of the small intestine. Te circular folds force the chyme to spiral through
Brush border enzymes are enzymes associated with the
microvilli of the small intestine mucosal cells.
A lacteal is a blind-ended
lymphatic capillary that picks up lymph (ﬂuid and proteins leaked from the
blood stream), which is then returned to the blood.
IgA, HCl, defensins,
and lysozyme protect the intestinal cells from bacterial damage.
triad is a region at the corner of a hepatic lobule that contains a branch of
the hepatic portal vein, a branch of the hepatic artery, and a bile duct.
Te enterohepatic circulation is an important recycling mechanism for
retaining bile salts needed for fat absorption.
Stellate macrophages rid
the blood of bacteria and dead cells.
Zymogen granules contain inactive
Pancreatic acini produce the exocrine products of the
pancreas (digestive enzymes and bicarbonate-rich juice). Te islets produce
pancreatic hormones, most importantly insulin and glucagon.
the pancreatic duct is bicarbonate-rich, enzyme-rich pancreatic juice. Fluid
in the cystic and bile ducts is bile.
CCK is secreted in response to the
entry of chyme rich in protein and fat into the duodenum. It causes the pan-
creatic acini to secrete digestive enzymes, stimulates the gallbladder to con-
tract, and relaxes the hepatopancreatic sphincter.
Distension of stomach
walls enhances stomach secretory activity. Distension of the walls of the
small intestine reduces stomach secretory activity (to give the small intestine
time to carry out its digestive and absorptive activities).
more important for moving food along the small intestine.
MMC is the
migrating motor complex, a pattern of peristalsis seen in the small intestine
that moves the last remnants of a meal plus bacteria and other debris into
the large intestine. MMC is important to prevent the overgrowth of bacteria
in the small intestine.
Mass movements and haustral contractions are
unique to the large intestine. Mass movements are long, slow, powerful con-
tractions that move over large areas of the colon three or four times a day,
forcing the contents toward the rectum. Haustral contractions are a special
type of segmentation.
Activation of stretch receptors in the rectal wall
initiates the defecation reﬂex.
Enteric bacteria synthesize B vitamins and
some of the vitamin K the liver needs to synthesize clotting proteins.
food digestion depends on hydrolysis reactions.
Amylase is to starch as
lipase is to fats.
Bile salts emulsify fats so that they can be acted on eﬃ-
ciently by lipase enzymes, and form micelles that aid fat absorption.
digestive system mucosa develops from the endoderm.
Te thick vis-
cous mucus produced in cystic ﬁbrosis patients clogs pancreatic ducts and
prevents the delivery of pancreatic ﬂuid to the duodenum, thus inhibiting
fat digestion and absorption.
Colon and stomach cancers are dangerous
because they have few early signs and symptoms.
Review Questions 1.
Case Study 1.
Mr. Gutteman’s statement about the eﬀects of milk on his
digestive tract suggests that he may be deﬁcient in lactase, a brush border
enzyme that breaks down lactose (milk sugar).
His responses to the
questions reduced the possibility that he has gastric ulcers. Mr. Gutteman’s
diarrhea may be due to gluten-sensitive enteropathy. ±o verify this diag-
nosis, Mr. Gutteman should be screened for speciﬁc IgA antibodies in his
blood. If these screening tests are positive, a biopsy of the intestinal mucosa
would be performed. Observation of damaged intestinal villi and microvilli
would conﬁrm the diagnosis. A positive diagnosis of gluten-sensitive enter-
opathy would lead to a lifelong dietary restriction of all grains except rice
and corn. Grains should not be restricted prior to the biopsy.
Check Your Understanding 1.
Te six major nutrients are carbo-
hydrates, proteins, fats, water, minerals, and vitamins.
provides ﬁber, which helps in elimination.
