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ESSENTIALS OF A&P
FOR EMERGENCY CARE
CHAPTER
16
The Gastrointestinal
System: Fuel for the Trip
Essentials of A&P for Emergency Care
Bruce J. Colbert • Jeff Ankney • Karen T. Lee • Bryan E. Bledsoe
Copyright ©2011 by Pearson Education, Inc.
All rights reserved.
Multimedia Asset Directory
Slide 16
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Slide 96
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Slide 154
Swallowing and Digestion Animation
GERD Video
Appendicitis Animation
Eating Disorders Video
Anorexia Nervosa Video
Bulimia Video
Dieticians Video
Dental Assisting and Dental Hygiene Video
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Bruce J. Colbert • Jeff Ankney • Karen T. Lee • Bryan E. Bledsoe
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Introduction
• The gastrointestinal system has the
following functions:
– Take in (ingest) raw materials
– Break down (digest) raw materials to usable
elements
 Physically
 Chemically
– Absorb elements
– Eliminate what isn’t usable
Essentials of A&P for Emergency Care
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Introduction
• These functions are accomplished through
an array of amazing main and accessory
organs with food traveling through what is,
essentially, a tube until waste products are
eliminated.
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Learning Objectives
• Locate and describe the functions of the
main organs of the digestive system.
• Locate and describe the functions of the
accessory organs for digestion.
• Differentiate between ingestion and
digestion, and between chemical and
mechanical processing of food.
• Trace the journey of a bolus of food from
the mouth to the anus.
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Learning Objectives
• Discuss the structure of teeth.
• Describe the various enzymes and
chemicals needed for digestion.
• Describe common disorders of the
gastrointestinal system.
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Pronunciation Guide
Click on the megaphone icon before each item to hear the pronunciation.
adventitia (ADD ven TISH ah)
alimentary tract (AL ah MEN tar ee)
appendicitis (ah PEN dih SIGH tis)
appendix (ah PEN dicks)
cecum (SEE kum)
cementum (see MEN tum)
cholecystitis (KOH lee sis TYE tis)
cholelithiasis (KOH lee lih THY ah sis)
chyle (KILE)
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Pronunciation Guide
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chyme (KIME)
defecation (def eh CAY shun)
duodenum (DOO oh DEE num)
emulsification (ee MULL sih fih KAY shun)
epiglottis (ep ih GLAH tis)
esophagus (eh SOFF ah gus)
frenulum (FREN you lum)
fundus (FUN dus)
gingiva (JIN jih vuh)
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Pronunciation Guide
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ilium (ILL ee um)
jejenum (jee JOO num)
labia (LAY bee ah)
mastication (MASS tih CAY shun)
mesentery (MEZ in TARE ee)
pancreatitis (PAN kree ah TYE tis)
peristalsis (pair ih STALL sis)
pharynx (FAIR inks)
plicae circulares (PLY kay sir cue LAIR es)
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Pronunciation Guide
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ptyalin (TYE ah lin)
pyloric sphincter (pye LOR ik SFINK ter)
pylorus (pye LOR us)
rugae (ROO gay)
serosa (seh ROSE ah)
villi (VILL eye)
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System Overview
• The digestive tract, often called the alimentary
tract or canal, is a muscular tube that contains
the organs of digestion.
• The tube begins with the mouth and ends at the
anus.
• In between these two points are the pharynx,
esophagus, stomach, small intestine, and large
intestine.
• Accessory organs of digestion include the teeth,
salivary glands, liver, pancreas, and gallbladder.
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Figure 16-1 The digestive system.
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Functions of the Gastrointestinal
Tract
• Ingestion – food enters the mouth
• Mastication (chewing) – mechanically
grinding food with the teeth and tongue
• Digestion – the chemical act of breaking
down food into small molecules
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Functions of the Gastrointestinal
Tract
• Secretion – release of acids, buffers,
enzymes, and water to aid in the
breakdown of food
• Absorption – food passes through lining of
digestive tract into blood stream
• Excretion or defecation – elimination of
waste products
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Oral Cavity
• The oral cavity is the opening behind the
mouth, the hard and soft palate is the roof,
the tongue is the floor, and the cheeks are
the walls.
• The uvula aids in swallowing, directing
food toward the pharynx and blocking food
from entering your nose.
• The mouth receives, tastes, mechanically
breaks down, and begins starch digestion.
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Oral Cavity
• Tongue
– The tongue’s base (area of attachment) and
the uvula are the barrier to the next part of the
system, the pharynx.
– Swallowing
 The uvula aids in swallowing, directing food toward
the pharynx, and blocking food from entering your
nose.
 The tongue pushes the food into a ball-like mass,
called a bolus, so it may be swallowed – passed to
the pharynx.
