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Chapter #15
The Digestive System
Chapter 15.1
Digestion is the mechanical and chemical
breakdown of foods and the absorption of
the resulting nutrients by cells.
The digestive system consists of the
alimentary canal, which extends about 9
meters (27 feet or 900 cm) from the mouth
to the anus.
Alimentary Canal
Mouth
Pharynx
Esophagus
Stomach
Small Intestine
Large Intestine
Rectum
Anus
1. Mouth Mechanical breakdown of food;
begins chemical digestion of
carbohydrates (bread).
Salivary glands secrete saliva, which
contains enzymes that initiate breakdown
of carbohydrates.
Pharynx connects mouth with
esophagus.
2. Esophagus peristalsis pushes food to
stomach.
Peristalsis wavelike motion that propels
food.
3. Stomach secretes acid and enzymes.
Mixes food with secretions to begin
enzymatic digestion of proteins.
4.




Small Intestine mixes food with bile and
pancreatic juice. Final enzymatic breakdown of
food molecules: main site of nutrient
absorption.
Liver produces bile, which emulsifies fat.
Gallbladder stores bile and introduces it into
small intestine.
Pancreas produces and secretes pancreatic
juice, containing digestive enzymes and
bicarbonate ions, into sm. Intestine.
Accessory organs are organs that are not a
direct route of the digestive system.
5. Large intestine absorbs water and
6.
7.


electrolytes to form feces.
Rectum regulates elimination of feces.
Anus eliminates feces.
The digestive system is a tube, open at
both ends, that has a surface area of 186
square meters.
The main function is to supply body with
nutrients.
15.2 General Characteristics
3 parts of the small intestine
1. Duodenum
2. Jejunum
3. Ileum
Alimentary Canal
1. Mucosa or mucous membrane the inner
most layer. Contains glands that secrete
mucus and digestive enzymes. Carries
on secretion and absorption. Also, has
projections that increase the surface
area. Lumen=passageway.
2. Submucosa contains loose connective
tissue, glands, blood vessels, lymphatic
vessels, and nerves. Carry away
absorbed materials.
3. Muscular layer produces the movements.
4. Serosa or serous layer the outer
covering of the digestive tube. Secretes
fluid that lubricates the tube’s outer
surface so organs slide freely against
one another.
15.3 The Mouth
The mouth receives food and begins
digestion by mechanically reducing the
size of food and mixes them with saliva.
Oral cavity includes the chamber between
the palate and tongue.
Palate forms the roof of the oral cavity and
is made of a hard palate (front) and Soft
palate (rear).
Tongues function is to move food toward
the palate. Made out of skeletal muscle.
During swallowing, muscles draw the soft
palate and uvula upward to separate the
oral and nasal cavities.
Salvia cleanse the mouth and teeth,
dissolve chemicals necessary to tasting
food, and help in the formation of food
bolus.
Tonsils
Palatine are lymphatic tissue in the back of
the mouth, on either side of the tongue
and closely associated with the palate.
Help to fight infection.
Pharyngeal or adenoids are on the
posterior wall of the pharynx. They can be
removed.
Tonsillectomy tonsil are surgically
removed.
Teeth
Humans have 2 sets of teeth.
Primary teeth or deciduous usually erupt
at 6months-4 years of age. 20 primary
teeth. 10 upper and 10 lower.
Secondary teeth or permanent consist of
32 teeth.
Good dental hygiene is essential because
once damaged, enamel cannot be
replaced.
Enamel cover the crown. White and shiny.
Dentin is found beneath the enamel.
Dentin is a substance similar to bone.
Pulp cavity contains blood vessels,
nerves, and connective tissue.
Root canals contains the root.
Teeth
1.
2.
3.
4.
4 types of teeth
Incisors (Front 4 teeth) bite off pieces of
food.
Cuspid grasp and tear food.
Bicuspids or premolars grind food.
Molars grind food.
15.4 Salivary Glands
The salivary glands secret saliva.
Saliva moistens food particles, helps
them bind, and begins the chemical
digestions of carbohydrates.
Saliva dissolves food so that they can be
tasted.
2 types of secretions from the salivary
glands.
1. Amylase digestive enzyme in mouth,
stomach, pancreas.
2. Mucus which binds with food particles to
lubricate for swallowing.
Types of Salivary Glands
Parotid glands the largest.
Submandibular glands located in the floor
of the mouth.
Sublingual glands the smallest of the
salivary glands, are on the floor of the
mouth.
15.5 Pharynx and Esophagus
Pharynx connects the nasal and oral cavities
with the larynx and esophagus.
3 parts
1. Nasopharynx communicates with the nasal
cavity and provides a passageway for air
during breathing.
2. Oropharynx is posterior to the soft palate and
inferior to the nasopharynx. It is the
passageway for food moving downward from
the mouth and for air moving to and from the
nasal cavity.
3. Laryngopharynx just inferior to the oropharynx,
is a passageway to the esophagus.
Epiglottis closes off the top of the trachea
(windpipe) so food is less likely to enter.
15.6 Stomach
The stomach is a J-shaped , pouchlike
organ that hangs inferior to the diaphragm
in the upper left portion of the abdominal
cavity and has a capacity of about 1 liter.
The stomach has thick folds of mucosal
and submucosal layers and disappear
when the stomach wall is distended.
Stomach
1.
2.
3.
4.

