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LESSON 10
THE DIGESTIVE SYSTEM
INTRODUCTION
The digestive system begins in the mouth where food enters the body, and ends
with the anus where feces leaves the body. The main functions of the organs of
the digestive system are to take complex food materials that are taken into the
mouth and break them down mechanically and chemically. Foods traveling
through the digestive tract are helped in their breakdown by digestive enzymes.
Complex proteins are broken down to simpler amino acids; complex sugars are
broken down to simple sugars such as glucose; and large fat molecules
(triglycerides) are broken down to fatty acids and glycerol.
After food is digested into their smallest components, its absorbed into the blood
and lymph vessels by passing through the lining of the small intestine. Nutrients
such as sugars, fats, and amino acids, can then travel to all the cells of the body.
Structures within the cell, like the mitochondria, metabolize nutrients in the
presence of oxygen to release energy (ATP) stored within the food. Cells may use
amino acids to build large protein molecules needed for growth and repair.
Although the walls of the small intestine absorb fatty acids and glycerol, many of
these nutrients enter lymphatic vessels rather than blood vessels. Fats eventually
enter the bloodstream via the lymph vessels in the upper chest region.
Another function of the digestive system is the removal of the solid waste
materials that cannot be absorbed into the bloodstream. The large intestine first
removes the water, then compacts the solids, and finally removes them from the
body through the anal meatus. The expelled wastes are known as feces.
ANATOMY
Mouth
The digestive system begins with the mouth or oral cavity. The sides of the mouth
are soft epithelial tissue. The roof of the mouth towards the anterior is a hard
palate; towards the posterior is the soft palate. Irregular ridges called rugae cover
the hard palate. Extending down from the soft palate is the uvula, which aids in
speech. The floor of the mouth is mostly composed of the tongue which aids in
the movement of food and contains the taste senses which are small papillae which
arise from the tongue’s surface. The tongue aids in producing sounds. Located to
the back of the mouth are the tonsils which are masses of lymphatic tissue found
on both sides of the oral pharynx. Tonsils act as filters to protect the body from
the invasion of microorganisms and produce lymphocytes, known as white blood
cells, that are able to fight disease.
The gums are made of fleshy tissue and surround the teeth. The human mouth
contains 32 teeth. They are:
central incisor
lateral incisor
cuspid or canine
first premolar
second premolar
first molar
second molar
third molar, or wisdom tooth
Three pairs of salivary glands surround the oral cavity. These exocrine glands
produce a fluid called saliva that contains important digestive enzymes. Saliva is
released from the parotid gland, submandibular gland, and sublingual gland on
each side of the mouth. Narrow ducts carry the saliva into the oral cavity. Small
stones sometimes form in these narrow ducts that can cause severe mouth pain.
Pharynx
The pharynx or throat is a muscular tube about 5 inches long, lined with a mucous
membrane. It serves as a common passageway for air traveling from the nose
(nasal cavity) to the windpipe (trachea) and food traveling from the oral cavity to
the esophagus. When swallowing occurs a flap of tissue, the epiglottis, covers the
trachea so that food cannot enter and become lodged there.
Stomach
Food passes from the esophagus into the stomach. The stomach is composed of an
upper portion called the fundus, a middle section known as the body, and a lower
portion, the pylorus. Rings of muscles called sphincter control the openings into
and from the stomach. The cardiac sphincter relaxes and contracts to move food
from the esophagus into the stomach, whereas the pyloric sphincter allows food to
leave the stomach when it has been sufficiently digested. Folds in the mucous
membrane (mucosa) which lines the stomach are called rugae. The rugae contain
digestive glands that produce enzymes and hydrochloric acid.
The role of the stomach is to prepare the food chemically and mechanically so that
it can be received in the small intestine for further digestion and absorption into
the bloodstream. Food does not enter the bloodstream through the walls of the
stomach. The stomach controls the passing of foods into the first part of the small
intestine so that it proceeds only when it is chemically ready and in small amounts.
Food leaves the stomach in 1-4 hours depending upon the amount and type of food
eaten.
Small Intestine
The small intestine extends for 20 feet from the pyloric sphincter to the first part
of the large intestine. It has three parts: duodenum, jejunum, and ileum. The
duodenum is the first section. It receives food from the stomach and bile from the
liver through the gallbladder. It also receives pancreatic juice from the pancreas.
Enzymes and bile help
to digest food before it passes the small intestine. The jejunum is about 8 feet
long. It connects with the third part, the ileum which is about 11 feet long. The
ileum attaches to the first part of the large intestine.
Millions of tiny, microscopic projections called villi line the walls of the small
intestine. The tiny capillaries (microscopic blood vessels) in the villi absorb the
digested nutrients into the bloodstream and lymph vessels.
