Respiratory System
Dr Archna Ghildiyal
Associate Professor
Department of Physiology
KGMU
LECTURE:9
Contents
• Chemical control of Respiration
• Chemoreceptors-Central
-Peripheral
• Effect of PCO2 and pH on Ventilation
• Lung receptors
• Cough Reflex
Learning Objectives
• Chemical Control of Respiration
• Chemoreceptors:Functional organization
• Ventilatory Responses:
To changes in acid-base balance
To CO2 excess
To Oxygen lack
Chemical control of respiration
Chemoreceptors
• Central: Chemosensitive Area
-Beneath ventral surface of
medulla
-Located bilaterally
• Peripheral: Aortic & Carotid Body
Functional Organization of
Chemoreceptors
• A rise in PCO2, a fall in pH or PO2 of arterial
blood increases respiratory neuron activity in
the medulla.
• Stimulus: a change in blood chemistry
• Sensed by: receptors called chemoreceptors
• Response:  rate & depth of breathing
(minute ventilation)
Central chemoreceptors
(medullary chemoreceptors)
• Location: brain stem, ventral surface
of medulla, near I neurons
• Project to respiratory neurons
• Mainly sensitive to changes in
PaCO2
• A rise in PaCO2 effectively stimulates
central chemoreceptors
H+ is the Main Stimulus (in the
CNS)
• In chemosensitive areas of the respiratory
center, increased H+ is the main stimulus
• Blood-brain barrier is not very permeable to H+
• CO2 (lipid soluble) easily diffuses across the
BBB
• CO2 diffuses into the chemosensitive regions of
the CNS, H+ is formed and stimulates the dorsal
respiratory group of neurones
• Increase in respiratory rate
Contd…
• Central respiratory response to elevated
PCO2 does not continue beyond few days
• Due to Renal readjustment of H+ ion conc
in circulating blood
Effect of PCO2 and pH on Ventilation
Peripheral Chemoreceptors
• Located in carotid and aortic bodies
• 2 types of cells
Type I or glomus cells contain oxygen
sensitive K channels (Chemoreceptors)
• Sense arterial O2 levels (PO2)
• Most sensitive at PO2 30-60 mmHg
• Blood flow rate: 2000 ml/100 g tissue/min
Peripheral Chemoreceptors
Contd..
• Low PO2 levels stimulates the dorsal
respiratory group
• CO2 & H+ conc –Rapid stimulation(onset
of exercise)
• The signal is sent to the respiratory center
via the vagus or glossopharyngeal nerve
• Type II cells are supporting cells
Contd…
• Arterial Pco2 &  H+(Peripheral
chemoreceptor stimulation is 5 times as rapid
as central stimulation,eg: during onset of
exercise)
• Dopamine initiates action potentials in
sensory nerve
• arterial Po2 & high Pco2 is greater than the
sum of their individual effects
Carotid body receptor and its
response
Integrated effects Of PO2,PCO2 &
pH on alveolar ventilation
Lung receptors
•
Pulmonary stretch receptors (also
called slowly-adapting pulmonary
stretch receptors) Responsible for
the Hering-Breuer reflex
•
J receptors (juxta-capillary receptors)
•
Irritant receptors (also called rapidlyadapting pulmonary stretch receptors)
Irritant receptors
• Location: Trachea,major airways,mostly
in Larynx & Carina(point where trachea
divides into bronchi)
• Stimulus: Cold air,Mucus,Dust
• Via Vagus to CNS
• Response:
Bronchoconstriction,Hyperpnoea(deepr &
rapid breathing than normal),Cough
Cough reflex
•
•
•
•
•
•
Stimulus: noxious gas,foreign body
Receptors: irritant (airway,larynx,carina)
Mechanism:Sequence of eventsDeep inspiration
Closure of epiglottis & vocal chords
Contraction of expiratory muscles
including abdominal muscles
Contd…
• Steep rise in lung pressure( due to closed
outlet)
• Sudden opening of epiglottis & VC
• Explosive release of air from lungs
• Particle blown out
References
• Guyton & Hall.Text book of Medical
Physiology
• Ganong’s Review of Medical
Physiology
• Berne & Levy Physiology
• http://meded.ucsd.edu/ifp/jwest/resp_
phys/student_files.html
Question:1
Raised alveolar Pco2 though a respiratory
stimulant,can cause respiratory depression
when the level(in mm Hg) exeeds:
A) 10
B) 20
C) 40
D) 60
Question:2
Carotid bodies have:
A) Glomus cells
B) Innervated by vagus
C) Blood flow of 200ml/g/min
D) High A-V difference
Question:3
Type I or Glomus cells contain
chemoreceptor as:
A) O2 sensitiveNa channels
B) CO2 sensitive K channels
C) CO2 sensitive Na channels
D) O2 sensitive K channels
Question:4
The peripheral Chemoreceptors:
A) Have a nonlinear response to paO2
changes
B) Respond to increase in PaO2
C) Respond to a fall in PaCO2
D) Are in the carotid sinus
Question:5
Highest density of Irritant receptors is
present at
A)Trachea
B)Bronchioles
C)Alveoli
D)Larynx
Answers
1- D
2- A
3- D
4- A
5- D