regulation of ventilation

Question 1

why is the buffer system so effective?

Answer 1

when acid is added to the body fluids, concentration of HCO3- decreases by conversion to H2CO3 (made from water and CO2), CO2 is eliminated by respiration, minimizing the effect of change in numerator of fraction in equation, and also pH.

Question 2

COPD is?

Answer 2

elasticity of the lung is lost-> incomplete exhalation and therefore retention of CO2. CO2 increases, pH decreases-> respiratory acidosis
increase CO2 also causes shift in O2 dissociation curve-> less O2 bound to Hb.

Question 3

hyperventilation causes respiratory…?

Answer 3

alkalosis. CO2 is blown off and pH increases. when CO2 decreases, respirations slow and may even temporarily stop-> hypoxia

Question 4

what is primary factor in respiratory control?

Answer 4

CO2

Question 5

What does the voluntary control of ventilation?

Answer 5

neurons in cerebral cortex. Impulses sent to respiratory motoneurons via corticospinal tracts-> function in speech, voluntary breath holding, fear and pain

Question 6

what do the centers in the medulla and pons do?

Answer 6

generate rhythmic, patterned excitatory output to muscle groups or either inspiration or expiratory muscles. Lower motor neurons located in phrenic nucleus (C3-C5)

Question 7

what does transection of the brainstem below medulla do the respiration?

Answer 7

stops it completely

Question 8

If transecting above medulla does not stop breathing completely, what does this mean?

Answer 8

indicates that medulla contains neurons sufficient for rhythmic breathing-> constitute central pattern generator (CPG)

Question 9

what group of neurons are apart of the CPG?

Answer 9

neurons capable of rhythmic patterned output in absence of outside influence or sensory feedback. If cut the sensory neurons in vagus nerve, does not block patterned breathing

Question 10

what is the primary stimulus for inspiration?

Answer 10

Dorsal respiratory group (DRG).

Question 11

Where does DRG get stimulus inputs from?

Answer 11

central and peripheral chemoreceptors, pulmonary stretch receptors, somatic pain receptors and mechanoreceptors.

Question 12

how does inspiration increase tidal volume?

Answer 12

during inspiration, phrenic nucleus activity increases in terms of rate and number of units discharged-> increase causes more and more muscle fibers to be recruited-> increase in number of motor units increases tidal volume

Question 13

how is inspiration terminated?

Answer 13

by natural CPG rhythm modulated by sensory feedback

Question 14

how is expiration termed?

Answer 14

primarily passive, although always tonic expiratory output and this may increase and become important in forced exhalation

Question 15

what does the ventral respiratory group neurons control?

Answer 15

contain both inspiratory and expiratory neurons, inspiratory neurons go to accessory muscles

Question 16

transection of pons causes?

Answer 16

no effect on breathing

Question 17

why does a transcetion of the inferior pons cause sustained gasping?

Answer 17

due to unregulated output by inspiratory neurons by apneustic center which is regulated by pneumotaxic center in superior pons. cutting of inferior pons causes prolonged inspiration

Question 18

how can inspiration be stopped with a cut inferior pons?

Answer 18

is vagus is cut and proximal stump is stimulated then inspiration can be stopped.

Question 19

Hering-breuer reflex?

Answer 19

vagal feedback is from stretch receptors in the lungs which when activated send efferent impulses via vagus to inhibit inspiration

Question 20

what is the main conclusion about breathing control?

Answer 20

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

Question 21

what are the chemical controls of ventilation?

Answer 21

CO2 and H+ in CSF acting on central chemreceptors and by carotid and aortic body receptors responsive to pH, CO2 and O2.

Question 22

what is the principal chemical control of ventilation?

Answer 22

arterial CO2 acting at central chemoreceptors

Question 23

why CO2 an effective means of control?

Answer 23

CO2 production is directly related to rate of oxidative metabolism and to pH via the bicarbonate system

Question 24

what nerves are associated with carotid and aortic bodies?

