Respiratory 3 Flashcards
The Basics of Neural Control of Breathing
- Healthy people do not need to make a conscious effort to breath It is initiated and controlled by the —- nervous system
Breathing is a —- activity
autonomic
rhythmic
What happens in inspiration and expiration?
Inspiration:
Respiratory muscles contract
Expiration:
Respiratory muscles relax and lungs empty primarily though elastic recoil
What are the 3 respiratory muscles?
What type of muscle are they?
What input do they require?
Diaphragm, intercostals, abdominals.
Skeletal.
Require neural input for stimulation.
What nerve innovates the diaphragm?
Where does this nerve originated from?
What innervates the intercostal muscles?
Phrenic nerve.
From the brain stem between cervical vertebrae C2 and C5.
Segmental spinal nerves.
Where is the basic rhythmicity of breathing generated?
Medulla oblongata
How do these brain centres initiate and regulate breathing?
- explain the DRG
There is a dorsal respiratory group on either side of the medulla.
This contains the inspiratory neurones.
These demonstrate rhythmic activity and stimulate inspiratory muscles.
Dorsal respiratory group also receives afferent inputs from lung receptors via the vagus nerve.
Explain the VRG
where does it also receive inputs from?
Ventral Respiratory Group:
- Either side of the medulla
- VRG contains neurons with a degree of spontaneous rhythmic electrical pacemaker activity
- VRG contains neurons that stimulate respiratory muscles to initiate:
Inspiration = inspiratory neurons
Expiration = expiratory neurons
VRG also receives inputs from DRG and central chemoreceptors.
The medulla has neurons for what?
Recognise changes in gas concentrations in the blood.
Explain how the ventral and dorsal respiratory group work together
- in normal quiet breathing
They form the central respiratory rhythm generator.
Inspiratory and expiratory neurons tend to inhibits each other, inspiratory neurons are more active. Net result is more stimulation of inspiratory neurons as these are more active - more stimulation of inspiratory muscles in quiet breathing.
During normal quiet breathing, what stimulates inspiratory neurons causing contraction of inspiratory muscles?
Respiratory rhythmic generator
How does expiration mainly occur?
By passive elastic recoil, so neurone activity is minimal.
What happens to expiratory muscles during exercise?
Give the key point about this
Expiratory neurons are actively stimulated, thus stimulating expiratory muscles (abdominals).
Mutual inhibition of inspiratory and expiratory neurons results in alternate stimulation of inspiratory and expiratory muscles.
Where does the pons receives input from and what are the two centres of the pons region?
Receives input from cerebrum and hypothalamus and feed them into the medullary respiratory centre.
- pneumotaxic centre (smooth transitions between inspiration and expiration by regulating apneustic and DoralRespiratoryGroup
- apneustic centre (stimulates the DRG to promote inspiration, thus increasing breath duration
Where is pons found and what does it add to the medulla?
Found about the medulla.
Offers a fine-tuning of the basic rhythmicity generates in the medulla.
What are the two systems that lead to a change in temperature and emotional state?
What takes over in hyperventilation?
Hypothalamus and limbic system.
Limbic system
Why does someone need voluntary control?
Explain this
Damage to the brain stem - means they can still breathe.
The voluntary system can over-ride the respiratory centre.
Motor neurons in the cerebral cortex concoct directly to motor nerves supplying the respiratory muscles, in the spinal column, bypassing the medulla.
Important in speech, which eating, diving.
Explain how stretch receptors work in the lungs
Inspiration stretches airways which activates stretch receptors in bronchial smooth muscle. The vagus nerve sends impulses to dorsal respiratory group are inhibited. This inhibits further inspiration giving expiration to occur
(negative feedback).
What is the name of the reflex which can sense where the lungs stop being inflated?
Hering-Breur Inflation reflex
This is important in exercise to give the body time to breath out again when you are taking deep breaths.
