L18 Flashcards
The Bohr effect is characterised by a right shift in the lungs
BECAUSE
Hb has a high affinity for
oxygen at low PCO2.
In the lungs there is a left shift because O2 should be higher than CO2. therefore if the statement said left shift the first statement would be true
right = release left = loading
• Why do we need to maintain normal levels of O2 and CO2
for metabolic and biochemical stability (e.g pH)
O2 usage and CO2 production quite variable. Despite this, O2 and CO2 are normally kept within
close limits.
HOW???
By tight control of ventilation
what is the central control
the pons, medulla and other parts of the brain
what is the role of the central control
Sets pattern /rhythm of breathing
coordinates sensors and effectors to
maintain respiratory homeostasis
what are the sensors that send signals to the central control
chemoreceptors, lungs and other receptors
that is the role of the sensors
Receives a variety of neural and chemical inputs from central and
peripheral receptors
what are the effectors of the central control
respiratory muscles
what is the role of the effectors of the central control (respiratory muscles)
to adjust ventilation
what is the role of the respiratory rhythmic centers
Generate cycles of contraction and
relaxation in the diaphragm, establishing
pace of respiration
modify activity in response to chemical and pressure signals
what is the Pre-Botzinger complex
- Respiratory rhythm generator
what does Inspiratory center of the dorsal respiratory group (DRG) do
DRG sends signals to diaphragm and external intercostals for inspiration (just diaphragm at rest and external when you need more) they have no effect on expiratory muscles
which of DRG or VRG function at rest
DRG
when does Ventral respiratory group (VRG) function
when exercising
what is the role of VRG
it controls both expiratory and inspiratory neurons therefore when exercising it signals both to inspiratory and expiratory muscles
what is the role of Pre-Botzinger complex (PBC)
PBC is the base generatory of the respiratory system (like the SA node in the heart)
It generates the cyclic contraction and relaxation of the diaphragm and maintains/establishes the normal rate of respiration
what respiratory structures are located in the medulla
DRG, VRG, PBC
these are the respiratory rhythmicity centers
what is the role of the Apneustic and Pneumotaxic
Centers in the Pons
they Adjust the output of the respiratory
rhythmicity centers
what is the Pneumotaxic center also known as
pontine respiratory group (PRG)
what is the role of the Apneustic centres
they stimulate DRG
what is the role of the Pneumotaxic
Center
to inhibit the Apneustic centres
when and why would the Pneumotaxic Center want to inhibit the Apneustic centre
By doing this it stops the inspiratory signals and activates the active exhalation. This happens when you want to push lots of CO2 out of your system as it stops inhalation and cativates expiration
what are the higher centres of the respiratory control
- Cerebral cortex
- Limbic system
- Hypothalamus
what is the role of the higher centres of respiratory control
Higher Centers
Can alter the activity of
the pneumotaxic centers
The higher centres can override the respiratory system to take control
what do chemoreceptors respond to
Respond to a change in the chemical composition of blood or other fluid surrounding it
what chemicals are in respiratory system
CO2 + H2O ↔ H2CO3 ↔ H+ and HCO3-
and O2
where do the different chemicals act
CO2 and H+ acts mainly on respiratory centre
O2 acts mainly through peripheral chemoreceptor
what are the 2 types of chemoreceptors
- Central chemoreceptors
- Peripheral chemoreceptors
describe the central chemoreceptors
Specialized cells on the ventrolateral surface of the medulla.
Sensitive to the PCO2
but not PO2 of blood
- Insensitive to hypoxia
- Very sensitive to hypercapnia and hypocapnia (as CO2 is easily diffusible across blood brain barrier)
- Sensitive to pH of the surrounding extracellular fluid
- Insensitive to arterial acidity
central chemoreceptors cause what % of the increase in ventilation in response to hypercapnia
~70%
where are the peripheral chemoreceptors located
in the carotid and aortic bodies
describe peripheral chemoreceptors
• Quite close to but distinct from arterial baroreceptors
• Stimulated mainly by
decrease in PO2 and an increase in arterial H+ concentration. (note H+ could increase for a number of reasons not just from CO2)
which is the predominant peripheral chemoreceptor
• Carotid body input is the predominant peripheral chemoreceptor
what are the peripheral chemoreceptors stimulated by
- hypoxia (decreased O2)
- metabolic acidosis (increased H+)
- respiratory acidosis (increased CO2)
what is the central chemoreceptors stimulated by
H+
explain how central chemoreceptors are stimulated
CO2 diffused across the BBB (H+ is not very good at getting across)
in the CSF there is carbonic anhydrase which breaks down CO2 into H+ and bicarbonate
H+ acts on the central chemoreceptors
Which one of the following is NOT correct regarding the
respiratory control centre?
