19. Control of Breathing Flashcards
How is Breathing Controlled?
- Unaware: until something goes wrong - dyspnea
○ e.g. high altitude / disease - Aware: scuba diving, partners to sleepy snorers
Describe the Local Control P(O2) and P(CO2) In Active Tissues.
Increased P(CO2) = Increased CO2 removal + vasodilation = Increase Blood Flow
Decreased P(O2) = Increased O2 delivery
Describe the Local Control of Gas Transport (Lung Persuasion)
Decreased P(O2) = vasoconstriction = Decreased blood flow
→ direct blood to areas of higher PO2
Describe the Local Control of Gas Transport (Alveolar ventilation)
Increased P(CO2) = bronchodilator = Increased air flow
→ direct airflow to areas of higher PCO2
- improve efficiency of gas transport
Describe the process of Central Control of Ventilation.
- Sensors Detect Change: Central & Peripheral Chemoreceptors, Mechanoreceptors
- Central Controller coordinates response: Respiratory Centres in the pons and medulla
- Effectors cause change: Muscles of ventilation
Role of Central chemoreceptors.
- 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
Describe the location of Peripheral chemoreceptors.
- 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
Role of Mechanoreceptors.
Lung receptors
Respond to stretch
○ rapidly adapting receptors
○ slowly adapting receptors
○ C-fibres receptors
Define Dyspnoea
Difficult or laboured breathing
Factors influencing rate & depth of breathing
- 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
Which gas has no effect on central chemoreceptors?
↓ PO2
Function of Peripheral Chemoreceptors
- Peripheral chemoreceptors are vital for response to ↓ PO2
(no effect on central chemoreceptors)
What stimuli effect the Peripheral Chemoreceptors?
Stimulated by ↓PO2, ↑ PCO2, ↓ pH in arterial blood
- hypoxia
- hypercapnia
What happens if P(O2) changes?
- 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
What happens if P(CO2) decreases?
CO2 + H20 ↔ H2CO3 ↔ H+ + HCO3-
Equation pushes left
= ↓ H+ = pH increases = alkaline = Respiratory alkalosis
What happens if P(CO2) increases?
CO2 + H20 ↔ H2CO3 ↔ H+ + HCO3-
Equation pushes right
= ↑H+ = pH decreases = acidic = Respiratory acidosis
Name the 3 types of Mechanoreceptors in Lung Tissue and Airways.
- Slowly adapting Stretch Receptors (bronchopulmonary stretch receptors)
- Rapidly adapting Stretch Receptors (Irritant receptors)
- C-fibres receptors (J receptors)
Describe the role of Slowly adapting Stretch Receptors.
bronchopulmonary stretch receptors
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
Describe the role of Rapidly adapting Stretch Receptors
Irritant receptors
- 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)
Describe the role of
C-fibres receptors (J receptors)
- 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)
What are the 2 central controllers of ventilation?
Rhythmicity centre in the medulla oblongata
Pneumotaxic and Apneustic centres in the pons
What is the Rhythmicity centre in the medulla oblongata?
- Controls automatic breathing (sets pace for respiratory movements)
- interacting neurons that fire either during :
○ inspiration (I neurons) or
○ expiration (E neurons).
What is the Pneumotaxic and Apneustic centres in the pons?
- 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
Role of inspiration (I neurons) in the Rhythmicity centre in the medulla oblongata.
“I” neurons in Dorsal Respiratory Group (DRG) regulate activity of phrenic nerve allows it to set rhythm & stimulate muscles of quiet inspiration.
