Ch. 22: Respiratory System 4 (no lecture)

1. CHAPTER 22:
RESPIRATORY SYSTEM
(4): CONTROL AND
ADJUSTMENTS
Human Anatomy and Physiology II –
BIOL153

2. Goals/Objectives
 Describe the neural controls of respiration
 Compare and contrast the following influences on
respiratory rate and depth:
 Arterial pH
 Arterial partial pressures of oxygen and carbon
dioxide
 Lung reflexes
 Compare and contrast the hyperpnea of exercise
with hyperventilation
 Describe the process and effects of

3. Control of Respiration
 Involves higher
brain centers,
chemoreceptor
s, and other
reflexes

4. Control of Respiration
Pons
Medulla
Pontine respiratory centers
interact with medullary respiratory centers to
smooth the respiratory pattern.
Ventral respiratory group (VRG)
contains rhythm generators whose output
drives respiration.
Pons
Dorsal respiratory group (DRG)
integrates peripheral sensory input and
modifies the rhythms generated by the VRG.
To inspiratory
muscles
External
intercostal
muscles
Diaphragm
Medulla
 Neural
controls
 Neurons in
reticular
formation
of medulla
and pons

5. Control of Respiration
Pons
Medulla
Ventral respiratory
group (VRG)
Pons
To inspiratory
muscles
External
intercostal
muscles
Diaphragm
Medulla
 Ventral respiratory
group (VRG)
 Rhythm-generating
and integrative center
 Sets eupnea (12–15
breaths/minute)
 Normal respiratory rate
and rhythm
 Its inspiratory neurons
excite inspiratory
muscles via phrenic
(diaphragm) and
intercostal nerves
(external intercostals)
 Expiratory neurons
inhibit inspiratory

6. Control of Respiration
Pons
Medulla
Pons
Dorsal respiratory
group (DRG)
To inspiratory
muscles
External
intercostal
muscles
Diaphragm
Medulla Dorsal respiratory
group (DRG)
 Near root of cranial
nerve IX
 Integrates input from
peripheral stretch and
chemoreceptors;
sends information 
VRG

7. Control of Respiration
Pons
Medulla
Pontine
respiratory
centers
Pons
To inspiratory
muscles
External
intercostal
muscles
Diaphragm
Medulla
 Influence and modify
activity of VRG
 Smooth out transition
between inspiration
and expiration and
vice versa
 Transmit impulses to
VRG  modify and
fine-tune breathing
rhythms during
vocalization, sleep,
exercise

8. Generation of the Respiratory
Rhythm
 Not well understood
 One hypothesis
 Pacemaker neurons with intrinsic rhythmicity
(even if pacemakers were blocked, breathing
continued)
 Most widely accepted hypothesis
 Reciprocal inhibition of two sets of interconnected
pacemaker neurons in medulla that generate
rhythm

11. Factors influencing Breathing Rate
and Depth
 Depth determined by how actively
respiratory center stimulates respiratory
muscles
 Rate determined by how long inspiratory
center active (ex. If only active a short
amount of time, rate is shorter)
 Both modified in response to changing
body demands
 Most important are changing levels of CO2,
O2, and H+

12. Chemical
Factors - Pco2
Arterial PCO2
PCO2 decreases pH
in brain extracellular
fluid (ECF)
Central chemoreceptors in
brain stem respond to H+
in brain ECF (mediate
70% of the CO2 response)
Peripheral chemoreceptors
in carotid and aortic bodies
(mediate 30% of the CO2
response)
Afferent impulses
Medullary
respiratory centers
Efferent impulses
Respiratory muscle
Ventilation
(more CO2 exhaled)
Arterial PCO2 and pH
return to normal
Initial stimulus
Physiological response
Result
 If blood Pco2 levels rise,
CO2 accumulates in brain
 CO2 in brain hydrated 
carbonic acid 
dissociates, releasing H+
 pH drops
 H+ stimulates central
chemoreceptors of brain
stem
 Chemoreceptors synapse
with respiratory regulatory
centers  increased
depth and rate of

