A&p Ii, Mechanics Of Respiration, Part I

Front 1

The lungs are located in which cavity?

Back 1

the thoracic cavity, one on each side of the mediastinum

Front 2

What is the central compartment of the thoracic cavity?

Back 2

the mediastinum

Front 3

How many subdivisions does the mediastinum have?

Back 3

four, each of which contains certain anatomical structures

Front 4

What surgical procedures that involve the mediastinum?

Back 4

coronary artery bypass, thymectomy, and mediastinoscopy

Front 5

Each lung is surrounded by?

Back 5

a double-layered membrane known as a pleura

Front 6

Parietal pleura

Back 6

lines the inner chest wall, diaphragm, and mediastinum and reflects back to form the visceral pleura that covers the outer surface of the lung

Front 7

Noxious stimuli can activate?

Back 7

nociceptors in the parietal pleura and cause pain

Front 8

Pleural space (or intrapleural space)

Back 8

the space between the pleurae

Front 9

What is contained in the pleural space?

Back 9

several mL of pleural fluid, which acts to hold ("glue") the lungs against the inner chest wall

Front 10

The thoracic cavity is normally a?

Back 10

closed compartment

Front 11

The apex of the thoracic cavity (thoracic inlet) allows?

Back 11

passage of the trachea, esophagus, nerves (phrenic, vagus, recurrent laryngeal, sympathetic trunk), blood vessels (carotid and subclavian arteries; internal jugular and subclavian veins), and lymphatics

Front 12

What is the base of the thoracic cavity formed by?

Back 12

the diaphragm

Front 13

The pleural space is normally?

Back 13

subatmospheric (negative) due to elastic recoil of the lung and chest wall

Front 14

What does the pleural pressure surround?

Back 14

the alveoli

Front 15

What is the average pleural pressure at end-expiration?

Back 15

-5cm H20

Front 16

What is the average pleural pressure during normal inspiration?

Back 16

-7.5 cmH20

Front 17

Does pressure increase or decrease during inspiration?

Back 17

decrease

Front 18

What situations can cause gas or liquid to accumulate in the pleural space and trigger pain and impair ventilation?

Back 18

pheumothorax, tension pneumo, hemothorax, pleural effusion, empyema or pyothorax, fibrothorax, chylothorax

Front 19

What is alveolar pressure?

Back 19

pressure within the lung alveoli

Front 20

What is normal alveolar pressure?

Back 20

it is equal to atmospheric pressure (O cm H20) when the glottis is open and no air is moving into or out of the lung

Front 21

What happens to alveolar pressure during normal inspiration?

Back 21

it falls -1 cm H20, causing movement of a volume of air (500mL) into the lungs over a period of approximately 2 sec

Front 22

What happens to alveolar pressure during normal expiration?

Back 22

it increases to +1 cm H20, causing expiration of the same volume of gas over a period of 2-3 sec

Front 23

Transpulmonary pressure equals?

Back 23

alveolar pressure - pleural pressure (the value is normally positive)

Front 24

What is the transpulmonary pressure or what does it do?

Back 24

it is a distending pressure that tends to keep the alveoli expanded

Front 25

What can transpulmonary presssure be a measure of?

Back 25

the elastic forces that tend to collapse the lung at any point of its expansion

Front 26

What is normally the most important muscle of inspiration?

Back 26

diaphragm

Front 27

Describe the diaphragm

Back 27

sheet of skeletal muscle that inserts into the lower ribs - arranged as two domes (hemidiaphragms) that form the base of the thoracic cavity and that can function independently

Front 28

What type of fibers exist in the diaphragm?

Back 28

50:50 mix of slow twitch endurance muscle fibers and fast twitch fibers

Front 29

The slow twitch endurance muscle fibers are used when?

Back 29

for continual breathing without fatigue

Front 30

Fast twitch fibers are useful for?

Back 30

short bursts of maximal ventilatory effort

Front 31

What are the hemidiaphragms innervated by?

Back 31

the phrenic nerves

Front 32

The phrenic nerves originate from spinal nerves?

Back 32

C3-C5 ("C3,4,5 keep the diaphragm alive")

Front 33

The phrenic nerves are what type of nerves?

Back 33

somatic, and thus are blocked by muscle relaxants

Front 34

What will injury to or local anesthetic block of a phrenic nerve cause?

Back 34

paralysis of the ipsilateral hemidiaphragm

Front 35

Contraction of the diaphragm forces abdominal contents which direction?

Back 35

downward, increasing the superior-inferior (vertical) dimension of the thorax

Front 36

During normal breathing (eupnea) the diaphragm moves how far?

Back 36

approximately 1-2 cm

Front 37

During forced breathing its total excursion may reach?

Back 37

10 cm

Front 38

External intercostal muscles

Back 38

skeletal muscles that connect adjacent ribs; slope downward and forward

Front 39

What pulls the ribs upward and forward?

Back 39

contraction of the external intercostal muscles ("bucket handle movement"), increases the anterior-posterior diameter of the thorax

Front 40

External intercostal muscles are innervated by?

Back 40

intercostal nerves (somatic nerves) that originate from spinal cord segments at the same level

Front 41

What do the external intercostal muscles do during eupnea?

Back 41

assist the diaphragm - not normally required for breathing at rest

Front 42

When are the external intercostal muscles more important?

Back 42

during forceful inspiration

Front 43

Cervical strap muscles or?

Back 43

infrahyoid muscles

Front 44

Cervical strap muscles are important?

Back 44

inspiratory accessory muscles -- assist elevation of the sternum and upper chest wall

Front 45

When do the cervical strap muscles become the primary inspiratory muscles?

