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Control Of Respiration Flashcards

(69 cards)

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1
Q

Carbonic acid equilibrium

A

CO2 + H2O <—> H2CO3 <—> H+ + (HCO3)-

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2
Q

Carbonic acid equilibrium enzyme

A

Carbonic anhydrase

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3
Q

Requirement of respiration

A
  • Ensure haemoglobin is as close to full saturation with oxygen as possible
  • Efficient use of energy resource
    -Regulate PaCO2 carefully
    variations in CO2 and small variations in pH can alter physiological function quite widely
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4
Q

Breathing is autonomic

A

No conscious effort for the basic rhythm
Rate and depth under additional influences
Depends on cyclical excitation and control of many muscles
-Upper airway, lower airway, diaphragm, chest wall
-Near linear activity
-Increase thoracic volume

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5
Q

Input signals to respiratory control centres

A

Central chemoreceptor a
Voluntary control (cerebrum)
Lung receptors; stretch, J receptors, irritant
Peripheral chemoreceptors: carotid, aortic
Muscle proprioceptors

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6
Q

Respiratory control centres- basic breathing rhythm

A

Medulla and pons

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7
Q

3 types of Lung receptors

A

Stretch
J receptors
Irritant

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8
Q

Pons

A

Pneumotaxic and apneustic centres

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9
Q

Medulla oblongata

A

Phasic discharge of action potentials
2 main groups:
1. Dorsal respiratory group (DRG)
2. Ventral respiratory group (VRG)

Each are bilateral, and project into the bulbo-spinal motor neuron pools and interconnect

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10
Q

When is DRG active

A

predominantly active during inspiration

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11
Q

When is VRG active

A

active in both inspiration and expiration

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12
Q

Central pattern generator

A

Neural network (interneurons)
Located within DRG/VRG
-Precise functional locations not known
-Start, stop and resetting of an integrator of background ventilatory drive

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13
Q

What does desire to take a breath come from

A

PaCO2

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14
Q

Inspiration

A

Progressive increase in inspiratory muscle activation
-Lungs fill at a constant rate until tidal volume achieved
-End of inspiration, rapid decrease in excitation of the respiratory muscles

DRG and VRG prevent over inflation of the lungs

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15
Q

Expiration

A

Largely passive due to elastic recoil of thoracic wall
-First part of expiration; active slowing with some inspiratory muscle activity
-With increased demands, further muscle activity recruited
-Expiration can be become active also; with additional abdominal wall muscle activity

DRG and VRG prevent over deflation of the lungs

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16
Q

What % influence from PaCO2 on central chemoreceptors

A

60%

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17
Q

What % influence from PaCO2 on peripheral chemoreceptors

A

40%

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18
Q

Chemoreceptors

A

Stimulated by [H+] concentration and gas partial pressures in arterial blood
Brainstem [primary influence is PaCO2]

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19
Q

Peripheral chemoreceptors

A

Carotids and aorta [PaCO2, PaO2 and pH]
-Significant interaction

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20
Q

Central chemoreceptors

A

Located in brainstem
Pontomedullary junction
Not within the DRG/VRG complex

Sensitive to PaCO2 of blood perfusing brain (also influenced by PaO2)
Blood brain barrier relatively impermeable to H+ and HCO3-
PaCO2 preferentially diffuses into CSF

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21
Q

Carotid bodies

A

Bifurcation of the common carotid
Glossopharyngeal (IX) cranial nerve afferents

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22
Q

Aortic bodies

A

Ascending aorta
Vagal (X) nerve afferents

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23
Q

Peripheral chemoreceptors

A

Responsible for [all] ventilatory response to hypoxia (reduced PaO2)

Generally not sensitive across normal PaO2 ranges

When exposed to hypoxia, type I cells release stored neurotransmitters that stimulate the cuplike endings of the carotid sinus nerve

Linear response to PaCO2

Interactions between responses

[Poison (e.g. cyanide) and blood pressure responsive]

