The Digestive System
1.Digestion
 The mechanical and chemical
breakdown of food into molecules
that can be absorbed across the
lining of the small intestine and
into the bloodstream as nutrients
for the body.
2,3 Mechanical Digestion
 Mechanical digestion breaks food up into
small pieces that are more accessible to
digestive enzymes.
 It includes the chewing of teeth, the
churning of food in the stomach and
peristalsis throughout the entire digestive
process.
4,5,6 Chemical Digestion
 Chemical digestion refers to the
action of the digestive enzymes.
 The various digestive juices contain
enzymes that digest particular types of
food.
 Examples:
 Salivary amylase: breaks starch down
into maltose
 Pepsin: breaks proteins down into amino
acids
7,8,9. Flow chart of
Digestion:
Salivary Glands
Mouth
Pharnyx
Pancreas
Large
Intestine
Rectum
Liver
Esophagus
Gallbladder
Small Intestine
Anus
Stomach
10-13 Mouth
 Food enters the mouth, where it is
mechanically digested. The teeth, the palate
(roof of mouth) and the tongue break the food
down into small pieces.
 The Salivary Glands secrete Salivary Amylase
into the mouth that begins the chemical
digestion of carbohydrates.
 Carbohydrates are broken down into simple
sugars. (glucose)
 Food leaves the mouth in a bolus (moist, ball of
food)
CLEFT PALATE
CLEFT PALATE
CLEFT PALATE: BEFORE
AND AFTER
14,15 Pharynx
 Food (bolus) travels through the
throat “pharynx” on the way to
the esophagus.
 There is a flap of tissue called
the epiglottis that prevents food
from going down the trachea.
Pharynx
16-20
Esophagus
 The esophagus is a muscular tube that joins the
pharynx with the stomach.
 Swallowing pushes the bolus into the esophagus.
 Rhythmical contractions called peristalsis pushes
food through the esophagus to the stomach.
 When the bolus reaches the end of the esophagus it
goes through the cardiac sphincter into the stomach.
 This is the sphincter muscle that prevents the acidic
contents of the stomach from entering the
esophagus.
21,22 Heartburn
 Normally, the cardiac sphincter
prevents the acidic contents of
the stomach from entering the
esophagus.
 Sometimes, heartburn, which
feels like a burning pain rising up
into the throat, occurs when
some of the contents of the
stomach escape into the
esophagus.
23-31 Stomach
 The stomach is a thick walled “J” shaped organ that lies
underneath the diaphragm muscle.
 The stomach stores food and starts the digestion of proteins.
 The wall of the stomach has three muscular layers and
contains deep folds called “rugae”.
 The muscular walls of the stomach churn, mixing the
contents.
 Gastric glands secrete gastric juice into the stomach.
 Gastric Juice contains HCl acid and a digestive enzyme called pepsin.
 Pepsin digests protein and breaks in down into amino acids.
 Normally the stomach empties in 2-6 hours.
 When food leaves the stomach it is semisolid mixture called
chyme.
Lap band
Gastric bypass
Rugae
(Inside walls of stomach)
32-34 ULCER
 Normally the wall of the
stomach is protected by a thick
layer of mucus, but if chance,
Hydrochloric Acid penetrates
this mucus, an ulcer can form.
 An ulcer is an open sore in the
stomach wall caused by gradual
breakdown of the mucus
membrane that lines the
stomach
 The most frequent cause of an
ulcer is an infection caused by
the bacterium helicobacter
pylori.
35-38 Small Intestine
 The small intestine is named for its small
diameter. (In comparison to the large
intestine)
 The small intestine averages about 10 feet
in length.
 The small intestine receives secretions
from the pancreas and liver.
 The primary function of the small intestine
is absorption.
Note the area in which the liver and pancreas
secrete into the Duodenum of the small intestine.
The digestive tract
39-41 Three parts of the
small intestine:
 Duodenum (du”o-de’num): The first 25 cm of the
small intestine. This part receives the pancreatic
secretions and bile from the liver.
 Jejunum (je-joo’num): The next 3 feet of the
small intestine. This part contains the villi.
(fingerlike extensions that absorb nutrients)
 Ileum: (il’e-um): The last 6-7 feet of the small
intestine. This part also contains villi to absorb
nutrients from the digestive system to the
circulatory system.
42-45 Villi
 The wall of the small intestine is made up of
fingerlike extensions called villi.
 The epithelial cells of each villi have
extensions called microvilli.
 The large number of villi and their microvilli
increase the surface area of the small
intestine to provide more area for absorption.
 The surface area of the small intestine is
equal to a tennis court.
villi
46-49 Large Intestine
 Includes the cecum, colon,
rectum and anal canal.
 Larger in diameter than the
small intestine
 The cecum (se’kum): is the
first portion of the large
intestine. This is where the
small intestine attaches to the
large intestine.
