Secreted by

alveolar cells. 90% phospholipids and some

Function of surfactant is the reduce the surface tension of

and prevent fluid accumulation. Also

the work of breathing and helps keep alveoli

ventilated. Surface tension of water and surfactant is proportional to

so it helps equal ventilation of small and large alveoli. It is

to inflate small alveoli, so surfactant makes is easier.

receptors are activated by mechanical and chemical stimulation and

receptors detect chemical stimulation. The long reflex travels along the afferent -

- to the CNS, which will then travel to the ganglion via the efferent and stimulate

and SM

The short reflex (e.g. coughing) travels straight to the

This increases the fluid and mucus secretions into the

CNS activation increases

release from parasympathetic nerves, which bind to

receptors and increase the

concentration, causing bronchoconstriction. The CNS also uses

"non-adrenergic, non-cholinergic transmitters" to release either

or VIP. VIP binds to VIP receptors and increases

in SM, causing

Substance P binds to

which increases the

concentration in SM and causes bronchoconstriction.

Histamine increases SM

and

vascular permeability, causing airway

and mucus secretion.

Prostaglandins and Thromboxane cause

or contraction of SM.

Leukotrienes cause

of SM.