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Oral Cavity
• Tongue
– Your tongue provides taste stimuli to your
brain, determines temperature, and
manipulates food.
– The lingual frenulum, a membrane under the
tongue, keeps you from swallowing your
tongue and aids in speaking.
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Figure 16-2 The mouth and oral cavity.
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Figure 16-2 (continued) The mouth and oral cavity.
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Clinical Application:
Sublingual Medication
• The area under the tongue has many
blood vessels. This sublingual blood
vessel network readily absorbs
substances and is a rapid means of
administering medication.
• One medication given by this route is
nitroglycerine, used to treat angina.
Angina develops as a result of poor
oxygen supply to the myocardium because
of diminished blood flow.
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Clinical Application:
Sublingual Medication
• Nitroglycerine dilates arteries, improving
blood supply and oxygenation – hopefully
relieving angina symptoms.
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Oral Cavity
• Salivary glands (accessory organ)
– There are two pairs of salivary glands
controlled by the autonomic nervous system.
– A large parotid salivary gland is found slightly
inferior and anterior to each ear. These are
the ones that swell when you get mumps.
– The sublingual salivary glands are found
under the tongue.
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Oral Cavity
• Salivary glands (accessory organ)
– The submandibular salivary glands are
located along both sides of the inner surface
of the mandible.
– The ducts from these glands empty into the
upper portion of the oral cavity.
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Oral Cavity
• Saliva
– The salivary glands produce 1–1.5 liters of saliva
daily.
– Small amounts of saliva keep the mouth moist, but
the idea or presence of food increase production
significantly.
– Saliva is 99.4% water, and contains antibodies,
buffers, ions, waste products, and enzymes.
 One enzyme, salivary amylase, speeds the chemical activity
of breaking down carbohydrates.
 After eating, saliva cleans the oral surfaces, reducing the
amount of bacteria that grows in your mouth.
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Figure 16-3 The salivary glands.
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Oral Cavity
• Teeth
– The first set of teeth you grow as a baby are
the deciduous teeth. They will fall out in time.
– The 1st tooth appears around 6 months of
age. The lower central incisors appear first,
with all 20 teeth in place by age 2½.
– Between 6 and 12 years these teeth fall out
and are replaced by 32 permanent teeth.
– Wisdom teeth appear by the time we turn 21.
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Oral Cavity
• Types of teeth
– Incisors are located at the front of the mouth, are
blade-shaped, and are used to cut food.
– Canine teeth are for holding, tearing, or slashing
food. They are also known as eyeteeth or
cuspids, and are located next to incisors.
– Bicuspids, or premolars, are transitional teeth.
– Molars have flattened tops. Both bicuspids and
molars are responsible for crushing and grinding
food.
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Oral Cavity
• Tooth anatomy
– Teeth have a crown, neck, and root.
– The crown is the part you normally see and is
covered by the hardest biologically
manufactured substance, enamel.
– The neck is the transitional section that leads
to the root.
– Internally, most teeth are made up of dentin, a
mineralized bone-like substance.
– The next layer is connective tissue, pulp,
located in the pulp cavity.
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Oral Cavity
• Tooth anatomy
– The pulp cavity contains blood vessels and
nerves providing nutrients and sensation. The
nerves and blood vessels get to the pulp
cavity via the root canal.
– The root is nestled in a bony socket and is
held in place by fibers of the periodontal
ligament.
– In addition, cementum, a soft version of bone,
covers the dentin of the root, aiding in
securing the periodontal ligament.
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Oral Cavity
• Tooth anatomy
– Healthy gums, or gingiva, help hold the teeth
in place.
– Epithelial cells form a tight seal around the
tooth to prevent bacteria from coming into
contact with the tooth’s cementum.
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Figure 16-4 Types, location and, structures of teeth.
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Figure 16-4 (continued) Types, location and, structures of teeth.
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Pharynx
• There are three parts to the pharynx:
– The nasopharynx is primarily part of the
respiratory system, blocked by the soft palate.
– The oropharynx and the laryngopharynx act
as a passageway for food, water, and air.
– The epiglottis covers the trachea to prevent
food from entering the lungs, forcing food into
the opening for the esophagus.
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Esophagus
• The esophagus is approximately 10 inches
long and is connected to the stomach,
normally collapsed.
• It extends from the pharynx, through the
thoracic cavity, through the diaphragm,
connecting to the stomach in the
peritoneal cavity.
• Rhythmic contractions, called peristalsis,
push food down the esophagus.
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Esophagus
• The esophageal walls
– Lined with stratified squamous epithelium
– Outer layer is adventitia not serosa
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Esophageal Sphincters
• A muscular ring at the top of the
esophagus, called the
pharyngoesophageal sphincter, relaxes to
open the esophagus so food can enter.
