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The Digestive
System
By Mr. Danilo Villar Rogayan Jr.
Instructor I, Department of Natural Sciences
RMTU San Marcelino
Introduction
• Digestion
• Mechanical and chemical breakdown of
foods into forms that body cells can
absorb
• The organs of the digestive system carry
out digestion
• Two categories
• Alimentary canal organs
• Accessory organs
Characteristics of the
Alimentary Canal
•
Wall of alimentary canal
• Mucosa
•
•
•
Inner most layer; epithelial tissue
Secretes enzymes and mucus into lumen
Absorbs nutrients
• Submucosa
•
•
Inferior to mucosa; loose connective tissue, blood
vessels, glands, and nerves
Blood vessels carries away absorbed nutrients
• Muscular layer
•
•
Just outside submucosa; layers of smooth muscle
Contracts to move materials through the canal
Characteristics of the
Alimentary Canal (cont.)
• Serosa
•
Double-walled outermost layer: peritoneum
• Visceral peritoneum
• Innermost wall of serosa
• Secretes serous fluid to keep outside of canal moist
• Parietal peritoneum
• Abdominal lining
•
Movements
• Churning – mixes substances in the canal
• Peristalsis – propels substances through the tract
Checkpoint!
What are the layers of the wall of the alimentary canal and
what do they do?
ANSWER: The layers are:
Mucosa: innermost layer; secretes enzymes and mucus into the canal and
absorbs nutrients
Submucosa: inferior to the mucosa; carries away absorbed nutrients
Muscular layer: just outside the submucosa; contracts to move materials
through the canal
Serosa: double-walled outer layer; secretes serous fluid to keep outside of
canal moist
The Mouth
• Buccal cavity
• Mechanical digestion
• Takes in food and reduces its
size by chewing
• Starts chemical digestion
• Saliva contains enzyme
amylase, which breaks down
carbohydrates
The Mouth (cont.)
• Cheeks hold food in mouth
• Lips – sensory nerve fibers that judge
temperature of food
• Tongue
• Skeletal muscles covered by mucous membrane
• Lingual frenulum – holds tongue to floor of mouth
• Mixes food, holds food between teeth, contains
taste buds
• Lingual tonsils – lymphatic tissue destroys bacteria
and viruses on back of tongue
The Mouth (cont.)
• Palate
• Roof of mouth
• Separates oral cavity from nasal cavity
• Uvula – portion of soft palate that hangs down in
throat
• Lymph tissue
• Palatine tonsils (oropharynx)
• Pharyngeal tonsils – adenoids (nasopharynx)
The Mouth (cont.)
• Teeth – decrease size • Salivary glands
of food particles
• Cells
• Incisors – bite off food
pieces
• Cuspids – tear tough
food
• Bicuspids and molars
– grind food
• Serous
• Mucous
• Glands
• Parotid
• Submandibular
• Sublingual
Video Clip:
How Does Dental Plaque Form
Pharynx
• Throat
• Functions
• Connects nasal cavity
with oral cavity for
breathing
• Pushes food into
esophagus
• Divisions
• Nasopharynx
• Behind nasal cavity
• Oropharynx
• Behind oral cavity
• Laryngopharynx
• Behind larynx
• Continues as
esophagus
Pharynx (cont.)
•
Swallowing – automatic
process
1.
Soft palate raises, uvula
covers opening between nasal
and oral cavity
2.
Epiglottis covers larynx,
keeping food out of it
3.
Tongue presses against roof of
mouth, forcing food into
oropharynx
Pharynx (cont.)
4. Muscles in pharynx
contract, moving food
toward esophagus
5. Esophagus opens
6. Food is pushed into
esophagus by muscles
of pharynx
The Esophagus
• Muscular tube connecting pharynx to stomach
• Esophageal hiatus – hole in diaphragm through
which esophagus passes
• Cardiac sphincter
• Circular band of muscle at the opening of the
stomach
• controls movement of food into stomach
Video Clip:
Why do we brush our teeth?
