Surfactant

					Anitha Mittapalli
					BME 403

SURFACTANT

	A Surfactant(wetting agent or detergent) is a substance which
lowers the surface tension of water, especially of the alveolar lining
fluid within the lung and is physiologically advantageous to the lung in
various respects.

	The lung with its numerous tiny alveoli has the benefit of having
a large surface area for the diffusion of gases but unfortunately this
benefit is counter-acted by another complication known as surface tension.
This tension results due to the small radius size of the alveoli and as a
result tends to collapse the alveoli.  Surface tension is caused due to
the unequal attraction forces between water molecules at the surface of
the alveoli.  The relationship between the tension on the surface and
transmural pressure is given by the Laplace law which states that
PTM=2*T/R.   Thus,  surface  tension is proportional to the radius and
thus the surface area of the alveoli.   Hence, for the smaller alveoli the
tension on the surface can become disadvantageous.

	Surfactant, during such a situation acts like a savior due to its
main surface-tension-lowering substance, dipalmitoyl
phosphatidylcholine(DPPC). This substance, containing hydrophobic chains
towards the surface side of the alveoli stabilizes them and as a result
alveoli resist compression during lung deflation. 

	By lowering the surface tension and compression surfactant becomes
an important advantage to the physiological function or mechanics of the
lung.  It 1. increases the compliance of the lung and thus reduces the
work of breathing. 2. Alveoli are stabilized  3. alveoli are kept dry and
4. it lowers the elastic recoil at low lung  volume(FRC), thus preventing
the alveoli from collapsing  at the end of each expiration. Surfactant is
important physiologically as well as to the course since lung mechanics
depends a lot on the substance and a deficiency of it can result in the
stiffening of the lung and causes Respiratory Distress Syndrome.

    As one web page mentions,(http://www.mosbych.com/mhc/top/001783.htm)
surfactant can also be given to newborns and to premature babies with low
birthweight or breathing problems.


EXAMPLE OF TEST QUESTION;
Most likely the test question on the surfactant topic is multiple choice ,
fill-in, T/F.

1. Surfactant’s main constituent or its main surface-tension lowering
substance is 
____________________.
Answer: dipalmitoyl phosphatidyl choline(DPPC).
2. List two advantages due to surfactant:
Answer: 

	1. increases compliance of lung and thus reduces the work of
	   breathing.

        2. keeps alveoli dry.

email address: mittapal@aludra.usc.edu

Sample Problems:

Answers:

For more information on this topic, please refer to West , page .

Also, check out the following links that may be helpful:

• And, as always, if you have questions, or if you can suggest a helpful link, please e-mail me.

No!
Please don't make me go to any of those pages!
I want to go somewhere completely different!

This page was written by , a student in this course.

BME 403 Pages maintained by the T.A., Douglas Miles.