• At the entrance to the stomach is the lower
esophageal sphincter, or cardiac
sphincter, opening the door to the stomach
and closing to prevent acidic gastric juices
from splashing into the esophagus.
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Figure 16-5 The movement of a bolus of food from the mouth to the stomach via the
esophagus.
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Figure 16-5 (continued) The movement of a bolus of food from the mouth to the stomach
via the esophagus.
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Walls of the Alimentary Canal
• The innermost layer, the mucosa, lines the
lumen of the canal.
– This layer is composed mostly of surface
epithelium with some connective tissue and
has a thin smooth muscle layer surrounding it.
– The mucosa also possesses cells that secrete
digestive enzymes to break down foodstuffs
and goblet cells that secrete mucus for
lubrication.
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Walls of the Alimentary Canal
• The submucosa is the next layer, and is
composed of soft connective tissue.
– This layer contains blood vessels, lymph
vessels, lymph tissue (called Peyer patches)
and nerve endings.
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Walls of the Alimentary Canal
• The next layer is called the muscularis
externa, and is composed of two layers of
smooth muscle.
– The innermost layer of muscle encircles the
canal, while the outer layer of muscle is
longitudinal in nature, so it lies in the direction
of the canal.
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Walls of the Alimentary Canal
• The outermost layer, the serosa, is
composed of a single, thin layer of flat,
serous fluid producing cells supported by
connective tissue.
– The serosa is the visceral peritoneum in most
of the canal.
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Figure 16-6 Basic tissue type and structures of the alimentary canal.
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Peritoneum
• The peritoneum is a serous membrane in
the abdominopelvic cavity.
– The visceral peritoneum covers the organs,
and the parietal peritoneum lines the wall of
the abdominopelvic cavity.
– Between the layers is a fluid-filled potential
space called the peritoneal cavity.
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Peritoneum
• The peritoneum is a serous membrane in
the abdominopelvic cavity.
– The peritoneum is different from the other
serous membranes.
 Some abdominal organs are not surrounded by
peritoneum and are called retroperitoneal organs.
 The peritoneum has several extensions called
mesentery that drape over the abdominal organs.
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Figure 16-7
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Peritoneum.
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From the Streets:
Swallowed Foreign Bodies
• Swallowed foreign bodies are a common
reason people seek emergency care.
• Objects that lodge in the esophagus usually
require intervention.
• Treatment may include medications and
surgical intervention.
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Stomach
• The stomach is located in the left side of the
abdominal cavity, under the diaphragm, and
is covered completely by the liver.
• It is approximately 10 inches long with a
diameter that depends on how much you just
ate.
• It can hold up to 4 liters when filled.
• Rugae, or folds, help the stomach expand
and contract.
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Stomach Functions
• The stomach has four functions:
– Temporary holding area for food
– Secretes gastric acids and enzymes that mix
with food, performing chemical digestion
– Regulates the rate the new, partially digested
food (a thick, heavy, cream-like liquid called
chyme) enters the intestine
– Absorbs small amounts of water and
substances on a very limited basis (the
stomach does absorb alcohol)
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Figure 16-8 The stomach.
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Figure 16-8 (continued) The stomach.
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Regions of the Stomach
• The stomach is divided into four regions.
– Near the heart is the cardiac region,
surrounding the lower esophageal sphincter.
– The fundus, laterally and slightly superior to
the cardiac region, temporarily holds the food
as it enters the stomach.
– The body is the mid-portion of the stomach.
The two curves are the lesser curvature
(concave) and the greater curvature (larger
convex curve).
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Regions of the Stomach
• The stomach is divided into four regions.
– The funnel-shaped, terminal end of the
stomach is called the pylorus. Most of the
work of the stomach is performed here. This
is where food passes through the pyloric
sphincter into the small intestine.
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Muscle Layers of the Stomach
• The muscular action of the stomach works
like a cement mixer, achieved by three
layers of muscles.
– The longitudinal layer, circular layer, and
oblique layer.
– The stomach churns food.
– The stomach works the food toward the
pyloric sphincter through peristaltic activity of
the muscles.
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Muscle Layers of the Stomach
• It takes about four hours for the stomach
to empty following a meal.
– Liquids and carbohydrates pass through fairly
quickly.
– Proteins take more time to pass through.
– Fats take the longest, usually between 4–6
hours.
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Gastric Juice
• Gastric juice is comprised of hydrochloric
acid (HCl), pepsinogen, and mucus.
– Pepsinogen is secreted by the chief cells
while HCl is secreted by parietal cells
combining to produce pepsin, the chief
digestive enzyme.
 Pepsin breaks down protein. HCl breaks down the
connective tissue.
 HCl has a pH of 1.5–2, and is effective at killing
pathogens.
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Gastric Juice
• Mucous cells generate a thick layer of
mucus shielding the stomach from the
effects of the stomach acids.
