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Hsslive-XI-zoology-06-BREATHING
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Hsslive-XI-zoology-06-BREATHING
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Navas Cheemadan The nasal chamber opens into the
C HAPTER 06 pharynx, a portion of which is the
common passage for food and air.
BREATHING AND EXCHANGE OF GASES The pharynx opens through the larynx
region into the trachea.
Breathing: Larynx is a cartilaginous box which
process of exchange of O2 from the helps in sound production and hence
atmosphere with CO2 produced by the cells is called the sound box. / Voice box
called breathing, commonly known as During swallowing glottis can be covered
respiration. by a thin elastic cartilaginous flap called
epiglottis to prevent the entry of food into
RESPIRATORY ORGANS the larynx.
Trachea is a straight tube extending up to
Respiratory organs Examples the mid-thoracic cavity, which divides at
the level of 5th thoracic vertebra into a
sponges, exchange of O2 with right and left primary bronchi.
coelenterates, CO2 by simple Each bronchi undergoes repeated
flatworms diffusion over their divisions to form the secondary and
entire body surface tertiary bronchi and bronchioles
Earthworms moist cuticle ending up in very thin terminal
Insects Tracheal system bronchioles.
aquatic arthropods Gills (branchial The tracheae, primary, secondary and
and mollusks, fish respiration) tertiary bronchi, and initial bronchioles are
Frogs Skin(cutaneous supported by incomplete cartilaginous
respiration) rings.
Man Lungs(Pulmonary Each terminal bronchiole gives rise to a
respiration ) number of very thin, irregular-walled and
vascularised bag-like structures called
Human Respiratory System alveoli.
LUNGS
The branching network of bronchi,
bronchioles and alveoli comprise the
lungs.
They are covered by a double layered
pleura, with pleural fluid between them.
It reduces friction on the lung-surface.
The outer pleural membrane is in close
contact with the thoracic lining whereas
the inner pleural membrane is in contact
with the lung surface.
The lungs are situated in the thoracic
chamber which is anatomically an air-tight
chamber.
The thoracic chamber is formed dorsally
by the vertebral column, ventrally by
Human respiratory system starts with a the sternum, laterally by the ribs and
pair of external nostrils opening out on the lower side by the dome-shaped
above the upper lips. diaphragm
It leads to a nasal chamber through the
nasal passage.
navas9895@gmail.com SOHSS-AREEKODE
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, Navas Cheemadan
Human respiratory system has two EXCHANGE OF GAS
parts
Alveoli are the primary sites of exchange
of gases.
Exchange of gases also occur between
blood and tissues.
O2 and CO2 are exchanged in these sites
by simple diffusion mainly based on
pressure/concentration gradient.
Factors affecting rate of diffusion
1.Solubility of the gases
2. The thickness of the membranes involved
in diffusion
A-Conducting part of respiratory system The solubility of CO2 is 20-25 times higher
The part starting with the external than that of O2, the amount of CO2 that
nostrils up to the terminal bronchioles can diffuse through the diffusion
constitute the conducting part membrane per unit difference in partial
pressure is much higher compared to that
The main function of the conducting part of O2
is
1. Transports the atmospheric air to the
alveoli
2. Clears it from foreign particles
3. Humidification of the air
4. Brings the air to body temperature
B-Respiratory or exchange part
The alveoli and their ducts form the
respiratory or exchange part of the
respiratory system.
The diffusion membrane is made up of
Exchange part is the site of actual three major layers namely,
diffusion of O2 and CO2 between blood o the thin squamous epithelium of
and atmospheric air. alveoli,
o the endothelium of alveolar
Respiration involves the following steps: capillaries and
o the basement substance in
(i) Breathing or pulmonary ventilation by between them.
which atmospheric air is drawn in and CO2 total thickness of diffusion membrane
rich alveolar air is released out. is much less than a millimetre
(ii) Diffusion of gases (O2 and CO2) across
alveolar membrane.
(iii) Transport of gases by the blood.
(iv) Diffusion of O2 and CO2 between blood
and tissues.
(v) Utilisation of O2 by the cells for catabolic
reactions and resultant release of CO2
navas9895@gmail.com SOHSS-AREEKODE
Downloaded from www.hsslive.in
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