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24
Q

What are central chemoreceptors sensitive to

A

PaCO2

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25
What are peripheral chemoreceptors sensitive to
PaO2, PaCO2 and pH
26
What mediates the response to CO2 by central chemoreceptors
H+ produced during the carbonic acid equilibrium bind to receptors and increase ventilation
27
Lung receptors
Stretch, J and irritant Afferents; vagus (X) Combination of slow and fast adapting receptors Assist with lung volumes and responses to noxious inhaled agents
28
Stretch lung receptors
Smooth muscle of conducting airways Sense lung volume, slowly adapting
29
Irritant lung receptors
Larger conducting airways Rapidly adapting [cough, gasp]
30
J (juxtapulmonary capillary) lung receptors
Pulmonary and bronchial C fibres
31
Nose, nasopharynx and larynx airway receptors
Chemo and mechano receptors Some appear to sense and monitor flow Stimulation of these receptors appears to inhibit the central controller
32
Pharynx airway receptors
Receptors that appear to be activated by swallowing - respiratory activity stops during swallowing protecting against the risk of aspiration of food or liquid
33
Muscle proprioceptors
Joint, tendon and muscle spindle receptors Intercostal muscles > > diaphragm Important roles in perception of breathing effort
34
If ascending up a hill….
Ascending; PiO2 falls (FiO2 remains constant) Decreased PAO2 Decreased PaO2 Peripheral chemoreceptors fire (e.g carotid) Activates increased ventilation (VA) Increased PAO2 Increased PaO2
35
PaCO2 and pH
The pH of the CSF is established by the ratio of pCO2 : [HCO3–]. The HCO3– levels remain relatively constant. CO2 freely diffuses across the blood brain barrier, from the arterial blood supply into the CSF. CO2 reacts with H2O, producing carbonic acid, which lowers the pH. This means that the pH of the CSF is inversely proportional to the arterial pCO2. A small decrease in pCO2­ leads to an increase in the pH of the CSF, which stimulates the respiratory centres to decrease ventilation. A small increase in pCO2 leads to a decease in the pH of the CSF, which stimulates the respiratory centres to increase ventilation.
36
Ventral respiration group
the VRG sends inhibitory impulses to the apneustic centre, decreasing the duration of inspiration, leaving more time for longer expiration during forced expirations
37
Dorsal respiratory group
initiates respiration and determines the basic rhythm of breathing by adjusting the frequency of inspiration. When it receives information regarding an increase in PaCO2, the DRG causes the diaphragm to contract (via the phrenic nerve) to increase the vertical length of the thoracic cavity, and through the intercostal nerves to the external intercostal muscles, which contract and cause the ribs to move up and out, increasing the lateral size of the thoracic cavity. This causes airflow into the lungs
38
Apneustic centre
When O2 requirement is higher (eg during exercise) the apneustic centre of the pons is activated, stimulation excites the DRG in the medulla, prolonging the period of action potentials in the phrenic nerve, prolonging contraction of the diaphragm and so preolonging inspiration
39
Pneumotaxic centre
To prevent over inflation of the lungs, the pneumotaxic centre is activated, which limits the burst of action potentials in the phrenic nerve, making the diaphragm contract less- stopping inspiration and allowing for expiration to happen
40
When low PaO2 detected
afferent impulses travel via the Glossopharyngeal and vagus nerves to the medulla oblongata and pons in the brain stem. In order to restore PaO2, respiratory rate and tidal volume are increased to allow more oxygen to enter the lungs and diffuse into the blood. Also, blood flow is directed towards the kidneys and brain (as these organs are most sensitive to hypoxia), and cardiac output is increased to maintain blood flow
41
Hypercapnia
Hypercapnia, also known as hypercarbia, is a condition that occurs when a person has too much carbon dioxide (CO2) in their bloodstream. It can cause confusion as increased CO2 levels cause the brain to reduce metabolism and spontaneous neural activity and enter a lower arousal state.
42
In response to what stimuli cause chemoreceptors in the medulla to increase respiratory rate
Increase in carbon dioxide of cerebral spinal fluid
43
Normal respiratory rate
10-12 breaths per minute
44
Acid-base balance
CO2 +H20 <-> H2CO3 <-> (HCO3)- + H+ Carbonic anhydride enzyme
45
Respiratory control of acid-base balance is
Rapid
46
Renal control of acid base balance is
Slow
47
Opioids
Depress control of respiration
48
Amphetamines
Stimulate respiration
49
Large respiratory reserve
Minute ventilation : 7.5 L/min Can increase to 30L/min
50
Flow of air
(Alveolar pressure - atmospheric pressure) / resistance
51
Pneumotaxic centre
Inhibits inspiration- enables expiration
52
Apneustic centre
Increases inspiration
53
Pontine respiratory group
Pneumotaxic centre Apneustic centre
54
Dorsal respiratory group
Inspiration: contracts Diaphragm External intercostals
55
Pre-Bötzinger complex
Rhythm generator of breathing (pacemaker cells)
56
Ventral respiratory group
Inspiration and forced expiration Contracts: Internal intercostal muscles Accessory muscles
57
Central chemoreceptors
detect changes in PaCO2. The pH of the CSF is established by the ratio of pCO2 : [HCO3–]. • The HCO3– levels remain relatively constant. CO2 freely diffuses across the blood brain barrier, from the arterial blood supply into the CSF. CO2 reacts with H2O, producing carbonic acid, which lowers the pH.  This means that the pH of the CSF is inversely proportional to the arterial pCO2. • A small decrease in pCO2­ leads to an increase in the pH of the CSF, which stimulates the respiratory centres to decrease ventilation. • A small increase in pCO2 leads to a decease in the pH of the CSF, which stimulates the respiratory centres to increase ventilation. • The DRG (dorsal respiratory group) initiates respiration and
58
What is main driver for respiration
CO2 chemoreceptors respond to small CO2 changes but large O2 changes
59
Prolonged hypoxia
Type II sustenacular cells (supporting) ——> type I glomus cells (O2 sensing)
60
Carotid sinus is innervated by
Glossopharyngeal nerve
61
Aortic arch is innervated by
Vagus nerve
62
Which nerve do pulmonary stretch and irritant receptors inhibit the respiratory centre by
Vagus nerve
63
Irritant receptors
Larger conducting airways Fast adapting- cough
64
Stretch receptors
Lung inflation in smooth muscle Slowly adapting Inhibit inspiration (inflation)
65
J receptors
Alveoli Unmyelinated C fibres Irritants, noxious agents, volume Bronchoconstriction and shallow breathing
66
Rapidly adapting stretch receptors
Airway epithelial cells that respond to rate of change of volume and irritants Can cause bronchoconstriction and long deep breathing
67
The central chemoreceptors, located in the ventral medulla help regulate the internal environment. What do they respond to?
CSF pH
68
Chemoreceptors regulate the internal environment by monitoring changes to various substances. Changes in which of these substances stimulate the carotid chemoreceptors?
Oxygen, carbon dioxide and H+ ions
69
The body uses a variety of chemoreceptors to regulate the internal environment. Where are the main peripheral chemoreceptors located?
Carotid arteries and aortic arch

CVR (22 decks)

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