Topic: Gaseous exchange• Subtopics:• Gaseous exchange• Respiration and breathing• Breathing in man• The air passageway and lungs• Mechanism of breathing• The effect of physical activity on rate

of breathing

Gaseous exchange• Unlike every organisms we

humans also need some materials from environment to fulfill our body requirements, and need to expel some waste materials this is possible through gaseous exchange.

• We take in O2 and take out CO2 to fulfill our body requirement the process is known as gaseous exchange.

Respiration and breathingRespiration • It is simply a energy

releasing process in which glucose is broken down by 02 to provide energy

• It is a catabolic process.• It is involuntary action

as we cannot stop our cellular activities.

Breathing • It is simply exchange of

gases i.e. intake of O2 and outtake of CO2.

• It is a physical process.• It is voluntary in action

means we can stop breathing for a while

Breathing in man Breathing in man can be divided into two

stages or two parts: The air passageway (ventilation) The lungs (gaseous exchange)

The air passageway It contains all those parts of

our body which are responsible for the exchange of gases in and out of body.

Starting from the nose which is the entrance of the gases possess the two entries called nostrils which are divided by a wall both entries have hairs and mucous which helps to filter the air and to keep the air temperature almost equal to body temperature.

The air passageway(continued)

Nose encloses the nasal cavity which leads to pharynx by two small openings called internal nostrils. Pharynx is a muscular passage which is common to both food and air. It leads to esophagus and larynx. The air passes by through larynx, as we know the epiglottis is a flap of tissues at pharynx which performs the function to pass the air by larynx.

The air passageway The larynx is a cartilaginous box

present between pharynx and trachea, two pairs of fibrous bands known as vocal cords are present in it they vibrate when air passes by which produces sound so its also called voice box. Under larynx here comes the trachea also called as windpipe about 12 cm long tube which lies along esophagus.

When it enters the chest cavity, it divides itself into two smaller tubes called bronchi, each bronchus subdivides into its lung by dividing itself into two sub branches called as bronchioles.

The air passageway• The smaller subunits bronchioles

become narrower and ends as a tubules called as alveolar ducts, which opens into group of pouches known as alveoli.

• The alveoli are sac like structure which are main unit of respiratory system as they are responsible for the gases exchange in blood, as it is bounded outside by capillaries, as we have studied the pulmonary artery carrying deoxygenated blood enters the lungs by dividing into arterioles and then capillaries present around alveoli the alveoli provides oxygen to the blood and take out C02 from it which then is again transferred to heart by pulmonary vein.

Here a question arises!How the O2 is transported to whole organs of a body?

• As we have studied that blood possess blood cells blood plasma as well as a special unit i.e. hemoglobin which we can say that is the major carrier of O2 as it possess the storage capacity of 02. the blood flows in whole body and everywhere it transports O2 for there proper functioning or for their cellular respiration as the O2 is the main component needed for breaking down of glucose to form ATP and release energy.

The lungs• Lungs are the respiratory organs present in the

thoracic cavity, the chest wall is made up of 12 pairs of ribs and the rib muscles called intercostal muscles. A thick muscular structure called diaphragm is also present below the lungs.

• The left lung consists of two lobs while the right lung possess three lobes.

• Each lung is covered by two membranes called the outer and inner pleural membranes, a fluid is also present between them which provide lubrication and free expanding of lungs.

The lungs and the pleural membranes

The mechanism of breathing There are two phases of breathing: Inhalation: Exhalation:

Inhalation During inhalation, the rib

muscles contract so the ribs are raised and the diaphragm contracts and is lowered these movements increase the size of thoracic cavity which reduces pressure on lungs, as a result lungs expand and the air pressure inside them decreases so the outer air enters in the lungs to maintain the pressure in lungs.

Exhalation• After the air exchange in lungs

the impure air is expelled out of body.

• The ribs muscles relax and the ribs come back to their mean position, the diaphragm muscles also relax and it gets its own shape this reduces the space in chest cavity and increases pressure on lungs as the pressure will increase the volume will decrease so the lungs contract and air is expelled out of body

Effect of physical activity on breathing

Normally we humans breath 16 to 20 times per minute, the rate of breathing is controlled by respiratory centre in brain which is very sensitive to concentration of CO2.

When we do any physical activity our body does not get normal amount of oxygen while our muscle cells carry more cellular respiration so results in production of more CO2 which is dangerous to our body so the respiratory centre sends message to ribs and diaphragm to increase the rate of breathing to expel the CO2 to maintain the concentration of both gases.