Gas Exchange in Humans

Question: How does gaseous exchange occur in humans? Or Explain the respiratory system in humans.

Ans. Human and higher Animals of the land have a developed respiratory system.

This respiratory system can be developed into two parts.

1) Air passageway 2) The Lungs

1) AIR PASSAGEWAY:

Air passageway consist of the following parts.

1)Nose 2)Pharynx 3) Larynx

4)Trachea 5)Bronchi 6)Bronchioles

1) NOSE:

The nose encloses in the nasal cavity. It lies on the ventral side of the head. They allow air into two nasal cavities from outside. The nasal cavity is divided into two portions by a wall. Each nasal cavity is lined by fine hair and mucous membrane. They perform three important functions. 1) Mucous membranes act as a filter to remove dust and impurities from air.

2) Warming up the inhaled air.

3) Addition of moisture. Nose breathing is much better than mouth breathing. Where there is no such protection.

2) PHARYNX:

The nasal cavities lead into the pharynx. It is 4.5 inches long. It is a muscular passage and is common to food and air. Pharynx is lined with mucous membrane. The pharynx contains lymphatic tissues in the form of tonsils and adenoids which are used to trap and filter microorganisms.

3) LARYNX:

The air moving from the pharynx into the larynx is called the sound box. It is a cartilaginous structure. It is the upper part of trachea. The opening of the larynx is called glottis. The glottis is guarded by epiglottis. Epiglottis prevent the entry of food and liquid into larynx during swallowing

4) TRACHEA:

It is a tubular structure made of 16-29 C-shaped cartilaginous rings. These rings prevent the trachea from collapsing and thus keep the passage of air open. The inner surface of the trachea is ciliated and secrets mucous. This cilia and mucus help filter, moist, warm and clean the incoming air, which enters the lungs.

5) BRONCHI:

The Trachea divides into two smaller tubes called bronchi (singular bronchus). Each bronchus enters the lungs of its own side. The bronchi are also made of rings but are smaller than those of trachea.

6) BRONCHIOLES:

Each bronchiole inside the lung divided further into many smaller branches called bronchioles. Bronchioles have no cartilage. It is made of smooth muscle and elastic fibers Bronchioles further divide deep into the lungs. Finally these bronchioles open into a large number of air sacs, called alveolar.

7) ALVEOLI:

Alveoli are the functional units of the lungs. Alveoli form the inner surface of lungs. Alveoli have a network of blood capillaries through which gaseous exchange occurs between air (oxygen) and blood.

(2)LUNGS:

Lungs are the respiratory organs in humans. Lungs are two close balloons like sacs. It is connected to the outside through trachea.

Lungs are spongy sacs due to the presence of millions of alveoli. The lungs are located in the chest cavity which is surrounded by 24 ribs and muscle. Lungs are covered with a double membrane pleural membrane. Pleural are filled with a fluid which reduces friction inside the thorax and also helps the lungs in expanding and contracting freely.

MECHANISM OF BREATHING IN HUMAN:

Breathing is inhalation and exhalation of air. Oxygen is taken in and carbon dioxide is given out.

There are two phase in breathing:

(1) Inspiration OR Inhalation

(2) Expiration OR exhalation

INSPIRATION OR INHALATION:

The process by which air is taken inside the lungs is called inhalation.

MECHANISM OF INHALATION:

During respiration, the rib muscles contract. At the same time the muscle of the diaphragm contracts and is lower due to this moment the volume of Thorax and lungs increase and air enters into the lungs.

(2) EXPIRATION OR EXHALATION:

The process by which impure air is expelled out from lungs is called exhalation.

MECHANISM OF EXHALATION:

(i) The ribs muscles relax.

(ii) The ribs go down and diaphragm becomes dome-shaped. The decrease in the volume of thorax occurs.

(iii) The space in the chest cavity decreases. As a result pressure is exerted on the lungs. The lungs contract and the air are expelled out.

QUESTION: Why breathing rate increase during exercise

ANSWER

The normal breathing rate of a human is 16-20 times per minute in normal condition but it can increase up to 30-40 times during exercise or other hard physical work. We can control breathing rate but not for a long time.

At rest, breathing rate is controlled by the respiratory Centre in the brain, medulla. This respiratory Centre is very sensitive to the concentration of carbon dioxide in the blood.

During exercise the concentration of carbon dioxide increases in blood. More oxygen is required for oxidation of glucose to get more energy. As a result the respiratory Centre is stimulated then a message in the form of nerve impulse is sent to the rib muscle and diaphragm muscles to increase the rate of breathing. Thus more oxygen is inhaled which is required for cellular respiration and to remove the excess of carbon dioxide from the blood.