Respiratory 5

Question 1

Describe how the NS adjusts the rate of alveolar ventilation.

Answer 1

-PO2 & PCO2 in arterial blood = hardly altered
[VE = VT x f]
[VA = f x (V-VD)]

Question 2

What are the 4 components of the control of breathing?

Answer 2

1. Control center for breathing in brain stem
2. Chemoreceptors for O2 & CO2
3. Mechanoreceptors in lung & joints
4. Respiratory muscles (activity is directed by brain stem centers)
   *voluntary control can be exerted by commands from CC = override brain stem
   >EX: breath holding or voluntary hyperventilation

Question 3

Describe what the respiratory center is composed by.

Answer 3

-groups of neurons located bilaterally in medulla oblongata & pons
1. Dorsal respiratory group = MEDULLARY RESPIRATORY CENTER
2. Ventral respiratory group = MEDULLARY RESPIRATORY CENTER
3. Pneumotaxic center = PONS

Question 4

Describe the DRG.

Answer 4

-controls respiration
-neurons located in nucleus of tractus solitarius (NTS)
-NTS = sensory termination of both the vagal & glossopharyngeal nerve = transmit sensory signals into the respiratory center from:
1. Peripheral receptors
2. Baroreceptors
3. Types of receptors in the lungs

Question 5

Describe how the basic rhythm of respiration is generated in the DRG neurons.

Answer 5

-nervous signal transmitted to inspiratory muscles (diaphragm) = NOT instantaneous burst of APs
>begin weak, increases (inspiration) in a ramp manner for 2s, ceases for 3s
>turns off excitation of diaphragm = allows elastic recoil of lungs (expiration)
-another cycle begins & repeats

Question 6

What are the 2 qualities of the inspiratory ramp that are controlled?

Answer 6

1. Rate of increase of ramp signal
   -heavy respiration = ramp increases
2. Limiting point where ramp ceases
   -controls rate of respiration
   -earlier the ramp ceases = shorter duration of inspiration/expiration = increase in freq

Question 7

Describe the pneumotaxic center.

Answer 7

-transmit signals to inspiratory area
-controls ‘switch-off’ point in inspiratory ramp
>limit inspiration = control duration of filling phase of lung
>increase rate of breathing
—limitation of inspiration also shortens expiration

Question 8

Describe a weak VS strong pneumotaxic signal.

Answer 8

WEAK:
-reduce rate to 3-5 breaths per min
STRONG:
-increase rate to 30-40 breaths per min

Question 9

Describe the ventral respiratory group.

Answer 9

-overdrive mechanism
-when high levels of pulmonary ventilation are required (ex. Exercise)
-neurons inactive during normal respiration
dont participate in rhythmic oscillation that controls respiration

Question 10

How does the brain stem control breathing?

Answer 10

1. processing sensory info
   -PAO2
   -PACO2
   -pH
   *sensory info rely on peripheral & central chemoreceptors
2. sending motor info to diaphragm

Question 11

Describe central chemoreceptors.

Answer 11

-located in brain stem
-minute-to-minute control of breathing
-receptors communicate w inspiratory center (DRG)
-sensitive to increase in PCO2
>decrease in PO2
>decrease in pH (increase in H+ ions)
—increase in acidity

Question 12

Describe how CO2 enters the CSF.

Answer 12

-CO2 in blood performs hydration reaction
-BBB is impermeable to H+ & HCO3 = ions are tapped in vascularity (dont enter brain)
-CO2 is permeable
>enters ECF of brain & crosses brain-CSF barrier & enters CSF

Question 13

How do central chemoreceptors respond to changes in PCO2?

Answer 13

-in CSF, CO2 is converted to H+ & HCO3
>increase in arterial PCO2 = increase in PCO2 of CSF = decrease in pH
-decrease in pH detected by the central chemoreceptors near CSF = signals inspiratory center to increase breathing rate = HYPERventilate

Question 14

Describe peripheral chemoreceptors.

Answer 14

-located in carotid & aortic bodies (high blood flow)
-info relayed to DRG via glossofarigeal & vagal n
-sensitive to decrease in PO2
>increase in PCO2
>decrease pH
HYPOventilation

Question 15

How do peripheral chemoreceptors respond to change in PCO2?

Answer 15

-when O2 conc in arterial blood is below (60mmhg) - chemoreceptors are stimulated
-low PO2 excites nerve endings in carotid & aortic bodies = glandular cells ‘glomus cell’
>cells synapse directly/indirectly with nerve endings
>chemoreceptor

Question 16

Describe the stimulation of the glomus cell chemoreceptor by O2 deficiency.

Answer 16

*When PO2 decreases below 60mmhg, K channels close & cause depol ->
*voltage gated Ca channels open & increase cytosolic Ca which stimulates transmitter release (ATP & ACH) ->
*transmitter activates afferent fibers that send signals to CNS & stimulates respiration

Question 17

Describe what happens to the firing rate of sensory neurons when there’s a decrease in PO2.

Answer 17

-rate increases
-sensitive to PO2 60-30mmhg
>hemoglobin saturation with O2 decrease
-info relayed to DRG & breathing rate increases

Question 18

Describe lung stretch receptors.

Answer 18

-mechanoreceptors in smooth muscle of airways
-stimulated by distension of lungs = reflex decrease in breathing rate = “hering-breuer reflex”
>prolongs expiratory time
>lungs dont over-inflate

Question 19

Describe joint & muscle receptors.

Answer 19

-mechanoreceptors in joints & muscles
-detect movement of limbs = instruct inspiratory center to increase breathing rate
-info from joints & muscle = imp in early ventilators response to exercise (anticipatory)

Question 20

Describe irritant receptors.

Answer 20

-noxious chemicals
-located between epithelial cells lining airways
-chemical & mechanical stimuli
-info from receptors travel to medulla = reflex constriction of bronchial smooth muscle = increase breathing rate

Question 21

Describe the response of the respiratory system during exercise.

Answer 21

-demand for O2 increases & more O2 is supplied by increasing ventilation rate
-matching between O2 consumption & CO2 production & ventilation
-moderate exercise: no change in arterial PO2, PCO2, or pH
>venous PCO2 increases

Question 22

Describe the short term response to high altitude.

Answer 22

-hyperventilation
-stimulate peripheral chemoreceptors
-medullary inspiratory centers activated & increase breathing rate
>respiratory alkalosis (increase in pH)
>increase in pH = inhibit central & peripheral chemoreceptors & offset increase in ventilation rate
*hours/days = bicarbonate excretion increases & pH decreases to normal

Question 23

Describe the long term adjustments to hypoxia.

Answer 23

1. Production of more erythrocytes (via erythropoietin)
2. Decreases affinity of hemoglobin for O2 due to increased conc of (2,3-DPG) unloading of O2
3. Increases capillary density in muscle = angiogenesis
   recall briskets disease