46 & 47: Respiratory Muscles & Breathing Cycle

Question 1

Muscles of Inspiration

Answer 1

Scalene
Sternomastoid
External Intercostals

Diaphragm contracts

Question 2

Muscles of Expiration

Answer 2

Rectus Abdominis
Internal Intercostals
Obliques
Transversus Abdominis

Diaphragm relaxes

Bucket Handle

muscles pull ribcage downwards and inwards, increasing IP pressure, squeezing air out of lungs

Question 3

Diaphragm

Answer 3

main muscle responsible for driving ventilation during tidal breathing

contraction and shortening pull it flatter

increase the volume inside the thoracic cavity

Question 4

Pleural Membrane

Answer 4

visceral pleural:
is physically attached to the lung surface

parietal pleural:
membrane is attached to the wall of the thorax and diaphragm

Question 5

Pressure Equation

Answer 5

Force/Area

increasing area (volume) decreases pressure

Question 6

Combined Gas Laws

Answer 6

P1V1/T1 = P2V2/T2

increase temperature = increase in volume

Question 7

Boyle’s Law

Answer 7

P1V1 = P2V2

closed system: pressure falls as volume expands

open system: airflow inward until pressure inside = P(ATM)

Question 8

Intrapleural pressure (PIP)

Answer 8

pressure inside pleural space

Question 9

Alveolar pressure (PA)

Answer 9

pressure inside alveolus

Question 10

Transmural pressure (PTM)

Answer 10

any pressure gradient across a wall

Question 11

Transpulmonary pressure (PTP)

Answer 11

lung elastic recoil pressure

transmural pressure across the alveolar wall (PA-PIP)

Question 12

Pressure Changes during Breathing

Answer 12

Pleural pressure falls (from -5 to -8)

Transpulmonary pressure gradient increases
(PTP = PA – PIP)

alveolar expansion

Alveolar pressure falls (from 0 to -1)

Question 13

How long does inspiration take?

Answer 13

2 seconds

Question 14

How long does expiration take?

Answer 14

3 seconds

longer than inspiration b/c of increased airway resistance, pressure gradient larger

Question 15

Lung Compliance

Answer 15

Pressure Volume Relationship

C = ΔV(l)/ ΔP(tp)

C = 1/E

Question 16

Hysteresis

Answer 16

the pressure/volume relationship differs depending on inflation or deflation

Question 17

What forces are needed to overcome in lung compliance?

Answer 17

Airway resistance
Frictional forces
Inertia of air + tissues
Elasticity of lung

Question 18

What happens if lungs are filled with saline so there is no surface tension?

Answer 18

hysteresis is not apparent

Question 19

Surface Tension

Answer 19

Intermolecular forces of attraction

Molecules at surface are only attracted from below and with each other

the surface of liquid acts as an elastic sheet

Force per unit length/ energy per unit area

Question 20

LaPlace’s Law

Answer 20

P = (n)T / r

T surface tension, r radius

↑ radius ↓P
↓ radius ↑P

Question 21

Surface Tension and Alveoli

Answer 21

Small alveoli develop a large pressure

Large alveoli develop a smaller pressure

air from smaller to larger alveoli

small alveoli collapse and large alveoli to fill

Question 22

Surfactant

Answer 22

lipoprotein rich in phospholipid

secreted by type II cells

reduces surface tension by increasing lung compliance

alveoli shrink, surfactant conc. increases, surface tension decreases

Question 23

Surfactant Constituents

Answer 23

90% Phospholipids:(phosphatidylcholine; DPPC)

10% Proteins:
SPA, SPB, SPC, SPD

Question 24

Surfactant and Surface Area

Answer 24

Smaller surface area, surfactant closely packed, surface tension is less

Larger surface area, surfactant spread out, surface tension is more

Question 25

Lung High Compliance

Answer 25

Walls of lung thinner

Higher surfactant

Large volume change; lung inflates easily and has little elastic recoil

air trapped inside must use extra force to get it out

Emphysema
COPD

Question 26

Lung Low Compliance

Answer 26

Walls of lung thicker

lung inflates with difficulty due to large elastic recoil

Low surfactant, labored breathing

Pulmonary fibrosis
Respiratory distress syndrome

Question 27

FRC

Answer 27

Functional Residual Capacity

Volume of the lung at rest between breaths

lung volume at which the inwardly directed lung recoil is exactly
balanced by the outwardly directed chest wall recoil

the volume of the lung when there is no active muscle input