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Respiratory: Physiology > Control of Respiration > Flashcards

Control of Respiration Flashcards

1
Q

What are the 2 types of control in respiration?

A

Neural and chemical

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2
Q

What is the rhythm of respiration?

A

Inspiration followed by expiration

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3
Q

What is the major neural rhythm generator?

A

The medulla

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4
Q

What neurones is the breathing rhythm generated by?

A

Pre-Botzinger complex

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5
Q

Where is the Pre-Botzinger complex located?

A

Upper end of the medullary respiratory centre

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6
Q

What is rhythm of inspiration generated by?

A

Pre-Botzinger complex

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7
Q

How is the rhythm of inspiration generated by the Pre-Botzinger complex?

A
  • Excites dorsal respiratory group neurones (inspiratory)
  • Fire in bursts
  • Firing leads to contraction of inspiratory muscles - inspiration
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8
Q

What happens when firing of dorsal respiratory group neurones stops?

A

Passive expiration

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9
Q

Where is the medulla located?

A

Between the pons and spinal cord

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10
Q

How is active expiration induced during hyperventilation?

A
  • Increased firing of dorsal neurones excites a second group - ventral respiratory group neurones
  • Excites internal intercostals, abdominals etc - resting in forceful (active) expiration
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11
Q

Are ventral respiratory group neurones stimulated in normal breathing?

A

No, in normal quiet breathing ventral neurones do not activate expiratory muscles

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12
Q

What can the rhythm generated in the medulla be modified by?

A

Neurones in the pons

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13
Q

How is inspiration inhibited by neurones in the pons?

A
  • Stimulation of the pneumotaxic centre (PC) by firing of dorsal respiratory neurones
  • Stimulation terminates inspiration
  • Inspiration inhibited
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14
Q

What would happen if there was no pneumotaxic centre?

A

Apneusis - breathing would be prolonged inspiratory gasps with brief expiration

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15
Q

What is apneusis?

A

Breathing is prolonged inspiratory gasps with brief expiration

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16
Q

What causes apneusis?

A

If pneumotaxic centre is non-functioning

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17
Q

What other centre involve din respiration (other than the PC) is present in the pons?

A

Apneustic centre

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18
Q

What 2 respiratory centres are present in the medulla?

A

Dorsal and ventral respiratory group neurones

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19
Q

What 2 respiratory centres are present in the pons?

A

Pneumotaxic and apneustic centre

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20
Q

What is the role of the apneustic centre?

A

Prolongs inspiration

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21
Q

How does the apneustic centre prolong inspiration?

A
  • Impulses from bpneustic centre excite inspiratory area of medulla
  • Prolong inspiration
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22
Q

Where is respiratory rhythm generated?

A

Medulla

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23
Q

Where can respiratory rhythm be modified?

A

In the pons

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24
Q

What stimuli are respiratory centres influenced by?

A
  • Higher brain centres e.g. cerebral cortex, limbic system, hypothalamus
  • Stretch receptors in the walls of bronchi and bronchioles - Hering-Breur reflex, guards against hyperinflation
  • Juxtapulmonary (J) receptors - stimulated by pulmonary capillary congestion, pulmonary oedema (caused by e.g. left heart failure), and pulmonary emboli
    Joint receptors – stimulated by joint movement
    Baroreceptors: increased ventilation rate in response to decreased blood pressure
  • Central chemoreceptors
  • Peripheral chemoreceptors (involved in chemical control of respiration)
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25
Q

How does stimulation of juxtapulmonary receptors by pulmonary emboli affect breathing?

A

Rapid shallow breathing

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26
Q

What are examples of involuntary modifications of breathing?

A
  • Pulmonary stretch receptors - Hering-Bruer Reflex
  • Joint Receptors Reflex in Exercise
  • Stimulation of Respiratory Centre by temperature,
    adrenaline, or impulses from cerebral cortex
  • Cough reflex
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27
Q

How do pulmonary stretch receptors modify breathing?

A
  • Activated during inspiration, afferent discharge inhibits inspiration (Hering-Breuer reflex)
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28
Q

Do pulmonary stretch receptors switch off inspiration during normal respiratory cycle?

A

No - only activated at large (> 1 litre) tidal volumes

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29
Q

When is Hering-Breuer reflex important?

A
  • In newborn babies

* May prevent over-inflation of the lungs during hard exercise

30
Q

How do joint receptors modify breathing?

A

Impulses from moving limbs reflexly increase breathing

31
Q

How do joint receptors contribute in exercise?

A

Contribute to ventilation during exercise

32
Q

What are factors that increase ventilation during exercise?

A
  • Reflexes originating from body movement (joint receptors)
  • Adrenaline release
  • Impulses from the cerebral complex
  • Increase in body temperature
  • Accumulation of CO2 and H+ generated by active muscles
33
Q

What is the ventilatory response to exercise?

A

Rapid increase in ventilation followed by gradual increase in ventilation

34
Q

What causes the initial rapid increase in ventilation during exercise?

A
  • Joint receptors

* Cerebral cortex

35
Q

What causes the gradual increase in ventilation during exercise?

A

Chemical changes

36
Q

What causes the recovery of normal ventilation after exercise?

A

Removal of neural/chemical stimuli

37
Q

What is the cough reflex?

A

Vital part of body defence mechanisms - helps clear airways of dust, dirt or excessive secretions

38
Q

When is cough reflex activated?