The Stomach
• Below the diaphragm in
the upper left quadrant of
the abdominal cavity
• Functions
• Receive food from
esophagus
• Mix bolus with gastric juice
• Start protein digestion
• Move food into small
intestine
• Sections
•
•
•
•
Cardiac region
Fundus
Body
Pylorus
• Pyloric sphincter
• Controls movement of
substances into small
intestine
The Stomach (cont.)
• Lining of stomach
• Rugae – folds of the inner lining
• Gastric glands
• Mucous cells – secrete mucus to protect the
lining
• Chief cells – secrete pepsinogen  pepsin,
which digests protein
• Parietal cells
• Hydrochloric acid needed to convert pepsinogen to
pepsin
• Intrinsic factor needed for vitamin B12 absorption
The Stomach (cont.)
• Gastric glands stimulated by
• Parasympathetic nervous system
• Gastrin (hormone)
• Cholesystokinin (hormone) secreted by the
small intestine inhibits gastric glands
• Stomach absorbs alcohol, water, and some fatsoluble drugs
• Chyme – mixture of food and gastric juices
Checkpoint!
What are the functions of the stomach?
ANSWER: The stomach’s functions are to
receive the bolus of food, mix it with gastric
juice, start protein digestion, and move food
into the small intestine. It also absorbs
alcohol, water, and some drugs.
Video Clip:
How Digestion Works
The Small Intestine
• Tubular organ
extending from the
stomach to the large
intestine
• Duodenum
• C-shaped
• Short
• Jejunum
• Functions
• Digestion
• Absorption of
nutrients
• Coiled
• Majority of small
intestine
Small
Intestine
The Small Intestine
• Ileum
• Attached to large intestine
• Mesentery
• Fan-like tissue that holds jejunum and ileum in the
abdominal cavity
• Attaches to the posterior wall of the abdomen
• Ileocecal sphincter
• Controls movement of chyme from the ileum to the
cecum of the large intestine
Small
Intestine
The Small Intestine (cont.)
• Lining of small intestine
• Microvilli – increase surface area
• Intestinal glands
• Mucus and water
• Enzymes
• Peptidases – digest proteins
• Sucrase, maltase, and lactase – digest sugars
• Intestinal lipase – digests fats
• Primary controls
• Parasympathetic nervous system
• Stretching of intestinal wall
Checkpoint!
Your patient states that she is lactose intolerant.
What does that mean?
ANSWER: She cannot produce lactase and cannot
digest lactose, which is the sugar in dairy products.
The Large Intestine
• Extends from the ileum to the anus
• Cecum
• Beginning of large intestine
• Veriform appendix
• Ascending colon
• Portion that goes up the right side of the abdominal
cavity
The Large Intestine (cont.)
• Transverse colon
• Crosses abdominal cavity from right to left
• Descending colon
• Down left side of abdominal cavity
• Sigmoid colon
• S-shaped portion in pelvic cavity
• Absorbs water and electrolytes
Large
Intestine
The Rectum and Anal Canal
• Rectum – off sigmoid colon
• Anal canal
• Last few centimeters of rectum
• Opening to outside of body is the anus
Large
Intestine
The Rectum and Anal Canal
• Feces
• Leftover chyme
• Consists of undigested solid materials, little water,
ions, mucus, cells of intestinal lining, and bacteria
• Defecation reflex
• Triggered by periodic contractions of large intestine
• Allows anal sphincters to relax
Video Clip:
What Causes Constipation
The Liver
• Lobular organ in right upper quadrant
• Large right lobe and smaller left lobe
• Hepatic lobules – contain macrophages
• Hepatocytes – process nutrients in blood and
make bile
• Part of liver’s function
• Store vitamins and iron
The Liver (cont.)
• Hepatic portal vein – carries
blood from digestive organs to
hepatic lobules
• Hepatic duct – bile from liver
• Hepatic duct merges with cystic
duct from gallbladder and forms
common bile duct
• Common bile duct – delivers
bile to duodenum
The Gallbladder
• Small sac-like
structure located
beneath the liver
• Only function is to
store bile
• Cholecystokinin
causes the gallbladder
to release bile
Gallbladder
Chekpoint!
