Chapter 18b
Gas Exchange and
Transport
Reflex Control of Ventilation
KEY
16
Stimuli
Sensory
receptors
Afferent
neurons
Integrating
centers
CO2
O2 and pH
Higher
brain
centers
Medullary
chemoreceptors
Carotid and aortic
chemoreceptors
15
1
2
14
13
3
Efferent
neurons
Effectors
Emotions
and voluntary
control
4
12
5
Limbic
system
Afferent sensory
neurons
6
7
8
11
Medulla oblongata
and pons
10
9
Inspiration
Somatic
motor neurons
(inspiration)
Somatic
motor neurons
(expiration)
Expiration
Scalene and
sternocleidomastoid
muscles
External
intercostals
Diaphragm
Internal
intercostals
Abdominal
muscles
Figure 18-16
Regulation of Ventilation
KEY
PRG = Pontine respiratory group
DRG = Dorsal respiratory group
VRG = Ventral respiratory group
NTS = Nucleus tractus solitarius
Higher
brain
centers
Pons
PRG
NTS
Medullary
chemoreceptors
Sensory input
from CN IX, X
(mechanical and
chemosensory)
DRG
Medulla
pre-Bötzinger
complex
VRG
Output to expiratory,
some inspiratory,
pharynx, larynx, and
tongue muscles
Output
primarily to
inspiratory
muscles
Figure 18-17
Regulation of Ventilation
• Respiratory neurons in the medulla
control inspiration and expiration
• Rhythmicity center Inspiration and Expiration
• VRG and DRG of medulla
• Rhythmic pattern of breathing arises
from a network of spontaneously
discharging neurons
Neurons in the pons modulate ventilation
• Ventilation is subject to modulation by
chemoreceptor-linked reflexes and by
higher brain centers
• Apneustic and Pneumotaxic
• Apenustic – inspiration
• Pneumotaxic – anatagonistic – inhibit
inspiration
Rhythmicity of breathing
Regulation of Ventilation
• Neural activity cycles during quiet breathing
Figure 18-18
Regulation of Ventilation
• Peripheral chemoreceptors
• Located in carotid and aortic arteries
• Specialized glomus cells
• Sense changes in PO2, pH, and PCO2 central
chemoreceptors
• Changes in CO2
Regulation of Ventilation
Blood vessel
Low PO2
• Carotid body oxygen
sensor releases
neurotransmitter
when PO2
decreases
1 Low PO
2
2 K+ channels close
Glomus cell
in carotid
body
3 Cell
depolarizes
5 Ca2+
entry
4 Voltage-gated Ca2+
channel opens
6 Exocytosis of
neurotransmitters
Receptor on
sensory neuron
Action potential
7 Signal to medullary
centers to increase
ventilation
Figure 18-19
Regulation of Ventilation
• Central
chemoreceptors
monitor CO2 in
cerebrospinal fluid
Cerebral capillary
Blood-brain
barrier
H+
PCO2
CO2 + H2O
H2CO3
CA
H+ + HCO3–
Cerebrospinal
fluid
Central chemoreceptor
Medulla
Respiratory
control
centers
Ventilation
Figure 18-20
Regulation of Ventilation
• Chemoreceptor response to changes in
plasma CO2
Plasma
PCO2
PCO2 in CSF
CO2
in
CSF
Arterial PCO2
H+ + HCO3–
CO2
Stimulates
central
chemoreceptor
H+ + HCO3–
in
plasma
Stimulates
peripheral
chemoreceptor
Plasma PO2
< 60 mm Hg
Ventilation
Plasma PO2
Negative feedback
Plasma PCO2
Figure 18-21
Control of Ventilation
PLAY
Interactive Physiology® Animation: Respiratory System:
Control of Respiration
Regulation of Ventilation
• Protective reflexes
• Irritant receptors
• Bronchoconstriction
• Sneezing
• Coughing
• Hering-Breuer inflation reflex
• Don’t over stretch and damage
Summary
• Diffusion and solubility of gases
• Gas exchange
• Gas transport
• Transport of oxygen and carbon dioxide
• Factors affecting oxygen-hemoglobin binding
• Carbonic anhydrase and chloride shift
Summary
• Regulation of ventilation
• Central pattern generator
• Dorsal versus ventral respiratory groups
• Peripheral versus central chemoreceptors