±riglycerides are used for
A±P synthesis, body insulation and protective padding, and to help the
body absorb fat-soluble vitamins. Cholesterol is the basis of our steroid
hormones and bile salts, and stabilizes cellular membranes.
decrease in the degree of oxygen saturation of hemoglobin. As Barbara’s
respiratory eﬀorts cease, her alveolar P
will fall, so there is less oxygen to
load onto hemoglobin. In her peripheral tissues, what little oxygen hemo-
globin carries will be consumed, leaving these tissues with a bluish tinge.
Injury to the spinal cord at the level of the C
vertebra will cause quad-
riplegia (paralysis of all four limbs).
Atelectasis is the collapse of a lung.
Because it is the right thorax that is compressed, only her right lung is af-
fected. Because the lungs are in separate pleural cavities, only the right lung
Barbara’s fractured ribs probably punctured her lung tissue
and allowed air within the lung to enter the pleural cavity.
will be reversed by inserting a chest tube and removing the air from the
pleural cavity. Tis will allow her lung to heal and reinﬂate.
Check Your Understanding 1.
Te esophagus is found in the thorax. Tree
alimentary canal organs found in the abdominal cavity include the stomach,
small intestine, and large intestine.
Te usual site of ingestion in a healthy
person is the mouth.
Te process of absorption moves nutrients into the
Reﬂexes associated with the GI tract promote muscle contraction
and secretion of digestive juices or hormones.
Te term “gut brain” refers
to the enteric nervous system or web of neurons closely associated with the
Te visceral peritoneum is the outermost layer of the di-
gestive organ; the parietal peritoneum is the serous membrane covering the
wall of the abdominal cavity.
Te pancreas is retroperitoneal.
patic portal circulation is the venous portion of the splanchnic circulation.
From deep to superﬁcial the layers of the alimentary canal are the mu-
cosa, submucosa, muscularis externa, and serosa.
He should temporarily
refrain from eating because the parasympathetic nervous system oversees
Te oral vestibule is the region between the cheek
and the teeth. Te oral cavity proper is the area enclosed by the teeth.
Te palate forms the roof of the mouth. Te hard palate supported
by bone is anterior to the so² palate (no bony support).
Te tongue is
important for speech, particularly for uttering consonants, and taste.
Te serous portion of saliva is rich in salivary amylase, an enzyme that
chemically breaks down starch. Additionally, the serous portion of saliva
helps to hydrate the foodstuﬀs and helps provide protection against micro-
Antimicrobial substances found in saliva include lysozyme,
defensins, and IgA antibodies.
±ina’s “show and tell” tooth is a primary
tooth, also called a deciduous tooth.
Enamel is harder than bone. Pulp
consists of nervous tissue and blood vessels.
Te molars are grinding
Te pharynx is part of the digestive and respiratory systems.
Te esophageal mucularis externa undergoes a transformation along its
length from skeletal muscle superiorly to smooth muscle near the stomach.
Te esophagus is merely a chute for food passage and is subjected to a
good deal of abrasion, which a stratiﬁed squamous epithelium can with-
stand. Te stomach mucosa is a secretory mucosa served well by a simple
Te tongue mixes the chewed food with saliva,
compacts the food into a bolus, and initiates swallowing.
lowing the larynx rises and the epiglottis covers its lumen so that foodstuﬀs
are diverted into the esophagus posteriorly.
Te stomach has three
layers of smooth muscle—longitudinal, circular, and oblique. Addition
of the oblique layer allows the stomach to pummel food in addition to its
Te chief cells produce pepsinogen, which is the
inactive enzyme pepsin, and the parietal cells secrete HCl needed to activate
Te mucosal barrier consists of the thick alkaline mucus
secreted by the mucous cells, the fact that the epithelial cells of the mucosa
are joined by tight junctions, and the quick replacement of dead or dying
cells by stem cells.
Te three phases of gastric secretion are the cephalic,
gastric, and intestinal phases.
Te presence of food in the duodenum
inhibits gastric activity by triggering the enterogastric reﬂex and the secre-
tion of enterogastrones (hormones).
Venous blood leaving the stomach
during a meal becomes more alkaline due to the alkaline tide occurring dur-
ing HCl secretion.
All of these modiﬁcations increase the surface area