Exam 3 - Regulation of Ventilation

Question 1

what buffer system is the most important regulator for ventilation?

Answer 1

HCO3- buffer system

• plasma: 75%
• red cells: 30%
• interstitial fluid: 90%
• other cells: 2%

Question 2

at what pK does the HCO3- buffer system function best and given this, why is it possible that this system is most important in our body, where the pH is 7.4?

Answer 2

pK = 6.1
When acid is added to body fluids, [HCO3-] decreases by conversion to H2CO3, which dissociates to H2O + CO2. CO2 is then eliminated by respiration, minimizing the effect of a change in the ratio of HCO3- to CO2 (H-H eq), which minimizes the effect on pH.

Question 3

what is the CO2 dissociation equation?

Answer 3

CO2 + H2O H2CO3 H+ + HCO3-

Question 4

COPD

Answer 4

elasticity of lung is lost -> incomplete exhalation -> retention of CO2 -> pH decreases -> respiratory acidosis -> shift O2 dissociation curve to right -> less Hb-bound O2

Question 5

hyperventilation

Answer 5

CO2 blown off -> pH increases -> respiratory alkalosis

-another sign: paresthesia around mouth or fingers

Question 6

what is the primary factor in respiratory control?

Answer 6

CO2 - when [CO2] decreases, respirations slow and may even temporarily stop -> hypoxia (can cause a seizure)

Question 7

what is a CPG?

Answer 7

central pattern generator - group of neurons capable of rhythmic patterned output in the absence of outside influence or sensory feedback

Question 8

what is the primary stimulus for inspiration?

Answer 8

DRG (dorsal respiratory group)

• input from central/peripheral chemoreceptors, pulmonary stretch receptors, somatic pain receptors, mechanoreceptors, etc.
• increased discharge of phrenic n. during inspiration -> recruit more muscles -> increase TV
• inspiration terminated by CPG too, then expiration passive

Question 9

ventral respiratory group (VRG)

Answer 9

contains inspiratory and expiratory neurons

-inspiratory are mainly to the accessory muscle

Question 10

which parts of the brainstem are responsible for which parts of respiration?

Answer 10

the medulla is capable of sustaining patterned breathing but the pattern can be fine-tuned by neurons in the pons and by feedback via the vagus.

Question 11

what two brainstem centers function to prevent excessive inhalation?

Answer 11

pneumotaxic center (pons) and stretch receptors (vagus) provide negative feedback to the apneustic center (medulla) to prevent excessive inhalation
-cut out either of these, get gasping because too much inhalation

Question 12

describe chemical control of ventilation

Answer 12

concentration changes in CO2 and H+ in CSF (central chemoreceptors) + changes in pH, CO2, and O2 (carotid/aortic bodies)

Question 13

what is the principal chemical control of ventilation?

Answer 13

arterial CO2 acting on central chemoreceptors

Question 14

describe the response of the carotid/aortic bodies to changes in pH

Answer 14

increase their discharge with decrease in pH -> increase ventilation by increasing both rate and TV

Question 15

when do the carotid bodies become sensitive to O2?

Answer 15

only at very low concentrations of O2 - they are primarily sensitive to decrease in pH and increase in CO2

Question 16

what are the central chemoreceptors exclusively sensitive to?

Answer 16

H+ directly and CO2 indirectly:
-BBB poorly permeable to H+, but CO2 can cross, where it is then hydrated into H2CO3, then dissociated to H+ and HCO3- -> acidosis of CSF -> increase TV

Question 17

describe the locations of the central chemoreceptors

Answer 17

• ventral surface of the medulla near cranial nerves VI-X

- no direct contact w/ arterial blood, but bathed in CSF

Question 18

describe the process of adaptation

Answer 18

ventilatory response to high PCO2 decreases after hours due to compensatory transport of HCO3- across BBB via anion exchanger w/ Cl- -> then PO2 drive in the periphery becomes major influence on ventilation

Question 19

describe the ventilatory responses to changes in acid-base balance

Answer 19

• if metabolic acidosis, try to compensate w/ respiratory alkalosis (hyperventilation to drop blood H+ by blowing off CO2)
• if metabolic alkalosis, try to compensate w/ respiratory acidosis (hypoventilation to increase CO2 and H+ back to normal)

Question 20

list some causes of metabolic acidosis

Answer 20

hyperchloremic:
- diarrhea
- acetazolamide
- IV hyperalimentation
- interstitial renal disease
- renal tubular acidosis

increased undetermined anion:

• generalized renal failure
• DKA
• alcholic ketoacidosis
• lactic acidosis

Question 21

list some causes of metabolic alkalosis

Answer 21

• vomiting
• nasogastric suction
• diuretics
• alkali treatment
• corticoid treatment
• severe K+ depletion
• Cl- restriction

Question 22

list some causes of respiratory acidosis

Answer 22

• respiratory failure
  
  • obstructive lung disease
  • chest wall disease
  • mechanical hypoventilation
• CNS depression
• severe pulmonary edema
• status asthmaticus
• primary hypoventilation
• pneumothorax
• abdominal distension

Question 23

list some causes of respiratory alkalosis

Answer 23

• hyperventilation
• G(-) sepsis
• pulmonary emboli
• pneumonia
• hepatic failure
• high altitude
• severe anemia

Question 24

describe the relationship between alveolar PCO2 and ventilation rate

Answer 24

nearly linear, direct relationship

-but when PCO2 of inspired air comes near to alveolar PCO2 (40 mmHg), CO2 elimination becomes difficult

Question 25

explain the mechanism of CO poisoning

Answer 25

• CO binds to Hb with greater affinity than O2 binds Hb
• also, binding of CO to one of four O2 binding sites on Hb results in retention of O2 at the other sites -> fail to release O2 to tissues

shifts O2 dissociation curve to the left

Question 26

describe 3 non-chemical influences on ventilation

Answer 26

• proprioceptors and stretch receptors - stimulate ventilation in response to physical disturbance (slap, tickle)
• irritant receptors - chemical/mechanical irritants or histamine/bradykinin in allergic response -> rapid shallow breathing + bronchoconstriction
• other pulmonary receptors - Hering-Breuer reflex: stretch receptors in vagus inhibit respiration; deflation receptors - rapid, shallow breathing

Question 27

what is the RAS

Answer 27

reticular activating system - diffuse network of neurons in midbrain and medulla that contribute to many of the autonomic functions