• The stomach also secretes intrinsic factor,
allowing vitamin B12 to be absorbed.
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Table 16-1 Gastric Glands and Their Functions.
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Control of Stomach Action
• The stomach’s activity is controlled by the
parasympathetic nervous system,
particularly the vagus nerve.
• Vagus nerve stimulation increases the
motility and secretory rates of the gastric
glands.
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Control of Stomach Action
• There are three phases of gastric juice
production:
– Cephalic phase – sensory stimulation (sight or
smell of food) stimulates parasympathetic
nerves via the medulla oblongata, stimulating
the release of gastrin. Gastrin travels through
the blood stream and reaches the stomach,
stimulating gastric gland activity.
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Control of Stomach Action
• There are three phases of gastric juice
production:
– Gastric phase – 2/3 of the gastric juices are
secreted as food enters the stomach and
distends the walls, which signals the stomach
to secrete more gastric fluid.
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Control of Stomach Action
• There are three phases of gastric juice
production:
– Intestinal phase – food enters the duodenum,
distending and sensing the acidity, causing
intestinal hormones to be released, slowing
gastric gland secretions. This lasts until the
bolus leaves the duodenum.
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Figure 16-9 Phases of gastric secretions.
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Figure 16-9 (continued) Phases of gastric secretions.
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Figure 16-9 (continued) Phases of gastric secretions.
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Control of Stomach Action
• The rate of the movement of chyme is very
important.
• If it moves too slowly the rate of nutrient
digestion and absorption is decreased and may
allow the acidity of the chyme to cause erosions
of the stomach lining.
• If chyme moves too quickly, the food particles
may not be sufficiently mixed with gastric juices
leading to insufficient digestion. Chyme that isn’t
given time to neutralize can cause erosion of the
intestinal lining.
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From the Streets:
Peptic Ulcers
• Peptic ulcers are erosions caused by gastric
acid.
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Figure 16-10 Peptic ulcer disease (PUD).
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From the Streets:
Peptic Ulcers
• Signs and symptoms
• Nonsteroidal anti-inflammatory drugs (NSAIDs),
acid-stimulating products or Helicobacter pylori
bacteria are the most common causes.
• Diagnostic test
• Treatment
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Small Intestine
• The small intestine is located in the central and
lower abdomen.
• It functions as the major organ of digestion
because it is where most of your food is
digested.
• The small intestine is small in diameter, not
length. The small intestine is the longest section
of the alimentary canal, with an average length
of 6–20 feet and a diameter ranging from 4 cm
where it connects to the stomach and 2.5 cm
where it meets the large intestine.
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Figure 16-11 The small intestine.
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Small Intestine Function
• The walls of the small intestine secrete
digestive enzymes, which are important for
the final stages of chemical digestion, and
hormones that stimulate the pancreas and
gallbladder to act, and control stomach
activity. Secretin is one of these hormones
that stimulates the pancreas.
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Small Intestine Function
• Eighty percent of the absorption of usable
nutrients occurs when chyme comes in
contact with the mucosal walls. Amino
acids, fatty acids, simple sugars, vitamins,
and water are all absorbed here.
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Small Intestine Function
• The remaining 20% is absorbed in the
stomach.
• Any residue that is not utilized in the small
intestine is sent to the large intestine for
removal from the body.
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Regions of the Small Intestine
• There are three regions of the small intestine.
– The duodenum is approximately 25 cm long and
is located near the head of the pancreas. The
duodenum gets its name from duo (two) and
denum (ten) which equals 12 – the number of
finger widths long that this organ is (10 inches).
– The jejunum is the middle section and is
approximately 2.5 m long.
– The terminal end of the small intestine is the
ileum, which is 2 m long, and attaches to the
large intestine at the ileocecal valve.
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Duodenal Function
• The pyloric valve is important, allowing
small portions of chyme to enter the
duodenum. The small intestine can only
process small amounts of food at a time.
• Muscular action occurs in two different
ways – segmentation causes the mixing of
chyme and digestive juices like a cement
mixer while peristalsis moves the food
toward the large intestine.
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Duodenal Function
• The pancreas and gallbladder add
secretions.
– Bile from the gallbladder and liver, and
pancreatic juice from the pancreas.
– Bile emulsifies fat, making fat disperse in
water.
– Pancreatic juice contains sodium bicarbonate
which neutralizes the acidic chyme and
enzymes to digest food.
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Duodenal Function
• Hormones
– Cholecystokinin, CCK
 Secreted by the small intestine; stimulates
gallbladder and pancreas activity; slows stomach
activity
– Secretin
 Secreted by small intestine; stimulates liver and
pancreas; slows stomach
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Duodenal Function
• Digestive enzymes
– Intestinal and pancreatic
– The mechanical and chemical irritation of
acidic chyme, plus the distention of the
intestinal walls, creates the localized reflex
action that causes the release of the enzymes
and the two hormones.
