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Chapter 3
Anatomy for
Nutrition’s Sake
ASK YOURSELF:
True or False?
1. Essential nutrients are those nutrients that
can be made by the body.
2. The body’s cells need nutrients 24 hours a
day.
3. Each part of the digestive tract has specific
functions.
4. Digestion begins in the mouth.
5. It takes approximately two days for a meal to
empty from the stomach.
6. Nutrients are absorbed in the small intestine.
7. The small intestine is longer than the large
intestine.
8. The small intestine is lined with finger- like
projections (called villi) that increase the
absorptive area so that if the lining of the
small intestine could be spread out flat, it
would cover an area the size of a tennis
court.
9. The liver determines the metabolic fate of
every nutrient absorbed.
10. The pancreas plays no role in the digestive
process.
Introduction to the Human Body
• The body is
composed of
millions of cells.
• Each cell is a selfcontained living
entity.
• The body cells
need:
 Energy (or fuel)
 Oxygen
 Water
 Nutrients
Cells:
The smallest units
in which independent
life can exist. All
living things are
single cells or
organisms made of
cells.
Introduction to the Human Body
• Cells are organized into tissues
designed to perform specialized tasks.
Some of these tasks include the
formation of muscles and organs.
• Several organs work cooperatively to
form a body system.
• The digestive system consists of organs and
tissues working together to supply energy,
water, and essential nutrients to every body
cell.
Digestive System
The hypothalamus monitors the
body’s conditions & sends signals to
the brain’s thinking portion, the
cortex, which decides on actions.
• Hypothalamus:
 Detects fuel
deprivation
 Generates
nerve impulses
that signal
hunger to the
conscious part
of the brain
Cortex
Hypothalamus
Spinal cord
Digestive System
• The gastrointestinal (GI) tract supplies
the body with a constant supply of
water and nutrients by controlling:





Passage of food through GI tract
Secretion of digestive juices and enzymes
Digestion of food
Absorption of water and nutrients
Circulating blood through digestive system to
distribute absorbed substances
Digestive System
Each part of the
digestive tract has
specific functions
such as:
Basic passage of
food
Temporary storage
unit
Digest food
Absorb food
The digestive system
Salivary
glands
Esophagus
Stomach
Liver
Mouth
Tongue
Airway to lungs
Gallbladder
Pancreas
Pancreatic
duct
Pyloric
sphincter
Bile duct
Colon
(large
intestine)
Small
intestine
Appendix
Rectum
Anus
Layers of the Digestive Tract
• Mesentary
(outermost):
 Attaches the intestines to the
abdominal wall.
• Muscularis externa:
 Moves food along the GI tract.
 Mixes food with digestive
juices and enzymes.
Layers of the digestive tract
• Mucosa
(innermost):
 Secretes gastric juices and
digestive enzymes to aid
digestion.
 Secretes mucus to help
protect the lining of the GI
tract.
Peristalsis
The Mouth
• Digestive process begins in the mouth
through mechanical digestion
(physically breaking down foods).
 Breaks down indigestible membranes
and uncovers nutrient-rich portion of
foods.
 Exposes surface area of food to
digestive enzymes.
 Contains salivary glands which secrete
digestive enzymes and help to moisten
food and make it easier to swallow.
The Mouth
• When food is chewed the mixture of food
particles and saliva is called a bolus.
• The bolus moves from the mouth to the
esophagus through swallowing.
 The first part of swallowing which moves food
toward the pharynx is voluntary.
 After food reaches the pharynx, swallowing is
considered to be involuntary and cannot be
stopped.
 The trachea (windpipe) closes and the
pharynx propels the bolus toward the
esophagus.
The Esophagus
• No digestion takes place in the esophagus.
• Food passes from the mouth to the stomach
and travels through the esophagus.
• Sphincters open and close to allow the bolus
to pass.
 Sphincter: a circular band of muscle fibers
that constrict a passage or close a natural
opening in the body.
• Peristalsis: Longitudinal and circular muscle
layers of the esophagus rhythmically push the
bolus down the esophagus.
The Stomach
• Three jobs of the stomach:
 Stores food until it can be processed.
 Forms chyme: the semi-liquid blend of food
and gastric secretions that forms in the
stomach during digestion.
 Controls movement of chyme into the small
intestine at a rate suitable for digestion and
absorption by the small intestine.
• An empty stomach holds about 3
tablespoons but can stretch to about
one liter for holding food and drinks.
The Stomach
•Food passes through
the gastroesophageal
sphincter to enter the
stomach.
•Peristalsis causes
the stomach to
churn, mixing the
food with HCL and
gastric secretions to
form chyme.