Explain irritant receptors in the lungs
Irritant chemicals&smoke and dust activated the irritant receptors between epithelial cells. Vagus nerve sends impulses to medullae which either causes…
- coughing (help remove irritants)
- bronchoconstriction (prevent irritants from getting into alveoli)
- stimulates surfactant release&deep augmented breaths (prevents slow collapse of lungs)
What neurones are activated in the dorsal and ventral respiratory groups?
Dorsal - inspiratory neurones
Ventral - inspiratory and expiratory neurones
What is alveolar PCO2 determined by?
Balance between ventilation and carbon dioxide production.
Explain hyper-ventiliation
- what is it in proportion to?
- what two things can it lead to?
- In proportion to metabolism
- Can lead to hypocapnia (lowers arterial PCO2 below normal levels) and respiratory alkalosis (less bicarbonate produced)
What does low PCO2 cause and what are the effects of this?
Causes cerebral vasoconstriction and this causes cerebral hypoxia and dizziness.
What can hypo-ventilation lead to?
- hypercapnia (raise in arterial PCO2)
- respiratory acidosis
- hypoxia
explain chemical control of breathing
Metabolism by tissues results in carbon dioxide production and oxygen consumption and H+ production.
The most important of these is PCO2.
How do PCO2 changes affect respiration?
Increase in PCO2, linear increase in ventilation.
Small increases in PCO2 has a large affect on ventilation rate. Ventilation never goes to zero even at very low PC02 (so death does not occur!)
Depression at very high PCO2 because this means that breathing uses more oxygen in the skeletal muscle than it is taking in (counter-productive).
Acidosis
Hard physical exercise, producing —- acid in muscle, thus lowering pH. This is normal and transien.t
Patho-physiological situations such as HCO3- loss in —- disease or in gut due to diarrhoea or diabetes.
These are examples of —- acidosis
Metabolic alkalosis
Occurs if there is an increase of pH, e.g. H+ loss from the stomach during —-, or during diuretic use, which causes loss of water but retention of HCO3- in —- space
How do these changes affect the PCO2 – ventilation relationship?
Low pH (acidosis) increases ventilation
High pH (alkalosis) decreases ventilation
lactic
renal
metabolic
vomiting
extracellular
On a alveolar PCO2 and ventilation graph, what does acidosis and alkalosis do to to the graph?
Acidosis pushes it left (higher ventilation at lower pCO2).
Alkalosis pushes it right.
What is the name for the how PCO2 and PO2 values work?
What fold increase in ventilation do these cause?
- individually mild hypercapnia or hypoxia
- combined mild hypercapnia and hypoxia
Synergy
2 fold increase
6 fold increase
What are the two chemoreceptors called?
Where are they found?
What do they detect?
1) Central chemoreceptor found in the medulla. Detect [H+] and PCO2.
2) Peripheral chemoreceptor found in carotid and aortic bodies. Detect PO2, PCO2 and [H+].
Where are central chemoreceptors located and how do they indirectly detect changes in blood PCO2?
Located on the ventrolateral surface of medulla, near the entry of the vagus and glossopharyngeal nerves.
They sense pH of cerebrospinal fluid rather than of blood.
Blood-brain barrier prevents permeation of H+ and HCO3- into brain tissue.
CO2 is free to cross the blood-brain barrier.
Conversion back to H+ and HCO3- means that H+ IN css is directly proportional to PCO2 in blood.
Where are peripheral chemoreceptors found?
Details
- Aortic and carotid bodies
Aortic bodies present on upper part of the aortic arch and innervated by the vagus.
Carotid body present at the top of the bifurcation of the common carotid artery, innervated by the carotid sinus nerve.
What does the carotid body contain and what does this do?
Glomus cells - respond to decrease in PO2, increase in PO2 and [H+]. Main O2 sensing cells in respiration. .
Upon activation they release dopamine at nerve endings.
Show synergistic response of releasing dopamine to combined stimuli (PO2 and PC02).
Very fast response to acute changes in blood gas pressure such as oscillations in partial pressures during inspiration and expiration.
