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Regulation of Respiration
Notes from lecture
57
Nursing
Graduate
06/17/2014

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Term
Medullary Respiratory Center
Definition
* generates the spontaneous cycle of respiration
* located in reticular formation of the medulla, just under the floor of the 4th ventricle
Term
Respiratory Center responds to input from:
Definition
* the brain
* the autonomic nervous system
* central and peripheral receptors
Term
What are the 3 major groups of neurons that make up the respiratory center?
Definition
1. Dorsal Respiratory Group (DRG)
* deals with inspiration
2. Ventral Respiratory Group (VRG)
* deals with expiration
3. Pneumotaxic Center (located in the pons)
* controls the rate and depth of respiration
Term
What is the general location of the 3 major groups of neurons that make up the respiratory center?
Definition
bilaterally in the medulla oblongata and pons of the brain stem
Term
Dorsal Respiratory Group (DRG)
Definition
deals with inspiration
Term
Ventral Respiratory Group (VRG)
Definition
deals with expiration
Term
Pneumotaxic Center (located in the pons)
Definition
controls the rate and depth of respiration
Term
Location of Dorsal Respiratory Group (DRG)
Definition
Extends the length of the medulla
Term
Where are most of the neurons in the DRG located?
Definition
In the nucleus of the tractus solitarius
Term
What nerves transmit signals into the DRG from the peripheral chemoreceptors, baroreceptors and other lung receptors?
Definition
The vagus and glossopharyngeal nerves
Term
The DRG controls what aspect of respiration?
Definition
the Rhythmicity of respiration (pacemaker of normal respiration)
Term
How does the DRG control the Rhythmicity of respiration?
Definition
* works by ramping up a signal over a period of 2 seconds and then shutting down (it does not work by turning a signal on with one quick burst)
* This results in diaphragmatic stimulation and even inspiration (vs short gasps to gradually increase the lung volume)
* the shutting down is also important because it allows time for elastic passive lung recoil
* the ramping up time can be shortened during heavy breathing or exercise and the expiratory phase can also be shortened
Term
Hering-Breuer Inflation Reflex
Definition
* when the lungs become over inflated, they signal a feedback that “switches off” the inspiratory ramp

* the over stretch leads to vagal stimulation which transmits to the DRG switching off the “ramp up” phase
Term
At what point does the Hering-Breuer Inflation Reflex occur?
Definition
* we think that the “over stretch” doesn’t come into play until the tidal volume is > than 1.5L (or 3x greater than normal)
Term
What receptors are used in activating the Hering-Breuer Inflation Reflex?
Definition
the stretch receptors in the muscle walls of the bronchi and bronchioles (they transmit important info about lung stretch to the DRG)
Term
What is the main effect of the Hering-Breuer Inflation Reflex (the end result)?
Definition
To protect against excessive lung inflation and barotrauma/pneumothorax
Term
What can happen temporarily when the Hering-Breuer Inflation Reflex is activated?
Definition
apnea
Term
Chemical or mechanical airway irritation can result in what?
Definition
A reflex cough, sneeze, hyperpnea, bronchoconstriction and increase in BP.
Term
Juxtopulmonary capillary (J) receptors
Definition
responsible for the subjective “shortness of breath” or dyspnea encountered during pulmonary congestion and edema due to LV failure
Term
What stimulates the Juxtopulmonary capillary (J) receptors?
Definition
pulmonary vascular congestion or an increase in interstitial fluid leading to tachypnea
Term
Location of Juxtopulmonary capillary (J) receptors
Definition
The walls of the pulmonary capillaries or interstitium
Term
C-Fibers
Definition
-innervate the pulmonary J receptors
-the afferent pathway from the J-receptors
Term
C-Fibers Location
Definition
They "lie near the pulmonary microcirculation"
Term
Are C-Fibers slow or fast, and are they myelinated or unmyelinated?
Definition
Slow & Unmyelinated
Term
According to the powerpoint, what nerve are C-fibers IN (within)?
Definition
The vagus nerve
Term
What lung receptors respond to interstitial fluid or pulmonary edema? (Dr. Louren's example test question from class)
Definition
Juxtopulmonary capillary (J) receptors
Term
Pneumatic Center
Definition
primary function is to control the switch off point of the inspiratory ramp (DPG)
Term
Pneumatic Center Location
Definition
In the Pons
Term
What happens if the signal from the pneumatic center is strong?
