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PHSL 232 > L18 > Flashcards

L18 Flashcards

1
Q

The Bohr effect is characterised by a right shift in the lungs

BECAUSE

Hb has a high affinity for
oxygen at low PCO2.

A

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
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2
Q

• Why do we need to maintain normal levels of O2 and CO2

A

for metabolic and biochemical stability (e.g pH)

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3
Q

O2 usage and CO2 production quite variable. Despite this, O2 and CO2 are normally kept within
close limits.

HOW???

A

By tight control of ventilation

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4
Q

what is the central control

A

the pons, medulla and other parts of the brain

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5
Q

what is the role of the central control

A

Sets pattern /rhythm of breathing
coordinates sensors and effectors to
maintain respiratory homeostasis

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6
Q

what are the sensors that send signals to the central control

A

chemoreceptors, lungs and other receptors

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7
Q

that is the role of the sensors

A

Receives a variety of neural and chemical inputs from central and
peripheral receptors

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8
Q

what are the effectors of the central control

A

respiratory muscles

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9
Q

what is the role of the effectors of the central control (respiratory muscles)

A

to adjust ventilation

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10
Q

what is the role of the respiratory rhythmic centers

A

Generate cycles of contraction and
relaxation in the diaphragm, establishing
pace of respiration

modify activity in response to chemical and pressure signals

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11
Q

what is the Pre-Botzinger complex

A
  • Respiratory rhythm generator
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12
Q 
what does Inspiratory
center of the dorsal
respiratory group (DRG) do
A

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

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13
Q

which of DRG or VRG function at rest

A

DRG

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14
Q

when does Ventral respiratory group (VRG) function

A

when exercising

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15
Q

what is the role of VRG

A

it controls both expiratory and inspiratory neurons therefore when exercising it signals both to inspiratory and expiratory muscles

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16
Q

what is the role of Pre-Botzinger complex (PBC)

A

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

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17
Q

what respiratory structures are located in the medulla

A

DRG, VRG, PBC

these are the respiratory rhythmicity centers

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18
Q

what is the role of the Apneustic and Pneumotaxic

Centers in the Pons

A

they Adjust the output of the respiratory

rhythmicity centers

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19
Q

what is the Pneumotaxic center also known as

A

pontine respiratory group (PRG)

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20
Q

what is the role of the Apneustic centres

A

they stimulate DRG

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21
Q

what is the role of the Pneumotaxic

Center

A

to inhibit the Apneustic centres

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22
Q

when and why would the Pneumotaxic Center want to inhibit the Apneustic centre

A

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

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23
Q

what are the higher centres of the respiratory control

A
  • Cerebral cortex
  • Limbic system
  • Hypothalamus
24
Q

what is the role of the higher centres of respiratory control

A

Higher Centers
Can alter the activity of
the pneumotaxic centers

The higher centres can override the respiratory system to take control

25
Q

what do chemoreceptors respond to

A

Respond to a change in the chemical composition of blood or other fluid surrounding it

26
Q

what chemicals are in respiratory system

A

CO2 + H2O ↔ H2CO3 ↔ H+ and HCO3-

and O2

27
Q

where do the different chemicals act

A

CO2 and H+ acts mainly on respiratory centre

O2 acts mainly through peripheral chemoreceptor

28
Q

what are the 2 types of chemoreceptors

A
  • Central chemoreceptors

- Peripheral chemoreceptors

29
Q

describe the central chemoreceptors

A

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
30
Q

central chemoreceptors cause what % of the increase in ventilation in response to hypercapnia

A

~70%

31
Q

where are the peripheral chemoreceptors located

A

in the carotid and aortic bodies

32
Q

describe peripheral chemoreceptors

A

• 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)

33
Q

which is the predominant peripheral chemoreceptor

A

• Carotid body input is the predominant peripheral chemoreceptor

34
Q

what are the peripheral chemoreceptors stimulated by

A
  1. hypoxia (decreased O2)
  2. metabolic acidosis (increased H+)
  3. respiratory acidosis (increased CO2)
35
Q

what is the central chemoreceptors stimulated by

A

H+

36
Q

explain how central chemoreceptors are stimulated

A

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

37
Q

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.

A

E

because it says at rest. if it said when exercising then it would be correct

38
Q

Breathing Responses to…

A
  • Hypoxia (decrease in O2)
  • Hypercapnia (increase in CO2)
  • Arterial acidity (increase in H+) concentration – not
    due to changes in CO2
39
Q

what could lead to a decrease in PO2

A

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

40
Q

what happens when PO2 decreases

A

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

41
Q

when will we get an increase in ventilation (in terms of O2)

why

A

• 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

42
Q

at what pressure of O2 will we see an increase in ventilation

A

below 60mmHg

43
Q

what happens when we live in at a higher altitude

short term

A

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

44
Q

what happens when we live in at a higher altitude

long term

A

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

45
Q

explain the breathing response to hypercapnia

A

• 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)

46
Q

• Reflex mechanisms controlling ventilation prevent even small
increase in arterial PCO2

what diseases is this reflex commonly seen in

A

• This reflex is commonly seen
in emphysema – retention of
CO2 – respiratory acidosis

• Reduced CO2 – respiratory alkalosis – psychiatric disorders (eg excessive breath holding)

47
Q

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

A

30%

48
Q

what is Metabolic acidosis

A

– increased lactic acid

during exercise

49
Q

what is Metabolic alkalosis

A

– loss of H+ by vomiting

50
Q

is metabolic acidosis/alkalosis sensed by peripheral or central chemoreceptors

A

peripheral as H+ cant get across the BBB

51
Q

describe the Control of ventilation during exercise

A

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

52
Q

Exercise can increase alveolar ventilation by how much

A

• Exercise can increase alveolar ventilation 20-fold

53
Q

what is the main stimulis for ventilation

A
  • The major stimuli for the increased ventilation at moderate exercise is not only due to increased CO2 production
  • Exercising muscles produce more CO2
54
Q

what is exercises effect on PACO2

A

• As the alveolar ventilation also
increases in exact proportion to
the CO2 increase, there is no
change.

Aleveolar PCO2 =
CO2 production /
Alveolar ventilation

55
Q

exercise increases venous PCO2 but not arterial PCO2

why is this

A

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

PHSL 232 (30 decks)

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