Flashcards in Control of Breathing Deck (23):
What are the three requirements for a respiratory control system?
1. Must be automatic so it can work even when you're not awake
2. Must be adaptable to put up with your increased or decreased O2 and CO2 content
3. Must still have some voluntary control
How can we control PaO2, PaCO2, and pH when we exercise?
Increasing minute volume
How do respiratory control centers work?
These are found in our brain and they work to control our breathing by affecting motor neurons that cause the contraction of respiratory muscles. This leads to inflation and deflation of the lung that affects the volume and rate of your breathing. This then causes you to have a set alveolar P02 and PCO2 that go on to define your arterial P02 and PCO2
You have sensors that detect the PO2 and PCO2 levels and report back to the respiratory centers so that you can control your breathing as needed. Also have sensors on your respiratory muscles and on your lungs that report back.
What are the three respiratory system motor neurons?
1. Phrenic motor neurons: C3 to C5 and they innervate the diaphragm
2. Intercostal motor neurons: Thoracic spinal cord segments
3. Larynx & Pharynx motor neurons: Nucleus ambiguus of the medulla
Why does a transection in the mid-pons lead to apneustic breathing?
Apneustic breathing is when you have a long, emphasized inspiration followed by quick expiration...almost looks like you have sustained inspiration
occurs due to damage of the pneumotaxic center in the rostral pons that promotes the transition from inspiration to expiration. W/o this you get his weird non-rhythmic breathing.
What are the three respiratory control centers?
Pneumotaxic center (rostral pons), Ventral Respiratory group, & Dorsal respiratory group
What are the components of the VRG? Describe their functions.
1. Pre-Botzinger Complex: Central pattern generator that allows of rhythmic breathing
2. Rostral VRG: Inspiratory neurons for the phrenic motor neurons
3. Caudal VRG: Expiratory neurons for the spinal cord
4. Nucleus ambiguus: found in the caudal VRG
What is the nucleus solitarius?
This is found in the DRG and it compiles together many sensory afferent inputs
What is the pontine nuclei?
Part of the pneumotaxic center, this is responsible for promoting the transition from inspiration to expiration
What is the hering-Breuer Reflex?
An increase in the lung volume causes slow stretch receptors in the airway smooth muscle to be stimulated. This travels to the vagus nerve and then to the neurons in the medulla. Here you get a signal to reduce the lung volume and thus you inhibit further inspiration.
If you cut off the vagus nerve, then your tidal volume will automatically increase since the reflex is cut
What are irritant receptors?
These are receptors found in the nasal mucosa, upper airways, trachea, and bronchial tree
They respond to mechanical and chemical stimuli and cause coughing, sneezing, and bronchoconstriction
What are Juxta-pulmonary capillary receptors (J-receptors)?
These are found in the alveolar walls and they respond to increased interstitial volume (i.e. pulmonary edema) and cause tachypnea (rapid, shallow breathing)
Where is the carotid body found? What does it do?
It's a small chemoreceptor that is in the carotid sinus and the baroreceptors. It is innervated by the glossopharyngeal nerve and it gets a large amount of blood for it's very small size. However, in receiving this large blood flow, the carotid body relies primarily on dissolved oxygen and uses it to sense the PaO2
If PaO2 is low, then the afferent fibers of the carotid body start firing like crazy
How does the carotid body work?
When you have low oxygen, this causes the K channels to be closed. This further depolarizes the cell and then causes calcium channels to open. As calcium flows into the type 1 glomus cell, it triggers the release of vesicles w/ neurotransmitters that help to create an AP at the afferent nerve fiber
What happens to carotid body firing if PaCO2 is increased, along w/ the decreases PaO2?
This would cause it fire even more rapidly and strongly
This also happens if the pH becomes more acidic
Why does minute ventilation only increase significantly after we've reached a state of hypoxia?
The reason for the low level of sensitivity in early drops of PO2 is that your oxygen dissociation curve has very high hemoglobin saturation until about a P02 of 60 mm Hg.
This is about the same pressure at which your ventilation starts to rise significantly, indicating a mirroring effect where ventilation rises as hemogobin saturation drops significantly
Why is CO2 the major drive to our breathing?
Our body has a much stronger sensitivity to PCO2 than to PO2 (where we need to get to hypoxia before it really starts working)
What are central chemoreceptors?
These sense elevated PCO2 levels by sensing the pH in the CSF
If you have an increase in PaCO2, the CO2 will diffuse into the CSF at capillary beds and raise the PCO2. This causes the pH of the CSF to become more acidic. The central chemoreceptors on the ventral medulla sense this decreased pH and fire!
What factors reduce our sensitivity to PaCO2? What increase it?
Metabolic acidosis increases our sensitivity
Sleep, anesthesia, and narcotics decrease our sensitivity
Why do opiate drugs result in respiratory depression?
Neurons in the VRG and in the pre-Botzinger complex have receptors that bind to the opiates as well and this causes the reduction
Describe the acclimatization process for someone who is at high altitudes or in an environment w/ low P02
As your PiO2 drops, this causes your PAO2 and your PaO2 to decreases. Your carotid bodies sense this decrease and fire more rapidly, causing you to increase ventilation. This increased ventilation will cause your PaCO2 to decrease. This decrease will want to force your alveolar ventilation down. Eventually, you reach a point where you have normal ventilation, slightly above normal PaCO2, but severely low PaO2.
After about a week or so, your ventilation slowly starts to increase and you PaCO2 drops, while your PaO2 increases
What are some ways to cope w/ the increasing altitude?
1. Increased sensitivity of respiratory centers to hypoxia
2. Increased plasma EPO levels
4. Increased 2,3-DPG
5. Excretion of bicarbonate by kidneys to compensate for the respiratory alkalosis of having higher than normal PaCO2