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Table 16-2 Hormones in the Digestive Process.
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From the Streets:
Upper GI Bleeding
• Upper GI bleeding occurs proximal to the
ligament of Treitz, which is where the
duodenum and jejunum meet.
• Causes
• Signs and symptoms
• Diagnostic tests
• Treatment
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Wall of the Small Intestine
• Modifications to increase surface area
– Circular folds called plicae circulares
– Finger-like protrusions into the lumen called
villi
 Each villus contains a network of capillaries and a
lymphatic capillary called a lacteal.
 Intestinal glands are located between villi.
 The capillaries absorb and transport nutrients to
the liver for further processing.
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Wall of the Small Intestine
• Modifications to increase surface area
– Finger-like protrusions into the lumen called
villi
 Lipids become chyle and are absorbed by the
lymphatic system.
 These villi are tightly packed together, giving a
velvety texture and appearance.
 The villi also have outer layers of columnar
epithelial cells that possess microscopic extensions
known as microvilli.
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Figure 16-11 The small intestine.
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Figure 16-12 Villi.
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Clinical Application:
Lactose Intolerance
• This condition is the inability to digest the
sugar (lactose) found in milk and dairy
products. It is caused by a deficiency of
lactase, an intestinal enzyme. As a result,
lactose is not sufficiently digested. Normal
bacteria found in the intestine utilize these
undigested sugars, with gas production as
a by-product, causing a feeling of being
bloated. The undigested lactose prevents
normal water absorption, causing diarrhea.
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Clinical Application:
Lactose Intolerance
• There seems to be a genetic basis. Fifteen
percent of Caucasians develop lactose
intolerance, while 80–90% of African
American and Asian populations develop
this condition to some degree.
• To avoid this symptoms, patients need to
avoid dairy or take an oral form of the
enzyme lactase before eating dairy.
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Large Intestine
• Beginning at the junction of the small
intestine, the ileocecal orifice, and
extending to the anus is the large
intestine.
• The large intestine borders the small
intestine.
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Large Intestine
• The functions of the large intestine are:
– Water absorption
– Absorption of vitamins produced by the
normal bacteria in your large intestine
– Packaging/compacting waste products for
elimination from the body
• There are no villi in the large intestine so
little nutrient absorption occurs here.
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Figure 16-13 The large intestine.
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Regions of the Large Intestine
• Approximately five feet long and 2.5
inches in diameter, the large intestine can
be divided into three main regions
– Cecum
– Colon
– Rectum
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Regions of the Large Intestine
• Cecum
– A pouch-shaped structure, the cecum,
receives any undigested food and water from
the ileum.
 The appendix is attached to the cecum. It is a 3
inch long, slender, hollow, dead-ended tube lined
with lymphatic tissue. It has no known purpose. If it
becomes blocked or inflamed it causes appendicitis
and must be treated with either antibiotics or
surgical removal.
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Regions of the Large Intestine
• Cecum
– A pouch-shaped structure, the cecum,
receives any undigested food and water from
the ileum.
 Some of the water used in digestion and
electrolytes are reabsorbed in the cecum. The
water absorbed is a small amount, but essential to
maintaining normal fluid balance.
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Click here to view an animation on the topic of Appendicitis.
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Regions of the Large Intestine
• Colon: four sections
– The ascending colon travels up the right side
to the level of the liver. Absorbs some water.
– The transverse colon travels across the
abdomen just below the liver and the
stomach.
– The descending colon bends downward near
the spleen and travels to the left side
becoming the sigmoid colon.
– The sigmoid colon extends to the rectum.
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Regions of the Large Intestine
• The rectum opens to the anal canal that
leads to the anus.
• The anal sphincter opens and closes to
allow the passage of solid waste (feces).
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From the Streets:
Appendicitis
• Appendicitis is an inflammation of the
veriform appendix located at the ileocecal
junction.
• The most common cause is obstruction of
the lumen of the appendix.
• Signs and symptoms
• Diagnostic tests
• Treatment
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Figure 16-14 McBurney’s point is located along a line approximately 1 1/2 to 2 inches above
the right anterior iliac crest along an imaginary line drawn between the right anterior iliac crest
and the umbilicus.
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From the Streets:
Diverticulitis
• Diverticulitis is a common complication of
diverticulosis in which intestinal
outpouchings (diverticula) push through
the outermost layer of the intestine.
• Diverticula commonly trap small amounts
of fecal material which can become
infected.
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Figure 16-16 Diverticula, which are outpouchings of the wall of the colon, can become
infected (diverticulitis) or bleed (diverticulosis).
