Control of breathing
From Iusmphysiology
- started here on 02/17/11 at 11AM.
- Quiz:
- Healthy person in airplain:
- Answer is "will cause a modest reduction..."
- Arterial blood sample with pH of 7.21
- respiratory acidosis
- Restrictive lung
- Everything is down
- Vascular resistance reduced by
- Increased pulmonary artery pressure
- Total amount of oxygen in the blood
- Is most closely related to hb content
- Healthy person in airplain:
[edit] Control of breathing
- It is spontaneous
- CNS initiates
- Brain stem initiates breathing.
- MOdification occurs, too:
- Hypovolemic input from cerebral cortex
- Stretch receptors in the lungs that tell brain stem that the lungs are over or under streched or irritated.
- Mechanoreceptors in the muscle tell the brain that muscle is being used so breathing should probably go up.
- Chemoreceptors inthe aortic arch, the medulla, and the corotid body sense changes in PO2 and PCO2.
- This is supper important! KNow it!
[edit] Medullary respiratory center
- The pink are the mains points.
- Drive to breath control:
- Dorsal respiratory group of neurons
- Generate inspiration
- Inhibited by CN 9 and 10 afferents
- Ventral respiratory group
- Both inspirationa and expiration impt.
- Dorsal respiratory group of neurons
[edit] Pontine centers
- Higher leves are for fine tuning
- Apneustic center
- Lives in pons
- Reinforces inspiratory drive
- Inhibited by CN10 afferents
- Apneusis is a long inspiration.
[edit] Regulation of Respiratory Rhythm
- If you cut the brains tem above the pneumotastic center, you can breath normally, though you don't knwo who you are or anything.
- If vagus is then cut, inspiratory efforts are much deeper.
- If you cut below apneustic you get prety normal
- If you then cut vagus you get apneustis, big long breaths.
- Cut below ventral center breathing is irregular
- Then cut vagus:
- Cut below dorsal and you die
- Dead even if vagus is cut, too.
[edit] Influence of higher brain centers
- Hypothal:
- Affects breathing in the emotional states
- Affects breathing and cardiovascular function
Missed second
[edit] Motor outflow to muscles of breathing
- Phrenic comes from c3-c5
- Thoracic segment supply the intercostals
Missed one
[edit] Spinal respitoratyr motor neuron tracts
- Don't need to know this.
[edit] Slowly adapting receptors in lungs
- Know big conceptual pictures.
- Know the red things.
- Stretch receptros = mechanorecptors
- In larg eand small airways
- Affect airway tone and resistance
- Herring brewer reflex
- Inflation: cannot overinflate and pop our lungs
- During fast inspiration, these receptors can cut inflation short so over inflation doesn't occur.
[edit] Rapidly adapting receptors
- These are for irritants, generally.
- These regulate deflation.
- In the case of pneumothorax these kick in to keep lungs from deflating too fast.
[edit] C-fibers ending in the lungs
- Sense things that are bad: breathed in or injested.
[edit] Mechano- and Chemo receptors in upper airways
- Detect irritants, cause sneezes.
- Diving reflex:
- Throw water in face, causes bradycardia and apnea
[edit] Reflex mechanismas controling inspiration
- This slide is awesomely important.
- Know the big picture.
[edit] Other Refex mechanisms
- Pain can affect respiration
- Somatic pain usually causes hyperventilation
- Visceral pain usually cuases hypoventilation
[edit] Magnitude of ventilation in response to extreme physiological stress
- At rest: 6 liters / min
- Voluntairy hperventilation = 170 l / min
- Exercise = 110 l / min
- High CO2 inspiration = 90 l / min
[edit] Mechanisms regulating control of breathing
- Chemoreceptors
- There to tell brain stem that something is wrong: PO2 low or CO2 high.
- Peripheral chemoreceptors:
- Carotid bodies and aortic arch (same as baroreceptors).
- Respond to PO2 (not oxygen content) and PCO2 (and a little pH).
- Central chemoreceptors:
- Resopnd to pH
[edit] Peripheral chemoreceptors
- These chemo receptors dtect low PO2 and high PCO2 to cause brain to breath.
- DO NOT RESPOND TO OXYGEN CONTENT!
[edit] Cells in carotid body
- Get mechanism off this slide
[edit] Ventilatotry response to PAO2
- As PAO2 goes down, we need to breath more.
- As we do this, PCO2 will go down which will cause suppression of breathing.
- So there's a happy balance between PAO2 and PCO2.
- If PCO2 is held constantly, (43), the red line demonstrates our ventilation.
- This is a fxn of peripheral chemoreceptors.
[edit] Ventilatory response to hypoxia
[edit] Ventilatory respones to PACO2
- PACO2 is the most important regulatory of ventilation in healthy conditions.
- Normally tightly regulated.
- Ventilation is tightly regulated by small changes in PACO2.
- An high PACO2 will be responded to very quickly with increased ventilation.
- What is stimulating ventilation:
- First, high PCO2
- Next, low PO2
- These are sensed by chemo receptors
[edit] Factors which alter the ventilatory response to PACO2
- Metabolic acidosis:
- Ventilatory response is augmented
- Sleep:
- Reduce
- Narcotics:
- Reduces response
[edit] CO2, ventilation and central chemoreceptors
- These only respond to pH (not PO2!).
- CO2 crosses BBB to interact with chemoreceptors in the brain.
[edit] Flow chart
[edit] Integrated response to hypercapnia
- Acute situations are handled by peripheral chemoreceptors
- Long term is responded to by central.
[edit] Ventilatory response to H+
- As H+ increases, ventilation is increased but not as fast as PCO2 increases ventilation.
- This is regulated by chemo receptors.
[edit] Acid-base balance
- DAvenport
- stopped here on 02/17/11 at 12PM.