Lecture 9 - Breathing Control Flashcards
Why is taking in oxygen necessary?
requirement for generating ATP through oxidative phosphorylation
what is a by-product of respiration?
CO2
What is minute ventilation
breathing frequncy x tidal volume
10 breaths in a minute x 500 ml = 5L per minute
Why is minute ventilation less than 500 ml?
due to the dead space in the upper airways
reduces 500 ml to around 350ml which is alveolar minute ventilation at rest
what happens to o2 consumption during rest?
can increase to more than 10 fold
What happens to breathing at a higher altitude?
less O2 in the air so need to work harder to maintain O2 supply
How does disease affect breathing?
compromise gas exchange or delivery
Give examples of diseases that compromise gas exchange or delivery
Pulmonary diseases - emphysema cardio - heart and vasculature sleep apnoea opioid depression of breathing conditions of chronic hypercapnia - require oxygen sensing
Describe control of respiratory output
factors/sensors providing information to the respiratory centre act as an input to the respiratory centre and act as output to target muscles controlling ventilation
What is the function of the pons and the medulla
medulla is the primary centre
pons: regulates medulla
Dorsal respiratory group
Contains neurones which fire during inspiration
Ventral respiratory group
contain mixed neurones some fire during inspiration and some during expiration
What happens to the Ventral and dorsal respiratory group during exercise?
there is reciprocal inhibition during exercise. Inspiratory nerve activity is high and expiratory nerve activity is low and they alternate between high and low in a dna shape
What role does the pons play in stimulating respiratory activity
Stimulates the Apneustic and pneumotaxic centre
What depresses inspiratory activity?
hypoxia, wide variety of therapeutic drugs (opiates, barbirates and anaesthetics) and inhibition of blood supply
What are the main centres providing information to the respiratory centre?
- Voluntary - higher centers (cerebral cortex control over breathing
- Automatic - respiratory centres in medulla regulated by pons
What are the factors providing information to the respiratory centre causing negative activity?
stretch receptors in the lungs
irritant receptors in the lungs (trachea)
What are the factors providing information to the respiratory centre causing positive activity?
Peripheral chemoreceptors in aorta and carotid artery - detect decrease in O2, increase in CO2 and H+
Central chemoreceptors - increase in CO2 and H+
Receptors in muscles and joints
Describe the higher brain centre influences
Cortical (Cortex) - voluntary hyperventilation - hypocapnia (low CO2) - Alkalosis
voluntary breath holding - hypoxia (low O2) - unsustainable
Hypothalmic - emotions - anger, anxiety - hyperventilation
Sensory reflexes - pain and cold - gasping and hyperventilation
How do pulmonary stretch receptors function
afferent fibres from smooth muscles of bronchi and trachea run in the vagus nerve to the respiratory centre in the medulla
so as inspiration progresses, the dorsal respiratory group that increases inspiration is inhibited and VRG is stimulated (expiration)
What is Hering-Breuer lung inflation reflex
it is a reflex that prevents overinflation of the lung
limits breathing frequency (f) x tidal volume (Vt)
How to irritants/cough receptors affect respiration?
receptors through airways when stimulated initiate explosive expiration - cough
afferent fibres from these receptors run in the vagus to the respiratory centre
irritant receptors also found in upper airways and nose. Stimulation leads to hyperpnoea and airway constriction which can lead to coughing or sneezing
What does local anaesthetics do to reflexes?
They prevent them when passing endotracheal and nasogastric tubes into patients
What factors affect muscle/joint receptors and proprioreceptors?
muscle spindles rich in intercostals, few in diaphragm
activated by stretch associated with contraction of breathing, but spindles in exercising muscles
proprioceptors in joints also relay information about activity induced motion which can influence ventilation
What role do baroreceptors play in neural modulation?
detect change in blood pressure and can influence ventilation (increase in BP leads to lower ventilation and vice versa)
What role do Juxtacapillary receptors play in neural modulation
lie close to capillaries around the alveolar walls. they are activated by traumas such as pulmonary oedema, fluid in the alveoli, inflammatory agents, pneumonia. Their activation triggers increased ventilation
What are central chemoreceptors?
specialised regions close to the medulla respiratory centres, but also close to a rich blood supply.
sensitive to CO2 and H+.
h+ cannot cross the blood-brain barrier, but CO2 can, which informs about H+ levels:
rise in CO2 or a rise in H+ stimulates chemoreceptors and increases ventilation
What and where are peripheral chemoreceptors?
located in carotid and aortic bodies
sensitive to hypoxia and hypercapnia (high CO2)
and acidosis (high H+)
Type of peripheral chemoreceptor
glomus cell which is a primary detector of hypoxia
How does the glomus cell initiate action potentials to the respiratory centre
hypoxia triggers ca2 influx into glomus cells via depolarisation (like nerve terminal). the Ca2+ triggers release of neurotransmitters which initiate action potentials in the afferent nerve
Dopamine: one transmitter released, but excitation is from ATP and acetylcholine
