19. Control of Breathing Flashcards Preview

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Flashcards in 19. Control of Breathing Deck (28)
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1
Q

How is Breathing Controlled?

A
  • Unaware: until something goes wrong - dyspnea
    ○ e.g. high altitude / disease
  • Aware: scuba diving, partners to sleepy snorers
2
Q

Describe the Local Control P(O2) and P(CO2) In Active Tissues.

A
Increased P(CO2) = Increased CO2 removal + vasodilation 
= Increase Blood Flow

Decreased P(O2) = Increased O2 delivery

3
Q

Describe the Local Control of Gas Transport (Lung Persuasion)

A

Decreased P(O2) = vasoconstriction = Decreased blood flow

→ direct blood to areas of higher PO2

4
Q

Describe the Local Control of Gas Transport (Alveolar ventilation)

A

Increased P(CO2) = bronchodilator = Increased air flow

→ direct airflow to areas of higher PCO2

  • improve efficiency of gas transport
5
Q

Describe the process of Central Control of Ventilation.

A
  1. Sensors Detect Change: Central & Peripheral Chemoreceptors, Mechanoreceptors
  2. Central Controller coordinates response: Respiratory Centres in the pons and medulla
  3. Effectors cause change: Muscles of ventilation
6
Q

Role of Central chemoreceptors.

A
  • Located just beneath the ventral surface of the Medulla.
  • Change in pH
    ○ Stimulated by acidic pH in the cerebrospinal fluid
  • Hypercapnia -> CO2 levels in blood too high
    ○ Stimulated by high PCO2 in the cerebrospinal fluid
  • No effect of hypoxia
  • Not affected by oxygen
  • Close to entry of VIII & XI cranial nerves
7
Q

Describe the location of Peripheral chemoreceptors.

A
  • Outside brain
  • Carotid body at bifurcation of carotid arteries
  • Innervated by carotid sinus nerve (CSN) → glossopharyngeal
  • Aortic bodies above and below aortic arch
  • Innervated by the vagus
8
Q

Role of Mechanoreceptors.

A

Lung receptors

Respond to stretch
○ rapidly adapting receptors
○ slowly adapting receptors
○ C-fibres receptors

9
Q

Define Dyspnoea

A

Difficult or laboured breathing

10
Q

Factors influencing rate & depth of breathing

A
  • Changing body demands, e.g. exercise
  • Altitude – acute mountain sickness
  • Disease
  • In the arterial blood changing levels of;
    ○ CO2
    ○ H+
    ○ O2
    → Only a problem when PO2 of alveolar gas and arterial blood falls below 60mmHg
11
Q

Which gas has no effect on central chemoreceptors?

A

↓ PO2

12
Q

Function of Peripheral Chemoreceptors

A
  • Peripheral chemoreceptors are vital for response to ↓ PO2

(no effect on central chemoreceptors)

13
Q

What stimuli effect the Peripheral Chemoreceptors?

A

Stimulated by ↓PO2, ↑ PCO2, ↓ pH in arterial blood

  • hypoxia
  • hypercapnia
14
Q

What happens if P(O2) changes?

A
  • If PO2 goes up, e.g. breathing oxygen-rich gas mixtures
    ○ Generate free radicals leading to coma and death
  • If PO2 goes down
    ○ Arterial PO2 must drop below 60 mmHg before ventilation is increased
    ○ Central chemoreceptors switch off
    ○ Peripheral chemoreceptors increase breathing rate
15
Q

What happens if P(CO2) decreases?

A

CO2 + H20 ↔ H2CO3 ↔ H+ + HCO3-

Equation pushes left
= ↓ H+ = pH increases = alkaline = Respiratory alkalosis

16
Q

What happens if P(CO2) increases?

A

CO2 + H20 ↔ H2CO3 ↔ H+ + HCO3-

Equation pushes right
= ↑H+ = pH decreases = acidic = Respiratory acidosis

17
Q

Name the 3 types of Mechanoreceptors in Lung Tissue and Airways.

A
  1. Slowly adapting Stretch Receptors (bronchopulmonary stretch receptors)
  2. Rapidly adapting Stretch Receptors (Irritant receptors)
  3. C-fibres receptors (J receptors)
18
Q

Describe the role of Slowly adapting Stretch Receptors.

bronchopulmonary stretch receptors

A

Hering-Breuer reflex
= prevents the lungs from over-inflating on inspiration

  • Stretch receptors in the visceral pleura, bronchioles & alveoli

OverInflation = ↑discharge = inhibition of respiratory centres

19
Q

Describe the role of Rapidly adapting Stretch Receptors

Irritant receptors

A
  • In airway epithelia (close to mucosa)
  • Shape the ventilatory pattern and protecting the airway
  • Initially fire rapidly but then soon decrease their firing rate

Noxious gases, Smoke/dust, Cold air = ↑discharge = Bronchoconstriction (COUGHING REFLEX)

20
Q

Describe the role of

C-fibres receptors (J receptors)

A
  • In alveoli wall (close to the capillaries) and conducting airways (bronchial mucosa)
  • In alveoli wall (close to the capillaries) and conducting airways (bronchial mucosa)

Chemical/ mechanical stimuli = ↑discharge = Bronchoconstriction (rapid shallow breathing, mucus secretion)

21
Q

What are the 2 central controllers of ventilation?

A

Rhythmicity centre in the medulla oblongata

Pneumotaxic and Apneustic centres in the pons

22
Q

What is the Rhythmicity centre in the medulla oblongata?

A
  • Controls automatic breathing (sets pace for respiratory movements)
  • interacting neurons that fire either during :
    ○ inspiration (I neurons) or
    ○ expiration (E neurons).
23
Q

What is the Pneumotaxic and Apneustic centres in the pons?

A
  • Modify firing pattern of medullary centres
  • Apneustic centre in the pons increases the intensity of inhalation
  • Pneumotaxic centre in the pons stops inhalation and promotes exhalation
24
Q

Role of inspiration (I neurons) in the Rhythmicity centre in the medulla oblongata.

A

“I” neurons in Dorsal Respiratory Group (DRG) regulate activity of phrenic nerve allows it to set rhythm & stimulate muscles of quiet inspiration.

25
Q

Role of Expiratiory (E neurons) in the Rhythmicity centre in the medulla oblongata.

A

“E” neurons in Ventral Respiratory Group (VRG) → Passive process.
○ Activity of E neurons inhibit I neurons.

26
Q

What happen is the Apneustic Centre?

A
  • promotes inspiration, stimulates the I neurons

- ↑ intensity of inhalation during respiratory cycle

27
Q

What happens in the Pneumotaxic centre?

A
  • Inhibits apneustic centre = stops inhalation & promotes exhalation
28
Q

How do Central neurons determine ventilation rate (VR)?

A

Central neurons determine ventilation rate (VR) by regulating tidal volume (TV) and respiratory rate (f)
VR = TV x f

  • Steep rise in VR with ↑ PCO2
  • Mainly due to central chemo-receptors
  • ↓ PO2 = ↑ slope (↑sensitivity)
    ○ Due to peripheral chemoreceptors