The stomach is divided into four regions.
Cardiac
Fundic is the area that acts as a
temporary storage area for ingested
food.
Body
Pyloric
Fatty food stay in the stomach the
longest.
Gastric Secretions
Gastric juice
1. Hydrochloric acid
2. Pepsin begins to digest protein
 Chyme is a semifluid paste of food
particles and gastric juice.
Time Spent in organs
Mouth a few minutes
Esophagus a few minutes
Stomach 4 hours
Small Intestine 12 hours
Large Intestine 5 hours
Total time in digestive system 21 hours.
15.7 Pancreas
The pancreas make three different
enzymes. One enzyme break down fats
(pancreatic lipase), one enzyme break
down protein (proteolytic), and the third
enzymes break down carbohydrates.
15.8 Liver
The liver is the largest organ in the body it
is the heaviest organ in the body at around
3 pounds.
It makes the chemical bile.
Bile is a green liquid that breaks large fat
droplets into small fat droplets.
Gallbladder is a small, baglike part located
under the liver. It stores bile until it is
needed by the small intestine.
Hepatitis
Hepatitis is an inflammation of the liver.
Types of Hepatitis
1. Hepatitis A spreads by contact with food
or objects contaminated with viruscontaining feces.
2. Hepatitis B spreads by contact with viruscontaining body fluids, such as blood,
saliva, or semen.
3. Hepatitis C is believed to be responsible
for about ½ the cases of hepatitis.
Transmitted in blood-by sharing razors or
needles, from pregnant woman to fetus,
or in blood transfusions.
4. Hepatitis D occurs in people already
infected with hepatitis B. It is blood borne
and associated with blood transfusions
and intravenous drug use.
5. Hepatitis E virus is usually transmitted in
the water contaminated with feces.
6. Hepatitis F passes from feces and can
infect other primates.
7. Hepatitis G accounts for many cases of
fulminant hepatitis.
15.9 Small Intestine
Small Intestine is a tubular organ that
extends from the pyloric sphincter to the
beginning of the large intestine. This is
where most of the nutrients are absorbed.
Receives secretions from the pancreas
and liver.
Completes digestion, absorbs the products
of digestion, and transports the residues to
the large intestines.
1.
2.
3.



The small intestines constits of three portions.
Duodenum
Jejunum
Ileum
Mesentery suspense the small intestine.
Intestinal villi is the inner wall of the small
intestine appears velvety.
¼ of feces is dead epithelial cells from the sm.
Intestine.
The small intestine compared to the large
intestine is narrower and longer.
Heartburn is caused by acid moving from the
stomach into the esophagus.
Animals that do not have a digestive system
absorb nutrients through their body covering.
Example Tapeworm.
Plant eating animals have longer digestive
systems because of the intake of cellulose which
is not absorbed by the intestine.
Digestion is the breaking down of food into
small, usable molecules usually glucose.
Digestive enzymes
Salivary glands make chemicals that
digest only carbohydrates.
Pancreas makes chemicals that digest fat,
protein, and carbohydrates.
Liver makes chemicals that digest only fat.
Stomach makes chemicals that digest only
protein.
Small intestine makes chemicals that
digest protein and carbohydrates.
Large intestine makes no chemicals to
digest food.
15.10 Large Intestine
Large intestine is so named because its
diameter is greater than that of the small
intestine. Large intestine are about 1.5
meters long, and begins in the lower right
side of the abdominal cavity.
The large intestine absorbs water and
electrolytes.
1.
2.
3.
4.
The 4 parts of the large intestine:
Cecum is the beginning
Colon is divided into 4 portions the ascending,
transverse, descending, and sigmoid colons.
The colon is home to 100 trillion bacteria.
Rectum extends about 5 cm below the tip of
the coccyx (tailbone).
Anal canal the last 2.5 to 4 cm of the large
intestine.
Feces include materials that were not digested
or absorbed, water, electrolytes, mucus,
intestinal cells, and bacteria. Feces is about
75% water. Feces pungent odor results from a
variety of compounds that bacteria produce.
15.11 Nutrition and Nutrients
Nutrition is the study of nutrients and how
the body utilizes.
Nutrients all the chemicals that food is
made up of which in include
carbohydrates, lipids, proteins, vitamins,
minerals, and water.
Nutrients that human cells cannot
synthesize, such as certain amino acids,
are called essential nutrients.
Carbohydrates
Are organic compounds used primarily to
supply energy for cellular processes.
Found in foods such as starch and sugar
Not stored in large amounts in the body
Needed in greatest amount each day.
Cellulose is a complex carbohydrate that
is abundant in food- it gives celery its
crunch. Humans cannot digest so
cellulose provides bulk (fiber or roughage)
which facilitates food movement through
the digestive system.
Lipids
Lipids are organic compounds that include
fats, oils, and fatlike substances.
Found in foods such as butter and oil
The food that is often stored and used
later as an energy source.
The nutrient stored under the skin and
around body organs.
Protein
Proteins are polymers of amino acids with
a wide variety of functions.
Used to form muscle, bone, and skin
Food rich in protein include meats, fish,
poultry, cheese, nuts, milk, eggs, and
cereals.
Vitamins
Are organic compounds that are required in
very small amounts for normal metabolic
processes. Not an energy source.
Riboflavin and niacin are examples
Vitamins allows cells to use carbohydrates
and proteins.
Vitamins are needed for growth and tissue
repair.
Amount given as % RDA. Recommended
Daily Allowance.
Minerals
Are elements other than carbon that are
essential in human metabolism.
Found on the Periodic Table. Calcium,
iron, potassium, sodium, zinc, and
magnesium are examples.
Need in very small amounts
May cause anemia or muscle twitching if
missing from diet.
Amount Given as % RDA.
Not an energy source.
Water
Water is needed to cool the body, to
chemical reactions in the body, and to
carry away body waste.
50% to 60% of the human body is water.
The average adult needs about 2 liters of
water a day.
Diets
Balanced diet is a diet with the right
amount of each nutrient.
Malnutrition if a persons diet lacks
essential nutrients or a person fails to use
available foods.