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physiology final > Mechanisms of Gas exchange > Flashcards

Mechanisms of Gas exchange Flashcards

1
Q

the most important muscle in inspiration is? What happens when it contracts

A

diaphragm

  • contraction:
    • pushes abdominal contents downward
    • increase intrathoracic volume
    • decrease in intrathoracic pressure
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2
Q

function of sternocleidomastoid and scalenes in inspiration

A
  • sternocleidomastoid: elevates sternum
  • scalenes: elevates upper ribs
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3
Q

air is driven out of the lungs by what between the lungs and atmosphere

A

reverse pressure gradient

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4
Q

what are the expiratory muscles. Which is most important

A
  • abdominal muscles: most important
  • internal intercostals: pull ribs inward and downward
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5
Q

What nerves are responsible for the diaphragm descending and the external intercostal muscles enlarging the thoracic cavity during inspiration

A
  • phrenic nerve
  • intercostal nerves
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6
Q

is expiration a passive or active process? Why?

A
  • passive
  • accomplished by elastic property of lungs (stretched lungs recoil) and relaxation of the inspiratory muscles
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7
Q

What are the pressures involved in ventilation

A
  • atmospheric
  • intra-alveolar
  • intra-pleural

**when intra-alveolar < atmospheric; flow of air into lungs

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8
Q

relationship between intra-alveolar pressure and intrapleural pressure throughout the cycle? This creates what type of pressure gradient?

A
  • intra-alveolar pressure > intrapleural pressure
  • transmural pressure gradient
    • lung is always stretched
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9
Q

transmural pressure

A

= alveolar pressure - intrapleural pressure

  • lung is always stretched to some degree, even during expiration
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10
Q

lung elastic recoil is due to

A
  • collagen and elastic fibers
  • **favors collapse
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11
Q

why are changes in thoracic dimensions accompanied by changes in lung dimensions?

A
  • antagonist action of lung elastic recoil and chest wall elastic forces generates negative intrapleural pressure
    • intrapleural pressure and fluid cohesiveness counteract the elastic forces
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12
Q

lung compliance

A

change in lung volume for a given pressure change

C= change in V/change in P

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13
Q

relationship between lung compliance and lung elasticity

A

lung compliance is inversely correlated with the lungs elastic properties

  • more elastic tissue = decreased compliance
  • **if lungs have high compliance, inflation is easier but elastic tissue is less
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14
Q

relate volume of lung with negative pressure outside the lung

A
  • lung is inflated with negative pressure outside
  • lung is deflated by decreasing negative pressure outside
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15
Q

Slope of lung volume vs negative pressure outside of lung gives

A

lung compliance

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16
Q

relate compliance between inspiration and expiration

A

compliance is different for inspiration and expiration

  • for a given pressure, expiratory volume > inspiratory volume
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17
Q

What is pneumothorax? what is the consequence?

A
  • object punctures intrapleural space
    • air is introduced
    • intrapleural P = atmospheric P
  • consequence
    • lungs collapse bc no negative intrapleural pressure to keep lungs open
    • chest wall springs out bc no negative IPP to prevent chest wall from springing out
18
Q

what happens to lung compliance in emphysema (obstructive disease)? consequence?

A
  • emphysema: less of elastic fibers in lungs
  • compliance increases
    • compliance increases with lower lung volumes
  • therefore, at a given volume the elastic recoil (collapsing) force on the lungs decreases
    • chest becomes barrel shaped
19
Q

what happens to lung compliance in fibrosis (restrictive disease)?

A
  • stiffning of lung tissues
  • compliance decreases
  • **lung compliance decreases with high lung volumes
20
Q

Law of Laplace

A
  • pressure generated by each sphere (alveolus)
  • P = 2T/r
    • P= collapsing pressure on alveolus
    • T: surface tension
    • r: radius
21
Q

role of surfactant in alveolus

A

surfactant reduces the collapsing pressure

  • disrupts intermolecular forces in the fluid lining the alveoli
22
Q

collapsed alveoli are called

A

atelectasis

23
Q

synthesis of surfactant begins at week what in a fetus?

A
  • week 24
  • always present by week 35
24
Q

equation relating flow of air to resistance

A
  • Q = change of pressure/R
    • Q= airflow rate
25
Q

what is the primary determinant of resistance

A

airway radius

R= 8nl/π(r^4)

26
Q

what is the major site of airway resistance

A

medium sized bronchi

27
Q

what ANS system is responsible for relaxation of bronchial smooth muscle

A
  • SNS adrenergic
  • via activation of B2 receptors
    • i.e. epinephrine/albuterol
28
Q

what ANS system is responsible for constriction of bronchial smooth muscle

A
  • PNS cholinergic
    • activation of muscarinic agonists
29
Q

presentation

  • airway resistance increased
  • thickening of walls from inflammation and histamine induced edema
  • plugging of airway by secretion of mucus
  • airway hyperresponsiveness, constricting spasms
A

asthma

30
Q

treatment of asthma

A
  • B adrenergic agonist -> relax SM
  • corticosteroids -> decrease inflammation
31
Q

lungs are protected by a1-antitrypsin. What happens in emphysema?

A
  • collapse of airways and destruction of alveolar walls
    • macrophages release trypsin
      • overrides the protective ability of a1-antitrypsin
32
Q

type A emphysema

A
  • pink puffers
    • mild hypoxemia
    • normal PCO2
33
Q

type B emphysema

A
  • Blue bloaters
    • hypoxemia
    • hypercapnia: Increased PCO2
34
Q

elastic forces of the chest wall favor

A

expansion

35
Q

Fick’s law

A

volume of gas transferred/unit time (Vx) = (D x A x change in P) / change in X

  • D: diffusion coeff
  • A: surface area
  • P: partial pressure difference of gas
  • X: membrane thickness
36
Q

the driving force for the diffusion of a gas comes from

A

partial pressure difference of gas

37
Q

diffusion coefficient of a gas (D) depends on

A
  • molecular weight
  • solubility
38
Q

diffusion for CO2 is what compared to diffusion of O2

A

D for CO2 is 20x higher than for O2

39
Q

how does lung diffusing capacity vary in emphysema? In fibrosis? In anemia? In exercise?

A
  • emphysema: DL decreases
    • destruction of alveoli -> decreased surface area
  • Fibrosis: DL decreases
    • diffusion distance increases
  • Anemia: DL decreases
    • decreased Hb in RBC
  • Exercise: DL increases
    • additional capillaries perfused-> increased surface area
40
Q

Henry’s law of dissolved gas

A

Cx = Px x solubility

41
Q

in solutions (blood), gas is carried in what three forms? give ex

A
  • dissolved
    • nitrogen: only in dissolved form
  • bound
    • O2, CO2 bind to proteins in blood
  • chemically modified
    • conversion of CO2 to HCO3-

physiology final (7 decks)

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