Large Intestine
The large intestine extends from the end of the ileum to the anus. It is divided into
four parts: cecum, colon, sigmoid colon, and rectum. The cecum is a pouch on the
right side that attaches to the ileum by the ileocecal sphincter. The appendix
hangs from the cecum; its function is like other lymph structures to aid in the
control of bacteria moving into the small intestines. The excessive bacteria may
cause the appendix to become inflamed.
The colon is about 5 feet long and has three divisions. The ascending colon
extends from the cecum to the under surface of the liver where it turns to the left
to become the transverse colon. The transverse colon passes horizontally to the
left toward the spleen and turns downward into the descending colon. The
sigmoid colon, shaped like an S, lies at the distal end of the descending colon and
leads into the rectum. The rectum terminates in the lower opening of the
gastrointestinal tract, the anus.
The large intestine receives the fluid waste products of digestion and stores these
wastes until they can be excreted from the body. Because the large intestine
absorbs most of the water within the waste material, the body can expel solid
feces. Diarrhea can result from lack of absorption of the water through the walls
of the large intestine. Constipation happens when the feces stops moving, which
is mostly related to diet.
Liver, Gallbladder, and Pancreas
Three important additional organs of the digestive system - the liver, gallbladder,
and pancreas - play crucial roles in the proper digestion and absorption of
nutrients. The liver is located in the right upper quadrant and produces a thick,
yellowish-brown fluid called bile. Bile contains cholesterol, bile acids, and
several bile pigments. One of these pigments, bilirubin, is produced from the
breakdown of hemoglobin in the liver. The liver combines bilirubin with bile and
then excretes both into the duodenum. They are expelled from the body with the
feces.
The liver continuously produces bile. Bile moves from the liver through the
hepatic duct, to the cystic duct, and then is stored in the gallbladder. Upon eating
fatty food the body releases bile into the common bile duct which joins with the
pancreatic duct just before the entrance to the duodenum. The duodenum thus
receives a mixture of bile and pancreatic juices. Bile has a detergent-like effect on
fats in the duodenum. It breaks apart large fat globules so that enzymes from the
pancreas can digest the fats. This is called emulsification. Without bile, most of
the fat taken into the body would remain undigested.
Besides producing bile, the liver has several other vital and important functions
including keeping the glucose in the blood at a normal level. The liver removes
excess glucose from the bloodstream and stores it as glycogen. When the blood
sugar level becomes dangerously low the liver can convert stored glycogen back
into glucose via a process called glycogenolysis. In addition, the liver can convert
proteins and fats into glucose when the body needs sugar by a process called
gluconeogenesis.
The liver’s other functions include production of some blood proteins, particularly
those necessary for blood clotting, destruction of old erythrocytes and release of
bilirubin, and removal of poisons or detoxification of the blood.
The hepatic portal system brings blood to the liver directly from the intestines.
Digested foods pass into the portal vein directly after being absorbed into the
bloodstream from the small intestine, thus giving the liver its first chance at using
the nutrients.
The pancreas has both an exocrine and an endocrine organ function. As an
exocrine gland, it produces pancreatic juices filled with enzymes (amylase and
lipase) to digest food. These pass into the duodenum through the pancreatic duct.
As an endocrine gland (secrets into the bloodstream), the pancreas secretes insulin
and glucogon.
LESSON 10 GRAPHICS
TERMS FOR LESSON 10: THE DIGESTIVE SYSTEM
Anatonomical Terms to Know
mouth
palate
pharynx
esophagus
stomach
antrum
pyloric sphincter
small intestine
duodenum
jejunum
ileum
large intestine
cecum
colon
rectum
anus
Accessory Organs to Know
salivary gland
liver
gallbladder
pancreas
peritoneum
appendix
abdomen
Word Roots to Know: Digestive System
