lecture 7- control of respiration part 2 Flashcards
What are the 2 main mechanisms for controlling respiration in the body?
CENTRAL PATTERN (AUTOMATIC)
* Inspiratory and expiratory muscles
controlled by neurons in the medulla
& fine tuned by Pons
VOLUNTARY
* Cerebral cortex (origin)
* Additionally influences respiratory
centre
Why is the medulla important?
- Inspiratory and expiratory muscles
controlled by neurons in the medulla - Medulla coordinates quiet and forced
breathing - Medulla controls frequency of ventilation
What happens at the pons?
- Integration of sensory information occurs
in the Pons to fine tune signals. Together
these make the Respiratory centre - Pons controls volume & depth of
ventilation
What does the medulla control?
Medulla controls frequency of ventilation
Compare the functions of the medulla and the pons
at the pons:
* Integration of sensory information occurs
in the Pons to fine tune signals. Together
these make the Respiratory centre
* Pons controls volume & depth of
ventilation
at the medulla:
* Inspiratory and expiratory muscles
controlled by neurons in the medulla
* Medulla coordinates quiet and forced
breathing
* Medulla controls frequency of ventilation
What are the DRG and VRG? What do they do?
Two control centres:
DORSAL RESPIRATORY GROUP (DRG)
* Controls the diaphragm and external
intercostal muscles
* Involved in inspiration and expiration in
quiet breathing
VENTRAL RESPIRATORY GROUP (VRG)
* Controls accessory inspiratory and
expiratory muscles
* Involved in inspiration and
expiration during forced breathing
What is the equation that shows how CO2 is dissolved in the bloodstream ?
co2+h2o–>h2co3–>H+ +HCO3-
When does blood pH fall? Why? How is the medulla alerted of this and what does it do as a response?
blood pH falls when there is rising levels of co2 in tissues, as co2 which dissolves and releases H+ions
-sensors in major blood vessels detect the fall and alert the medulla
- the medulla then sends signals to the rib muscles and diaghrams to increase rate and depth of ventilation
- this results in blod c02 levels falling and pH rising
What is the difference between respiratory acidosis and alkalosis?
acidosis is when we have lots of H+ ions
alkalosis is when there is very few hydrogen ions so the pH increases (low co2 and low H+ions)
Why is the CO2 triggering breathing and not the O2?
the sensors in the blood vessels detect the changes in H+ ions caused by the amount of carbon dioxide in tissues
What are the respiratory reflexes?
Changes to the basic rhythm of breathing
brought about by
CHEMORECEPTORS and BARORECEPTORS
What is the difference between chemo and baroreceptors?
CHEMORECEPTORS
* Respond to changes in Pco, Po2 and [H+]
* Central and peripheral locations
* Most effective in altering ventilation
BARORECEPTORS
* Detect changes in blood pressure
* Located in carotid body and aortic arch
What triggers changes in breathing?
hydrogen ion concentration tiggers changes in breathing
Where are the central chemoreceptors? What do they respond to?
CHEMORECEPTORS
* Respond to changes in Pco2, Po2 and [H+]
* located in CNS cerebellum, CNS
* Most effective in altering ventilation
What is the chemistry of ventilation?
co2+h2o–>h2co3–>H+ +HCO3-
central chemoreceptors detect H+ ion concentration, they send signals to the medula respiratory neurons which in turn adjust the ventilation rate and depth
When can the depth and rate of ventilation be reduced?
by the medulla and respiratory neurons
Medulla responds to hypercapnia- what does this mean and what does this result in?
hypercapnia is a buildup of carbon dioxide in the blood stream,
The medulla responds to the H+ ion concentration in the cerebral spinal fluid
What do stretch receptors do?
in the lungs and thorax and they stop us overinflating our lungs
Where are central chemoreceptors located? What do they monitor? What do they respond to? What does their stimulation lead to?
- Located on the ventro-lateral surface of the
medulla oblongata - Monitor composition of the cerebrospinal fluid
(CSF) - Respond only to a rise in [H+] and Pco2
- their Stimulation increases depth and rate of respiration
via stimulation of the DRG
What factors affect chemoreceptors?
- Chronic CO2 retention reduces sensitivity of the
respiratory centre - H+ also increased by non-respiratory causes such
as diabetic ketoacidosis - Other factors affecting chemoreceptors - Sleep,
age, narcotics, alcohol, anaesthetics, drugs e.g.
aspirin
Where are peripheral chemoreceptors located? What do they do and respond to? Why does anaemia not trigger them?
- Located in carotid body & aortic arch – where there is a
high blood flow - Respond to low arterial Po2 = HYPOXIA
- Decreased PO2 = increased firing = increased ventilation
Anaemia (low O2
carrying capacity) does not
trigger firing as dissolved PO2
is the same
(Hb content/capacity differs)
When are chemoreceptors triggered? And what are the main controls?
- Chemoreceptors switch on, full power (i.e. above the THRESHOLD) only when Po2 gets
below 60 mm Hg in OXYGENATED blood. - Decreased Po2 not as powerful a stimulator
of respiration as increased Pco2. - Main control is by central chemoreceptors
in response to altered pH.
Draw a flow diagram showing how peripheral chemoreceptors work
What happens to your blood at high altitudes when the alveolar pH can fall below 40 mm Hg?
At VERY high altitude the alveolar Po2
can fall below 40 mm Hg
→ Increased ventilation
→ large difference in O2
loading into
the blood
What are some stimulators of peripheral chemoreceptors?
