GASEOUS EXCHANGE AND RESPIRATION
Ø This refers to the exchange of respiratory gases (oxygen and carbon
dioxide) across the respiratory surface
Respiratory surfaces
Ø
This is an organ through which gaseous exchange takes place.
|
ORGANISM |
RESPIRATORY SURFACE |
|
Amoeba |
Cell membrane |
|
Insects |
Tracheal system |
|
Spider |
Book lung |
|
Fish |
Gills |
|
Plants |
Leaves, stem and roots |
|
Amphibians |
Skin gills and lungs |
|
Mammals |
Lungs |
|
Birds |
Lungs |
|
Reptiles |
Lungs |
|
Earth worm |
Skin |
Features of respiratory
surfaces
Ø They have thin walls to facilitate diffusion
of respiratory gases
Ø They have moist surfaces to allow respiratory gases to dissolve
before diffusion
Ø They have large surface area for maximum
exchange of gases
Ø They are have dense network
of blood capillaries to facilitate transport of respiratory gases.
Ø They are well ventilated so that gaseous
passes easily
Adaptation of respiratory system
Ø The trachea and bronchi are lined with mucus membrane which trap dust, bacteria
and viruses
Ø The trachea and bronchi are lined with ciliated cells in mucus s membrane which sweep to the esophagus
trapped bacteria, virus and dust.
Ø Trachea is made up of rings of cartilages which prevent collapse of the respiratory tract.
Ø Each lung possess numerous air sacs called alveoli. This increase surface area for gaseous
exchange
Breathing
Breathing is the process of taking
in and out of respiratory gases.
Types
of breathing
Breathing is divided
into two types, namely:
(i)
Breathing in (inhalation)
(ii)
Breathing out (exhalation)
Inhalation (inspiration)
This is the process whereby
air is taken inside
the lungs.
Exhalation (expiration)
This is the process whereby
air is taken outside the lungs.
The mechanism of gaseous exchange (breathing) in mammals
|
During inhalation (breathing in) |
During exhalation
(breathing out) |
|
External intercostal muscles contract. |
External intercostal muscles relax |
|
Internal intercostal muscles relax. |
Internal intercostal muscles contract. |
|
Ribcage moves outwards and upwards. |
Ribcage moves downwards and inwards. |
|
The diaphragm contracts and flattens. |
Diaphragm relaxes
and become dome-shaped. |
|
The volume
of the thoracic cavity
increases |
Volume of thoracic cavity
decreases |
|
Air pressure decreases |
Air pressure in the thoracic cavity decreases. |
|
Air enters
the alveoli through
the nostrils, pharynx, glottis, trachea,
bronchioles and finally alveoli. |
Air is forced
out of the alveoli through the bronchioles, trachea, glottis, pharynx, and finally nostrils. |
|
Breathing in  |
Breathing out  |
Factors affecting gaseous exchange (breathing) in mammals
The following
are factors affecting the rate of gaseous exchange (breathing) in mammals:
i)
physical activities or exercise
Vigorous activities or exercise increases the breathing rate because more oxygen is required to burn
glucose to release energy required
by muscle.
ii)
Age
Young people have a higher metabolic rate and therefore breathe
faster than old people.
iii)
Health status of the body
The rate of breathing increases during sickness so as to remove
toxins from the body.
iv)
Carbon dioxide concentration
High concentration of carbon dioxide in the blood increases the rate of gaseous exchange. This provides the tissues with adequate amounts of oxygen and lower
carbon dioxide concentration in the blood.
v) Haemoglobin concentration.
The rate of
gaseous exchange increases when the concentration
of haemoglobin is low due to anemic condition,
hence small amount of oxygen reaches the cells. Breathing rate increases so that to compensate the
shortfall and meet the oxygen demand in the body.
vi) Altitude
The breathing
rate is higher at high altitudes than at low
altitude because there is a lower concentration of oxygen in the atmosphere at higher altitudes.