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Clinical Application:
Colostomy
• Sometimes, due to disease, a portion of
the colon needs to be bypassed due to
disease to allow for healing and/or surgical
repair.
• A new opening needs to be made and this
procedure is called a colostomy. This can
be temporary or permanent depending on
the condition.
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Figure 16-15 Colostomy sites.
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Defecation
• As the rectum fills with feces, a defecation
reflex occurs which causes rectal muscles
to contract and the anal sphincter to relax.
– If fecal matter moves through too rapidly, not
enough water is removed and diarrhea
occurs.
– Conversely, if fecal matter remains too long in
the large intestine, too much water is removed
and constipation occurs.
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Defecation
• As the rectum fills with feces, a defecation
reflex occurs which causes rectal muscles
to contract and the anal sphincter to relax.
– Two sphincters surround the anal opening,
the internal anal sphincter, which is
involuntary, and the external anal sphincter,
which is voluntary.
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Defecation
• As the rectum fills with feces, a defecation
reflex occurs which causes rectal muscles
to contract and the anal sphincter to relax.
– When feces enter the rectum, the wall
stretches, triggering the defecation reflex. The
walls contract, and the internal sphincter
relaxes and opens. The external sphincter
only relaxes when you decide to open it. You
have control, within limits, of when and how
often you defecate.
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Bacteria
• Bacteria in the bowel play two important
roles:
– The bacteria help break down indigestible
materials
– Produce B complex vitamins and most of the
vitamin K that we need for proper blood
clotting
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Accessory Organs
• Besides the salivary glands found in the
mouth, there are other accessory organs
needed for digestion:
– The liver
– The gallbladder
– The pancreas
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The Liver
• The liver weighs 1.5 kg, is located inferior
to the diaphragm, and is the largest
glandular organ in the body, and the
largest organ in the abdominopelvic cavity.
• This organ conducts many functions vital
to life.
• It is divided into the large right lobe and a
smaller left lobe. The right lobe has two
smaller inferior lobes.
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The Liver
• It receives about 1½ quarts of blood every
minute from the hepatic portal vein
(carrying blood full of the end products of
digestion) and hepatic artery (providing
oxygen-rich blood).
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Figure 16-17 The liver.
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Functions of the Liver
• The liver performs many functions:
– Detoxifies the body of harmful substances
such as certain drugs and alcohols
– Creates body heat
– Destroys old blood cells and recycles their
usable parts while eliminating unneeded
parts, such as the pigment bilirubin eliminated
in bile, and giving feces their distinctive color
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Functions of the Liver
• The liver performs many functions:
– Forms blood plasma proteins, such as
albumin and globulin
– Produces the clotting factors fibrinogen and
prothrombin
– Creates the anticoagulant heparin
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More Functions of the Liver
• And that’s not all the liver does!
– Manufactures bile, needed for the digestion of
fats
– Stores and modifies fats for a more efficient
usage by the body’s cells
– Synthesizes urea, a by-product of protein
metabolism, so it can be eliminated by the
body
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More Functions of the Liver
• And that’s not all the liver does!
– Stores the simple sugar, glucose, as
glycogen; when the blood sugar level falls
below normal, the liver reconverts glycogen to
glucose, releases enough of it into the blood
stream to bring blood sugar levels back to an
acceptable concentration
– Stores ions, vitamins A, B12, D, E, and K
– Makes cholesterol
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Bile
• Secretion of the hormone secretin stimulates
bile production, a critical liver digestive
function.
• The salts found in bile act like a detergent,
breaking fat up into tiny droplets. This
process called emulsification, makes the
work of digestive enzymes easier.
• Bile helps absorb fat from the small intestine
and transports bilirubin and excess
cholesterol to the intestine for elimination.
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Bile
• Bile leaves the liver via the hepatic duct,
travels through the cystic duct to the
gallbladder, and is stored there until
needed by the small intestine.
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From the Streets:
Portal Hypertension
• The portal system includes veins from the
spleen, stomach, pancreas, gallbladder,
and intestine that drain blood into the
portal vein that flows to the liver.
• Portal hypertension occurs when the blood
flow is obstructed through any part of the
portal system.
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From the Streets:
Portal Hypertension
• Long-term portal hypertension results in:
– Varices
– Ascites
– Splenomegaly
– Hepatic encephalopathy
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Figure 16-18b Postmortem liver specimen illustrating cirrhotic liver.
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Figure 16-19 Esophageal varices in patient with portal hypertension secondary to alcoholic
cirrhosis.
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Figure 16-19 (continued) Esophageal varices in patient with portal hypertension secondary
to alcoholic cirrhosis.
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Gallbladder
• The gallbladder is a sac-shaped organ, 3–
4 inches long, located under the liver’s
right lobe.