Back 45

when diaphragm function is impaired, eg, in patients with cervical cord transection

Front 46

Sternocleidomastoid muscles do what?

Back 46

raise the sternum

Front 47

Scalene muscles do what?

Back 47

elevate the first two ribs

Front 48

Are the sternocleidomastoid and scalene muscles used during normal breathing? When are they important?

Back 48

not active during resting breathing, but become important during forceful inspiration (eg, exercise)

Front 49

Expiration

Back 49

during normal breathing, is a passive process and results from elastic recoil of the lung and chest wall

Front 50

Muscles are recruited for?

Back 50

active expiration (coughing, exercise, voluntary hyperventilation)

Front 51

Muscles of the abdominal wall, include?

Back 51

rectus abdominus, transversus abdominus, internal and external oblique

Front 52

What do the muscles of the abdominal wall do?

Back 52

contraction increases intra-abdominal pressure, raising the diaphragm

Front 53

Internal intercostal muscles pull?

Back 53

pull ribs downward and inward

Front 54

What law includes pressure and volume?

Back 54

Boyles law

Front 55

How can this be applied to the thoracic cavity?

Back 55

its a normally closed compartment

Front 56

In regards to Boyles law, during inspiration what occurs?

Back 56

Increase in volume and decrease in pressure (including pleural pressure and alveolar pressure)

Front 57

In regards to Boyles law, during expiration what occurs?

Back 57

Decrease in volume and increase in pressure

Front 58

Increase in volume of thoracic cavity decreases?

Back 58

pleural pressure and alveolar pressure, allowing inspiration of air and expansion of lungs

Front 59

Hysteresis (in regards to the pressure-volume curve)

Back 59

inspiratory curve is different from the expiratory curve

Front 60

In regards to the pressure-volume curve of the lung, the slope at any point is the?

Back 60

compliance of the lung (usually measured on the inspiratory curve)

Front 61

C=

Back 61

difference in V/difference in P

Front 62

Compliance of the lung is?

Back 62

the extent to which the lungs expand for each unit change in pleural or transpulmonary pressure

Front 63

What is the normal range of transpulmonary pressure?

Back 63

5-10cm H20

Front 64

In the normal range of transpulmonary pressure the lung is?

Back 64

highly compliant (steeper slope of compliance curve)

Front 65

What happens to compliance when the transpulmonary pressure is outside of the normal range?

Back 65

compliance is less at low and high volumes, as reflected by the flatter portions of the pressure-volume curve

Front 66

Factors that reduce compliance include?

Back 66

interstitial edema, fibrosis, obesity, and external compression of lung tissue

Front 67

Factors that increase compliance?

Back 67

aging and emphysema - both are associated with reduced elastic tissue in the lung

Front 68

What does reduced elastic tissue in the lung cause?

Back 68

premature closure of small airways during expiration - traps gas

Front 69

What are 2 sources of elastic forces of the lungs?

Back 69

1. Elastic recoil of interwoven elastic fibers (collagen and elastin) in the alveolar walls and around blood vessels and bronchi
2. Surface tension in the liquid film lining the alveoli- air/water interface

Front 70

Why does surface tension arise at an air/water interface?

Back 70

Stronger attraction between water molecules close to the surface

Front 71

What are the SI units of surface tension?

Back 71

N/m or dyne/cm

Front 72

Surface tension tends to cause?

Back 72

collapse of alveoli; it effectively causes an elastic contractile force in all of the alveoli

Front 73

Surface tension accounts for what % of total elastic forces in the lungs?

Back 73

66%, and thus contributes significantly to the pressure-volume work of the lung

Front 74

Pulmonary surfactant reduces?

Back 74

surface tension in the alveoli

Front 75

What cells produce surfactant?

Back 75

type II epithelial cells in the alveoli

Front 76

What is one component of surfactant?

Back 76

dipalmitoyl lecithin - amphipathic molecule (polar head group and FA tails)

Front 77

Reduced surface tension increases?

Back 77

lung compliance and reduces work of breathing

Front 78

Surfactant promotes?

Back 78

stability of the alveoli

Front 79

Is surfactant reduced more in small or large alveoli?

Back 79

smaller alveoli

Front 80

If surface tension isn't reduced in smaller alveoli, they would tend to empty into larger alveoli and collapse , why?

Back 80

Greater pressure builds in the smaller alveoli and air then moves into larger alveolus due to the pressure gradient and therefore the smaller alveoli then collapse

Front 81

Surfactant undergoes?

Back 81

rapid turnover

Front 82

Cessation of blood flow to a region of the lung (eg, embolus) may?

Back 82

deplete surfactant in that region and cause atelectasis

Front 83

When does production of surfactant begin in the fetus?

Back 83

approximately 28-32 weeks of gestation

Front 84

If babies are born without adequate amounts of surfactant may develop infant respiratory distress syndrome, this includes?

Back 84

1. stiff lungs (low compliance)
2. areas of atelectasis
3. fluid in alveoli

Front 85

What can an amniocentesis be used to measure?

Back 85

the L/S ratio (lecithin/spingomyelin ratio), which indicates the amount of mature surfactant present in the fetus

Front 86

Like the lung, the thoracic wall has its own?

Back 86

elastic and viscous properties

Front 87

When air is introduced into the pleural space, pleural pressure becomes?

Back 87

atmospheric, the lung collapses inward, and the thoracic wall springs outward

Front 88

Compliance of the lung-thorax combination is approximately? How much transpulmonary pressure is needed to expand the lung-thorax combination?

Back 88

1/2 that of the lung alone; thus, about twice as much transpulmonary pressure is necessary to expand the lung-thorax combination than is necessary to expand the lung alone