Definition
The inspiration lasts for a shorter period of time
Term
What happens if signal from the pneumatic center is weak?
Definition
The inspiration lasts for a longer period of time.
Term
The pneumatic center can control respiratory rate and increase or decrease it to what levels?
Definition
- Up to 30-40 bpm or as little as 3-5 bpm
Term
VRG (Ventral Respiratory Group) Location
Definition
In the medulla near the DRG's
Term
Do the ventral respiratory group neurons fire during normal quiet breathing?
Definition
No
Term
VRG (Ventral Respiratory Group)
Definition
* Stimulation may lead to either inspiration or expiration
* These neurons provide a powerful signal to the abdominal muscles to help with exhalation during heavy breathing
Term
How does the VRG "act as a contributory to the DRG"?
Definition
When the respiratory drive increases, then the signals from the DRG spill over into the VRG area.
Term
Ultimate goal of respiration
Definition
homeostasis of oxygen, carbon dioxide, and hydrogen ions (pH)
Term
The respiratory center is very sensitive to changes in the chemical concentrations of what?
Definition
O2, CO2, H ions
Term
What effect does excessive CO2 have on the central respiratory center?
Definition
Increases inspiration and expiration mechanisms
Term
Does O2 directly impact the central medullary respiratory center?
Definition
No, but it does act on the peripheral chemoreceptors located in the carotid and aortic bodies.
Term
Can carbon dioxide directly stimulate the DRG , VRG, or pneumatic center
Definition
No
Term
How does carbon dioxide indirectly stimulate the DRG, VRG, and pneumatic center?
Definition
Via chemosensitive neurons located near these centers that are most sensitive to changes in HYDROGEN IONS
Term
Can hydrogen ions readily cross the blood brain barrier?
Definition
No, because they are polar
Term
Can carbon dioxide quickly cross the blood brain barrier?
Definition
Yes
Term
What happens to stimulate the respiratory center after CO2 crosses the blood brain barrier?
Definition
* CO2 combines with H2O to form carbonic acid
* Carbonic Acid is then dissociated into bicarbonate ions and hydrogen ions
* This is how hydrogen ions stimulate the chemoreceptors
Term
Do changes in blood CO2 have a little or a huge impact on the respiratory system?
Definition
a HUGE impact
Term
What do high levels of PaCO2 do to minute ventilation?
Definition
-Increase minute ventilation (in an attempt to return the pH to normal).
Term
HOW LONG DOES THE CO2 DRIVEN STIMULATION OF THE CENTRAL CHEMORECEPTORS LAST?
Definition
ONLY FOR A COUPLE OF DAYS
Term
Why does the CO2 driven stimulation of central chemoreceptors only last for a couple of days?
Definition
* As levels of bicarbonate ions build, they then recombine with hydrogen ions (the formula is driven in the opposite direction).
* AND the kidneys react to the the lower pH by RETAINING bicarbonate.
* For this reason, an elevation in CO2 is a strong stimulus for a couple of days and then the effect disappears (COPD)
Term
True or false:
In normal circumstances, the HGB has an ability to shift its affinity and delve adequate amounts of oxygen despite changes in lung ventilation (up to a point) to tissue.
Definition
True
Term
What is the most effective way to impact blood oxygen concentration?
Definition
Changing the FiO2
Term
What is the most effective way to impact PaCO2?
Definition
By changing minute ventilation (and changing tidal volume is the most effective way to change minute ventilation)
Term
What is a special mechanism for respiratory control?
Definition
Peripheral chemoreceptors located OUTSIDE THE BRAIN, that work when the tissue gets in trouble due to lack of oxygen.
Term
Location of peripheral chemoreceptors
Definition
In the aortic root (specifically in the aortic body), and the bifurcation of the carotids (specifically the carotid bodies)
Term
At what PaO2 are the peripheral chemoreceptors stimulated?
Definition
When the PaO2 falls to <70mmHg
Term
The peripheral chemoreceptors send signals via which nerves?
Definition
* Hering’s Nerve (also called the pharyngeal branch) of the GLOSSOPHARYNGEAL nerve from the carotid bodies
* AND the VAGUS NERVE from the aortic bodies.
Term
When is the peripheral chemoreceptors stimulus especially important?
Definition
When the PaO2 falls between 30-60 mmHg.
Term
In which disease state are peripheral chemoreceptors especially important?
Definition
COPD
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