Lecture 6: Regulation Of Respiration Flashcards
Where is the respiratory center located?
Medulla oblongata and pons
Three major respiratory center groups
- Dorsal respiratory
- Ventral respiratory
- Pneumotaxic center
Which respiratory group plays the most fundamental role in control of breathing?
Dorsal respiratory group
The DRG controls ___ and ___
Inspiration and respiratory rhythm
Where is the DRG located?
Medulla; most neurons are contained in the nucleus of the tractus solitarius
What two nerves deliver sensory information to DRG?
- Vagus (X)
- Glossopharyngeal (IX)
DRG receives signals from three sources:
- Peripheral chemoreceptors
- Baroreceptors
- Lung receptors
The DRG generates the ___
Basic rhythm of respiration
What is the inspiratory “RAMP” signal?
The motor signal transmitted from the DRG to the diaphragm
The inspiratory ramp signal is NOT…
An instantaneous action potential burst
The inspiratory ramp signal begins ___
Weakly
The inspiratory ramp signal increases steadily in a…
‘Ramp-like’ manner for 2 seconds to cause contraction of the diaphragm (inspiration)
How does the ramp signal allow expiration to occur?
The excitatory ramp signal abruptly stops for 3 seconds to allow relaxation of diaphragm (expiration)
How does the ramp signal cause inspiration to occur?
Signal begins weakly and increases steadily in a ‘ramp-like’ manner for 2 seconds to cause contraction of diaphragm (inspiration)
What is the advantage of the ramp signal?
It causes a steady increase in inspiratory volume
What are two ways that the ramp is controlled?
- Control of the rate of ramp signal increases
- Control of limiting point at which ramp ceases
Ramp signal ___ during activity, lungs ___
Increases more rapidly during activity; lungs fill more rapidly
The earlier the ramp ceases, the ___ the inspiration duration
Shorter; this also shortens the duration of expiration
The earlier the ramp ceases, the frequency of respiration ___
Increases
The pneumotaxic center transmits signals to ___
DRG inspiratory area
The pneumotaxic center functions to ___ inspiration phase of breathing cycle and secondarily ___ the rate of breathing
Limit inspiration phase of breathing; secondarily increases the rate of breathing
The pneumotaxic center controls the ___ point of the inspiratory point
‘Switch-off’ point
The pneumotaxic center ___ entire respiratory cycle
Shortens
Strength of inhibitory signal determines the ___ and ___
Duration of filling phase and rate of the breathing cycle
When pneumotaxic signal is strong, ___ inspiration phase and ___ rate
Shorter inspiration phase (0.5 sec); increased rate (30 to 40 bpm)
When pneumotaxic signal is weak, ___ inspiration phase and ___ rate
Longer inspiration phase (5 sec); reduced rate (3 to 5 bpm)
Where is the ventral respiratory group located?
In the medulla, anterior and lateral to DRG
VRG stimulation causes ___ as well as ___
Expiration as well as inspiration
VRG is important during…
High levels of pulmonary ventilation (exercise)
VRG is ___ during normal quiet respiration
Inactive; does not appear to participate in basic rhythmic oscillation which controls respiration
VRG contributes to respiratory drive to increase ___
Pulmonary ventilation
VRG stimulates ___ to assist in forced exhalation
Abdominal muscles
Where is the apneustic center located?
In lower pons
What does the apneustic center do?
- Signals the DRG to prevent or slow down the ‘switch-off’ of inspiratory ramp stimuli
- Lungs become almost completely filled with air with only occasional short expiratory gasps
The apneustic center operates in association with the ___
Pneumotaxic center to control the intensity of inspiration
What is the Hering-Breuer Reflex?
A protective feedback reflex which limits the over-inflation of lungs
How does the Hering-Breuer Reflex work?
- Stretch receptors are located in muscular portions of bronchi and bronchioles
- These receptors transmit signals via the vagus nerve (X) to the DRG when lung is overstretched (TV>1.5L)
- Feedback responses switches off the inspiratory ramp and stops further inflation
The Hering-Breuer Reflex ___ the rate of respiration
Increases
What is the ultimate goal of respiration?
To maintain proper concentrations of oxygen, carbon dioxide, and hydrogen ions in the tissue
Excess ___ or ___ in the blood act directly on the respiratory center to increase strength of both inspiratory and expiratory motor signals
Carbon dioxide or hydrogen ions
Does oxygen have a direct effect on respiratory centers?
No—acts on peripheral chemoreceptors in carotid and aortic bodies
What is the chemosensitive area of brainstem?
Highly sensitive area on the ventral medulla surface
The chemosensitive area is responsive to changes in ___ or ___
Blood PCO2 or hydrogen ion concentration
Do hydrogen ions easily cross the blood-brain barrier?
No
Changes in the blood hydrogen ion concentration have ___ effect in stimulating the chemosensitive neurons than changes in blood carbon dioxide
Less effect
How does CO2 stimulate neurons in the chemosensitive area of the brainstem?
By changing the hydrogen ion concentration
Respiratory center activity is increased very strongly by elevations in ___
Blood carbon dioxide levels
CO2 has a ___ effect on the chemosensitive area
Potent, direct effect via H+
CO2 is ___ permeable to the blood-brain barrier, so blood and brain concentrations of CO2 are ___
Highly; equal
How does CO2 react with water to affect the chemosensitive area of the brain?
