Name: Sudipta Ghosh Roll No.: 14MM91R06 Subject Code: MM61501

Assignment 5: Role of Surfactant in Human Respiratory System?

Surfactant consists mainly of phospholipids that lower the alveolar surface tension to prevent

lung collapse at expiration. They also support mechanical elimination of inhaled pathogens

by reducing the viscosity of airway mucus. Approximately 8-10% of surfactant is made up of

proteins. Among them, specific proteins SP-A and SP-D play a crucial role in the innate

defence system. They belong to collectins family and serve as the first step in immune

response to inhaled pathogens. In limited extent, SP-B and SP-C are also involved in

immune-modulation.

Surfactant reduces surface tension, so that the alveoli in the lungs are able to expand. It is

essentially a biological detergent. Surfactant reduces surface tension. Without surfactant, the

wet surfaces of the alveoli in our lungs would stick together and our lungs would not be able

to expand - so, we would not be able to breathe. The alveoli are the tiny sacs in our lungs

where oxygen is captured from inhaled air and absorbed into our bloodstream. They are very

small and are have moist surfaces. Wet surfaces stick together due to surface tension, which

is caused by the attraction that water has for itself. To demonstrate how strong surface tension

is, take two small glass panes, wet them slightly and press them together until there is no air

between them. Now try to pull them apart. It's extremely difficult (you usually have to slide

them apart because they will not separate otherwise). However, if we mix dish detergent in

the water first, it will be much easier to pull them apart, because the detergent is a surfactant -

a substance which combines with water and by doing so reduces the surface tension of the

water. About three to four weeks before birth, you lungs begin to produce surfactant. When

we are born and take our first breath, we have to open the fluid-filled alveoli to allow air in.

Without surfactant, this would be nearly impossible, which is why very premature infants

have so much difficulty breathing. These very early preemies are given surfactant (either

artificial or derived from calf lungs) down a tube going to their lungs, to help their alveoli

open and allow air entry. Some medical conditions cause loss of surfactant. In pulmonary

edema, fluid from the blood invades and floods the alveoli. Among other problems, this

causes dilution and washout of the surfactant, so that alveoli are more likely to collapse.

Inflammation of the lungs also causes reduced surfactant production, so again the alveoli

collapse due to increased surfaced tension. In cystic fibrosis, excess mucus production

displaces the surfactant (and mucus has an even higher surface tension than water). Patients

with CF are given extra surfactant to make up for this loss and to provide enough surfactant

that it can act on the mucus as well as the normal alveolar fluid.