ЛЕКЦИЯ № 28. Surface tension forces

In a liquid, the proximity of adjacent molecules results large, inter-molecular, attractive (Van der Waals) forces that serve to stabilize the liquid. The liquid-air surface produces inequality of forces that are strong on the liquid side and weak on the gas side because of the greater distance between molecules in the gas phase. Surface tension causes the surface to maintain as small an area as possible. In alveoli, the result a spherically-curved, liquid lining layer that tends to be pulled inward toward the center of curvature of the alveolus. The spherical surface of the alveolar liquid lining behaves in manner similar to a soap bubble. The inner and outer surface of a bubble exert an inward force that creates a greater pressure inside than outside the bubble. Interconnected alveoli of different sizes could lead to collapse of smaller alveoli (atelectasis) into larger alveoli, because of surface tension, the pressure inside the small alveolus (smaller radius of curvature) is greater than that of the larger alveolus. Without surfactant, gas would therefore move from smaller to larger alveoli, eventually producing or giant alveolus.

Pulmonary surfactant: Pulmonary surfactant is a phospholipid (comprised primari ly of dipalmitoyl phosphatidylcholine) synthesized by type II alveolar epithelial cells. Surfactant reduces surface tension, thereby preventing the collapse of small alveoli. Surfactant increases the compliance of the lung and reduces the work of breathing.

Surfactant keeps the alveoli dry because alveolar collapse tends to draw fluid into the alveolar space. Surfactant can be produced in the fetus as early as gestational week 24, but is synthesized most abundantly by the 35 th week of gestation. Neonatal respiratory distress syn drome can occur with premature infants, and results in areas of atelec-tasis, filling of alveoli with transudate, reduced lung compliance, and V/Q mismatch leading to hypoxia and CO₂ retention.

New words

surface tension forces – поверхностные силы напряжения

liquid – жидкость

proximity – близость

adjacent – смежный

large – большой

intermolecular – межмолекулярный

to stabilize – стабилизироваться

surface – поверхность

to produce – производить

side – сторона

weak – слабый

greater – больше

distance – расстояние

between – между

phase – фаза

tension – напряженность

spherically-curved – сферически-кривой

lining – выравнивание

inward – внутрь

toward – к

curvature – искривление

spherical – сферический

similar – подобный

soap – мыло

inner – внутренний

to exert – проявить

interconnected – связанный

something – что-нибудь, что-то

everything – все

Употребление something, anything, nothing или everything

1. Утвердительная форма:

I can see something on the table.

2. Отрицательная форма:

I can see nothing on the table. I cannot see any thing on the table.

3. Вопросительная форма:

Can you see anything on the table?

Вставьте something, anything, nothing или everything.

1… is all right, the patient is much better today.

2. Is there… interesting in the programme of the concert?

3. I could see…: it was quite dark.

4. Give me… to drink.

5. I didn't take any money with me, so I couldn't buy…

6. My new eyeglasses are very good, I can see… now.

7. I saw… near the wood that looked like a tent.

8. Give me… to read, please.

9. I don't know… about your town. Tell me… about it.

10. Please give me… warm: it is cold here.

11. I understand… now. Thank you for your explanation.

12. There is… white in the box. What is it?

13. Is there… that you want to tell me?

14. Where is the book? – It is on the table. – No, there is… there.

15. I know. about it.

16. Tell me. about your family.

Answer the questions.

1. What forces serve to stabilize the liquid?

2. What does the liquid air produces?

3. Where are the liquid – air forces strong and weak?

4. Why are the liquid – air forces strong and weak?

5. What does the surface tension cause?

6. Where the liquid lining layer tend to be pulled?

7. In what manner does the spherical surface of the alveolar liquid lining behave?

8. What creates a greater pressure inside than outside the bubble?

9. Where interconnected alveoli of different sizes could lead?

10. What is a pulmonary surfactant?

Make the sentences of your own using the new words (10 sentences).

Make your own sentences using something, anything, nothing everything (10 sentences).

Find one word, which is a little bit different in meaning from others (найдите одно слово, которое немного отличается от других по смыслу):

1) a) eyelashes; b) lips; c) eyelid;

2) a) skull; b) head; c) heart;

3) a) esophagus; b) vein; c) intestines;

4) a) knee; b) blood; c) vein;

5) a) capillaries; b) arteries; c) bones.