Respiration in Human beings: Notes for class 10th Biology

HUMAN RESPIRATORY SYSTEM

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 structure which 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).