Lecture 24: Regulation Of Respiration Flashcards
1
Q
5 Respiratory Centers
A
- Dorsal respiratory group: DRG
- Ventral respiratory group: VRG
- Pontine respiratory group: PRG
- Botzinger complex: BotC
- Pre-Botzinger complex
2
Q
Generation of Normal Breathing Pattern
A
- Medullary respiratory centers:
- These centers that initiate breathing are located in the reticular formation of the medulla. These centers include:
- The DORSAL RESPIRATORY GROUP (DRG): Located in the nucleus of the tractus solitarius
- The VENTRAL RESPIRATORY GROUP (VRG)
- Pontine respiratory centers:
- The pontine respiratory centers include two areas located in the pons:
- The APNEUSTIC CENTER
- The PNEUMOTAXIC CENTER (= Pontine Respiratory Group (PRG)
- See Slide 6-9
3
Q
Dorsal Respiratory Group
A
- Located in the dorsal portion of the medulla
- Sets basic rhythm of respiration
- Most of the neurons are in the nucleus of the tractus solitarius (NTS) and medulla reticular substance.
- NTS is the sensory termination of both the Vagal and Glossopharyngeal nerves.
- Receives information from:
- Peripheral chemoreceptors
- Baroreceptors
- Several types of receptors in the lungs
- Principal initiators of phrenic nerve activity
- Receive many fibers from the ventral respiratory group
- Receives lots of sensory information via the nucleus tractus solitarius
- Mainly associated with inspiration:
- Establishes ramp signal
4
Q
Ramp Signal
A
- The nervous signals transmitted to the inspiratory muscles (mainly diaphragm) during normal respiration:
- Begin weakly
- Increase steadily for about 2 seconds
- Cease abruptly for about 3 seconds:
- Allows for elastic recoil of lungs and chest wall to cause expiration
- During heavy respiration:
- Rate of increase of ramp signal increases rapidly.
- Usual method for controlling rate of respiration:
- Control limiting point at which ramp suddenly ceases
- The earlier the ramp ceases, the shorter the duration of inspiration and expiration.
- Thus, the primary function of the PRG (Pneumotaxic center) is to control the “switch-off” point of the inspiratory ramp.
- A strong PRG signal results in 30-40 breaths per minute.
- A weak PRG signal results in 3-5 breaths per minute.
- See Slide 13
5
Q
Pontine Respiratory Group
A
- Pneumotaxiccenter
- Located in the superior pons
- In the 1920’s, lesions of the PRG were found to also influence respiratory timing.
- Specifically, lesions of the PRG result in the loss of the ability to turn off inspiration.
- Without additional input from vagus nerves
- Mainly controls rate and depth of breathing
- Transmits signals to the inspiratory center (DRG)
- Apneustic center:
- Located in the inferior pons
- Loss of function causes prolonged inspiratory gasping (apneuses).
- Normal function may be to limit lung expansion.
- See Slide 16
6
Q
Ventral Respiratory Group
A
- Located in the ventrolateral portion of the medulla
- Neurons of this group are found in the retrofacial nucleus, nucleus ambiguous and nucleus retroambiguous.
- The rostral part of the VRG is the Botzinger complex and may be associated with coordinating VRG output.
- The intermediate part of the VRG is associated with the dilation of the upper airway during inspiration.
- Neurons of the caudal region synapse with motor neurons to the internal intercostals and other muscles used for forced expiration.
- The neurons of this group are almost totally inactive during normal quiet respiration.
- These neurons do not participate in the basic rhythmical oscillation that controls respiration.
- During increased pulmonary ventilation, respiratory signals spill over from the DRG into the VRG, which then contributes to the increased respiratory drive.
- The retrofacial nucleus contains expiratory neurons which form the Botzinger complex.
7
Q
Pre-Botzinger Complex
A
- This is a small area in the rostral part of the VRG.
- Believed to be the site which generates the timing (frequency) of the respiratory rhythm (Central pattern generator).
- Deciding the length of inspiration and expiration is also important in determining the frequency.
