Respiratory System in Humans

Respiration is the stepwise oxidation of glucose (and other nutrients) which results in the release of energy that is stored in the cytosol in the form of ATP (adenosine triphosphate). Whenever energy is required by our body, ATP is broken down and large amount of energy is released.

Humans have a well developed respiratory system suitable for meeting the higher requirement of oxygen in the bodies. The respiratory system consists of nostrils, nasal cavity, pharynx, larynx, trachea, and bronchi. The two bronchi branch extensively into bronchioles, terminal bronchioles and ultimately end in the air sacs called alveoli.

The bronchioles, their branches and air sacs are enclosed in a double membrane called pleural membrane to form the lungs. The lungs are the main respiratory organs.

Air passes through nostrils into bronchi, to bronchioles and into air sacs which are thin walled sacs with a single layer of cells and heavily covered with blood capillaries. O₂ from alveoli passes into capillaries and CO₂ from other capillaries diffuses into alveoli for being removed. Alveoli are the organs where the actual gaseous exchange occurs.

The double layer pleural membrane covers the lungs for its protection. It contains pleural fluid, which makes the movement of the lungs easy. Each lung consists of a tree like system of branched bronchial tubes. The finest of them terminate into millions of tiny sac like structures called alveoli.

Alveolar membrane is very thin, moist and richly supplied with blood capillaries. The walls of both the capillaries and alveoli consist of a single layer of flattened epithelial cells.

Nostril / Nasal Cavity

Filtration of unwanted particles. Traps dust, bacteria; warms and moistens the air in the pharynx.

Pharynx (Throat)

The common passage for both respiratory gases and food moving into digestive passage, separated by epiglottis. Epiglottis is a flap like structure that closes the tracheal opening (opening of the wind pipe) called glottis when food is swallowed.

Larynx / Voice Box

Connects pharynx to the trachea; helps in sound production.

Trachea (Wind Pipe)

Passage for air up to bronchi.

Bronchus

Enters the lungs and divides to form secondary bronchi, tertiary bronchioles and ultimately terminal bronchioles. Together they form the bronchial tree.

Bronchioles

Convey air into alveoli.

Alveoli (Air Sacs)

Exchange of Gases.