Lecture 22: Respiratory 4, Regulation And Acid-base Balance Flashcards

0
Q

What are the respiratory control centres in the brainstem?

A

Motor neuron firing is triggered by synaptic input from brainstem control centres:

  • DRG (medulla)- mostly inspiratory neurons
  • VRG (medulla)-mostly expiratory neurons for active expiration
  • PRGs (pons)- transition from inspiration to expiration, fine tuning of control

Regular respiratory rhythm generated by the respiratory central pattern generator
-sets the rhythm, receives sensory input and changes rhythm

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1
Q

Motor neuron activity and the respiratory cycle

A
  • respiratory motor neurons have cyclical periods of activity and inactivity (AP bursts)
  • the pattern of AP firing depends on the type of breathing (forced of unforced)
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2
Q

Sensory input to the central pattern generator

A

-central pattern generator receives a wide array of inputs
Pain refer to this page don’t know number
Especially peripheral chemoreceptors and central chemoreceptors that pick up on conc of CO2, H+, O2 etc

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3
Q

What happens with the chemoreceptor reflex control of ventilation

A
Regulated variable: change in arterial blood gases 
⬇
Sensors: chemoreceptors 
⬇ Sensory receptors 
Integration centre: central pattern generator (brain stem) 
⬇Somatic motor neurons 
Effectors: respiratory muscles 
⬇
Change in alveolar ventilation 
⬇
Restoration of blood gases
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4
Q

Tell me about the chemoreceptor responses

A
  • chemoreceptors are cells that responds to a chemical change and send signals to other cells
  • monitor PCO2, H+ (pH) and PO2 in major arteries and brain
  • small changes in PCO2 and pH produce major changes in ventilation
  • PO2 has little effect on ventilation unless it drops very low (hypoxemia)
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5
Q

Tell me about the peripheral chemoreceptors

A
  • there located in carotid bodies, located near carotid sinus (and aortic bodies in arch of aorta)
  • send signal via sensory neurons to central pattern generator
  • direct contact with arterial blood

So
Increased (H+ and increased PCO2 and very low PO2) will = increased peripheral chemoreceptor activity therefore increased ventilation
Note: decreased (H+) or PCo2 will have the opposite effect, but increased PO2 won’t,

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6
Q

Tell me about the central chemoreceptors

A
  • Neurons in the medulla that respond directly to changes in H+
  • central chemoreceptors are indirectly activated by changes in arterial PO2
  • central chemoreceptors are not sensitive to changes in O2
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7
Q

Activation of central chemoreceptors

A

Central chemoreceptors in the brain respond to changes in H+

  • but, central chemoreceptors are protected by the blood brain barrier
  • H+ can’t cross this barrier

CO2 can diffuse across the BBB into the CsF

  • build up of Co2 in the CSF/medulla leads to H+ production
  • H+ produced in the CsF/medulla activates central chemoreceptors
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8
Q

Central vs. peripheral chemoreceptors

A

Peripheral: (carotid and aortic bodies)

  • responds quickly
  • respond to small changes in arterial PCO2, pH (H+ concentration)
  • respond to very low PO2

Central: (medulla of brain)

  • response is slower than peripheral chemoreceptors but stronger
  • respond directly t H+ changes in brain
  • will respond when there are changes in arterial PCO2, brain blood flow or brain metabolism
  • don’t respond to changes in Po2

Changes in arterial PCO are the main stimuli changes in ventilation

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9
Q

Ventilation- perfusion matching

A

For adequate gas exchange:

  • airflow to alveoli (ventilation) = blood flow to alveoli (perfusion)
  • total blood flow to lungs is controlled by the CVS
  • cardiovascular disorders can cause inadequate gas exchange
  • local mechanisms (via alveolar PO2 and PCO2) control blood vessels and bronchioles to ensure max gas exchange
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10
Q

Blood acid-base balance

A

PH is a measure of the concentration of H+ ions
-inverse relationship ie ⬆ in H+ causes decrease in pH.
Normal pH = 7.4
Blood pH is very tightly regulated
-a few seconds outside the pH range 6.8-8 leads to death.
-Acidosis (pH 7.42) leads to seizures, convulsions
H+ affect shape and function of proteins

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11
Q

What are the contributers to acid-base balance?

A

-blood pH can be altered by direct changes to the H+
(Adding extra H+ eg diet, keto acids, lactic acid)

-blood H+ and therefore pH is also influenced by the interaction of Co2 and H2O
-so changes in blood PCo2 or HCO3- will also alter blood pH
-⬆ PCO2 will shift the equation to Right and lead to ⬆ H+
-⬆ HcO3 will shift shift equation to left and leaf to decreased H+
Slide something

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12
Q

Disruptions to acid-base balance.

