Following are the main structures in the human respiratory system:
Nostrils:
There two nostrils which converge to form a nasal passage.
The inner line of the nostrils is lined by hairs and remains wet due to mucus secretion.
The mucus and the hairs help in filtering the dust particles out from inhaled air.
Further, air is warmed up when it enters the nasal passage.
Pharynx:
It is a tube-like structurewhich continues after the nasal passage.
Larynx:
This part comes after the pharynx. This is also called the voice box.
Trachea:
This is composed of rings of cartilage.
Cartilaginous rings prevent the collapse of trachea in the absence of air.
Bronchi:
A pair of bronchi comes out from the trachea; with one bronchus going to each lung.
Bronchioles: A bronchus divides into branches and sub-branches; inside the lung.
Alveoli:These are air-sacs at the end of bronchioles
Alveolus
It is composed of a very thin membrane and is the place where blood capillaries open.
This is alveolus;where oxygen mixes with the blood and carbon dioxide exits from the blood.
MECHANISM OF BREATHING
The cycle of breathing consists of two phases, i.e. inspiration and expiration.
Both these processes, i.e. inspiration and expiration are together referred to as respiratory movements
Inhalation – involves contraction of diaphragm and external intercostal muscles resulting in relaxation of rectus abdomen
Expiration involves contraction of abdomen and inner intercostal muscles resulting in relaxation of external intercostal muscles and diaphragm (become dome-shaped).