PinkMonkey Online Study Guide-Biology
17.1 Gaseous Exchange And Transport
Figure 17.2 Respiratory organs of man
In unicellular animals like Ameba, gaseous
exchange takes place directly through the plasma membrane and
in its surrounding medium, but higher multi-cellular animals are
provided with special organs such as skin, gills or
lungs through which gaseous exchange takes place. Whatever
may be the organ of respiration it is subject to the following conditions:
It should be naked namely without an exoskeleton
of any sort.
It should have great absorptive surface
exposed to the surroundings to absorb enough oxygen to fulfill
demands of the body cells.
It should be covered with a thin membrane permeable
to gaseous exchange .
It should be richly supplied with blood capillaries.
Human Respiratory System
The human respiratory system consists of two
(A) Respiratory pathway and
(B) Respiratory organs (lungs).
(A) Respiratory pathway includes nasal cavities
pharynx, larynx and trachea.
(i) Nasal cavities are a pair of cavities
in the nose, separated by a vertical cartilaginous septum and lined
by ciliated mucous membrane. While passing through these cavities
air is filtered, moistened and warmed. The nasal cavities open posteriorly
into the pharynx.
(ii) Pharynx serves as a common passage
for the transport of air to the larynx, and food from the mouth
to the esophagus.
(iii) Larynx (commonly known as "Adamís
apple") is situated in the neck just at the start of the trachea.
It is guarded against the entry of food particles by a flap-like
valve called the epiglottis. The larynx contains the vocal
cords hence it also serves as the organ of phonation
(i.e. producing sound).
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Gaseous Exchange and Transport
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