Download Ch 23 The Digestive System

The Digestive System
Digestion
Digestive Process
• Nutritionists classify foods into six groups.
– These six groups are: meat, milk, fruits,
vegetables, breads/cereals, and fats/oils/sweets.
• The USDA Food Guide Pyramid shows the
number of servings from each food group
needed for a balanced diet.
• Nutrients provide energy for powering
cellular processes.
Food Pyramid
Protein
Nutrients Needed
• The three nutrients needed by the body in
the greatest amounts are carbohydrates,
proteins, and lipids.
– All of these nutrients are called organic
compounds, which are compounds that contain
the elements carbon, hydrogen, and oxygen.
• An example of a carbohydrate is pasta; an
example of a protein is chicken; and an
example of lipids is olive oil.
• Vitamins, minerals, and water are nutrients
that do not provide energy but are required
for proper functioning of the body.
• Vitamins are organic compounds that
participate in chemical reactions by helping
to build various molecules in the body.
• Minerals are nutrients that are inorganic
compounds and are necessary for certain
body processes.
Importance of Vitamins
• Vitamins
– Vitamins work as coenzymes to enhance
enzyme activity.
– A diet should include vitamins because
they cannot usually be made in the body.
An exception to this is vitamin D.
– Vitamins can dissolve in water or fat.
Importance of Minerals
• Minerals
– Minerals are used to make certain body
structures, to carry out normal nerve and muscle
function, and to maintain osmotic balance.
– Minerals can come from plants we eat directly or
the plants other animals eat.
– Minerals are released out of the body through
urine and by perspiration.
Importance of Water
• Water
– Water, which is a main component in blood, helps
to transport gases, nutrients, and wastes
throughout the body.
– Water also is a reagent in some of the body’s
chemical reactions.
– Water also helps regulate body temperature by
absorbing and distributing the heat released in
cellular reactions.
The First Stages of Digestion
The Gastrointestinal Tract
• The process of breaking down food into molecules
the body can use is called digestion.
• Digestion occurs in the gastrointestinal tract, or
digestive tract, which is a long tube which begins at
the mouth and winds through the body to the anus.
• Organs next to the digestive tract also aid in the
digestion of food through the secretions that
they produce.
Digestive System of the Human
Body
The Mouth and the Esophagus
• Digestion includes the
mechanical and
chemical breakdown of
food into nutrients, the
absorption of nutrients,
and the elimination of
waste.
• Digestion begins in the
mouth with the first bite
of food.
• Mouth
– Mechanical digestion begins when the
teeth cut and grind food.
– The tongue also aids in mechanical
digestion by keeping the food between the
chewing surfaces of the teeth.
• Mouth, continued
– Saliva is produced by the salivary glands
to begin chemical digestion of food.
• Saliva is a mixture of water, mucus, and a
digestive enzyme called salivary amylase.
• Salivary amylase is the chemical in saliva that
begins the chemical digestion of
carbohydrates by breaking down certain
starches into maltose.
• Esophagus
– The ball of food is then forced by
swallowing action into the pharynx.
– The pharynx is an open area that begins at
the back of the mouth, and serves as a
passageway for both air and food.
– The ball of food is then forced from the
pharynx into the esophagus.
• Esophagus
– The ball of food is then
forced by swallowing
action into the pharynx.
– The pharynx is an open
area that begins at the
back of the mouth, and
serves as a passageway
for both air and food.
– The ball of food is then
forced from the pharynx
into the esophagus.
Stomach
• The stomach is an
organ involved in
both mechanical
and chemical
digestion.
• It is located in the
upper left side of the
abdominal cavity,
just below the
diaphragm.
• Mechanical Digestion
– The stomach has three
layers of smooth
muscle—a circular layer,
a longitudinal layer, and a
diagonal layer.
– These muscles churn the
food within the stomach
and help to carry out
mechanical digestion.
• Mechanical Digestion, continued
– The inner lining of the stomach is a mucous
membrane that is composed of epithelial cells and
openings called gastric pits.
– Gastric pits are the open ends of gastric glands that
release secretions into the stomach.
