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Unit 1: Animals : Structure
and Function
Chapter 10: The Digestive
System
Nutrition
Obtaining and Processing Food

All organisms, regardless of their size
or complexity, must have a way of
obtaining essential nutrients

Essential nutrients: the basic raw
materials they need to make their own
structures, perform their life functions,
and obtain energy for survival
Macromolecules

Organic molecules contain carbon
bonded to hydrogen, as well as to other
atoms, such as oxygen, sulfur, and
nitrogen.

Macromolecules are larger, more
complex assemblies of organic molecules,
also known as nutrients.

These are the raw materials that our
bodies need to provide energy, to
regulate cellular activities, and to build
and repair tissues.

Often grouped
into four major
categories:
◦ Carbohydrates
◦ Lipids
◦ Proteins
◦ Nucleic acids
Macromolecules

Energy released from
these macromolecules,
and matter supplied by
them, is used to
maintain the body’s
metabolism (all of the
chemical processes
carried out by cells to
maintain life)

Together, the four major
categories of
macromolecules are
known as essential
nutrients.
Carbohydrates

Are macromolecules that
always contain carbon,
hydrogen, and oxygen
◦ Almost always in the
same proportion:
◦ C1 : H2 : 01.

Provide short-term or longterm energy storage for
organisms.

There are two main types
of carbohydrates: simple
sugars and
polysaccharides.
Monosaccharides (Simple Sugars)
 Carbohydrate molecules with three to seven
carbon atoms.
◦ Examples: glucose (the sugar found in blood)
and fructose (the sugar found in fruit).
Disaccharides
 Made up of two simple sugars (di- = two).
◦ Examples: sucrose (table sugar), lactose (the
sugar found in dairy products) and maltose
(the sugar found in germinating grain)
Polysaccharides
 Complex carbohydrates that consist of many
linked simple sugars (poly- = many).
◦ Examples: Starch stores energy in plants, and
glycogen stores energy in animals.
Carbohydrates
Lipids

Are insoluble in water.

The basic structure of
lipids is a molecule of
glycerol
◦ 3 carbon atoms, each
attached to a fatty acid
chain

Store 2.25 times more
energy per gram than
other biological molecules;
function as energystorage molecules.
Lipids

Phospholipids, form
cell membranes.

Other Examples of
lipids are fats, such as
butter and lard, and
oils, such as olive oil
and safflower oil.
Proteins

Assembled from small sub-units known as amino acids

Polypeptides are chains for hundreds of amino acids
joined together by peptide bonds

Most enzymes are proteins, and so are antibodies,
which combat disease.

Proteins help build and repair muscles and cell
membranes
Nucleic Acids

Nucleic acids direct growth and development of all
organisms using a chemical code.

The two types of nucleic acids are ribonucleic acid (RNA)
and deoxyribonucleic acid (DNA)
Hydrolysis

From Greek: “Hydro” – water; “lysis” –
loosen

A water molecule (H2O) is added to the
macromolecule.

This breaks the chemical bonds that hold
together the smaller molecules from which
the macromolecule is made.

Digestive enzymes help to speed up the
process of hydrolysis.
Minerals and Vitamins

Inorganic and
organic substances
that enable
chemical
reactions to occur
and aid in tissue
development,
growth, and
immunity.

Needed by a
healthy, functional
human body.
Minerals
Mineral
Key function in the body
Possible Sources
Calcium
Forming bone, conducting nerve signals,
contracting muscle, clotting blood
Dairy products
Iron
Producing hemoglobin
Red meat
Magnesium
Supporting enzyme functions, producing Dark, leafy greens
protein
Potassium
Conducting nerve signals, contracting
muscle
Grains
Sodium
Conducting nerve signals, balancing
body fluids
Salt
Vitamins
Vitamin
Key function in the body
Possible Sources
A (carotene)
Good vision, healthy skin and bones
Fruits
B1 (thiamine)
Metabolizing carbohydrates, growth and
muscle tone
Beans
C (ascorbic
acid)
Boosting immune system, healthy bones,
teeth, gums, and blood vessels
Fruit
D
Absorbing calcium, forming bone
Fish
E
Strengthening red blood cell membranes
Fruit
Water


