3rd Factor: Surfactant
It's quite a boring topic but... I guess... It's wakariyasui mon~
III. Surfactants
Definition:
Complex mixture of lipoprotein substances and ions
Most important component:
Phospholipids dipalmityl lecithin, surfactant apoprotein and calcium ion
Synthesized and released from type II alveolar cells
Stored in lamellar bodies (Organelle)
Dynamic surfactant system with continuous formation and degradation:
o Phospholipids are synthesized from fatty acids
§ Reach lung from blood
§ Formed inside lung
o Degradation occurs by phospholipases enzymes present in alveoli
Release of surfactant is directly proportional to tidal volume once tidal volume increases above resting level, rate of surfactant released increases within 2 minutes
Main stimulus for surfactant release: Distortion of type II alveolar cells
Function:
1. Decrease surface tension
o Between fluid lining the alveoli and air inside alveoli
o Scatters among fluid molecule
o Decrease attraction between fluid molecule
o Lowers the surface tension
2. Activate and exert a stimulant effect on macrophage
3. Has bacteriolytic effect
o Render (Turn into) bacteria susceptible to alveolar macrophages
4. Phospholipids of surfactant acts directly on T lymphocytes cell membrane
o Prevent excess immune response
5. Assist ciliary movement in upper respiratory tract
o Helps removing any particles and mucus away from air passages
Conditions decrease surfactant
1. Respiratory distress syndrome
§ Surfactant won’t be produced before fetus reaches 8 months pregnancy
§ Premature babies
o Lungs with insufficient surfactant
o Collapsed alveoli
o Hyaline membrane disease
ü High surface tension causes plasma fluid to leak into alveoli
ü Produce a “glistering membrane” appearance and pulmonary edema (Abnormal large amount of fluid in intercellular tissues space)
§ Respiration distress syndrome is a fatal condition
§ Mechanical ventilation keeps premature babies alive until lungs can produce sufficient surfactant
§ More severe and common in infants with low plasma level of thyroid hormone
§ Size and number of inclusion in type II alveolar cell increased by thyroid hormone
2. Cigarette smoking - Destruct type II alveolar cells
3. After cardiac surgery - Pulmonary circulation is interrupted - Alveolar epithelium fails to secrete surfactant
4. Elective caesarean section
§ Surfactant isn’t produced in lungs before 8th months age
§ Premature delivery to save the mother but baby still can’t produce surfactant - Their lungs may collapsed
§ Inject mother with cortisone hormone - Essential for surfactant formation