Factors that Control
respiratory rate
1
“Respiratory centre”
• Specialized neuron groups in the medulla
oblongata & pons
Medullary rhythmicity area – medulla
– Inspiratory area,
– expiratory area
Pneumotaxic area – pons
Aneustic area - pons
2
3
Inspiratory area
• can excite auto rhythmically
• sets basic rhythm of respiration
4
Control of Basic rhythm of respiration
(Inspiration 2 sec, expiration 3 sec )
Inspiratory area automatically become active
for 2 sec, send impulses to diaphragm &
ext. Intercostals (normal inspiration)
Inspiratory area become inactive for 3 sec,
the muscles relax (normal expiration)
5
Control of Normal breathing
6
Control of Deep Breathing
7
Coordination of transition between
inspiration & expiration
1. Pneumotaxic area
send Impulses to inspiratory area & turn
off the inspiratory area before the lungs
become too full of air (facilitate
expiration)
2. Apneustic area
Send impulses to inspiratory area &
activate it (Prolong inspiration,
inhibiting expiration)
8
• Apneustic area send impulses to
inspiratory area when pneumotaxic area is
inactive
• When pneumotaxic area is active, the
impulses sent from apneustic area are
overpowered by the pneumotaixic area
9
Regulation of respiratory centre
activities
• Neural – influence by the cerebral cortex
• Chemicals
– increase in P CO2, H +
– decrease in P O2
• Pressure receptors
10
Influence by the cerebral cortex
• Respiratory center has connections with
the cerebral cortex , so we can voluntarily
change our breathing patterns.
• Gives a protection – it helps us to prevent
entering of Water or irritating gases to the
lungs
11
• See how long you can hold your
breath?
12
• Ability to stop breathing limited by increase
in CO2 in blood
When P CO2 increase to certain level
Inspiratory area strongly stimulated
Stimulate inspiratory muscles
Breathing resumes
(it is impossible for people to kill themselves by
holding breath!!!)
13
• Chemoreceptors that are sensitive to
P CO2 (and H+ ) and P O2 are in
– Chemosensitive area of medulla oblongata
– Walls of carotid artery and aorta
14
Control of breathing by changes
in blood p CO2 & P O2 and pH
Increase in arterial blood P CO2
(Or decrease in pH or p O2)
Chemoreceptors stimulated
Nerve impulses (input)
Inspiratory area
15
Inspiratory area
Nerve impulses (output)
Respiratory muscles contract
more forcefully & more frequently
Decrease in blood p CO2,
increase in blood pH &
increase in p O2
to normal levels
16
Effects of Blood pressure on
respiratory rate
• Blood pressure detected through
pressure receptors
– Sudden increase in blood pressure decrease
the respiratory rate
– Sudden drop in blood pressure increase
respiratory rate
17
Respiratory efficiency is low in smokers,
Why?
1. Nicotine constrict terminal bronchioles,
air flow into & out of lung drops
2. CO in smoke binds to Hb, reduction of
O2 carrying capacity of blood
3. Irritants in smoke slow down the air flow
due to


increased fluid secretion by bronchioles,
Swelling of lining of bronchioles
18
4. Irritants in smoke inhibit movement of cilia
in lining of respiratory system , excess
fluid, foreign material not removed,
breathing difficulties
5. With time , smoking can destruct elastic
fibres in the lung, collapse of small
bronchioles, gas exchange become less
efficient
19
summary
• Respiratory center- inspiratory area, expiratory
are, pneumotaxic area, apneustic area
• Basic rhythm of respiration set by inspiratory
area of medullary rhythmicity area
• Pneumotaxic area, apneustic area coordinates
the transition between inspiration & expiration
• Respiratory rate may be modified by several
factors : influence of cerebral cortex, P CO2, H+,
P O2 etc….
20