Needed for the proper functioning of all cells and
organs. Makes up 2/3 of body mass.
Functions include:
◦ Transporting dissolved nutrients into the cells
that line the small intestine
◦ Flushing toxins from cells
◦ Lubricating tissues and joints
◦ Forming essential body fluids, such as blood
and mucus
◦ Regulating body temperature (by sweating)
◦ Eliminating waste materials (in urine and
sweat)
Learning Check

Pg 406, Q 1-6:

1) What is the the primary function of
carbohydrates in the human body?
2) What is the difference between a
monosaccharide and a disaccharide? Given an
example of each.
3) Explain how macromolecules are broken
down in the body


Learning Check

Pg 406, Q 1-6:

4) If an athlete runs for 15 minutes, which
macromolecules are likely to break down first?
5) Which macromolecules would provide the
greatest benefit as a long-term energy storage
molecule to a bird that migrates long
distances?
6) Name the three functions of proteins in the
human body.


Types of Digestion

Intracellular digestion:

Extracellular digestion:
◦ Digestion inside the cell
◦ Phagocytosis - cell engulfs the food
 Ex: single-celled organisms
(paramecium, amoeba)
◦ Digestion outside the cells
◦ Food enters a tube and exits from the
other end
 Ex: most animals, human digestive
tract
Mechanical Digestion

The physical breakdown of large food
particles into smaller ones.
◦ Achieved through chewing, mashing,
chopping, breaking food into smaller
pieces.
◦ This increases the surface area of
the food, allowing more enzymes to
come into contact with the food.
Chemical Digestion

The chemical breakdown of large
molecules into smaller ones:
◦ Carbohydrates: polysaccharides (starch) are
broken into monosaccharides (simple sugars)
◦ Proteins: are broken down into amino acids
◦ Lipids: (mainly triglycerides) are broken down
into fatty acids and glycerol
Note: Food particles are broken down by
enzymes. Each enzyme has a pH at which it
performs best.
Types of Feeders

Autotrophs:
◦ Can feed themselves from
inorganic molecules
◦ Ex: plants use sun + H2O +
CO2 to form organic
compounds
◦ Self-sufficient

Heterotrophs:
◦ Depend on organic
compounds made by other
living things
◦ Ex: animals, fungi, bacteria,
etc.
◦ Not self-sufficient
Filter Feeders

Aquatic animals that use
a body structure similar
to a filter basket to
gather small organisms
suspended in the water.

Siphons water into its
mouth and then filters
it to obtain small
organisms to digest.

Examples include
flamingoes, tube
worms, clams,
barnacles, and baleen
whales.
Fluid Feeders

Obtain food by sucking
or licking nutrient-rich
fluids from live plants
or animals.

Mouth parts are
adapted to pierce or rip
skin or leaf tissue and
are used to suck or lick
the blood or sap that is
their food.

Examples: mosquitoes,
ticks, aphids, spiders,
bees, butterflies, vampire
bats, and hummingbirds.
Substrate Feeders

Live in or on their
food source and eat
their way through
it.

Examples:
caterpillars and
earthworms.

Caterpillars eat
their way through
the green tissues of
leaves.
Bulk Feeders

Include many animals and
most vertebrates (including
humans).

Bulk feeders ingest fairly
large pieces of food and
some, like the great blue
heron, swallow their food
whole.

