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


Contents

[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.

[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.
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