Respiratory Physiology
481
IV. Ventilation is refl exly stimulated, via the peripheral
chemoreceptors, by a decrease in arterial
P
O
2
, but only when
the decrease is large.
V. Ventilation is refl exly stimulated, via both the peripheral
and central chemoreceptors, when the arterial
P
CO
2
goes
up even a slight amount. The stimulus for this refl ex is not
the increased
P
CO
2
itself, but the concomitant increased
hydrogen ion concentration in arterial blood and brain
extracellular fl
uid.
VI. Ventilation is also stimulated, mainly via the peripheral
chemoreceptors, by an increase in arterial hydrogen ion
concentration resulting from causes other than an increase
in
P
CO
2
. The result of this refl ex is to restore hydrogen ion
concentration toward normal by lowering
P
CO
2
.
VII. Ventilation is refl
exly inhibited by an increase in arterial
P
O
2
and by a decrease in arterial
P
CO
2
or hydrogen ion
concentration.
VIII. During moderate exercise, ventilation increases in exact
proportion to metabolism, but the signals causing this are
not known. During very strenuous exercise, ventilation
increases more than metabolism.
a. The proportional increases in ventilation and metabolism
during moderate exercise cause the arterial
P
O
2
,
P
CO
2
,
and hydrogen ion concentration to remain unchanged.
b. Arterial hydrogen ion concentration increases during
very strenuous exercise because of increased lactic acid
production. This accounts for some of the hyperventilation
that occurs.
IX. Ventilation is also controlled by refl
exes originating in
airway receptors and by conscious intent.
Hypoxia
I. The causes of hypoxic hypoxia are listed in Table 13–11.
II. During exposure to hypoxia, as at high altitude, oxygen
supply to the tissues is maintained by the fi ve responses
listed in Table 13–12.
Nonrespiratory Functions of the Lungs
I. The lungs infl uence arterial blood concentrations of
biologically active substances by removing some from systemic
venous blood and adding others to systemic arterial blood.
II. The lungs also act as sieves that trap and dissolve small clots
formed in the systemic tissues.
Additional Clinical Examples
I. Acute respiratory distress syndrome is caused by a leakage of
protein and fl uid into the lung, which causes a decrease in
oxygen diffusion.
II. Sleep apnea is a periodic cessation of breathing during sleep
and is caused by decreased neural drive to breathe (central
sleep apnea) or inspiratory occlusion of the upper airway
(obstructive sleep apnea).
KEY TERMS
airway
443
alveolar dead space
457
alveolar pressure (
P
alv
)
446
alveolar ventilation (V
˙
A
)
456
alveolus
443
anatomic dead space (V
D
)
456
aortic body
470
apneustic center
470
atmospheric pressure (
P
atm
)
446
Boyle’s law
447
bronchus
443
bronchiole
444
carbamino hemoglobin
467
carbonic anhydrase
467
carotid body
470
central chemoreceptor
471
conducting zone
444
Dalton’s law
457
deoxyhemoglobin (Hb)
463
diaphragm
445
2,3-diphosphoglycerate
(DPG)
466
dorsal respiratory group
(DRG)
469
elastic recoil
448
expiration
443
expiratory reserve volume
(ERV)
455
fetal hemoglobin
469
functional residual capacity
(FRC)
454
globin
463
heme
463
hemoglobin
463
Henry’s law
458
Hering-Breuer refl ex
470
inspiration
443
inspiratory reserve volume
(IRV)
454
intercostal muscle
445
intrapleural fl
uid
446
intrapleural pressure
(
P
ip
)
446
J receptor
476
larynx
443
lateral traction
454
Law of Laplace
453
lung compliance (C
L
)
452
mediastinum
449
medullary respiratory
center
469
minute ventilation (V
˙
E
)
456
nitric oxide
468
oxygen-carrying capacity
463
oxygen-hemoglobin dissociation
curve
463
oxyhemoglobin (HbO
2
)
463
parietal pleura
446
partial pressure
458
percent hemoglobin
saturation
463
peripheral chemoreceptor
470
pharynx
443
phrenic nerves
450
physiologic dead space
457
pleura
445
pleural sac
445
pneumotaxic center
470
pontine respiratory group
470
Pre-Bötzinger complex
469
pulmonary
442
pulmonary stretch
receptor
470
residual volume (RV)
455
respiratory bronchiole
444
respiratory cycle
443
respiratory physiology (two
defi nitions)
442
respiratory quotient (RQ)
457
respiratory rhythm
generator
469
respiratory system
443
respiratory zone
444
surface tension
452
surfactant
452
thorax
444
tidal volume (V
t
)
454
total blood carbon dioxide
468
trachea
443
transmural pressure
448
transpulmonary pressure
(
P
tp
)
448
type I alveolar cell
444
type II alveolar cell
444
upper airways
443
ventilation
446
ventral respiratory group
(VRG)
469
visceral pleura
445
vital capacity (VC)
455
vocal cord
443
acute respiratory distress
syndrome (ARDS)
478
anemia
463
anemic hypoxia
476
anti-infl
ammatory drug
454
asthma
454
bronchodilator drug
454
carbon monoxide
465
carbon monoxide hypoxia
476
central sleep apnea
478
chronic bronchitis
478
chronic obstructive pulmonary
disease
454
continuous positive airway
pressure (CPAP)
478
cystic fi brosis
444
daytime somnolence
478
diffuse interstitial fi brosis
461
diffusion impairment
476
dyspnea
476
emphysema
477
forced expiratory volume in 1 s
(FEV
1
)
455
histotoxic hypoxia
476
hypercapnea
476
hyperventilation
460
hypoventilation
460
hypoxemia
476
hypoxia
476
hypoxic hypoxia
476
ischemic hypoxia
476
metabolic acidosis
473
metabolic alkalosis
473
CLINICAL TERMS
previous page 509 Vander's Human Physiology The Mechanisms of Body Function read online next page 511 Vander's Human Physiology The Mechanisms of Body Function read online Home Toggle text on/off