The Lungs (Human Anatomy): Picture, Function, Definition

LUNG

The lungs are a pair of respiratory organs situated in the thoracic cavity.Each lung invaginates the corresponding pleural cavity.The right and left lungs are separated by the mediastinum.

Characteristic features :

• Lung is porus,highly elastic and spongy in texture
• It crepitates to the touch and floats on water.In still born lungs sink in water
• In newborn it is rosy pink.In adult it is dark slaty gray due to deposition of carbonacious particles in the stroma of the lungs.

Presenting parts:

Each lung is half-conical in shape.It has:

• An apex at the upper end
• A base resting on the diaphragm
• Three borders:
1. Anterior
2. Posterior 
3. Inferior 

Two surfaces:

1. costal
2. medial:It is divided into
1. Vertebral parts
2. Mediastinal parts.

Lobes and fissures of the lungs:

1.  Right lung presents three lobes- upper,middle and lower- separated by oblique fissure and horizontal fissure.
2.  Left lung presents two lobes- upper and lower- separated by an oblique fissure.

Structure of lung:

Each lung is composed from outside inwards-

1. Serous coat(derived from pulmonary pleura)
2. Subserous areolar tissue (elastic fibro-areolar tissue)
3. Pulmonary substance(includes all structures within the lung lobules)

Bronchial tree

Bronchial tree:

Successive stages of division of trachea up to alveoli form the bronchial tree. Its divisions are-

Trachea
|
Right & Left principal bronchi
|
Secondary or lobar bronchus
(3 for right & 2 for left)
|
Tertiary or segmental bronchus
( 10 for each lung)
|
Terminal bronchus
|
Lobular bronchiole
|
Terminal bronchiole
|
Respiratory bronchioles
|
Alveolar duct
|
Atrium
|
Alveolar sac
|
Alveoli

 

A.Cells of conducting airway:

1. Ciliated columnar cells
2. Goblet cells
3. Clara cells
4. Basal cells
5. Brush cells
6. Neuroendocrine cells
7. Lymphocytes
8. Mast cells

B.Cells of lung alveoli:

1. Type- 1 pneumocyte
2. Type- 2 pneumocyte
3. Alveolar macrophage