What causes changes to H+, HCO3 and PCO2?

A

Changes to H+:

  • production of them by metabolism eg lactic acid, keto acids
  • excretion of H+ by kidneys
  • loss of stomach H+ by vomiting

Changes to HCO3:

  • changes to HCO3 added back to the blood by the kidneys
  • loss of HCO3 due to diarrhoea

Changes to PCO2

  • hypoventilation of
  • hyperventilation will in erase or decrease PCO2 respectively
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13
Q

How does the body compensate for acid-base disruptions

A

The body has 3 methods to limit blood pH disruptions

Buffering of H+
-by HCO3- and Hb

Respiratory compensation:
-changing blood PCO2 by changing ventilation

Renal compensation:
-change the amount of H+ excreted and HcO3- added to the blood

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14
Q

Tell me how buffering of H+ in the blood occurs?

A

Buffet = compound that binds to or releases, H+, altering pH

  • first and fastest line of defence against pH change
  • in plasma/ ECF, HCL3- is the most important buffer
  • intracellular buffers are phosphates and proteins including Hb
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15
Q

Tell me about respiratory compensation

A

Second line of defence against changes in pH
-activated within minutes

Change in ventilation rate in response to a pH disturbance

  • pH disturbance is detected by chemoreceptors
  • leads to reflex change in ventilation

Compensation: increasing/decreasing CO2 can partially reverse pH disturbance.

16
Q

Renal compensation

A

Third line of defence against changes in pH
Changes in the handling of H+ and HCO3- by the kidneys in response to a pH disturbance
-kidneys regulate H+ and HCO3 excretion
-kidneys regulate HcO3 synthesis
Most powerful compensatory system- can largely reverse pH changes

17
Q

What are some acid-base disturbances. There are 3, you need to list and explain each.
You are always given these values to figure it out in a test:
1. pCO2- 40 mmHg
2. HCO3- 24mM
3. Acidosis - pH < 7.35
4. Alkalosis - pH> 7.45

A
  1. RESPIRATORY ACIDOSIS is characterised by:
  2. Low pH (high H+)
  3. High PCO2

Causes eg
-hypoventilation due to pulmonary diseases, depression of respiratory control centre

Kidneys may compensate by:

  • increasing H+ excretion
  • or add more HCO3- to the blood
  1. RESPIRATORY ALKALOSIS characterised by:
    - high pH (low H+)
    - low PCO2

Causes: hyperventilation (fever, anxiety, hypoxia, aspirin overdose)

Kidneys may compensate by:

  • decreasing H+ excretion
  • decreasing HCO3- added to the blood
  1. METABOLIC ACIDOSIS
    Characterised by:
    -low pH (high H+)
    -low HCO3- (either due to HCO3- loss or H+ increase)

Causes: metabolic H+ production (lactic acid, keto acid in diabetes)

  • HCO3- loss following diarrhoea
  • reduced H+ excretion by kidneys (kidney failure)

Respiratory compensation may occur by:

  • increasing ventilation to reduce Co2 (low PCO2)
  • as CO2 decreases so too does H+, causing a pH increase
  1. METABOLIC ALKALOSIS characterised by:
    -high pH (low H+)
    -high HCO3- (either due to excess HCO3- or H+ loss)
    Causes:
    -H+ loss assosiated with vomiting
    -excessive use of antacids
    Respiratory compensation may occur by:
    -decreasing ventilation to increase CO2 (high PCO2)
    -as CO2 increases so too does H+ causing a pH decrease
18
Q

Diagnosing acid-base disturbances in blood

A

You are given a set of blood parameters (pH, PCO2, HCO3-) and normal reference range, you are expected to be able to:

1) decide whether the change is alkalosis or acidosis
- pH below normal ➡ acidosis
- pH above normal ➡ alkalosis
2) decide whether the change was due to a respiratory or metabolic disturbance
- of respiratory in origin, what would have to happen to PCO2 to bring about this change in pH
- if it was metabolic in origin, what would have to happen to HCO3- to bring about this change in pH
- which of these changes in consistent with the patient values?

19
Q

Diagnosing acid-base disturbances in blood

A

Decide whether compensation for the disturbances has occurred, and of so. Whether it was renal or respiratory compensation
-if the origin is respiratory then the respiratory system cannot compensate for the problem so we can only have renal compensation (or none). To look for renal compensation, look at the HCO3 level. Has this changes in a way that would help rice the problem and bring pH back towards normal? If so, then there is renal compensation occurring.

-if the disorder is metabolic, we can look for respiratory compensation by looking at the Co2. Has this changes in a way that would help reduce the problem and bring pH back towards normal? If so then there is respiratory compensation occurring.

20
Q

Listen to the worked examples on slide 35 and listen to lecture

A

Yep