•The pyloric sphincter
controls the emptying
of the stomach.
Anatomy of the stomach
Esophagus
Gastroesophageal
sphincter
Pyloric
sphincter
Duodenum
Stomach
folds
Smooth
muscle
The Stomach
Mixing of stomach contents and emptying of the stomach
Stomach
Esophagus
1
Gastroesophageal
sphincter
Pyloric sphincter
Duodenum
4
3
2
Movement
of chyme
Peristaltic
contraction
Gastric emptying
Direction of
movement
of peristaltic
contraction
6
5
Peristaltic
contraction
Gastric mixing
The Stomach
• The stomach empties in about four
hours.
Liquids pass the quickest. Solids stay
until mixed with stomach secretions.
Carbohydrate passes more quickly
than protein. Fat takes the longest to
digest.
• The rate of emptying is controlled
by the central nervous system
(CNS) and hormonal mechanisms.
The Small Intestine
• The small intestine is about 20 feet
in length.
• It is smaller in diameter than the
large intestine, thus the name
“small” intestine.
• It finishes the job of digestion and
absorption of nutrients.
The Small Intestine
• Chyme must touch the walls to make
contact with secretions and be absorbed
at the proper places.
• Peristalsis moves chyme through the
small intestine.
 Stimulated by fiber
 Slowed by fat
• The ileocecal valve controls the flow of
contents going into the large intestine.
The Small Intestine
• The small intestine works to break
down food and nutrients to their
smallest absorbable components.
• This breakdown is complex, requiring
many chemical reactions:
 Hormonal messages tell the gallbladder to
send its emulsifier, bile.
 Hormones send messages to the pancreas to
release the neutralizer, bicarbonate.
 Pancreatic and intestinal enzymes act to break
bonds of larger nutrients.
The Small Intestine
Bile
A compound made from cholesterol by the
liver, stored in the gallbladder, and secreted
into the small intestine. It emulsifies lipids to
ready them for enzymatic digestion.
Emulsifier
A compound with both water-soluble and fatsoluble portions that can attract lipids into
water to form an emulsion.
The Small Intestine
• After breakdown, these nutrient
components are able to cross
through the absorptive cells lining
the small intestine and enter the
blood and lymph supply.
• These cells are selective and
efficient as they absorb enough
nutrients to nourish all the body’s
other cells.
The Small Intestine
• The intestinal tract lining contains
an enormous absorbing surface.
 Villi
Fingerlike projections of the sheet of cells that
line the GI tract; the villi make the surface
area much greater than it would otherwise be.
 Microvilli
Tiny hairlike projections on each cell of the
intestinal tract lining that can trap nutrient
particles and translocate them into the cells.
DIGESTIVE TRACT SECRETIONS
Details of the lining of the small intestine
Stomach
Small
intestine
Folds with villi
on them
A villus
Capillaries
The wall of the
small intestine
Is wrinkled into
thousands of
folds and is
carpeted with
villi.
This photograph
shows part
of a human
intestinal cell
with microvilli.
Lymphatic
vessel
Muscle layers
beneath folds
Between the villi
tubular glands secrete
enzyme-containing
intestinal juice.
Artery
Vein
Lymphatic vessel
Microvilli
Three cells of a villus.
Each cell is covered
with microvilli.
The Small Intestine
• Simple sugars and water-soluble vitamins
are absorbed high in the small intestine
because they require no special handling.
• Nutrients released more slowly are
absorbed further down.
• When the mixture reaches the large
intestine, water, fiber, and dissolved
minerals are all that is left.
• The lymphatic system and circulatory
systems take over the job of transporting
nutrients.
The Large Intestine
•The large intestine
is about 1.5
meters long and is
larger in diameter
than the small
intestine.
•No digestive
enzymes are
secreted because
chemical digestion
is complete.
Anatomy of the large intestine
Transverse colon
Descending
colon
Ascending
colon
Ileocecal
valve
Cecum
Appendix
Rectum
Internal anal sphincter
(smooth muscle)
Sigmoid
colon
External anal sphincter
(skeletal muscle)
Anal canal
The Large Intestine
• Naturally occurring bacteria reside in the
large intestine and are responsible for:
 Digestion of some fiber and leftover
carbohydrate.
 Synthesis of absorbable vitamin K.
• Primary functions of the large intestine:
Absorb dissolved minerals and water.
Eliminate waste products.
The Large Intestine
• Final waste products are mixed with
mucus to form fecal matter.
• Fecal material normally consists of:
water, undigested fiber, bilirubin,
bacteria, small amounts of salt.
• Peristalsis is slower and occurs less
frequently.
• When the rectum fills with feces, the
defecation reflex expels the waste
products.
