breathing, surfactant and compliance Flashcards
how do muscles of respiration act to increase and decrease thoracic volume?
during inspiration the diaphragm moves down and contracts, increasing volume
during expiration the diaphragm moves up and relaxes, decreasing volume
describe boyle’s law
pressure exerted by a gas is inversely proportional to its volume
as volume increases pressure decreases
as volume decreases pressure increases
what muscles are involved in inspiration?
external intercostal (in-between ribs) diaphragm scarlenes and sternocleidomastoids (only under heavy respiratory load to lift upper ribs and clavicle)
what muscles are used during expiration?
internal intercostal (opposite direction than external intercostal, so they pull the ribcage down and inwards) abdominal
what is the pressure inside the thoracic cavity and lungs called?
alveolar (intra thoracic)
may be + or - compared to atmospheric pressure
what is the pressure inside the pleural cavity called?
intra-pleural pressure, always - in healthy lungs
what is transpulmonary pressure?
difference between alveolar and intra-pleural pressure
Pt=Pa-Pip
what 2 types of cells are alveolar walls made of?
type 1- permit gas exchange
type 2- secrete surfactant fluid
what must be overcome by the pressure required to inflate lungs?
the airway resistance and expand the elastic elements of the chest as measured by compliance
what is compliance determined by?
elastic forces, surface tension at the alveolar air-liquid interface and airway resistance
what is increased and decreased by the surfactant produced by the type II cells of the alveoli?
Alveolar surface tension is decreased
Compliance is increased
is surfactant more effective in small or large alveoli?
small because surfactant molecules come closer together and are more concentrated
when does surface tension occur?
wherever there is an air-water interface and refers to the attraction between water molecules
what’s the LaPlace equation?
P=2T/r
what is compliance?
change in volume relative to change in pressure
high compliance results on large increase in lung volume and small decrease in Ip pressure
low compliance results in small increase in lung volume and large decrease in Ip pressure
what happens to Ip (inter-pleural) pressure during inspiration?
the contractions of the diaphragm and inspiratory (external) intercostal muscles increase the volume of the thoracic cage.
This makes intrapleural pressure more subatmospheric (negative) and causes the lungs to expand.
what happens to alveolar pressure during inspiration?
makes alveolar pressure subatmospheric, which creates the pressure difference between atmosphere and alveoli to drive air flow into the lungs
what happens during normal expiration?
inspiratory muscles cease contracting, allowing the elastic recoil of the chest wall and lungs to return them to their original between-breath size, this raises alveolar pressure above atmospheric pressure and drives air out of the lungs
what happens during forced expiration?
contraction of expiratory (internal) intercostal muscles and abdominal muscles decreases thoracic dimensions, reducing duration of breathing cycle and allowing more breaths/min