What is the route of bile through the liver and
gall bladder?
ANSWER: Bile is made in the hepatocytes and leaves the
liver through the hepatic duct. The hepatic duct merges
with the cystic duct from the gall bladder to form the
common bile duct, which delivers bile to the duodenum.
The Pancreas
Located behind the stomach
 Acinar cells produce pancreatic juice, which contains
these enzymes:
 Nucleases – digests
 Pancreatic amylase
nucleic acids
–
digests
 Trypsin, chymotrypsin,
carbohydrates
and carboxypeptidase –
digest proteins
 Pancreatic lipase –
digests lipids

The Pancreas (cont.)
• Also secretes bicarbonate ions into duodenum
• Neutralize acidic chyme
• Enzyme release stimulated by
• Parasympathetic nervous system
• Hormones secretin and cholecystokinin (from small
intestine)
Checkpoint!
What are the pancreatic enzymes and what do they
do?
ANSWER: They are:
Pancreatic amylase – digests carbohydrates
Pancreatic lipase – digests lipids
Nucleases – digest nucleic acids
Trypsin, chymotrypsin, and carboxypeptidase – digest proteins
The Absorption of Nutrients
• Nutrients are necessary food
substances
•
•
•
•
•
•
Carbohydrates
Proteins
Lipids
Vitamins
Minerals
Water
The Absorption of Nutrients (cont.)
• Carbohydrates – provide energy
• Polysaccharides – starches
• Monosaccharides and disaccharides – simple sugars
• Cellulose – provides fiber or bulk
• Lipids – used for energy when glucose levels are
low
• Triglycerides
• Cholesterol – essential for cell growth and function
The Absorption of Nutrients (cont.)
• Protein – used for growth and repair of tissue
• Essential amino acids body can not make
• Vitamins
• Fat-soluble
• Water-soluble
• Minerals – used to make enzymes, cell
membranes, and proteins
Vitamins
• Vitamins are organic molecules required in the
diet in small amounts
• 13 vitamins essential to humans have been
identified
• Vitamins are grouped into two categories
• Fat-soluble (A, D, E, and K)
• Water-soluble
• Minerals - are simple inorganic nutrients usually
required in small amounts
Vitamins
• Vitamin A (Retinol)
• Lack: Night-blindness, Hyperkeratosis, and
Keratomalacia
• Overdose: Hypervitaminosis A
• Liver, orange, ripe yellow fruits, leafy
vegetables, carrots, pumpkin, squash, spinach,
fish, soy milk, milk
Vitamins
• Vitamin B1 (Thiamine)
• Lack: Beriberi, Wernicke-Korsakoff syndrome
• Over: Drowsiness or muscle relaxation with
large doses
• Pork, oatmeal, brown rice, vegetables,
potatoes, liver, eggs
Vitamins
• Vitamin B2 (Riboflavin)
• Lack: Ariboflavinosis,Glossitis, Angular
stomatitis
• Dairy products, bananas, popcorn, green
beans, asparagus
Vitamins
• Vitamin B3 (Niacin)
• Lack: Pellagra
• Over: Liver damage
• Meat, fish, eggs, many vegetables,
mushrooms, tree nuts
Vitamins
• Vitamin B5 (Pantothenic acid)
• Lack: Paresthesia
• Over: Diarrhea; possibly nausea and heartburn
• Meat, broccoli, avocados
Vitamins
• Vitamin B6 (Pyridoxine)
• Lack: Anemia; peripheral neuropathy
• Over: Impairment of proprioception, nerve
damage
• Meat, vegetables, tree nuts, bananas
Vitamins
• Vitamin B7 (Biotin)
• Lack: Dermatitis, enteritis
• Over: raw egg yolk, liver, peanuts, leafy green
vegetables
Vitamins
• Vitamin B9 (Folic acid)
• Lack: Megaloblastic anemiaand Deficiency
during pregnancy is associated with birth
defects, such as neural tube defects
• Over: May mask symptoms of vitamin B12
deficiency
• Leafy vegetables, pasta, bread, cereal, liver
Vitamins
• Vitamin B12 (Cyanocobalamin)
• Lack: Megaloblastic anemia
• Over: Acne-like rash
• Meat and other animal products
