This document discusses the mechanisms of gas exchange in the human body. It begins by defining diffusion and describing the basic process of gas exchange across membranes. It then describes the four main types of gas exchange systems: integumentary, gills, tracheal, and lungs. The majority of the document focuses on the human respiratory system, describing external respiration in the lungs where oxygen diffuses into blood and carbon dioxide diffuses out, and internal respiration where gases are exchanged at the cellular level. It concludes by explaining cellular respiration, where oxygen is used to break down food molecules and release energy, producing carbon dioxide as a waste product.

1. MECHANISMS OF
GAS EXCHANGE

2. GAS EXCHANGE
An essential process in energy metabolism, and gas exchange is an essential prerequisite to life,
because where energy is lacking life cannot continue.
The basic mechanism of gas exchange is diffusion across a moist membrane.
DIFFUSION – is a movement of molecules from a region of greater concentration to a
region of lesser concentration in the direction following the concentration gradient.

3. Breathing: The First Step in Respiration
So, what is breathing?
Breathing is the physical action of taking
oxygen into, and releasing the waste carbon
dioxide out of the lungs. We need to breathe
because all the cells in our body requires
oxygen. Without oxygen, your body wouldn’t
move.

4. IN ANIMALS THERE
ARE FOUR TYPES OF
GAS EXCHANGE
SYSTEMS

5. 1. Integumentary Exchange or
Cutaneous Respiration
occurs through the skin. Example of this is earthworm

6. 2. Gills
allow for exchange of gases underwater.

7. 3. Tracheal Systems
Used by insects

8. 4. Lungs
found in land animals.

9. The human brain regulates the breathing rate of the person
through a breathing center located in the medulla oblongata.
Although breathing is an automatic process, you can choose
to interfere with it temporarily.
Try holding your breathe now and observe yourself. After that
short breathe, carbon dioxide begins to build up in your blood,
and your body begins to ask for oxygen.

10. Breathing occurs because of air pressure changes between the lungs and
the atmosphere.
Breathing has two phases: inspiration (inhalation) and expiration
(exhalation).

11. EXTERNAL RESPIRATION:
TRANSPORT OF GASES WITH THE
CIRCULATORY SYSTEM
External respiration refers to gas exchange across the
respiratory membrane in the lungs.
Also called as “pulmonary gas exchange”
Each alveolus is surrounded by a network of tiny
blood vessels called capillaries. In the lung’s 600
million alveoli, the exchange of oxygen and carbon
dioxide between the blood and air take place.

12. Through the thin walls of the alveoli, oxygen enters the bloodstream and
is carried to the cells throughout the body. Carbon dioxide leaves the
bloodstream and returns to the alveoli to be blown out of your body with
your next exhalation.
The walls of the alveoli and the capillaries share a fused basement. They
are so close that oxygen and carbon dioxide diffuse (move freely)
between the respiratory system and the bloodstream. As a result, when air
enters the alveoli, oxygen in the air seeps through the thin walls of the
tiny sacs and into the surrounding capillaries.

13. HOW DOES THE OXYGEN ENTERS THE
BLOODSTREAM?
Oxygen enters the lungs, then passes through the alveoli and into the blood. The oxygen is
carried around the body in blood vessels. Carbon dioxide moves into the blood capillaries
and is brought to the lungs to be released into the air during exhalation.

14. INTERNAL RESPIRATION: EXCHANGE
OF GASES WITH BODY CELLS
Internal Respiration refers to the exchange of gas at the
level of body cells. It occurs in the metabolizing tissues,
where oxygen diffuses out of the blood and carbon dioxide
diffuses out of the cells.
Also called as “Peripheral gas exchange”
It involves the respiratory processes that occur within the
tissues of the body rather than the lungs. This can be seen
in the adjacent image.

15. It brings oxygen from your lungs to all the other
tissues in your body, and takes out carbon dioxide
from the tissues back to your lungs as a waste
product.
As blood slowly moves through the capillaries, it
picks up the oxygen and carries it to the cells
throughout the body.

16. When the oxygenated blood reaches the cells, it releases the oxygen. At the same
time, the blood picks up the carbon dioxide produced by the cells during respiration
and returns it to the alveoli, where it is released from your body when you exhale.

17. Because air is rarely in the lungs for more than a few
seconds, the exchange of gases (oxygen and carbon
dioxide) takes place quickly. This is where the tree-like
structure of the respiratory system comes in.

18. CELLULAR RESPIRATION: THE BODY’S ENERGY
RELEASING PROCESS
oThe process in which organisms take molecules broken down
from food and release the chemical energy stored in the
chemical bonds of those molecules.
oBody cells use the food they get from the blood and release
energy within it only if they get enough oxygen.
oThe energy-releasing process fueled by oxygen is called
cellular respiration.
oCellular respiration also produces carbon dioxide.

19. oCellular respiration requires a continuous supply of
oxygen in order to break down sugar from food and
release energy.
oGas exchange therefore involves the coordinated
work of the respiratory and circulatory systems.
oCarbon dioxide, as a metabolic waste product of
cellular respiration, is toxic to cells and must be
removed.