Surfactant In The Lungs: Functions, Synthesis, And Importance

Surfactant In The Lungs: Functions, Synthesis, And Importance

What is surfactant? Where it is synthesized? Explain three of its important functions. (or) Surfactant.
Answer:

Surfactant:

• It is a surface acting material or agent that is responsible for lowering the surface tension of a fluid.
• It is a mixture of protein-lipid complexes made up of mainly dipalmitoyl phosphatidyl choline lipid along with other lipids and proteins and ions like calcium.

Source of synthesis:

• Surfactant is produced by.

1. Granular pneumocytes

• It is alveolar lining epithelial type II cells.

2. Clara cells or bronchiolar exocrine cells.

• They are situated in the bronchioles

surfactant Functions:

1. Reduction of surface tension:

• The surfactant reduces the surface tension in the alveoli of lungs and prevents the collapsing tendency of lungs.

Reduction of Surface Tension Mechanism:

• Phospholipid molecule in the surfactant has two portion.
  1. Hydrophilic portion.
     • Formed by SP-A and SP-D proteins.
     • Hydrophobic portion.
     • This dissolves in water and lines the alveoli.
  2. Formed by SP-B and SP-C proteins.
     • It is directed towards the alveolar air.
     • Thus, surfactant spreads over the alveoli forms a layer between the fluid lining the alveoli and alveolar air and reduces surface tension in the alveoli of lungs.

2. Stabilization of the alveoli:

• Surfactant is responsible for stabilization of the alveoli.
• This helps to withstand the collapsing tendency of lungs.

3. Inflation of lungs:

• Secretion of surfactant begins from third month of intrauterine life.
• Until birth, the lungs are solid and not expanded.
• In infants, breathing occurs due to the stimulation of respiratory centers by hypoxia and hypercapnea.
• However, the lungs tends to collapse repeatedly when the infant attempts respiratory movements.
• Presence of surfactant in the alveoli prevents this collapsing of lungs.

4. Defensive function :

• Surfactant protects the lungs against infection and inflammation.
• SP-A and SP-D proteins of surfactant.
  1. Destroys bacteria and virus by opsonisation.
  2. Controls the formation of inflammatory mediators.