Vitamins
• Vitamin C (Ascorbic acid)
• Lack: Scurvy
• Over: Vitamin C megadosage
• Many fruits and vegetables, liver
Vitamins
• Vitamin D (Calciferol)
• Lack: Rickets and Osteomalacia
• Over: Hypervitaminosis D
• Fish, eggs, liver, mushrooms
Vitamins
• Vitamin D (Calciferol)
• Lack: Rickets and Osteomalacia
• Over: Hypervitaminosis D
• Fish, eggs, liver, mushrooms
Vitamins
• Vitamin E (Tocopherol)
• Lack: Deficiency is very rare;sterility in males
and abortions in females, mild hemolytic
anemia in newborn infants
• Over: Increased congestive heart failure
• Many fruits and vegetables, nuts and seeds
Vitamins
• Vitamin K (phylloquinone)
• Lack: Bleeding diathesis
• Over: Increases coagulation in patients taking
warfarin
• Leafy green vegetables such as spinach, egg
yolks, liver
Video Clip:
The 5 Fabulous Food Groups
Aging and the Digestive System
• Decreased motility –
GERD
• Decreased ability to
detoxify blood
• Decreased
absorption
• Sense of taste altered
• More likely to develop
ulcers and cancers
• Dietary changes due
to
• Isolation
• Depression
Common Diseases and Disorders
Disease / Disorder
Description
Appendicitis
Inflammation of the appendix; can be lifethreatening if not treated promptly
Cirrhosis
Chronic liver disease; normal tissue is
replaced with nonfunctional scar tissue
Colitis
Inflammation of the large intestine; can be
acute or chronic
Colorectal cancer
Arises from lining of rectum or colon; curable
if treated early
Common Diseases and Disorders
(cont.)
Disease / Disorder Description
Constipation
Difficult defecation
Crohn’s disease
Inflammatory bowel disease; typically effects
small intestine
Diarrhea
Watery and frequent feces; usually selflimiting
Diverticulosis
Abnormal pouches in the intestinal wall; no
inflammation present
Common Diseases and Disorders
(cont.)
Disease / Disorder
Description
Diverticulitis
Inflammation of diverticuli (abnormal pouches
in intestinal wall) of the intestine
Gastritis
Inflammation of the stomach lining; “upset
stomach”
Heartburn
Gastroesophageal reflux disease (GERD);
stomach acids push into esophagus
Hemorrhoids
Varicose veins of rectum or anus
Hepatitis
Inflammation of the liver; various types
Common Diseases and Disorders
(cont.)
Disease / Disorder
Description
Hiatal hernia
Portion of stomach protrudes into the chest
through an opening (usually the esophageal
hiatus) in the diaphragm
Inguinal hernia
Portion of large intestine protrudes in the
inguinal canal (where thigh and trunk meet)
or, in males, into the scrotum
Usually involves the lips or tongue but can
occur anywhere in the mouth; tends to spread
rapidly
Oral cancer
Common Diseases and Disorders
(cont.)
Disease / Disorder Description
Pancreatic cancer
Fourth leading cause of cancer deaths in the
U.S.
Stomach cancer
Commonly in cardiac portion of the stomach;
occurs more frequently in Japan, Chili, and
Iceland
Stomach ulcers
Breakdown in lining of the stomach; can be
caused by bacteria (H. pylori) or smoking,
alcohol, excessive aspirin use, and
hypersecretion of stomach acid
In Summary
• Purpose of the digestive system is to provide
nutrients to the body
• Organs of alimentary canal are responsible for
mechanical and chemical breakdown of food
• Accessory organs
• Assist in breakdown of food
• Eliminate waste
• Medical assistant must have
knowledge of this system
• Assist with procedures
• Patient education
Take all that is given whether
wealth, love or language;
nothing comes by mistake
and with good digestion
all can be turned to health.
~ George Herbert