Respiration and exchange of gases
Channel: ISHTA’s BIO ACADEMY
Date: 2021-03-17

We have a pair of external nostrils opening out above the upper lips.
It leads to a nasal chamber through the nasal passage. The nasal
chamber opens into the pharynx, a portion of which is the common
passage for food and air. The pharynx opens through the larynx region
into the trachea. Larynx is a cartilaginous box which helps in sound
production and hence called the sound box. During swallowing glottis
can be covered by a thin elastic cartilaginous flap called epiglottis to
prevent the entry of food into the larynx. Trachea is a straight tube
extending up to the mid-thoracic cavity, which divides at the level of
5th thoracic vertebra into a right and left primary bronchi. Each bronchi
undergoes repeated divisions to form the secondary and tertiary bronchi
and bronchioles ending up in very thin terminal bronchioles. The
tracheae, primary, secondary and tertiary bronchi, and initial
bronchioles are supported by incomplete cartilaginous rings. Each
terminal bronchiole gives rise to a number of very thin, irregular-walled
and vascularised bag-like structures called alveoli. The branching
network of bronchi, bronchioles and alveoli comprise the lungs (Figure
17.1). We have two lungs which are covered by a double layered pleura,
with pleural fluid between them. It reduces friction on the lung-surface.
The outer pleural membrane is in close contact with the thoracic