Answer 24

afferents from the carotid are carried to medulla by CN IX and aortic bodies by X.

Question 25

what does each peripheral chemoreceptor contain?

Answer 25

island of 2 cell types (I and II) surrounded by sinusoidal capillaries. Sensory nerve fibers make ending among two cell types. These endings are probably the sensory structures for gas and or H+. Type I cell makes synapses with nerve endings

Question 26

when do neurons in the carotid and aortic bodies increase firing?

Answer 26

increase their discharge when pH decreases. Effect is to increase ventilation by increasing both rate and tidal volume.

Question 27

what does ablation of the carotid bodies result in?

Answer 27

loss of compensatory ventilatory response to hypoxia and about 30% reduction in ventilatory response to high CO2. (same effect if both carotid and aortic body are cut).

Question 28

maximal receptor activity is at?

Answer 28

very low PO2 values, but hypercapnea and acidosis augment the response to lowered PO2.

Question 29

where does CSF PCO2 and arterial PCO2 equilibrate rapidly?

Answer 29

ventral surface of medulla (near CN 6-10 and 11) cell have no direct contain with arterial blood but are bathed in CSF. CSF in close proximity to choroid plexus Blood flow high

Question 30

What is the blood brain barrier is poorly permeable to?

Answer 30

H+

Question 31

Can CO2 cross BBB?

Answer 31

Yes. hydrated to H2CO3, which dissociates to CO2 and H+

Question 32

what does acidosis in medullary CSF case?

Answer 32

enhances tidal volume

Question 33

central chemoreceptors respond..?

Answer 33

directly to H+ and indirectly to CO2.

Question 34

why does ventilatory response to high PCO2 wane after a couple hours?

Answer 34

compensatory transport of HCO3- across BBB via anion exchanger (HCO3- for CL-)

Question 35

Metabolic acidosis produces what?

Answer 35

respiratory stimulation.

Question 36

hyperventilation causes?

Answer 36

Metabolic alkalosis because fall in blood H+ by blowing off CO2. this depresses ventilation causing a rise in arterial CO2 and H+ eventually restoring normal pH.

Question 37

what happens to ventilation when metabolism increases?

Answer 37

PCO2 rises and ventilation increases to lower PCO2.

Question 38

the relationship between alveolar PCO2 and ventilation rate is?

Answer 38

nearly linear, but when PCO2 of inspired air comes near to alveolar PCO2-> CO2 elimination becomes difficult.

Question 39

what happens when inhaled CO2 levels are above 7%?

Answer 39

arterial PCO2 rises rapidly resulting in CNS depression, including the respiratory centers, and eventually CO2 narcosis and coma

Question 40

decrease in PO2 below 60 mmHg increases what?

Answer 40

discharge from peripheral chemoreceptors (carotid and aortic bodies)

Question 41

Why is carbon monoxide poisonous?

Answer 41

CO binds to Hb forming carboxyhemoglobin-> affinity between Hb and CO is 230 times stronger than affinity to O2. Binding of CO causes retention of O2 and failure of O2 to be released to tissues, shift of curve to LEFT.

Question 42

what are some non-chemical influences on ventilation?

Answer 42

proprioceptors and stretch receptors-> located in muscles and joints-> can stimulate ventilation
irritant receptors-> stimulated by chemical or mechanical irritants (histamine) and bradykinin during allergic reactions-> receptors in trachea and extrapulonary bronchi cause coughing and receptors in lungs cause rapid shallow breathing and bronchoconstriction

Question 43

when does the hering-breuer reflex function in adults?

Answer 43

at tidal volumes of 1 liter, during strenuous exercise. important in normal breathing in human and infants and other mammals.

Question 44

what may contribute to ventilatory response during pulmonary congestion or edema?

Answer 44

deflation receptors that stimulate rapid shallow breathing