 The appendix is a small
projection from the cecum.
 Superior to the cecum the large intestine is
termed the ascending colon.
 At the level of the liver, the large intestine
bends sharply and becomes the transverse
colon, it travels across where it bends
again and becomes the descending colon.
 50,51
 At the lower region of the large intestine,
the descending colon turns in to form an
S shaped bend known as the sigmoid
colon.
 The last 20 cm of the large intestine is
known as the rectum, which ends in the
anal canal, which opens at the anus.
(The out shoot) 52,53
 The large intestine absorbs water and electrolytes.
 It prepares and stores non-digestible material
(feces)
 Feces contain bile pigments and large quantities
of bacteria (E-coli)
 The E-coli bacteria live off of the fecal matter.
When they break down this material, they emit
odorous molecules that cause the characteristic
fecal odor.
 Some of the vitamins (Vitamin K and some B
vitamins) and amino acids are produced by the Ecoli bacteria and absorbed by the intestinal lining.
 The E-coli bacteria are beneficial for humans in
this matter. 54-59
60,61 APPENDIX
 The appendix is a fingerlike extension of
the cecum of the large intestine.
 The appendix can become infected,
resulting in appendicitis, a very painful
condition in which the fluid content of the
appendix can increase to the point that it
bursts.
62-64 Diarrhea & Constipation
 Two common everyday complaints
associated with the large intestine are
diarrhea and constipation.
 In diarrhea, too little water is absorbed by
the large intestine.
 In constipation, too much water is
absorbed by the large intestine.
 The major causes of diarrhea are
infection of the lower tract and nervous
stimulation.
 In the case of infection, such as food
poisoning caused by eating
contaminated food, the intestinal wall
becomes irritated and peristalsis
increases.
 Lack of water absorption is a
protective measure by the body, and
diarrhea serves to rid the body of the
infectious organisms.
 When a person is under stress, the
Nervous System sometimes stimulates
the intestinal wall, resulting in diarrhea.
 Loss of water due to diarrhea may
lead to dehydration, a serious
condition in which the body tissues
lose their normal water content. 6569
Diarrhea
Constipation &
Hemorrhoids 70-73
 When a person is constipated, the feces are
dry and hard.
 Chronic constipation is associated with the
development of hemorrhoids.
 Hemorrhoids are masses of tissue within the
anal canal that contain blood vessels.
 Internal hemorrhoids are normal. It is when the
hemorrhoids descend through the anal canal
that they become painful and irritated.
Severe Grade 3 Hemorrhoids
Accessory Organs: 74-75




Salivary Glands
Pancreas
Liver
Gallbladder
•These organs are
essential to the process
of digestion, but food
does not actually travel
into any of these organs.
•These organs secrete
important fluids into the
primary organs of
digestion to speed up the
chemical digestive
process.
The salivary
glands 76-79
 The salivary glands secrete about 1 liter of saliva each day,
which enters the mouth by way of their ducts.
 Saliva contains mucus and a digestive enzyme called
salivary amylase.
 Salivary amylase begins the digestion of carbohydrates
into simple sugars.
 There are three pairs of salivary glands: the sublingual
glands (found underneath the tongue), the submandibular
glands (lie under the tongue at the back portion of the
mouth and the parotid glands which are located in front of
and below the ears.
The Pancreas
80-82
 The pancreas has both endocrine and exocrine
functions.
 The exocrine functions are the ones associated
with digestion.
 The pancreas produces pancreatic juice, which
contains sodium bicarbonate, a chemical that
neutralizes the HCl acid from the stomach, and
digestive enzymes that break down
carbohydrates, proteins and fats into simple
substances small enough to be absorbed by the
villi of the small intestine.
The Liver 83-88
 The liver is the largest gland of the body.
 The liver produces bile.
 Bile is a yellowish green fluid. It contains bile salts
that emulsify fats once bile reaches the small
intestine.
 The liver plays many other important roles in the body.
 It detoxifies the blood by removing poisonous
substances and metabolizing them.
 It stores glucose as glycogen after eating and the
breakdown of glycogen to glucose between meals to
maintain the blood glucose level.
•Cirrhosis is a chronic
disease of the liver in
which the organ first
becomes fatty and then
the liver tissue is
replaced by scar tissue.
Cirrhosis of the Liver
89,90
•This condition is most
often the result of
excessive amounts of
alcohol in which the
liver had to break down.
The Gallbladder 91,92
 The gallbladder is a pear shaped,
muscular sac attached to the liver.
 The liver produces bile and any excess
bile is stored in the gallbladder.
•This is the inside of the gallbladder of a patient
with gallstones.
•Gallstones are small, hard pellets that form in the
gallbladder. Gallstones can range from a few
millimeters to several centimeters in diameter.
Most gallstones are formed from cholesterol.