• While storing bile it absorbs much of its
water content, making it 6–10 times more
concentrated. If over-concentrated the bile
salts may solidify, forming gall stones.
• Fatty foods in the duodenum cause the
release of CCK.
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Gallbladder
• This release causes the smooth muscle
walls of the gallbladder to contract,
squeezing bile into the cystic duct, through
the common bile duct, and into the
duodenum.
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From the Streets:
Hepatitis
• Hepatitis is an inflammation of the liver
and can result from infectious and
noninfectious causes.
• Signs and symptoms
• Types of infectious hepatitis:
– Hepatitis A
– Hepatitis B
– Hepatitis C
– Hepatitis D
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Pancreas
• The pancreas plays a role in digestion, as
well as being an endocrine gland.
• It is 6–9 inches long, located posterior to
the stomach, and extends laterally from
the duodenum to the spleen.
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Pancreas
• The exocrine portion secretes buffers and
digestive enzymes through the pancreatic
duct to the duodenum.
• Buffers are needed to neutralize the
acidity of the chyme, to a pH ranging from
7.5–8.8, saving the intestinal walls from
damage.
• This secretory action is activated by the
release of hormones from the duodenum.
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Pancreas
• The general digestive enzymes of the
pancreas include:
– Carbohydrase – works on sugars and
starches
– Lipase – works on lipids
– Proteinase – breaks down proteins
– Nuclease – breaks down nucleic acids
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Figure 16-22 The pancreas.
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From the Streets:
Biliary Colic and Cholecystitis
• Cholecystitis is inflammation of the
gallbladder.
• Cholelithiasis is the formation of
gallbladder stones which can cause biliary
colic (gallbladder pain) due to the
expansion and contraction of the biliary
duct.
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Clinical Application: Cholecystitis
• Stones, often formed from cholesterol, in
the gallbladder is called cholelithiasis.
They can range in size from grains of sand
to marbles or larger.
• Stones lodged in the bile duct will cause
severe pain that radiates to the right
shoulder. If inflammation develops, it is
called cholecystitis.
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Clinical Application: Cholecystitis
• If the blockage causes back up of bile into
the liver it can cause jaundice.
• Treatment resolves the blockage of the
bile duct with medication, shock waves, or
surgical removal.
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Clinical Application:
Pancreatitis
• Problems can also occur with the pancreas
when the bile duct becomes blocked. In some
cases, the pancreatic enzymes back up into
the pancreas. As a result, those enzymes
begin to inflame and destroy the pancreas
causing pancreatitis.
• Causes include excessive alcohol
consumption, gallbladder disease, or some
irritation that causes abnormally high rates of
pancreatic enzyme activation. If this situation
isn’t resolved, death can occur.
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From the Streets:
Pancreatitis
• Pancreatitis is an inflammation of the
pancreas.
• Four main categories include:
–
–
–
–
Metabolic
Mechanical
Vascular
Infectious
• Common causes include obstructions of the
pancreatic duct or common bile duct.
• Inflammation increases as digestive enzymes
regurgitate into the pancreas.
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Common Disorders of the Digestive
System
• Symptoms of digestive disorders usually
include some or all of the following:
– Vomiting
– Diarrhea
– Constipation
– Abdominal pain
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Vomiting
• Vomiting is a protective mechanism, ridding
the digestive tract of an irritant or overload of
food that stimulates sensory fibers, sending a
signal to the vomiting center in the brain.
• Motor impulses are sent to the diaphragm
and abdominal muscles to contract,
squeezing the stomach muscles and opening
the cardiac sphincter at the esophageal
opening, and contents are regurgitated.
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Diarrhea
• Diarrhea results when the fluid contents in
the small intestine are rushed through the
large intestine without reabsorbing enough
water.
• The rapid movement reduces nutrient and
electrolyte absorption as well, and can
cause serious problems.
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Constipation
• Constipation is the opposite of diarrhea.
• Feces pass too slowly through the colon
and too much water is absorbed.
• The stool becomes hard and dry and
difficult to pass.
• Constipation does not refer to the
frequency of stooling, but instead to the
hard consistency of the stool.
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Peptic Ulcer Disease
• Peptic ulcer disease can affect the lining of
the esophagus, stomach, or duodenum.
• The most common region is the upper part
of the small intestine, or duodenum.
• It is caused by an imbalance in the juices
of the stomach that produce more acid
than normal and erode the mucosal lining
of the digestive tract.
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Peptic Ulcer Disease
• Helicobacter pylori is a bacteria implicated
in many ulcers. It opens a wound in the
lining of the intestine which is made worse
by exposure to digestive juices and
stomach acids.
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Figure 16-10 Peptic ulcer disease (PUD).
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Table 16-3 Pathology of the Digestive System.
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Table 16-3 (continued) Pathology of the Digestive Process.