Accessory Organs of Digestion
•Organs outside
the digestive
tract contribute
digestive juices
through a
common bile
duct into the
small intestine.
•The organs are:
Liver
Gallbladder
Pancreas
Accessory organs of digestion
Bile duct
from liver
Stomach
Duodenum
Hormones
(insulin,
glucagon)
Blood
Duct cells secrete Acinar cells
aqueous sodium secrete digestive
bicarbonate solutionenzymes
Exocrine portion of pancreas
(Acinar and duct cells)
Endocrine portion
of pancreas
(Islets of Langerhans)
The glandular portions of
the pancreas are grossly
exaggerated.
The Liver
• Determines the metabolic fate of every
nutrient we digest and absorb.
• Performs a wide variety of functions
which are essential for life.
• Produces bile which helps to emulsify
fat and improve the efficiency of fat
digestion.
The Gallbladder
• A sack attached to the liver where bile
is stored and concentrated.
• Bile empties from the gallbladder into
the common bile duct.
• When chyme with fatty contents enters
the small intestine, a hormone
stimulates the gallbladder to contract
and empty bile into the small intestine.
The Pancreas
• The Pancreas has both endocrine
and exocrine functions.
Endocrine:
A term to describe a gland secreting
or a hormone being secreted into the
blood.
Exocrine:
A secretion that is expelled through a
duct into a body cavity or onto the
surface of the skin.
The Pancreas
• Endocrine functions include:
Secretion of the hormones insulin and
glucagon which regulate blood
glucose levels.
• Exocrine functions include:
Secretion of digestive enzymes which
act on carbohydrates, proteins, fats
and bicarbonate. These are secreted
into the duodenum.
Metabolism
Breaking Down Nutrients for Energy:
• Nutrients are absorbed from the
digestive system into the blood
where they converge from
capillaries, into veins and then into
a single large vein.
• This vein carries nutrients to the
liver where they break up into a
vast capillary network.
Stomach
Small
intestine
Folds with villi
on them
A villus
Capillaries
The wall of the
small intestine
Is wrinkled into
thousands of
folds and is
carpeted with
villi.
This photograph
shows part
of a human
intestinal cell
with microvilli.
Lymphatic
vessel
Muscle layers
beneath folds
Between the villi
tubular glands secrete
enzyme-containing
intestinal juice.
Artery
Vein
Lymphatic vessel
Microvilli
Three cells of a villus.
Each cell is covered
with microvilli.
Metabolism
• Liver cells process the nutrients:
Converts carbohydrate into glucose.
Stores excess glucose as glycogen or
fat.
Reassembles fats and packages them
for transport or storage.
Alters amino acids as needed to make
protein or other amino acids.
Metabolism
• Nutrients leaving the digestive
tract by way of lymph as
chylomicrons circulate through the
body.
Cells can withdraw fats.
Some find their way into the blood
and circulate through to the liver.
Metabolism
• New products of liver metabolism
are released into the bloodstream
and circulate to other cells of the
body. These products are:
Glucose
Fat packaged with protein
(lipoprotein)
Amino acids
Metabolism
• Surplus fat can be removed by the cells
and made ready for storage.
 The human body has infinite storage
capacity.
• Liver glycogen provides a reserve
supply of glucose.
 The body can draw from this reserve during
intervals when glucose is not ingested and
absorbed.
 This supply lasts about 3 to 6 hours.
Metabolism
• The storage systems for glucose and fat
ensure that the cells will not go without
energy nutrients except under extreme
conditions.
• Other storage systems include:
 Liver and fat cells store many vitamins.
 Bones provide reserves of calcium and
sodium.
Metabolism
• The breaking down of body
compounds is known as catabolism.
• When the body needs energy, it
breaks down any or all of the four
basic units:
Glucose
Fatty acids
Glycerol
Amino acids
Metabolism
• When the body does not require
energy, end products of digestion
are used to build body compounds
in a process called anabolism.
• Catabolism and anabolism are
examples of energy metabolism.
Other Systems
• The body has many systems that
cooperate so each cell can carry on
life. Examples include: bones,
muscles, nerves, lungs,
reproductive organs, and others.
• Most of the body’s work is done
automatically and is finely
regulated through hormonal or
nerve-mediate messages.
Let Food Be Your Medicine
• Functional food:
A general term for foods that provide an
additional physiological or psychological
benefit beyond that of meeting basic
nutritional needs.
 Also called medical foods.
• Designer foods:
Foods “fortified” with phytochemicals or plants
bred to contain high levels of phytochemicals;
also known as “future foods.”
 Genetic engineering of foods—also called
biotechnology—is discussed in your text,
Chapter 12.
Functional food assortment