Breathing Or External Respiration

Respiration of Class 7

Breathing Or External Respiration

Breathing means taking in air rich in oxygen and giving out air rich in carbon dioxide with the help of respiratory organs. The taking in of air rich in oxygen into the body is called inhalation and giving out of air rich in carbon dioxide is known as exhalation. It is a continuous process which goeson all the time and throughout the life of an organism. The number of times a person breathes in a minute is termed as the breathing rate. During breathing inhalation and exhalation take place alternately. A breath means one inhalation plus one exhalation.

Human Respiratory System

The main organs of human respiratory system are :-

Nose or nostrils
Nasal cavity (or Nasal passage)
Pharynx
Larynx
Trachea
Bronchi
Bronchioles and alveoli
Lungs
Diaphragm

Nose and nostrils

The external part of the nose bears two nostrils separated by a cartilaginous septum.

In the nostrils, hairs are present which prevent large particles from entering the system. Nostrils also help in detecting odors through their sensory cells.

Human beings breathe through their nose or nostrils.

Nasal passage

The nasal passages are paired, tube-like structures, separated by a cartilaginous septum. The inner surface of the nasal passage is lined by ciliated epithelium and mucous secreting cells.

From the nostrils, air travels through the nasal cavities or chambers. The nasal chambers are lined with glands which secrete mucous. The nasal chambers perform following functions:

Warm the air.
Add moisture to the air.
the mucous entraps the dust and harmful particles thus, cleaning the air.

Pharynx (or throat)

The pharynx is situated at the back of the mouth. From the nasal cavities, the air moves into the pharynx which is a common area to both digestive and respiratory tracts.
The pharynx opens into the larynx or voice box which leads to the trachea. It is also connected to the oesophagus or food pipe, which leads further into the digestive system.
A cartilaginous flap called epiglottis guards the entrance to trachea. The epiglottis covers the trachea to prevent food or water from entering the respiratory tract.

Larynx (voice box)

The larynx or voice box is a cartilaginous box-like structure, located at the tracheal opening. It is hollow from inside.
When some food material is swallowed the larynx moves up or down allowing safe passage of air or food. Larynx also contains vocal cords which vibrate and produce sound while speaking.

Trachea (wind pipe)

The trachea or windpipe is a tube, about 11 cm in length and about 2.5 cm in diameter that extends into the thoracic cavity. It lies on the ventral side of oesophagus.
Its wall is provided with incomplete C-shaped cartilaginous rings which keep the trachea in dilated position and prevent it from collapsing.
The ciliated epithelial lining and the mucous secreting cells extend from the nasal cavities up to the trachea. The ciliated epithelial lining and mucous membrane help in preventing any dust particle or microbe from entering the lungs.
The trachea is split into two primary bronchi. The right bronchus is divided into three bronchi which extend separately into the three lobes of right lung. Similarly, the left bronchus is divided into two bronchi penetrating into the two lobes of the left lung.

Lungs

The lungs are a pair of highly elastic, hollow, bag-like structures situated in the thoracic cavity along with the heart. The broad lower surface of lungs rests on a sheet of muscle called the diaphragm which forms the floor of the thoracic cavity.
The right lung is larger than the left one. The right lung is divided into three lobes whereas the left lung has two lobes.
The lungs are surrounded by a narrow space called pleural cavity which is fixed by two membranes called pleural membranes. These membranes secrete an oily substance called pleural fluid that is present in the pleural cavity. It acts as a lubricant to reduce friction between the lungs and the thoracic wall during breathing.

human respiratory system