mechanics of breathing

Question 1

how does the pleural membrane surround the lungs

Answer 1

on both sides but the two sides arent connected

cover the lungs and interior of the thorax

Question 2

what is between the pleural membranes

Answer 2

an extremely thin layer of intrapleural fluid

Question 3

what is the role of intrapleural fluid

Answer 3

allows the membranes to glide across each other and reduces friction
the lungs are effectively stuck to the rib cage and diaphragm due to the cohesive force of the pleural fluid on the membranes, even though they are trying to pull apart from each other

Question 4

what are the 2 parts that make up the pleural membranes

Answer 4

visceral: coats the outer surface of the lungs
parietal: coats the inner surface of the ribs

Question 5

what is pleurisy

Answer 5

inflammation of the pleura
increased friction
breathing is difficult

Question 6

pneumothorax

Answer 6

air enters the pleural cavity and the 2 membranes are forced apart as air enters down a pressure gradient
the relationship between the 2 pleural membranes is lost and the affected lung becomes useless and collapses due to the elastic recoil of the lung and chest wall in opposite directions

Question 7

which muscles are involved in inspiration

Answer 7

external intercostals and the diaphragm

also the sternocleidomastoids and scalenes

Question 8

what muscles are involved in expiration

Answer 8

expiration is passive at rest

internal intercostals and abdominal muscles during severe respiratory load

Question 9

describe the changes in pressure in the thoracic cavity related to the diaphragm

Answer 9

diaphragm is dome shaped at rest
flattens when it contracts which decreases the thoracic pressure by increasing the volume - air moves into the lungs
vice versa on expiration

Question 10

how are the intercostal muscles involved in changing the dimensions of the rib cage

Answer 10

internal intercostals:
pump-handle motion - increases anterior-posterior dimension
bucket handle motion - increases the lateral dimension

external intercostals:
elevate the ribs and increase the lateral dimensions

Question 11

Asthma and smooth muscle

Answer 11

over-reactive constriction of bronchial smooth muscle
increases resistance
expiration phase is most affects as the airways are compressed by the physical forces of expiration

Question 12

Boyle’s law

Answer 12

pressure exerted by a gas is inversely proportional to its volume

gases also move from areas of high pressure to areas of low pressure

Question 13

define ventilation

Answer 13

the physical act of getting air in and out of the lungs

Question 14

intra-thoracic (alveolar) pressure

Answer 14

PA
pressure inside the thoracic cavoty
may be -ve or +ve compared to atmospheric pressure

Question 15

intra pleural pressure

Answer 15

Pip
pressure inside the pleural cavity
always -ve

Question 16

transpulmonary pressure

Answer 16

PT
difference between alveolar and intra pleural pressure
always +ve
PA - Pip

Question 17

Bulk flow of air relationships

Answer 17

bulk flow of air between the atmosphere and the alveoli is proportional to the difference between atmospheric and alveolar pressures and inversely proportional to the airway resistance
F = (Patm - PA)/R

Question 18

when is atmospheric pressure equal to alveolar pressure

Answer 18

between breaths at the end of an unforced expiration
no air is flowing
the dimensions of the lungs and thoracic cage are stable as a result of opposing elastic forces - lungs are stretched and attempting to recoil and the chest wall is compressed and attempting to move outwards
intrapleural pressure is subatmospheric and transpulmonary pressure opposes the forces of elastic recoil

Question 19

what does airway resistance determine

Answer 19

how much air flows into the lungs at any given pressure difference between atmosphere and alveoli

Question 20

what is the major determinant of airway resistance

Answer 20

the radii of the airways

Question 21

what are the 2 mechanical factors that affect respiratory minute volume

Answer 21

difference between alveolar and atmospheric pressures

airway resistance

Question 22

define respiratory minute volume

Answer 22

Respiratory minute volume is the volume of gas inhaled (inhaled minute volume) or exhaled (exhaled minute volume) from a person’s lungs per minute

Question 23

what are the 2 compartments in the thoracic cavity

Answer 23

alveolar and intra-pleural

Question 24

why is intrapleural pressure always less than alveolar pressure

Answer 24

alveolar pressure can be +ve or -ve
intrapleural pressure is always -ve as there is no air in the pleural cavity (normally)
transpulmonary pressure is the difference between alveolar and intrapleural pressure , it is always +ve because intrapleural pressure is always -ve