The respiratory system is a complex network of organs, tissues, and structures responsible for the process of respiration, which involves the exchange of oxygen and carbon dioxide in the body. Its primary function is to bring oxygen into the body and remove carbon dioxide, a waste product of cellular metabolism. Key organs and structures of the respiratory system include: 1. Nose and nasal cavity: The air enters the respiratory system through the nose. The nasal cavity helps filter, warm, and moisten the incoming air. 2. Pharynx: The pharynx, or throat, is a muscular tube that connects the nasal cavity and mouth to the larynx. It serves as a passage for both air and food. 3. Larynx: Commonly known as the voice box, the larynx houses the vocal cords and plays a crucial role in speech production. 4. Trachea: Also called the windpipe, the trachea is a tube that connects the larynx to the bronchi. It is reinforced by C-shaped cartilage rings to keep it open. 5. Bronchi: The trachea branches into two bronchi, which then further divide into smaller bronchioles. The bronchi and bronchioles carry air deep into the lungs. 6. Lungs: The lungs are a pair of spongy, elastic organs situated in the chest cavity. They are responsible for the exchange of oxygen and carbon dioxide. The left lung has two lobes, while the right lung has three. 7. Alveoli: The bronchioles terminate in tiny air sacs called alveoli. These are the primary sites of gas exchange, where oxygen is absorbed into the bloodstream and carbon dioxide is released. 8. Diaphragm: The diaphragm is a dome-shaped muscle located below the lungs. It plays a crucial role in breathing by contracting and relaxing to create changes in lung volume. The process of respiration involves two main processes: 1. Inhalation (inspiration): The diaphragm contracts, and the rib muscles expand the chest cavity. This creates a pressure difference, causing air to enter the lungs. 2. Exhalation (expiration): The diaphragm relaxes, and the rib muscles return to their resting position, decreasing the chest cavity volume. This increases the pressure in the lungs, causing air to be expelled. Throughout respiration, oxygen diffuses from the alveoli into the bloodstream, while carbon dioxide moves in the opposite direction to be expelled from the body. The respiratory system works in coordination with other body systems, such as the circulatory system, to ensure the delivery of oxygen to cells and the removal of waste gases like carbon dioxide.

1. Respiratory System
Dr Shivam Mishra

2. • Why do we breathe? Think of all the
reasons why we need a respiratory
system.
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3. Warning: terminology!
• “Respiration” is used several different ways:
• Cellular respiration is the aerobic breakdown
of glucose in the mitochondria to make ATP.
• Respiratory systems are the organs in
animals that exchange gases with the
environment.
• “Respiration” is an everyday term that is often
used to mean “breathing.”

4. Respiratory system function
• Respiratory systems allow animals to
move oxygen (needed for cellular
respiration) into body tissues and
remove carbon dioxide (waste product of
cellular respiration) from cells.

5. Gas exchange by Diffusion
• Some animals simply
allow gases to diffuse
through their skins.
• These animals have a
low metabolic rate.
Why?
• All of these are aquatic
animals. Why?

6. Specialized structures
• Structures
specialized for gas
exchange include:
• gills (aquatic
animals)
• spiracles
(terrestrial insects)
• lungs (most
terrestrial
vertebrates)

7. Countercurrent Exchange
• In a concurrent
system, exchange is
inefficient.
Equilibrium is
reached at one end.
• In a countercurrent
system, equilibrium
is not reached, so
gas exchange
continues, increasing
efficiency.

8. Fish Gills
• Fish increase gas
exchange efficiency
using countercurrent
exchange.
• Running blood through
the system in the
opposite direction to
water keeps a diffusion
gradient throughout the
entire exchange.

9. Gills exchange gases in fish. What is the
site of gas exchange in mammals?
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25% 25%
25%
25%
1. Alveoli
2. Tracheids
3. Bronchi
4. Esophagus

10. • Why are gills so widely seen in aquatic
animals but not in land animals?
• One group of land animals that have gills
is the Isopods (“pill bugs” and “sow
bugs”). How can these organisms
survive on land with gills?
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11. Human respiratory system
• Parts of the
respiratory system
include:
• Trachea
• Bronchi
• Bronchioles
• Alveoli

12. Moving air in and out
• During inspiration
(inhalation), the
diaphragm and
intercostal muscles
contract.
• During exhalation,
these muscles
relax. The
diaphragm domes
upwards.