Use tentacles, pincers, claws,
fangs, or jaws and teeth to
kill prey, to tear off pieces of
meat or vegetation, or to
take in mouthfuls of animal
or plant food.
The Digestive System
Introduction
There are four stages
to food processing:
1. Ingestion: taking in
food
2. Digestion: breaking
down food into
nutrients
3. Absorption: taking
in nutrients by cells
4. Egestion: removing
any leftover wastes

Digestion and the Alimentary
Canal
Length of the Digestive Tract

Cellulose walls in plant tissue are
more difficult to digest than animal
tissues

As a result, whose digestive tracts
would be longer?
 Herbivores/omnivores OR carnivores?
Section 10.1 Review

Pg 410 # 1-3, 6-9, 11
10.2

Introduction
The digestive
system is used for
breaking down
food into
nutrients which
then pass into the
circulatory system
and are taken to
where they are
needed in the
body.
Human Digestive System

Begins when food enters
the mouth (oral cavity).

It is physically broken
down by the teeth
(mechanical).

It is chemically broken
down by enzymes
released from the
salivary glands.
Human Digestive System

The tongue moves
the food around until
it forms a ball called
a bolus.

The bolus is passed
to the pharynx
(throat) and the
epiglottis makes
sure the bolus
passes into the
esophagus and not
down the trachea!
Human Digestive System

What structure
prevents food from
entering the nasal
passageway?

How?
Human Digestive System

The bolus passes
down the
esophagus by
peristalsis.

Peristalsis is a
wave of
muscular
contractions
that push the
bolus down
towards the
stomach.
Human Digestive System

To enter the
stomach, the bolus
must pass through
the lower
esophageal
sphincter, a tight
muscle that keeps
stomach acid out
of the esophagus.
Human Digestive System

The stomach has folds
called rugae and is a
big muscular pouch
which churns the
bolus (physical
digestion).

The bolus is mixed
with gastric juice, a
mixture of stomach
acid and enzymes
(chemical
digestion).
Human Digestive System

The stomach does do
some absorption too.

Some medicines (i.e.
aspirin), water and
alcohol are all
absorbed through the
stomach.

The digested bolus is
now called chyme and
it leaves the stomach
by passing through the
pyloric sphincter.
Learning Check

Pg 414, Q 7, 9, 11,12

7) Describe where the digestion of
carbohydrates begins in the body, the
major glands involved, and the digestive
secretions produced.

9) Would the epiglottis be closed or open
in each situation? Explain:
◦ A) while talking
◦ C) coughing
B) swallowing
D) chewing
Learning Check

11) A doctor orders a pH test of the
esophagus for patient who is complaining
about having heartburn and a burning
sensation in the chest. Identify the source
of the problem and explain why.

12) How do over-the-counter antacids
(eg. Calcium carbonate) help an individual
with stomach pain/gastroesophageal
discomfort?
Stages of Digestion
http://video.about.com/ibdcrohns/Digestion.
htm
Human Digestive System

Chyme is now in the
small intestine.

The majority of
absorption occurs here.

The liver and
pancreas help the
small intestine to
maximize absorption.

The small intestine is
broken down into three
parts:
Human Digestive System
1.

Duodenum
Bile enters
through the bile
duct. It emulsifies
fats.

The pancreas
secretes
pancreatic juice
containing
enzymes and
bicarbonate ions
Human Digestive System
2.


Jejunum
The jejunum is
where the majority
of absorption
takes place.
It has tiny fingerlike projections
called villi lining it,
which increase the
surface area for
absorbing nutrients.
Human Digestive System

Each villi itself has tiny fingerlike
projections called microvilli, which
further increase the surface area for
absorption.
Human Digestive System
3.

Ileum
The last portion of
the small intestine
is the ileum, which
has fewer villi and
basically compacts
the leftovers to
pass through the
caecum into the
large intestine.
Human Digestive System

The large
intestine (or
colon) is used to
absorb water
from the waste
material leftover
and to produce
vitamin K and
some B vitamins
using the helpful
bacteria that live
here.
Human Digestive System

All leftover waste is
compacted and
stored at the end of
the large intestine
called the rectum.

