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Principles of physiology > lecture 7- control of respiration part 2 > Flashcards

lecture 7- control of respiration part 2 Flashcards

1
Q

What are the 2 main mechanisms for controlling respiration in the body?

A

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

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2
Q

Why is the medulla important?

A
  • Inspiratory and expiratory muscles
    controlled by neurons in the medulla
  • Medulla coordinates quiet and forced
    breathing
  • Medulla controls frequency of ventilation
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3
Q

What happens at the pons?

A
  • Integration of sensory information occurs
    in the Pons to fine tune signals. Together
    these make the Respiratory centre
  • Pons controls volume & depth of
    ventilation
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4
Q

What does the medulla control?

A

Medulla controls frequency of ventilation

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5
Q

Compare the functions of the medulla and the pons

A

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

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6
Q

What are the DRG and VRG? What do they do?

A

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

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7
Q

What is the equation that shows how CO2 is dissolved in the bloodstream ?

A

co2+h2o–>h2co3–>H+ +HCO3-

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8
Q

When does blood pH fall? Why? How is the medulla alerted of this and what does it do as a response?

A

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

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9
Q

What is the difference between respiratory acidosis and alkalosis?

A

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)

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10
Q

Why is the CO2 triggering breathing and not the O2?

A

the sensors in the blood vessels detect the changes in H+ ions caused by the amount of carbon dioxide in tissues

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11
Q

What are the respiratory reflexes?

A

Changes to the basic rhythm of breathing
brought about by
CHEMORECEPTORS and BARORECEPTORS

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12
Q

What is the difference between chemo and baroreceptors?

A

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

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13
Q

What triggers changes in breathing?

A

hydrogen ion concentration tiggers changes in breathing

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14
Q

Where are the central chemoreceptors? What do they respond to?

A

CHEMORECEPTORS
* Respond to changes in Pco2, Po2 and [H+]
* located in CNS cerebellum, CNS
* Most effective in altering ventilation

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15
Q

What is the chemistry of ventilation?

A

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

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16
Q

When can the depth and rate of ventilation be reduced?

A

by the medulla and respiratory neurons

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17
Q

Medulla responds to hypercapnia- what does this mean and what does this result in?

A

hypercapnia is a buildup of carbon dioxide in the blood stream,

The medulla responds to the H+ ion concentration in the cerebral spinal fluid

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18
Q

What do stretch receptors do?

A

in the lungs and thorax and they stop us overinflating our lungs

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19
Q

Where are central chemoreceptors located? What do they monitor? What do they respond to? What does their stimulation lead to?

A
  • 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
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20
Q

What factors affect chemoreceptors?

A
  • 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
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21
Q

Where are peripheral chemoreceptors located? What do they do and respond to? Why does anaemia not trigger them?

A
  • 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)

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22
Q

When are chemoreceptors triggered? And what are the main controls?

A
  • 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.
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23
Q

Draw a flow diagram showing how peripheral chemoreceptors work

A
24
Q

What happens to your blood at high altitudes when the alveolar pH can fall below 40 mm Hg?

A

At VERY high altitude the alveolar Po2
can fall below 40 mm Hg
→ Increased ventilation
→ large difference in O2
loading into
the blood

25
Q

What are some stimulators of peripheral chemoreceptors?

A
  • 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)

26
Q

What are baroreceptors? Where are they situated and what are they triggered by?

A
  • 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

27
Q

What do baroreceptors do when triggered?

A

thye affect ventilation rate

28
Q

Can the medulla inhibit respiration from impulses from baroreceptors?

A

yes

29
Q

What are the lungs functionally?

A

Functionally - elastic bags resembling balloons.
Lack muscle which would allow them to expand or
contract themselves.

30
Q

At rest how many breaths do we take per minute? And how many mLs of air is in each breath?

A
  • At rest 12 and 15 breaths per minute –500 mLs air at each
    breath ~ 6 L per minute
31
Q

Do children breath faster?

A

yes

32
Q

What is anatomical dead space?

A

we dont necessarily expel every molecule of air in our lungs

33
Q

What is the difference between hypercapnia and hypocapnia?

A

hypercapnia- decreased alveolar ventilation and high pCO2

hypocapnia- increased alveolar ventilation and low pCO2

34
Q

What is the total lung capacity?

A

6 litres

35
Q

What is spirometry?

A

Ventilation of alveoli depends on tidal volume, airway resistance and compliance

36
Q

What does ventilation of alveoli depend on?

A
  • 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

37
Q

What is tidal volume?

A

vital capacity - inspiration reserve volume+expiratory reserve volume

38
Q

What is functional residual capacity?

A

the volume remaining in the lungs after a normal, passive exhalation

39
Q

What is residual volume?

A

the volume of air remaining in the lungs after maximum forceful expiration

40
Q

predict the effect of increased Po2

A
  1. drop in po2
  2. increase in chemoreceptor activity
  3. respiratory centres increase neural activity
  4. respiratory muscles increase contractions
  5. increase in ventilation to combat increase in Po2
41
Q

What are our reserved volumes?

A

Inspiratory reserve volume is the maximum amount of additional air that can be taken into the lungs after a normal breath

42
Q

What is our vital capacity?

A

the maximum amount of air you can forcibly exhale from your lungs after fully inhaling

43
Q

What does compliance of the lungs mean?

A

Lung compliance, or pulmonary compliance, is a measure of the lung’s ability to stretch and expand
- a measure of ease of lung expansion

44
Q

What does airway resistance refer to?

A
  • 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
45
Q

What does the neural control of breathing refer to?

A
  • 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
46
Q

How are upper and lower motor neurons related?

A

upper motor neurons drive the lower motor neurons

47
Q

What happens to the lungs during inhalation?

A

the diaphragm flattens
- external intercostal muscles contract
- volume of thoracic cavity increases
- lungs expand
- air flows down the pressure gradient and into the lungs

48
Q

What is the difference in the behaviour or upper and lower motor neurons during normal and high levels of ventilation?

A

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

49
Q

describe normal quiet inhilation

A
  1. DRG is active
  2. diaphragm contracts and external intercostal muscles contract during their most active phase
  3. normal quiet inhilation
50
Q

describe normal quiet exhalation

A
  1. DRG is inactove
  2. diaphgram relaxes and external intercostal muscles become less active and relax, followed by elastic recoil of the lungs
  3. normal quet exhalation
51
Q

describe forceful inhilation

A
  1. DRG activates VRG
    2.down the DRG pathway- 2. diaphragm contracts and external intercostal muscles contract during their most active phase
  2. down the VRG pathway- accessory muscles of inhilation contract
  3. forceful inhalation ensues
52
Q

describe forceful exhalation

A
  1. VRG group activates
    2.accessory muscles of exhalation contract
  2. forceful exhalation
53
Q

what do stretch receptors do? where are they found?

A

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

54
Q

describe airway pharmocology

A

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

55
Q

what do emotions and higher voluntary control?

A

DRG and diaphragm and external intercostals

56
Q

what do central and peripheral chemoreceptors control?

A

VRG (INSPIRATION)
AND inspiratory accessory muscles

57
Q

what do mechanoreceptors and baroreceptors control?

A

VRG expiration and expiratory accessory muscles

Principles of physiology (21 decks)

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