breathing, surfactant and compliance

Question 1

how do muscles of respiration act to increase and decrease thoracic volume?

Answer 1

during inspiration the diaphragm moves down and contracts, increasing volume
during expiration the diaphragm moves up and relaxes, decreasing volume

Question 2

describe boyle’s law

Answer 2

pressure exerted by a gas is inversely proportional to its volume
as volume increases pressure decreases
as volume decreases pressure increases

Question 3

what muscles are involved in inspiration?

Answer 3

external intercostal (in-between ribs)
diaphragm
scarlenes and sternocleidomastoids (only under heavy respiratory load to lift upper ribs and clavicle)

Question 4

what muscles are used during expiration?

Answer 4

internal intercostal (opposite direction than external intercostal, so they pull the ribcage down and inwards)
abdominal

Question 5

what is the pressure inside the thoracic cavity and lungs called?

Answer 5

alveolar (intra thoracic)

may be + or - compared to atmospheric pressure

Question 6

what is the pressure inside the pleural cavity called?

Answer 6

intra-pleural pressure, always - in healthy lungs

Question 7

what is transpulmonary pressure?

Answer 7

difference between alveolar and intra-pleural pressure

Pt=Pa-Pip

Question 8

what 2 types of cells are alveolar walls made of?

Answer 8

type 1- permit gas exchange

type 2- secrete surfactant fluid

Question 9

what must be overcome by the pressure required to inflate lungs?

Answer 9

the airway resistance and expand the elastic elements of the chest as measured by compliance

Question 10

what is compliance determined by?

Answer 10

elastic forces, surface tension at the alveolar air-liquid interface and airway resistance

Question 11

what is increased and decreased by the surfactant produced by the type II cells of the alveoli?

Answer 11

Alveolar surface tension is decreased

Compliance is increased

Question 12

is surfactant more effective in small or large alveoli?

Answer 12

small because surfactant molecules come closer together and are more concentrated

Question 13

when does surface tension occur?

Answer 13

wherever there is an air-water interface and refers to the attraction between water molecules

Question 14

what’s the LaPlace equation?

Answer 14

P=2T/r

Question 15

what is compliance?

Answer 15

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

Question 16

what happens to Ip (inter-pleural) pressure during inspiration?

Answer 16

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.

Question 17

what happens to alveolar pressure during inspiration?

Answer 17

makes alveolar pressure subatmospheric, which creates the pressure difference between atmosphere and alveoli to drive air flow into the lungs

Question 18

what happens during normal expiration?

Answer 18

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

Question 19

what happens during forced expiration?

Answer 19

contraction of expiratory (internal) intercostal muscles and abdominal muscles decreases thoracic dimensions, reducing duration of breathing cycle and allowing more breaths/min