13. Alveoli
• The alveoli are
moist, thin-walled
pockets which are
the site of gas
exchange.
• A slightly oily
surfactant prevents
the alveolar walls
from collapsing and
sticking together.

14. Circulation and Gas Exchange
• Recall the
interconnection
between circulation
and the respiratory
system.
• Gas exchange at
the lungs and in the
body cells moves
oxygen into cells
and carbon dioxide
out.

15. What happens when you breathe
in?
1 2 3 4
25% 25%
25%
25%
1. The rib muscles
relax.
2. The diaphragm
contracts.
3. Air leaves the
alveoli.
4. Air moves between
the chest wall and
the lung.

16. • Premature infants sometimes die of lung
collapse and other lung problems. What
might preemies be missing? How could
this be remedied?
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17. In the alveolus
• The respiratory
surface is made up
of the alveoli and
capillary walls.
• The walls of the
capillaries and the
alveoli may share
the same
membrane.

18. Gas exchange
• Air entering the lungs
contains more oxygen
and less carbon dioxide
than the blood that
flows in the pulmonary
capillaries.
• How do these
differences in
concentrations assist
gas exchange?

19. Oxygen transport
• Hemoglobin binds
to oxygen that
diffuses into the
blood stream.
• What are some
advantages to using
hemoglobin to
transport oxygen?

20. Carbon dioxide transport
• Carbon dioxide can
dissolve in plasma,
and about 70%
forms bicarbonate
ions.
• Some carbon
dioxide can bind to
hemoglobin for
transport.

21. At the cells
• Cells use up oxygen quickly for cellular
respiration. What does this do to the
diffusion gradient? How does this help
cells take up oxygen?
• Cells create carbon dioxide during
cellular respiration, so CO2 levels in the
cell are higher than in the blood coming
to them. How does this help cells get rid
of oxygen?

22. Diffusion of O2 from lungs to blood
is rapid because:
1 2 3
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33%
1. Active transport
moves oxygen.
2. Hemoglobin takes up
oxygen, keeping
plasma
concentration low.
3. Blood plasma is
oxygen-rich.

23. Most of the oxygen in blood is:
1 2 3 4
25% 25%
25%
25%
1. In the white cells.
2. Bound to
hemoglobin.
3. Combined with
carbon to make
carbon dioxide.
4. Dissolved in the
plasma.

24. Effects of smoking
• Inhaled smoke
contains:
• CO2, which affects the
CO2 diffusion gradient.
• carcinogenic chemicals
that can trigger tumors.
• toxic nicotine, which
paralyzes cilia that
normally clean the
lungs.
Gross, isn’t it?

25. Emphysema
• Besides cancer,
smoking can also lead
to emphysema. Alveoli
become dry and brittle,
and eventually rupture.
• Both active and passive
smoking (“second-hand”
smoke) can lead to can
lead to lung problems. All types of smoke, not just tobacco,
can cause cancers and emphysema.

26. Cystic Fibrosis
• Cystic fibrosis is one of
the most common
inherited disorders in the
Caucasian population in
the U.S.
• CF is caused by
mutation of a single
gene, the CFTR gene,
which controls salt
balance in the lungs.

27. Cystic Fibrosis
• A normal CFTR protein
regulates the amount of
chloride ions across the
cell membrane of lung
cells.
• If the interior of the cell
is too salty, water is
drawn from lung mucus
by osmosis, causing the
mucus to become thick
and sticky.

28. Cystic Fibrosis
• At this point there is no
cure for CF, though
there are therapies that
have extended the lives
of CF patients, including
lung transplants.
• Gene therapy may one
day insert “good” CFTR
genes into lung cells to
make them operate
normally.

29. “Two lies and a truth” – which one
is true?
1 2 3
33% 33%
33%
1. Cigarette smoke
cures colds because
it kills bacteria in the
lungs.
2. Nicotine is one of the
most potent
neurotoxins on earth.
3. “Passive” smoking is
less harmful than
“regular” smoking.

30. • When people quit smoking, if the lungs
are not damaged they can often clean
themselves because the cilia are no
longer paralyzed. People with cystic
fibrosis have trouble with lung infections
because their lung mucus is thick and
sticky. What roles do cilia and mucus
play in lung health?
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