1.4 Control of Respiration Flashcards
(63 cards)
1
Q
List the normal respiratory rates in:
1. Newborns
2. Infants
3. Children (1- 7 yrs)
4. Adults
A
- Newborns: 44
- Infants: 20-40
- Children (1- 7 yrs): 18-30
- Adults: 12-20
2
Q
What is the trend observed in respiratory rate and age
A
it decreases with age
3
Q
What is the main reason why newborns have a very relatively high respiratory rate of 44 breath/min
A
because of their high metabolic demand
4
Q
What are the 3 primary components involved in respiration which facilitates exchange of gas at cellular levels
A
- Central neural control (respiratory drive)
- Respiratory muscles & Lungs
- Sensory input systems
5
Q
What are the 3 main parts of the brain involved in the control of breathing/respiration and what is the main function of these control centres
A
- Cortex
- Medulla
- Pons
They help to generate and regulate the depth and rhythm of breathing
6
Q
What are the 4 types of sensory input systems involved in respiration
A
- Mechanoreceptors
- Metaboreceptors
- Peripheral chemoreceptors
- Central chemoreceptors
7
Q
What are the structures & muscles involved in respiration
A
Structures:
- Lungs
- Upper airway
Muscles:
1. Diaphragm
2. Intercostal muscles:
- External
- Internal
3. Abdominal muscles
8
Q
What are the 2 main modes of respiratory regulation?
A
- Chemical
- Neural
9
Q
What are the subdivisions of neural regulation& what are the parts of brain involved in each
A
- Voluntary: Cortex
- Involuntary/Autonomic: via the brainstem; medulla & pons
10
Q
Changes in levels of which chemicals mediate the chemical respiratory regulation
A
- O2
- CO2 (most potent)
- pH
11
Q
Where is the respiratory neuronal centra located at?
A
entire length of medulla & pons
12
Q
What are the 4 functional groups of Respiratory Neuronal Centra
A
- Dorsal respiratory group (DRG): medulla
- generates basic rhythm of respiration - Ventral respiratory group (VRG): medulla
- active during forced breathing - Apneustic center: pons (lower)
- stimulates deep & prolonged breathing - Pneumotaxic centre: pons (upper)
- Regulates the breathing rhythm by:
- inhibiting apneustic centre
- promoting switch from inspiration to expiration
13
Q
What is the location of the DRG
A
- Nucleus Tractus Solitarius (NTS) in the medulla oblongata
13
Q
Which 2 cranial nerves are the afferent input of the DRG
A
- CNIX: Glossopharyngeal
- CNX: Vagus
14
Q
What are the 3 main functions of the DRG
A
1.Set the basic rhythm of breathing
- generates the inspiratory drive
- Receive the signals from:
- Higher brain centres (voluntary control)
- Brainstem (automatic control)
- Reflexes (Hering-Breuer) - Sends output via:
- Phrenic nerve –> Diaphragm contraction
- Intercostal nerves –> external intercostal muscle contractions
15
Q
Describe the mechanism of Inspiratory Ramp Signal
A
- Gradual increase in neural firing during inspiration
- Duration:
- Inspiration: 2 seconds
- Expiration: 3 seconds
16
Q
What is the main advantage of Inspiratory Ramp Signal
A
ensures smooth and study lung expansion, instead of abrupt gasps
17
Q
What are the 3 afferent inputs that feed into the NTS (Nucleus Tractus Solitary’s) that modulate breathing
A
- Chemoreceptors
- Baroreceptors
- Lung & Airway receptors
18
Q
What is the main function of Ventral Respiratory Group (VRG)
A
activated during forceful or laboured breathing, such as during:
1. Exercise
2. Panic attacks
3. Respiratory distress
19
Q
What is the main output of Ventral Respiratory Group (VRG)
A
- Internal intercostal muscles & Abdominal muscles –> Expiration
- Accessory inspiratory muscles (during deep or laboured inhalation)
20
Q
What is the location of Pre-Botzinger complex
A
on either side of medulla
sandwiched between 2 nucleus:
- NA: nucleus ambiguous
- LRN: Left reticular nucleus
21
Q
What is the function of Pre-Botzinger complex
A
- acts as the primary pacemaker for breathing rhythm
- spontaneously active neurons fire in rhythmic bursts
- generates inspiratory rhythm
- relayed to the DRG & phrenic motor neurons to initiate the inspiration
22
Q
What is the location of the pneumotaxic centre
A
- upper pons
23
Q
What is the main function of pneumotaxic centre
A
- inhibits the apneustic centre
- active during inspiration & expiration
- controls the switch off point of inspiration –> Shortens the inspiratory duration
- it ensures smooth transition between inspiration & expiration (coordinates rhythm)
24
What is the location of the apneustic centre
- lower pons
25
What is the main function of apneustic centre
- stimulates the inspiratory neurons in the medulla (DRG)
- prolongs the inspiration (produces a deep gasping breath --> apneusis)
26
What inhibits the apneustic centre?