an/o
antr/o
cec/o
col/o
duoden/o
enter/o
esophag/o
gastr/o
ile/o
jejun/o
proct/o
rect/o
sigmoid/o
stomat/o
or/o
appendic/o
cheil/o
chol/o
diverticul/o
gingiv/o
gloss/o
lingu/o
hepat/o
herni/o
lapar/o
abdomin/o
palat/o
pancreat/o
peritone/o
pylor/o
sial/o
uvul/o
Diagnostic Terms to Know: Digestive System
appendicitis
cholecystitis
cholelithiasis
diverticulitis
diverticulosis
gastritis
gastroenteritis
gastroenterocolitis
gingivitis
hepatitis
hepatoma
palatitis
pancreatitis
proctoptosis
rectocele
sialolith
uvulitis
adhesion
anorexia nervosa
cirrhosis
Crohn’s disease
duodenal ulcer
gastric ulcer
intussusception
peptic ulcer
ulcerative colitis
volvulus
Surgical Terms to Know: Digestive System
anoplasty
antrectomy
appendectomy
cheilorrhaphy
cholecystectomy
colectomy
colostomy
diverticulectomy
esophagogastroplasty
gastrectomy
gastrojejunostomy
gastrostomy
gingivectomy
glossorrhaphy
herniorrhaphy
ileostomy
laparotomy
palatoplasty
pyloroplasty
uvulectomy
abdominoperineal resection
anastomosis
vagotomy
Diagnostic Procedural Terms to Know: Digestive System
cholecystogram
endoscope
endoscopy
esophagoscope
esophagoscopy
gastroscope
gastroscopy
sigmoidoscope
sigmoidoscopy
lower GI series
upper GI series
Additonal Terms to Know: Digestive System
abdominal
anal
apepsia
aphagia
abdominocentesis
bradypepsia
dyspepsia
dysphagia
gastromalacia
gastrodynia
glossopathy
ileocecal
nasogastric
oral
pancreatic
peritoneal
proctologist
proctology
stomatogastric
sublingual
ascites
feces
gavage
gastric lavage
nausea
PRACTICE EXERCISES FOR LESSON 10
THE DIGESTIVE SYSTEM
MATCHING
---- lower bulge of the stomach
---- hangs from roof of mouth
---- produces saliva
---- produces bile
---- roof of mouth
---- opening between stomach &
---duodenum
---- behind stomach
---- small pouch
---- abdominal lining
---- between pelvis and thorax
---- stores bile
DEFINE:
procto/o
gastr/o
an/o
cec/o
ile/o
stomat/o
duoden/o
col/o
or/o
enter/o
rect/o
antr/o
esophag/o
jejun/o
sigmoid/o
DEFINE:
herni/o
abdomin/o
a
b
c
d
e
f
g
h
i
j
k
l
salivary gland
pancreas
peritoneum
uvula
gallbladder
palate
abdomen
liver
appendix
pyloric sphincter
cecum
antrum
sial/o
chol/o
diverticul/o
gingiv/o
appendic/o
gloss/o
hepat/o
cheil/o
peritone/o
palat/o
pancreat/o
lapar/o
lingu/o
pylor/o
uvul/o
DEFINE:
cholelithiasis
diverticulosis
sialolith
pancreatitis
proctoptosis
gastritis
rectocele
hepatitis
cholecystitis
anorexia nervosa
Crohn’s disease
ASSIGNMENT FOR LESSON 10
Medical Terminology, HS 280
The Digestive System
MATCHING
---- 1
digestion mostly takes place
---- 2
holding tank for food
---- 3
lower bulge of stomach
---- 4
hangs from roof of mouth
---- 5
produces saliva
---- 6
produces bile
---- 7
roof of mouth
---- 8
small pouch with no function
---- 9
stores bile
---- 10
chops food
MATCHING
---- 11
an/o
---- 12
antro/o
---- 13
cec/o
---- 14
enter/o
---- 15
ile/o
---- 16
jejun/o
---- 17
proct/o
---- 18
sigmoid/o
---- 19
or/o
---- 20
duoden/o
a
b
c
d
e
f
g
h
i
j
cecum
intestines
ileum
anus
mouth
antrum
anus
jejunum
sigmoid colon
duodenum
MATCHING - May Be Used More Than Once
-------------------------------
21
22
23
24
25
26
27
28
29
30
ceo/o
col/o
duoden/o
enter/o
gastr/o
ile/o
jejun/o
stomat/o
proct/o
or/o
a
b
c
d
e
f
g
h
i
a
b
c
d
e
f
g
h
i
j
stomach
intestine
ileum
mouth
jejunum
rectal area
jejunum
cecum
duodenum
stomach
liver
salivary gland
plate
appendix
gallbladder
pyloric sphincter
teeth
small intestine
ovula
Assignment for Lesson 10, Digestive, pg. 2
MATCHING - May Be Used More Than Once
---- 31
appendic/o
a
tongue
---- 32
cheil/o
b
lip
---- 33
chole/o
c
gall, bile
---- 34
cholangi/o
d
gum
---- 35
diverticuli/o
e
hernia
---- 36
gingiv/o
f
liver
---- 37
gloss
g
bile duct
---- 38
hepat/o
h
appendix
---- 39
herni/o
---- 40
lingu/o
DEFINE: THE DIGESTIVE SYSTEM
appendectomy
cholelithiasis
diverticulitis
gastroenterocolitis
gingivitis
pancreatitis
proctoptosis
rectocele
Crohn’s disease
duodenal ulcer
peptic ulcer
cholecystogram
lower GI series
upper GI series
aphagia
dysplagia
glossopathy
proctologist
Assignment for Lesson 10, Digestive, pg. 3
DEFINE:
sublingual
ascites
gastric lavage
peritoneum
appendix
salivary glands
rectum
diverticulosis
gastritis
hepatitis
hepatoma
sialolith
uvulitis
cirrhosis
intussusception
ulcerative colitis
appendicectomy
cheilorrhaphy
cholecystectomy
colectomy
nausea