1. 20.2: The Respiratory System: the exchange of gases
Section Objectives:
Identify the structures involved in external respiration.
Contrast external and cellular respiration
Explain the mechanics of breathing.

2. Why do we need a respiratory system?
Need O2 in
for cellular respiration
make ATP
Need CO2 out
waste product
food
ATP O2
CO2

3. Passageways and Lungs
respiratory system consists of a pair of lungs & a system of tubes that carry air to them
Breathing is just one of the functions that the respiratory system carries out.

4. The path air takes air enters through the nasal cavity
It passes through the pharynx and larynx into the trachea
The trachea forks to form two bronchi
Each bronchus branches into numerous bronchioles
The bronchioles end in clusters of tiny sacs called alveoli

5. Lungs Structure spongy texture alveoli moist lining covered by cilia
high surface area
more absorption of O2
alveoli
small air sacs
moist lining
mucus traps dust, pollen, particles
covered by cilia
hair-like extensions of cells
move mucus upward to clear out lungs

6. Moving gases into bloodstream
Inhale
O2 passes from alveoli to blood
by diffusion
Exhale
CO2 passes from blood to alveoli
capillaries
(circulatory system)

7. Gas exchange: Diffusion of gases
Gases move by diffusion from high to low concentration
capillaries are thin-walled tubes of circulatory system
alveoli are thin-walled sacs of respiratory system
capillaries in lungs
capillaries in muscle O2 O2 O2 O2
CO2
CO2
CO2
CO2
External respiration: exchange of gases between alveoli and blood
Internal respiration: exchange of gases between blood and cells
blood
lungs
blood
body

8. The Mechanics of Breathing
Breathing ventilates the lungs
The action of your diaphragm and the muscles between your ribs enable you to breathe in and breathe out.
Breathing is the alternation of inhalation (active) and exhalation (passive)

9. Control of Respiration
Breathing is usually an involuntary process.
partially controlled by an internal feedback mechanism that involves signals being sent to the medulla oblongata about the chemistry of your blood.
measure blood pH
CO2 = pH (acid)
coordinate breathing, heart rate & body’s need for energy
will send nerve signals to the rib muscles and diaphragm.
nerve signals cause these muscles to contract, and you inhale.

10. Breathing and Homeostasis
ATP
Homeostasis
keeping the internal environment of the body balanced
need to balance O2 in and CO2 out
need to balance energy (ATP) production
Exercise
breathe faster
need more ATP
bring in more O2 & remove more CO2
Disease
poor lung or heart function = breathe faster
need to work harder to bring in O2 & remove CO2
CO2 O2

11. Cleaning dirty air
To prevent foreign material from reaching the respiratory system is lined with ciliated cells that secrete mucus.
The cilia constantly beat upward in the direction of your throat, where foreign material can be swallowed or expelled by coughing or sneezing