A

Activated by irritation of airways or tight airways (e.g. asthma)

39
Q

Describe the mechanisms of the cough reflex

A
  • Afferent discharge stimulates short intake of breath
  • Closure of the larynx
  • Contraction of abdominal muscles (increases intra-alveolar pressure)
  • Opening of the larynx and expulsion of air at a high speed
40
Q

Why is coughing a symptom of asthma?

A

Due to tight airways that stimulate cough reflex

41
Q

What is chemical control of respiration?

A

A negative feedback control system

42
Q

What are the controlled variables in chemical control of respiration?

A

Blood gas tensions - especially CO2

43
Q

What is the sensor for gas tensions?

A

Chemoreceptors

44
Q

Wha are the 2 types of chemoreceptors?

A
  • Peripheral

* Central

45
Q

What do peripheral chemoreceptors do?

A

Sense tension of oxygen, CO2 and H+ in the blood

46
Q

Where are central chemoreceptors located?

A

Near the surface of the medulla

47
Q

What do central chemoreceptors do?

A

Respond to the H+ concentration of the cerebrospinal fluid (CSF)

48
Q

What separates the CSF and blood?

A

Blood-brain barrier

49
Q

Describe the permeability of the blood-brain barrier

A
  • Relatively impermeable to H+ and HCO3

* CO2 diffuses readily

50
Q

How can central chemoreceptors respond to the H+ concentration in the CSF if the blood-brain barrier is impermeable to H*?

A
  • CO2 readily diffuses into CSF and reacts with water to form H2CO3
  • CSF is less buffered than blood, so results in increased H+ as H2CO3 dissociates
  • H+ can then be sensed by central chemoreceptors
    (They really respond to arterial PCO2 as arterial H+ cannot cross blood-brain barrier)
51
Q

Why is CSF less buffered than blood?

A

Less protein than blood

52
Q

Is the system more sensitive to O2 than CO2?

A

No - system is very sensitive to PCO2 (hypercapnia) than PO2 (hypoxia)

53
Q

Why is the system less sensitive to PO2 than PCO2?

A

Decrease in oxygen in blood - peripheral chemoreceptors are not stimulated until PO2 drops below 8.0 kPa

54
Q

What happens if PO2 continues to drop to critical levels?

A

Depresses neurones in CNS - depresses ventilation

55
Q

What receptors are involved in hypoxic drive of respiration?

A

Peripheral chemoreceptors

56
Q

When are peripheral chemoreceptors activated by hypoxia?

A

Stimulated only when arterial PO2 falls to low levels (<8.0 kPa)

57
Q

Is hypoxic drive of respiration important in normal respiration?

A

No, PO2 does not fall below 8.0 kPa in normal respiration

58
Q

When is hypoxic drive of respiration important?

A
  • In patients with chronic CO2 retention (e.g. patients with COPD)
  • Important at high altitudes
59
Q

What does partial pressure of inspired oxygen depend on?

A
  • Total pressure (e.g. atmospheric pressure)

* Proportion of oxygen in gas mixture (about 21% in atmosphere)

60
Q

What happens to atmospheric pressure as altitude increases?

A

It decreases, meaning PO2 in the body decreases

61
Q

What is hypoxia at high altitudes caused by?

A

Decreased partial pressure of inspired oxygen (PiO2)

62
Q

What is the acute response to hypoxia at high altitudes?

A
  • Hyperventilation

* Increased cardiac output

63
Q

What are symptoms of acute mountain sickness?

A
  • Headache
  • Fatigue
  • Nausea
  • Tachycardia
  • Dizziness
  • Sleep disturbance
  • Exhaustion
  • Shortness of breath
  • Unconsciousness
64
Q

What are chronic adaptations to high altitude hypoxia?

A
  • Increased RBC production (polycythaemia) - increases O2 carrying capacity of blood
  • Increased 2,3-Biphosphoglycerate produced in RBCs - O2 offloaded more easily into tissues
  • Increase in number of capillaries - blood diffuses more easily
  • Increase in number of mitochondria - O2 can be used more effectively
  • Kidneys conserve acid - decreases arterial pH
65
Q

What receptors play a role in the (non-carbonic acid) H+ drive of respiration?

A 
Peripheral chemoreceptors 
(H+ doesn't really cross blood-brain barrier but CO2 does)
66
Q

What does H+ drive of respiration by peripheral chemoreceptors play a major role in?

A

Adjusting for acidosis caused by addition of non-carbonic acid H+ to the blood

67
Q

What are causes of acidosis?

A
  • Lactic acid during exercise

* Diabetic ketoacidosis

68
Q

How do peripheral chemoreceptors counteract acidosis?

A

Stimulation by H+ causes hyperventilation and increases elimination of CO2 from the body (CO2 can generate H+ - its increased elimination helps reduce H+ in the body)

69
Q

What is H+ drive of respiration important in?

A

Acid-base balance

70
Q

What is the effect of arterial PCO2 (H+ in brain CSF) on peripheral and central chemoreceptors?

A
  • Peripheral chemoreceptors - weak stimulation

* Central chemoreceptors - strong stimulation (dominant control of ventilation)

71
Q

What is the effect of arterial PO2 on peripheral and central chemoreceptors?

A
  • Peripheral chemoreceptors - only become important if PO2 falls to <8 kPa
  • Central chemoreceptors - severe hypoxia depresses respiratory centre
72
Q

What is the effect of arterial H+ on peripheral and central chemoreceptors?

A
  • Peripheral chemoreceptors - stimulation (important in acid-base balance)
  • Central chemoreceptors - H+ cannot cross the blood-brain barrier

Respiratory: Physiology (6 decks)

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