Page 5 - class-XI-ch.8-Lesson notes

Trachea is also called wind pipe. It is a kind of tube with cylindrical shape. Its length is about 11.2 cm with a diameter of 2

to 2.5 cm. It lies in front of the esophagus and extends from the larynx. Then it gets divided into two bronchi, one for

each lung. The walls of trachea are made of hyaline cartilage. On the mouth the trachea there is a valve, called epiglottis.

The epiglottis prevents the food to enter the trachea.

Bronchi

The two bronchi, into which trachea divides, differ bronchiole slightly. The right bronchus is shorter, wider and
more vertical than the left bronchus. These enter the right and left lungs, respectively and then break up into a
greater number of smaller branches, which are called bronchial tubes and bronchioles.

Diaphragm

Diaphragm is a sheet of internal skeletal muscle that extends across the bottom of the ribcage. The Division of
bronchiole into alveoli diaphragm separates the thoracic cavity (heart, lungs and ribs) from the abdominal cavity and
performs an important function in respiration. When it contracts, the volume of thoracic cavity increases and air is drawn
into the lungs.
Lungs

There are two lungs in our body. Lungs are the vital organs of respiration. Lungs are cone-shaped organs with the apex
above. The base of the lungs lies resting on the floor of the thoracic cavity on the diaphragm. The lungs are divided into
lobes by fissures. The left lung has two Lobes and the right lung have three lobes. Each of these lobes enters a lobule and
as it divides and sub-divides, its walls become thinner and thinner and finally, these end in the air sacs of the lungs.

Types of Respiration:

There are two types of respiration, i.e., external respiration and internal respiration.

External Respiration:
02 is taken in when we inhale, It moves through nose, trachea and bronchial tubes to alveoli, where it comes into
a close contact with the blood in the pulmonary capillaries. Only 02 are taken in when we inhale, it moves
through nose, trachea and bronchial tubes to alveoli, where it comes into a close contact with the blood in the
pulmonary capillaries. Only single membrane separates the oxygen from the blood. 02 pass through this
membrane and are taken up by the hemoglobin of RBC. After that, it is carried to the heart, from where it is
pumped throughout the body. In the same way, in the lungs C02 passes through the membrane from blood to
alveoli. C02 comes out through bronchi, trachea and the nose.

Internal Respiration

The exchange of 02 and CO in the tissues constitutes internal respiration. It consists of the passage of 02 from the
blood into the tissue fluid, and from the tissue fluid into the tissue cells and the passage of C02 from the cells into
the tissue fluid, and from the tissue fluid into the blood.
Functions of Respiratory System
The main function of the respiratory system is to supply oxygen to the cells of the body continuously. The next
important function of this system is to exhale carbon dioxide, water vapors and other waste products from the body.
These two functions are performed by internal and external respiration.