- See Slide 20
8
Q
Hearing Breuer Inflation Reflex
A
- This reflex is a protective mechanism to prevent excess inflation of the lungs.
- It begins with stretch receptors in the muscular portions of the walls of the bronchi and bronchioles.
- See Slide 22
9
Q
Chemoreceptors
A
- An increase in carbon dioxide levels (hypercapnia) or a decrease in oxygen levels (hypoxia) result in decreased activity in most neurons.
- This would be counterproductive for chemoreceptors, because it would result in a decrease in gas exchange.
- Chemoreceptors INCREASE their rate of activity when hypoxia or hypercapnia occur.
10
Q
2 Types of Chemoreceptors
A
- Central:
- Located on ventral surface of medulla
- Indirectly sensitive to carbon dioxide levels in blood (based on pH)
- Peripheral:
- Sensitive to concentrations of oxygen (especially), carbon dioxide, and hydrogen ions
- Include:
- Receptors in aortic arch
- Carotid body receptors
11
Q
Central Chemoreceptors
A
- The central chemosensitive area is located bilaterally 0.2 mm beneath the ventral surface of the medulla.
- These receptors are especially sensitive to [H+].
- H+does not easily cross the blood-brain barrier.
- CO2 easily crosses the blood brain barrier.
- CO2 + H2O –> HCO3 + H+
- Heightened sensitivity to increased levels of carbon dioxide lasts for several hours but then begins to decline due to renal adjustments to the plasma pH.
- Kidneys increase blood bicarbonate levels:
- Reduces plasma and CSF [H+]
- Bicarbonate ions diffuse through the blood-brain barrier.
12
Q
Peripheral Chemoreceptors
A
- Peripheral receptors are more sensitive to changes in oxygen levels in the blood and less sensitive to changes in plasma concentrations of carbon dioxide and hydrogen ions.
- Some peripheral chemoreceptors are located in the aortic arch (aortic bodies).
- Most peripheral chemoreceptors are located in the carotid bodies at the bifurcation of the common carotids.
- (Note that these are not the same as the carotid baroreceptors, which are more important in regulating blood pressure.)
- Carotid body cells:
- Type I (glomus) cells:
- Chemosensors
- PO2-dependent K+channels result in K+ efflux when PO2 is high, leading to hyperpolarization of the cells.
- ↓PO2closes channels and results in a depolarization that opens calcium channels, leading to neurotransmitter release.
- Located close to fenestrated capillaries
- Type II (sustentacular cells).
- Play a support role similar to glial cells
- Note that:
- Chemoreceptors are exposed to PO2 of arterial blood not venous blood.
- PCO2and H+are mainly responsible for regulating ventilation (at sea level) for PO2 between 60 and 80 mm Hg
- See Slide 30-31
13
Q
Slow-adapting pulmonary stretch receptors:
A
- These receptors are located within the airways of the lungs.
- These are slowly adapting receptors that are sensitive to stretch of airways.
- Signals from these receptors travel in the vagus nerves to the medulla.
- Signals from these receptors:
- Terminate inspiration
- Prolong expiration
- Are probably not important in controlling tidal volume in adults at rest.
- Are important in controlling respiration in:
- Infants and Adults during exercise (Not sure if this is a mechanoreceptor)
14
Q
Rapidly-adapting pulmonary stretch receptors
A
- Appears to officially be a mechanoreceptor
- These receptors are located within the airways of the lungs.
- Sensitive to irritation, foreign bodies in airway, and stretch
- Signals from these receptors travel in the vagus nerves to the brain.
- Signals from these receptors elicit cough
- These receptors override the normal respiratory control mechanisms
15
Q
J Receptors
A
- These are sensory endings (C fibers) in the alveolar wall in juxtaposition to pulmonary capillaries.
- They are sensitive to:
- Pulmonary edema (i.e., congestive heart failure)
- Signals travel from these receptors to the brain via the vagus nerves.
- Stimulation of these receptors elicits:
- Cough
- Tachypnea
- These reflexes override the normal respiratory control mechanisms