Pressure receptors
are stimulated and
send a signal to the
brain to indicate
that elimination is
necessary. The anal
sphincter remains
under voluntary
control. Feces,
passes out of the
body through the
anus.
Chemical Digestion
Introduction

Food cannot be
broken down into
small enough
nutrients by physical
digestion alone.

Special enzymes in
our body help
chemically break
down food into small
nutrients.
Magic School Bus – “For Lunch”

http://www.peteava.ro/id-538489-02-forlunch
Enzymes

Enzymes are special
proteins made at
ribosomes.
There are different
classes of enzymes:
1. Carbohydrases
break down carbs
2. Proteases break
down proteins
3. Lipases break down
lipids.

Enzymes

These enzymes are
secreted into the
digestive system by
special groups of
secretory cells called
glands.

Glands are usually
connected to the
digestive system
through special
tubes called ducts.
Enzymes

The item that an enzyme
breaks down is called a
substrate. The enzyme is not
changed at all during this
process.

Every enzyme performs best
under its own optimal
conditions.

This depends on temperature,
pH and the presence/absence
of certain ions or vitamins and
minerals.
The Mouth

Three salivary
glands produce saliva
which contains:
◦ Water and mucous:
lubricates the food
◦ Sodium
bicarbonate:
reduces the acidity of
the bolus
◦ Salivary amylase:
enzyme that begins
to break down
carbohydrates
(amylose)
The Stomach

Hydrochloric acid (HCl)
kills off any invading
bacteria or viruses and is
very corrosive.

The enzyme pepsin breaks
down proteins. It is only
active at a low pH.

The enzyme lipase breaks
down lipids.

Mucus protects the lining of
the stomach from being
eaten away by the acid.
The Pancreas

Produces and releases into
the small intestine:
◦ Enzymes that act on
proteins, carbohydrates,
and fats.
◦ Bicarbonate ions to raise
the pH of the chyme.

Produces and releases into
the blood stream:
◦ Insulin that converts
glucose to glycogen, which
gets stored in the body
cells for later use.
Enzymes Video:
Amylases, proteases and lipases

http://video.about.com/nutrition/Enzymes
-and-Digestion.htm

http://www.youtube.com/watch?feature=
endscreen&NR=1&v=KED6BHVM97s
The Liver

Makes bile, which aids in fat
digestion

Most of the glycogen is stored
here

Vitamins A, D, E, K are stored
here


Detoxifies poisons that are
ingested (including ethanol)
◦ Cirrhosis: breakdown of
liver cells due to high levels
of poisons.
The Gall Bladder

Stores the bile
produced in the liver.

Releases bile into the
small intestine.

Illnesses of the gall
bladder include
◦ Gall stones: crystals of
bile salts around
cholesterol.
◦ Jaundice: collection of
bile pigment in blood.
Liver and Pancreas

http://www.youtube.com/watch?v=TWUZ
x738OZM&feature=related
Overview of Human Digestion

http://www.youtube.com/watch?v=08VyJ
OEcDos&feature=related
Digestion and Homeostasis

A large meal activates
receptors that churn
the stomach and empty
it faster.

If the meal was high in
fat, digestion is slowed,
allowing time for the fat
to be broken down.

Hence why we feel
fuller after eating a
high fat meal.
Digestion and Homeostasis

The endocrine, nervous,
digestive and circulatory
systems all work
together to control
digestion.

Before we eat, smelling
food releases saliva in
our mouths and gastrin
in our stomachs which
prepares the body for a
snack.
The Hormone Gastrin
Hormones

Hormones are chemical
regulators, they also help
control digestive enzymes.

The hormone gastrin
stimulates the digestive
glands around the stomach.

The hormone secretin
stimulates the pancreas to
release its enzymes which
help neutralize the stomach
contents as they enter the
small intestine.

Pg 417 13-18
Learning Check

HW pg 419 # 1, 11-13, 15