Respiratory 5 Flashcards
Describe how the NS adjusts the rate of alveolar ventilation.
-PO2 & PCO2 in arterial blood = hardly altered
[VE = VT x f]
[VA = f x (V-VD)]
What are the 4 components of the control of breathing?
- Control center for breathing in brain stem
- Chemoreceptors for O2 & CO2
- Mechanoreceptors in lung & joints
- 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
Describe what the respiratory center is composed by.
-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
Describe the DRG.
-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
Describe how the basic rhythm of respiration is generated in the DRG neurons.
-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
What are the 2 qualities of the inspiratory ramp that are controlled?
- Rate of increase of ramp signal
-heavy respiration = ramp increases - Limiting point where ramp ceases
-controls rate of respiration
-earlier the ramp ceases = shorter duration of inspiration/expiration = increase in freq
Describe the pneumotaxic center.
-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
Describe a weak VS strong pneumotaxic signal.
WEAK:
-reduce rate to 3-5 breaths per min
STRONG:
-increase rate to 30-40 breaths per min
Describe the ventral respiratory group.
-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
How does the brain stem control breathing?
- processing sensory info
-PAO2
-PACO2
-pH
*sensory info rely on peripheral & central chemoreceptors - sending motor info to diaphragm
Describe central chemoreceptors.
-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
Describe how CO2 enters the CSF.
-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
How do central chemoreceptors respond to changes in PCO2?
-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
Describe peripheral chemoreceptors.
-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
How do peripheral chemoreceptors respond to change in PCO2?
-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
Describe the stimulation of the glomus cell chemoreceptor by O2 deficiency.
*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
Describe what happens to the firing rate of sensory neurons when there’s a decrease in PO2.
-rate increases
-sensitive to PO2 60-30mmhg
>hemoglobin saturation with O2 decrease
-info relayed to DRG & breathing rate increases
Describe lung stretch receptors.
-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
Describe joint & muscle receptors.
-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)
Describe irritant receptors.
-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
Describe the response of the respiratory system during exercise.
-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
Describe the short term response to high altitude.
-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
Describe the long term adjustments to hypoxia.
- Production of more erythrocytes (via erythropoietin)
- Decreases affinity of hemoglobin for O2 due to increased conc of (2,3-DPG) unloading of O2
- Increases capillary density in muscle = angiogenesis
recall briskets disease