- Vascular stasis (decreased blood flow to the carotid)
- Cyanide – prevents O2 utilization at tissue level
- Nicotine – in sufficient amounts
- Exercise – due to increased [K+]
NOTE: Anaemia (low O2 carrying capacity) does not trigger firing as dissolved PO2
is the same (Hb content/capacity differs)
What are baroreceptors? Where are they situated and what are they triggered by?
- Afferent fibres in the carotid sinuses, aortic arch, atria
and ventricles stimulated by blood pressure - Impulses inhibit respiration via respiratory centre in the
medulla
when BP decreases they increase ventilation
when BP increases they decrease ventilation
Overall influence = VERY MINOR
What do baroreceptors do when triggered?
thye affect ventilation rate
Can the medulla inhibit respiration from impulses from baroreceptors?
yes
What are the lungs functionally?
Functionally - elastic bags resembling balloons.
Lack muscle which would allow them to expand or
contract themselves.
At rest how many breaths do we take per minute? And how many mLs of air is in each breath?
- At rest 12 and 15 breaths per minute –500 mLs air at each
breath ~ 6 L per minute
Do children breath faster?
yes
What is anatomical dead space?
we dont necessarily expel every molecule of air in our lungs
What is the difference between hypercapnia and hypocapnia?
hypercapnia- decreased alveolar ventilation and high pCO2
hypocapnia- increased alveolar ventilation and low pCO2
What is the total lung capacity?
6 litres
What is spirometry?
Ventilation of alveoli depends on tidal volume, airway resistance and compliance
What does ventilation of alveoli depend on?
- Compliance – a measure of ease of lung expansion
- Distensibility of lungs
- Retractive forces of lung balanced by semi-rigid structure
of the thoracic cage.
Airway resistance
* Distribution of air in the lungs uneven
* Airway resistance to airflow in normal individual occurs in
larger airways
* In disease airway resistance occurs in peripheral airways
What is tidal volume?
vital capacity - inspiration reserve volume+expiratory reserve volume
What is functional residual capacity?
the volume remaining in the lungs after a normal, passive exhalation
What is residual volume?
the volume of air remaining in the lungs after maximum forceful expiration
predict the effect of increased Po2
- drop in po2
- increase in chemoreceptor activity
- respiratory centres increase neural activity
- respiratory muscles increase contractions
- increase in ventilation to combat increase in Po2
What are our reserved volumes?
Inspiratory reserve volume is the maximum amount of additional air that can be taken into the lungs after a normal breath
What is our vital capacity?
the maximum amount of air you can forcibly exhale from your lungs after fully inhaling
What does compliance of the lungs mean?
Lung compliance, or pulmonary compliance, is a measure of the lung’s ability to stretch and expand
- a measure of ease of lung expansion
What does airway resistance refer to?
- Distribution of air in lungs uneven
- Airway resistance to airflow in normal individual occurs in
larger airways - In disease airway resistance occurs in peripheral airways
What does the neural control of breathing refer to?
- Distribution and
organisation of the
respiratory centre -
highly complex - Upper motor
neurones (UMNs)
“drive” lower motor
neurones (LMNs) - Impulses mediating
conscious change
travel via
corticospinal tract
How are upper and lower motor neurons related?
upper motor neurons drive the lower motor neurons
What happens to the lungs during inhalation?
the diaphragm flattens
- external intercostal muscles contract
- volume of thoracic cavity increases
- lungs expand
- air flows down the pressure gradient and into the lungs
What is the difference in the behaviour or upper and lower motor neurons during normal and high levels of ventilation?
Normal/quiet breathing:
Inspiratory UMNs fire, few
inspiratory LMNs
Expiratory UMNs active but do
not make LMNs fire
High levels of ventilation:
UMN activity increases
LMNs start to fire
Inspiratory intercostal
muscles then abdominal
muscles
describe normal quiet inhilation
- DRG is active
- diaphragm contracts and external intercostal muscles contract during their most active phase
- normal quiet inhilation
describe normal quiet exhalation
- DRG is inactove
- diaphgram relaxes and external intercostal muscles become less active and relax, followed by elastic recoil of the lungs
- normal quet exhalation
describe forceful inhilation
- DRG activates VRG
2.down the DRG pathway- 2. diaphragm contracts and external intercostal muscles contract during their most active phase - down the VRG pathway- accessory muscles of inhilation contract
- forceful inhalation ensues
describe forceful exhalation
- VRG group activates
2.accessory muscles of exhalation contract - forceful exhalation
what do stretch receptors do? where are they found?
Found in the muscular portion of the walls of the bronchi and bronchioles - prevent
over-inflation.
Reflect volume of the lungs (in visceral pleura & large airways send signal to
inspiratory neurones).
* prevent against excessive stretching
* Respond to expansion of the lungs - Inflation inhibits neurones in respiratory
centre via vagus nerve
* Involved in forced breathing ONLY
describe airway pharmocology
Airways contain afferent (sensory) and efferent (motor)
nerves
Cholinergic innervation
◦ Vagus nerve Ach
ASM constriction & Mucus secretion
Noradrenergic innervation
◦ Beta-2 adrenoceptors in ASM – tone regulation
what do emotions and higher voluntary control?
DRG and diaphragm and external intercostals
what do central and peripheral chemoreceptors control?
VRG (INSPIRATION)
AND inspiratory accessory muscles
what do mechanoreceptors and baroreceptors control?
VRG expiration and expiratory accessory muscles