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Table 16-3 (continued) Pathology of the Digestive Process.
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Table 16-3 (continued) Pathology of the Digestive Process.
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Table 16-3 (continued) Pathology of the Digestive Process.
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From the Streets:
Abdominal Pain
• Abdominal pain is one of the most
frequent reasons people seek emergency
care.
• The cause can be difficult to determine.
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From the Streets:
Emergency Vitamins?
• Two vitamins play an important role in
emergency care: Vitamin B1 and K
• Vitamin B1 (thiamine) is important in many
metabolic processes.
• Vitamin K is necessary for blood
coagulation.
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Snapshots from the Journey
• The digestive tract is a hollow tube
extending from the mouth to the anus. It
utilizes a variety of accessory organs that
allow the digestion of food and the
absorption of nutrients necessary for life.
• Food is processed mechanically and
chemically to efficiently break it down to
usable substances.
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Snapshots from the Journey
• The bulk of the digestive process and the
absorption of most nutrients occur in the
small intestine.
• Although not directly a part of the
gastrointestinal system, the accessory
organs (liver, gallbladder, and pancreas)
are needed for proper and efficient
functioning of the digestive process.
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Snapshots from the Journey
• The rate of speed that food travels through
the gastrointestinal system affects the
acidity of the digested food, the absorption
of nutrients, and the quality of the feces.
• Diseases of the gastrointestinal system
can be a result of heredity, the type and
amount of food consumed, substance
abuse, or emotions.
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Case Study
A patient presents in the emergency
department around 3 a.m. with a severe
burning sensation in the chest. The patient
is anxious and thinks he is having a heart
attack. All vital signs are within normal
limits, and no other pain or discomfort is
noted in other regions of the body. He
states he ate a large bowl of spicy
spaghetti around 11:30 p.m.
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Case Study
Before falling asleep, he was
uncomfortable and felt his large volume of
food hadn’t digested. He also states this
burning sensation has happened in the
past after eating, especially at night and
when laying on his right side.
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Case Study Questions
• Do you think this is a heart attack?
• What do you think the problem is?
• What physiological process is
malfunctioning?
• Why is the position of the patient
important?
• What suggestions would you make to the
patient to prevent future episodes?
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From the Streets
You are called to the scene of a 50-year-old
male complaining of severe epigastric pain
radiating to his back, nausea/vomiting, and a
low grade fever. He has a history of
alcoholism and gallstones. He is restless,
tachycardic, hypotensive, and has pale, cool
and clammy skin.
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From the Streets Questions
•
•
•
•
What is his most likely diagnosis?
What are the key contributing factors?
Describe the diagnosis?
What is his prognosis?
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From the Streets Questions
• What is his most likely diagnosis?
Pancreatitis
• What are the key contributing factors?
History of alcoholism and gallstones
• Describe the diagnosis? Pancreatitis
occurs when pancreatic enzymes back up
into the pancreas causing inflammation
and necrosis.
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From the Streets Questions
• What is his prognosis? This is a lifethreatening condition. He requires
supportive measures and transport.
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End of Chapter
Review Questions
1. Which of the following is not a
responsibility of the large intestine?
a. Production of vitamin K
b. Absorption of water
c. Digestion of carbohydrates
d. Elimination of feces
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Review Questions
2. Starches begin to be digested in the:
a. Oral cavity
b. Esophagus
c. Stomach
d. Large intestine
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Review Questions
3. This structure prevents food and liquid
from entering your lungs:
a. Uvula
b. Pharynx
c. Epiglottis
d. Glottis
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Review Questions
4. The liver receives approximately1.5
quarts of blood every minute from:
a. Hepatic artery
b. Hepatic vein
c. Hepatic portal vein
d. Both a & c
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Review Questions
5. Which of the following is NOT a colon
segment?
a. Transverse
b. Ascending
c. Descending
d. Absorbing
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Review Questions
1. _____ is the muscle action that mixes
chyme with digestive juices, while _____ is
the muscular action that moves food
through the digestive system.
2. This vermiform structure is attached to the
large intestine and is considered a vestigial
organ __________.
3. The exocrine portion of this important organ
secretes buffers needed to neutralize the
acidity of chyme and also secretes several
digestive enzymes: __________.
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Review Questions
4. _________ is the mechanical breaking up
of fat into smaller particles that can more
readily be acted upon by digestive
enzymes.
5. The end result of fecal matter remaining in
the large intestine too long, with too much
water being removed from it, is _______.
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Review Questions
1. Explain the difference between chyme
and chyle.
2. Explain the importance of bacteria in the
large intestine.
3. Discuss the importance of the liver in the
digestive process.
4. Could you live without a gallbladder?
Defend your answer.
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Review Questions
5. List the changes in the anatomy of the
walls of the alimentary canal from
esophagus to anus.
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