The respiratory system uses two types of respiration - internal and external. External respiration involves the exchange of gases between the external environment and cellular respiration, occurring through bulk transport via breathing and gas exchange in the lungs and blood circulated by the heart. Organisms use different respiratory structures depending on whether they reside in water or air, such as gills for fish and lungs for air-breathing organisms.

1. RESPIRATORY
SYSTEM

2. TWO DISTINCT OF
RESPIRATION:
 Internal or cellular respiration:
-refers to the intracellular metabolic
processes carried out within the
mitochondria, which use oxygen and
produce carbon dioxide during
derivation of energy from nutrient
molecules.

3.  External respiration:
-refers to the sequence of events
involved in the exchange of oxygen
and carbon dioxide between the
external environment and cellular
respiration.

4. BULK TRANSPORT
-In general, gases are not moved
through membranes by active
transport. The greatest
enhancements to moving gases are
collectively called bulk transport
or Exocytosis.

5. BREATHING
The term for active ventilation of
respiratory surfaces, it requires
motile devices to move the external
medium.
The two external medium:
 Inhalation
 Exhalation

6.  Another important process involves the
movement of blood by the circulatory
system.
 Gas exchange occurs in the pulmonary
alveoli by passive diffusion of gases
between the alveolar gas and the blood in
lung capillaries. Once these dissolved
gases are in the blood, the heart powers
their flow around the body (via the
circulatory system). The medical term for
normal relaxed breathing is eupnea.

7. WATER RESPIRERS
o Gills
- a nonintegumentary structures for
gas exchange evolved most water
breathers with larger sizes and
higher metabolisms. It is the
primary specialized respiratory
structure for the water respirers.

8.  Adult fish have a pair of gills. Each gill is
covered by a boney lid (removed from the
picture). A fish draws in water by closing
the lid over its gills and opening its
mouth. When the fish closes its mouth
and opens the gill lid the water is forced
out and over the respiratory surfaces of
the gill filaments.

9.  Inorder to live, fish must extract oxygen
from the water and transfer it to their
bloodstream. This is done by gills which are
richly supplied with blood vessels in order
to act as a respiratory organ. Extracting
oxygen from water is more difficult and
requires a greater expenditure of energy
than does extracting oxygen from air.
NOTE:
 Water is a thousand times denser than air,
and at 20 degree Celsius, it has 50 times
more viscosity than air and contains only
3% as much oxygen as an equal volume of
air.

10. AIR RESPIRERS
 Lungs
-specialized structures handle the
oxygen-carbon dioxide exchange.

11. MAMMALIAN LUNGS:
 The lungs of mammals have a sponge like
and soft texture and are honeycombed
with epithelium, having a much larger
surface area in total than the outer
surface area of the lung itself. The lungs
of humans are a typical example of this
type of lung.

13. AVIAN LUNGS
 Avian lungs do not have alveoli as
mammalian lungs do, they have Faveolar
lungs. They contain millions of tiny
passages known as parabronchi. There are
air vesicles, called atria, which project
radially from the walls of the parabronchi.

15. REPTALIAN LUNGS
 All
reptiles breathe using lungs. Aquatic
turtles have developed more permeable
skin, and some species have modified
their cloaca to increase the area for gas
exchange. Even with these adaptations,
breathing is never fully accomplished
without lungs.

16.  Lung ventilation is accomplished
differently in each main reptile group.
In squamates, the lungs are ventilated
almost exclusively by the axial
musculature. This is also the same
musculature that is used during
locomotion. Because of this constraint,
most squamates are forced to hold their
breath during intense runs.

17.  Crocodilians actually have a muscular
diaphragm that is analogous to the
mammalian diaphragm. The difference is
that the muscles for the crocodilian
diaphragm pull the pubis back, which
brings the liver down, thus freeing space
for the lungs to expand. This type of
diaphragmatic setup has been referred to
as the "hepatic piston."

18. AMPHIBIAN LUNGS
 The lungs of most frogs and other
amphibians are simple balloon-like
structures, with gas exchange limited to
the outer surface area of the lung.
 Amphibians have low metabolic demands
and also frequently supplement their
oxygen supply by diffusion across the
moist outer skin of their bodies.
 Unlike mammals, which use a breathing
system driven by negative pressure,
amphibians employ positive pressure.

19. RESPIRATION OF INSECTS
 Insect respiration is accomplished without
lungs.
 Instead, the insect respiratory system
uses a system of internal tubes and sacs
through which gases either diffuse or are
actively pumped, delivering oxygen
directly to tissues that need it via their
trachea. Since oxygen is delivered directly,
the circulatory system is not used to carry
oxygen, and is therefore greatly reduced.