A. It is located in the medulla.
B. Dorsal respiratory group (DRG) consists of only inspiratory
neurons and produce only inspiratory stimulus
C.Pre-Botzinger complex is the respiratory rhythm generator.
D.Sectioning the brain stem at the level of low medulla leads to respiratory arrest.
E. Ventral respiratory group (VRG) neurons produce inspiratory
and expiratory stimulus at rest.
E
because it says at rest. if it said when exercising then it would be correct
Breathing Responses to…
- Hypoxia (decrease in O2)
- Hypercapnia (increase in CO2)
- Arterial acidity (increase in H+) concentration – not
due to changes in CO2
what could lead to a decrease in PO2
This decrease in O2 won’t usually happen at sea level (might happen if you go up in altitude) therefore a decrease in O2 usually is because of disease like emphysema
what happens when PO2 decreases
less O2 is going to diffuse across into the arteries which will be sensed by the peripheral chemoreceptors
Any change in PO2 is sensed by the peripheral chemoreceptors which will send signals to the main peripheral chemoreceptors sensor (carotid bodies) which sends signals to the central controller –> DRG which will increase contraction to bring in more O2
When it goes back to normal then the chemoreceptors will stop sending signals
when will we get an increase in ventilation (in terms of O2)
why
• Total oxygen transport by the blood is not reduced very much until the 𝑃𝑎𝑂2 falls below 60mmHg.
• Increased ventilation would not result
in more oxygen added to the blood
until that point is reached.
This has to do with the O2-disassociationion curve . This is because the top part of the curve gives us some flexibility as above 60, Hb is pretty much saturated anyway so there is no point in bringing more in
Below 60 has an immediate response to increase O2
at what pressure of O2 will we see an increase in ventilation
below 60mmHg
what happens when we live in at a higher altitude
short term
as you go up the pressure decreases therefore the O2 decreases
↓ inspired O2
↓ PAO2
↓PaO2
peripheral chemoreceptors fire, increase in respiratory muscle contraction, increase in ventilation
what happens when we live in at a higher altitude
long term
the peripheral chemoreceptors stimulate ventilation
EPO which is a hormone is secreted by the kidneys which stimulates erythrocyte synthesis resulting in increased Hb conc therefore increasing O2 carrying capacity
you also get an increase in skeletal muscle capillary density (from the hypoxia), more mitochondria, and myoglobin which all increase O2 transfer
plasma volume can also be decreased to make the blood more concentrated with Hb
explain the breathing response to hypercapnia
• Central and peripheral chemoreceptors detect this
• Reflex mechanisms controlling ventilation prevent even small
increase in arterial PCO2
Any change in CO2 is going to have an effect on out pH
Even a small change in Co2 causes a huge change in venterlation (which does not happen with O2 because of the reserve)
• Reflex mechanisms controlling ventilation prevent even small
increase in arterial PCO2
what diseases is this reflex commonly seen in
• This reflex is commonly seen
in emphysema – retention of
CO2 – respiratory acidosis
• Reduced CO2 – respiratory alkalosis – psychiatric disorders (eg excessive breath holding)
CO2 has an immediate effect on breathing as it acts on the central chemoreceptors. This is responsible for 70% of the increase in venterlation
what % is peripheral chemoreceptors responsible for
30%
what is Metabolic acidosis
– increased lactic acid
during exercise
what is Metabolic alkalosis
– loss of H+ by vomiting
is metabolic acidosis/alkalosis sensed by peripheral or central chemoreceptors
peripheral as H+ cant get across the BBB
describe the Control of ventilation during exercise
When we exercise we are consuming more O2 therefore we are producing more CO2
This is detected by our receptors which cause signals to out muscles to increase ventilation
CO2 is not the only reason why we increase ventilation during exercise
Exercise can increase alveolar ventilation by how much
• Exercise can increase alveolar ventilation 20-fold
what is the main stimulis for ventilation
- The major stimuli for the increased ventilation at moderate exercise is not only due to increased CO2 production
- Exercising muscles produce more CO2
what is exercises effect on PACO2
• As the alveolar ventilation also
increases in exact proportion to
the CO2 increase, there is no
change.
Aleveolar PCO2 =
CO2 production /
Alveolar ventilation
exercise increases venous PCO2 but not arterial PCO2
why is this
This is because…
a. the level of arterial PCO2 is determined by alveolar PCO2
b. Alveolar PCO2
is determined by the ratio of CO2 production to alveolar ventilation