CO2 reacts with H2O to form carbonic acid, which dissociates into hydrogen and bicarbonate ions in interstitial fluid of medulla or CSF; release of H+ ions in brain stimulate respiratory center activity
Excitation of respiratory center by CO2 is greatest in ___
The first hours of carbon dioxide increase
After first 1 to 2 days of carbon dioxide exposure, the stimulatory respiration response ___
Declines
The effect of CO2 on the respiratory response after first 1 to 2 days decreases to about ___ the initial response
A fifth of the initial response
Why is there a decline in the respiratory response to CO2 after the first 1 to 2 days?
The decline results from renal adjustment of hydrogen ion concentration back to normal
Changes in blood CO2 concentration has ___ acute effect on controlling respiratory drive but a ___ chronic effect after a few days of adaptation
Potent acute effect; weak chronic effect
COPD patients have a ___ response to increased CO2
Blunted response
Increase in PCO2 (above 35 mm Hg) = ___ in ventilation
Drastic increase in ventilation
Steep part of curve =
Blood PCO2 above 35 mm Hg
Decreased pH causes a ___ increase in ventilation
Smaller increase in ventilation
Change in respiration is ___ times less with blood pH range between 7.3 and 7.5
10 times less
Changes in oxygen have ___ on respiratory center
No direct effect
Changes in O2 concentration act indirectly on ___
Peripheral receptors
Hemoglobin-oxygen buffer system delivers normal amounts of O2 to tissues over wide range of pulmonary O2 partial pressures—
60 mm Hg to 1000 mm Hg—the large O2 reserve created by this buffer system is the reason why the respiratory center is not affected by oxygen changes as drastically as the respiratory center responds to PCO2 changes
Blood oxygen levels below PO2 of ___ are sensed by peripheral chemoreceptors
70 mm Hg
Chemoreceptors are located in ___ and ___
Carotid and aorta
What are carotid bodies?
Bifurcations in common carotid
What type of nerve fibers are in the carotid bodies?
Afferent nerve fibers
Afferent nerve fibers pass via CN ___ to act on ___
IX (glossopharyngeal) to act on DRG
Where are the aortic bodies?
Aortic arch
Innervation of the aortic bodies
CN X (vagus) to DRG
What O2 range stimulates the chemoreceptors?
60 mm Hg to 30 mm Hg (hypoxia)—when hemoglobin-oxygen saturation decreases rapidly
Increases in CO2 and hydrogen ion concentration causes…
Increase in respiratory activity
Direct effect of CO2 and pH is ___ times more powerful
7 times
Peripheral stimulation occurs ___ times more rapidly
5 times
Peripheral receptors are important to increase response to CO2 at onset of ___
Exercise
Ventilatory drive by low blood oxygen content (when CO2 and pH remain normal) is not significant until PO2 falls below ___
100 mm Hg
Ventilation ___ when PaO2 falls below 60 mm Hg
Doubles
Acclimatization
The idea that oxygen drives the respiratory center in mountain climbers—respiratory center loses most sensitivity to PCO2 and pH changes over 2 to 3 days
Alveolar ventilation increases greater than ___ after acclimatization in response to low PaO2
400%
Alveolar ventilations curves are displaced to the ___ at higher pH
Right
Alveolar ventilation curves are displaced to the ___ at lower pH
Left
Strenuous exercise can increase oxygen consumption and carbon dioxide formation by ___
20-fold
Alveolar ventilation ___ with increased metabolism during exercise
Increases (linear relationship)
During strenuous exercise, PO2, PCO2, and pH remain ___
Almost exactly normal
What stimulates respiration during exercise?
The PCO2 and PO2 changes caused by exercising muscles
Neurogenic factors stimulate respiratory center to supply ___ and ___ removal
O2 and CO2 removal
Chemical factors provide adjustment in respiratory control to keep ___ and ___ normal
CO2 and pH
Is voluntary control of respiration mediated through the respiratory center?
No—pathway goes from cortex and higher centers downward through corticospinal tract to spinal neurons that drive respiratory muscles
What are the “J receptors”?
Sensory nerve endings in alveolar walls that juxtapose the pulmonary capillaries
The ‘J receptors’ become stimulated when…
Engorged by blood or when pulmonary edema occurs, as in CHF
How does brain edema affect respiratory center activity?
Depresses/inactivates activity (i.e.: head trauma, concussion)
Treatment for brain edema
Mechanical hyperventilation and hypertonic diuresis
What is periodic breathing?
Pattern of short intervals of deep breathing follow by periods of shallow or absent breaths—Cheyne-Stokes is most common periodic cycling
What causes Cheyne-Stokes breathing?
Over-breathing causes a decrease of CO2 and increases blood oxygen in pulmonary blood
Altered pulmonary blood is transported to brain to inhibit excess ventilation
Response is delayed in depressing respiratory center because it takes a few seconds for brain to respond
After a pause in breathing, the cycle resumes with rapid deep breaths again
The potential for C-S breathing is present in ___
Everyone!
Under normal conditions, C-S breathing is ___
Highly ‘damped’
Two separate conditions that allow C-S breathing to occur:
- Long delay in transport of blood from lungs to brain (low CO)
- Increased negative feedback gain (brain damage) due to hypoxia or severe metabolic abnormality