– These secretions form the acidic digestive fluid
that digests food in the stomach.
• Chemical Digestion
– Gastric fluid carries out chemical digestion
in the stomach.
• Gastric fluid is a liquid that is secreted by the
gastric glands in the stomach.
– Hydrochloric acid within the gastric fluid
helps dissolve food and minerals and keep
bacteria at bay.
• Chemical Digestion, continued
– Mucus secreted in the stomach forms a coating
that protects the lining of the stomach from
hydrochloric acid and other digestive enzymes.
– An ulcer will result if the mucous layer is absent
from the stomach lining.
• An ulcer is a lesion of the surface of the skin or a
mucous membrane of the stomach.
• Formation of Chyme
– After food enters the stomach, it closes by way of
the cardiac sphincter.
• The cardiac sphincter is a circular muscle located
between the esophagus and the stomach.
– While closed, the stomach churns to break up the
food and mixes it with the gastric fluid. This
process forms a mixture called chyme
• The other organs that help digestion
are the liver, gallbladder, and pancreas.
• Liver
– The liver performs numerous function in
the body including storing glucose,
making proteins, and breaking down toxic
substances.
– The liver produces bile, which is vital to
digesting fats.
• Gallbladder
– After the liver produces bile it travels
through a Y-shaped duct to the
gallbladder.
– The gallbladder is a saclike organ that
stores and concentrates bile.
– The gallbladder releases the bile through a
common bile duct into the small intestine.
• Pancreas
– The pancreas is an organ that lies behind the
stomach. The pancreas serves two roles in its
part in the digestive system.
• The first role it plays is to increase the pH of the
stomach acid by producing sodium bicarbonate.
• The second role it plays is to secrete enzymes that help
to further break down carbohydrates, proteins, lipids and
nucleic acids.
Small Intestine
Small Intestine
• The small intestine
includes three
sections—the
duodenum, the
jejunum, and the
ileum.
• The chyme from the
stomach will further
break down in the
small intestine.
• Absorption
– Absorption occurs mostly in the small
intestine. Absorption occurs when the end
products of digestion are transferred into
the circulatory system through the blood
and lymph vessels.
• Absorption, continued
– The surface area of the small intestine is large
due to the presence of many folds within the
lining of the small intestine and the millions of villi
that are also present.
– The surface area is further increased by the
presence of microvilli.
• Microvilli are extensions of the cell membranes present
on the villi.
• Absorption, continued
– Nutrients are sent to the correct place by the
lacteals.
• The lacteals are capillaries and tiny lymph vessels within
the villi.
– The lacteals will take the nutrients to either the
liver or the lymph vessels, and then the blood will
take over delivery of the nutrients to the cells.
Large Intestine
Large Intestine
• Once absorption is complete in the small
intestine, peristalsis will move the remaining
contents into the colon or large intestine.
• The colon has various sections, and all of
these sections work together to finish the
absorption of nutrients and water.
• The colon initiates contractions that move
the material out of the body.
• As nutrients and water are absorbed
from the matter in the colon, the matter
solidifies into feces.
• Feces leave the body by passing
through the rectum and the anal canal.
The Final Stages of Digestion
1. What is the primary function of
carbohydrates?
A. to aid in digestion
B. to break down molecules
C. to regulate the flow of chyme
D. to supply the body with energy
• Answer
• D. To supply the body with energy
2. How can dehydration best be prevented?
F. by perspiring
G. by inhaling water
H. by drinking water
J. by not drinking water
• Answer
• H. By drinking water
3. Why is the epiglottis important?
A. It regulates the flow of chyme.
B. It prevents food from going down the
trachea.
C. It separates the pharynx from the nasal
cavity.
D. It is the passage through which food
travels to the stomach.
• Answer
• B. It prevents food from going down the
trachea
4. Bile breaks up large
fat droplets.
Approximately how
long is the food in the
digestive tract before
it comes into contact
with bile?
F. 4 hours
G. 7 hours
H. 11 hours
J. 13 hours
• Answer
• F. 4 hours
Ulcers