13. Chemical Factors - Po2
 Peripheral chemoreceptors in aortic
and carotid bodies–arterial O2 level
sensors
When excited, cause respiratory centers
to increase ventilation
 Declining Po2 normally slight effect on
ventilation
Huge O2 reservoir bound to Hb
Requires substantial drop in arterial Po2

14. Chemical Factors - Arterial pH
 Can modify respiratory rate and rhythm even if
CO2 and O2 levels normal
 Mediated by peripheral chemoreceptors
 Decreased pH may reflect
 CO2 retention; accumulation of lactic acid; excess
ketone bodies
 Respiratory system controls attempt to raise
pH by increasing respiratory rate and depth

15. Clicker Question
The _________ is responsible for setting the
basic rhythm of breathing.
a) VRG
b) DRG
c) pontine respiratory group
d) pons

16. Clicker Questions
 When CO2 levels increase, ___________.
a) H+ stimulates central chemoreceptors of brain
stem
b) pH drops
c) Depth and rate of breathing increases
d) All of the above

17. Control of Respiration
 Involves higher
brain centers,
chemoreceptor
s, and other
reflexes

18. Influence of Higher Brain
Centers
 Hypothalamic controls act through limbic
(emotion) system to modify rate and depth of
respiration
 Example-breath holding that occurs in anger or gasping
with pain
 Rise in body temperature increases respiratory rate
(tissues are working harder; more waste products
produced and more oxygen needed)
 Cortical controls—direct signals from cerebral
motor cortex that bypass medullary controls
 Example-voluntary breath holding
 Brain stem reinstates breathing when blood CO2 critical

19. Pulmonary Irritant Reflexes
 Receptors in bronchioles respond to
irritants
 Communicate with respiratory centers via
vagal nerve afferents
 Promote reflexive constriction of air
passages
 Same irritant  cough in trachea or
bronchi; sneeze in nasal cavity

20. Inflation Reflex
 Hering-Breuer Reflex (inflation reflex)
 Stretch receptors in pleurae and airways
stimulated by lung inflation
 Inhibitory signals to medullary respiratory centers
end inhalation and allow expiration
 Acts as protective response more than normal
regulatory mechanism

21. Respiratory Adjustments:
Exercise
 Adjustments geared to
both intensity and
duration of exercise
 Hyperpnea
 Increased ventilation
(10 to 20 fold) in
response to metabolic
needs
 Pco2, Po2, and pH
remain surprisingly
constant during

22. Respiratory Adjustments:
Exercise
 Three neural factors cause increase
in ventilation as exercise begins:
Psychological stimuli
Simultaneous cortical motor activation of
skeletal muscles and respiratory centers
Excitatory impulses to respiratory
centers from proprioceptors in moving
muscles, tendons, joints

23. Respiratory Adjustments: High
Altitude
 Quick travel to altitudes above 2400
meters (8000 feet) may  symptoms of
acute mountain sickness (AMS)
 Atmospheric pressure and Po2 levels lower
 Headaches, shortness of breath, nausea, and
dizziness
 In severe cases, lethal cerebral and
pulmonary edema

24. Acclimatization to High Altitude
 Acclimatization—respiratory and
hematopoietic adjustments to long-term
move to high altitude
 Always lower-than-normal Hb saturation
levels
 Less O2 available

25. Clicker Question
_______ is produced by the _______ in
response to low blood oxygen levels.
a) Erythropoietin, kidneys
b) Growth hormone, pituitary gland
c) Hematopoietin, bone marrow
d) Hematopoietin, lungs

26. Acclimatization to High Altitude
 Acclimatization—respiratory and
hematopoietic adjustments to long-term
move to high altitude
 Always lower-than-normal Hb saturation
levels
 Less O2 available
 Decline in blood O2 stimulates kidneys to
accelerate production of EPO
 RBC numbers increase slowly to provide