileocecal valve.
• Longest portion of the digestive tract  7-13 feet
while alive and ~20 feet in a cadaver.
• Changes are because of loss of muscle tone when
deceased.
• Diameter ranges from 2.5 – 4 cm (1-1.6 in)
Duodenum
• Literally means “12 finger widths long”
• About 10 inches long.
• Only (and last) place where digestive juices
enter.
Duodenum
• Shortest section but
contains:
– Bile duct  delivers bile from
liver
– Main pancreatic duct 
carries pancreatic juice from
pancreas
– Hepatopancreatic ampulla 
where the two connect and
then open into the
duodenum via the major
duodenal papilla
Jejunum and Ileum
• Jejunum (“empty”) 8 ft
• Ileum (“twisted”) 12 ft
• Hang in sausage like coils in the central and
lower part of the abdominal cavity
• Highly adapted for nutrient absorption. Three
structures increase the surface area to the size
of a tennis court (250 m2).
Jejunum and Ileum
1)Plicae circulares 
deep, permanent folds
of the mucosa and
submucosa.
• These folds force
chyme to spiral through
the lumen, slowing its
movement and
allowing time for full
nutrient absorption
Jejunum and Ileum
2)Villi – “tufts of hair” 
finger like projections of the
mucosa (1mm), that give it a
velvety texture (like the nap
of a towel).
• The Villi are large and
leaflike in the duodenum
(most active absorption)
and gradually narrow and
shorten along the length of
the small intestine
Jejunum and Ileum
3)Microvilli  tiny projections of the plasma
membrane of absorptive cells of the mucosa.
• Give the surface a fuzzy appearance called the
brush border.
• The plasma membranes bear enzymes
referred to as brush border enzymes that
complete the digestion of carbohydrates and
proteins
Jejunum and Ileum
• Most absorption occurs in the proximal part of
the small intestines so the Plicae circulatures,
villi and microvilli decrease in number
towards the distal end.
Intestinal Juice
• 1-2 liters of intestinal juice are secreted daily.
• Major stimulus for its production is the
distention or irritation of the intestinal
mucosa by acidic chyme.
• Slightly alkaline (7.4-7.8)
• Largely water, but also contains some mucus.
Fairly enzyme poor because intestinal
enzymes are limited to the bound enzymes on
the brush border.