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Respiratory
System
Purpose-
 Gas exchange of O2 and
CO2 between the
organism and the outside
environment
Requirements for Gas exchange
at the respiratory surface:
1. Thin-walled –(so gases can freely
diffuse across)
2. Moist- (O2 and CO2 must be in
solution or dissolved)
3. In contact with O2 source-(outside
environment)
4. In contact with transport system
carrying dissolved gases
(Circulatory system/Blood)
Examples of gas respiratory
surfaces used for exchange
 Protists
(Amoeba/Paramecium)
 Surface: Cell
membrane
 Method: Simple
direct diffusion
through cell
membrane to water
 Earthworm
 Surface: moist skin
 Method: diffusion
through moist mucus
coated skin into blood
vessels
(has hemoglobin to help)
Examples of gas respiratory
surfaces used for exchange
 Fish
 Surface: Gills
 Method: diffusion from water to blood
vessels in the gills
 Grasshopper
 Surface: air tubes & sacs
 Method: air comes in through spiracles,
through the air tubes, moved by muscle
contraction (no hemoglobin/blood used)
Human Respiratory
System
 Surface: Moist air sacs (alveoli)
 Method: diffusion across air sacs into
blood stream (use hemoglobin to
increase amount of O2 that blood can
carry)
Alveoli
Structures:
Structure
Epiglottis
Function
Covers the trachea, prevents food from
entering the windpipe
Pharynx (Throat) Throat area where air enters from the nose
and mouth
Larynx
Voice Box- contains the vocal
cords
Vocal cord
Bands of tissue stretched and relaxed to
produce sound
Structures:
Trachea
Windpipe- carries air from
pharynx to and from the lungs
Cartilage rings to keep it open
C- shaped
Esophagus
Connects the mouth and the
stomach for food
Lungs
Mass of air sacs (alveoli) where O2
and CO2 are exchanged
Warms and cleans (filters) the air
Two branches of Trachea, connects
the trachea to the bronchioles
Nasal Cavity
Bronchi
Structures:
Bronchioles
Tiny air tubes branching from the
bronchi to the alveoli
Alveoli
Tiny air sacs in lungs where
gas exchange occurs
(into the blood)
Moves up and down causing
pressure that forces air into and
out of the lungs
Diaphragm
Breathing Process
 Four Stages of Gas Exchange :
1. Breathing- movement of air in and
out of the lungs
 Inhalation - chest cavity increases
 Diaphragm contracts (flattens) and lowers
 Ribs raise up and out
 Lungs inflate because during breathing
negative pressure creates a vacuum
which “sucks” air into the lungs
Four Stages of Gas Exchange :
 Exhalation - chest cavity is
decreases
 Diaphragm relaxes and moves
upward
 Ribs drop down and in
 Lungs deflate because positive
pressure pushes the air out of the
lungs
Four Stages of Gas Exchange :
2. External respiration- exchange of
gases between outside air and
bloodstream in the air sacs



Mucus coats air sacs (alveoli) to moisten
them
O2 diffuses across air sacs into
capillaries of air sacs and CO2 diffuses
in the opposite direction
O2 attaches itself to hemoglobin on the
red blood cells
Four Stages of Gas Exchange :
3. Transport- movement of gases in the
blood between the cells to the lungs
(circulatory system)
4. Internal respiration- exchange of
gases between the blood stream and
the cells of the body

At the capillaries, O2 diffuses into the
intracellular fluid and then into the body
cells & CO2 diffuses in the opposite
direction
CO2 Transport
 80% of CO2 dissolves in the Plasma
and/or combines with water in the plasma
to make carbonic acid (H2CO3)
 20% of CO2 is carried by hemoglobin
back to lungs
Respiratory Disorders
 Asthma- severe allergic reaction
where bronchioles go into spasm
and squeeze air passages making it
difficult to breathe
 Treatment- medication (inhaler)
Respiratory Disorders
 Bronchitis- Bronchial tubes become
irritated and swollen, and alveoli
become swollen and clogged with
mucus making it difficult to
breathe
 Treatment- antibiotics if bacterial
infection
Respiratory Disorders
 Emphysema- lungs lose their
elasticity and the air sacs become
damaged and it leads to shallow
breathing and even death. Most
disease is caused by years of
smoking.
 Treatment- stop smoking and
use of O2 tank for additional help
Respiratory Disorders
 Cystic Fibrosis- Body produces too
much mucus and the person is
unable to breathe and have frequent
infections
 Treatment- gene therapy