1. pneumotaxic centre
2. Vagus nerve
27
What is the overall aim of the chemical regulation of respiration
to maintain PaCO2, pH & PaO2 under varying conditions
28
What is the main regulatory purpose of adjusting minute ventilation
to regulate PaCO2
29
What are the locations of the peripheral chemoreceptors
1. Carotid bodies (via CNIX: Glossopharyngeal nerve)
2. Aortic bodies (via CNX: vagus nerve)
30
What are the main stimulus that trigger peripheral chemoreceptors
1. decreased O2 (especially lower than 60mmHg)
2. increased CO2
3. decreased pH (acidosis)
31
Which chemoreceptors are more sensitive to hypoxia and trigger emergency ventilatory processes in hypoxia
peripheral chemoreceptors
32
What is the location of the central chemoreceptors
in the ventral surface of the medulla, in the chemosensitive area
33
What is the main stimulus for central chemoreceptors
- H+ ions in the CSF
(CO2 crosses the blood-brain barrier BBB and reacted with H2O forms H+ ions)
- CO2 directly has little effect, it is the H+ ions in the that directly stimulate the chemoreceptors
34
What type of reflex is Hering-Breuer inflation reflex
a. protective reflex
35
What is the trigger, mechanism & purpose of Hering-Breuer inflation reflex
Triggers:
- steady inflation of lungs
- detected by stretch receptors in airway smooth muscles
Mechanism:
- Lung inflation --> stretch receptor activation
- Afferent via vagus nerve to the brainstem
- DRGs inspiratory ramp signals are switched off
- Inspiration is inhibited
- Expiration is prolonged
Purpose:
- prevent lung overinflation
- protects against barotrauma
36
Explain the significance of Hering-Breuer inflation reflex
1. inactive during quiet breathing
2. active during large inspirations (tidal volume >> 1-1.5L, eg: during exercise)
3. important in newborns: helps to regulate the neonatal breathing rhythm
37
What type of reflex is Hering-Breuer Deflation Reflex
a. protective reflex
38
Describe the following about Hering-Breuer Deflation Reflex:
1. Triggers
2. Mechanism
3. Purpose
1. Triggers:
Sudden lung deflation (eg: pneumothorax or atelectasis
2. Mechanism
- Deflation causes activation of irritant recceptoirs in the smooth muscles
- afferent via vagus nerve and stimulate DRG
- Inspiration is initiated
- Expiration is shprtened
3. Purpose
- restores ventilation in deflated lung areas
- encourages re-expansion of collapsed alveol
39
What is meant by hypercapnia
elevated levels of CO2 In the blood
40
What are some of the causes of hypercapnia
1. Hypoventilation
2. Airway obstruction
3. Increased metabolism
41
Describe the mechanism of hypercapnia drive
- increased CO2 in the blood
- CO2 + H20 --> H2CO3 --> H+ + HCO3-
- H+ stimulates the central chemoreceptors in the medulla
- Respiratory centres activated
- Ventilation increases (to remove the excess CO2)
42
What's the ventilation pattern triggered by the hypercapnic drive
- Deep, slow breaths
- Tidal volume increases more than respiratory rate
- minimizes dead space ventilation & maximises CO2 clearance
43
What is the importance of hypercapnia drive
1. maintains normal PaCO2 --> prevents respiratory acidosis
2. ensures proper pH balance --> pH drops (acidosis)
3. Adjusts ventilation dynamically --> matches metabolic demand (eg:during exercise)
44
What is the hypoxic drive
backup respiratory stimulus triggered by low PaO2
(esp when below 60mmHg)
45
What is the mechanism of hypoxic drive
- sensed by peripheral chemoreceptors
- respond directly to low PaO2
- sends signals via the CNIX & CNX
- activates brainstem respiratory centres
46
Is hypoxic drive active during normal breathing
- under normal conditions, CO2 is the main trigger, not O2
- Hypoxic drive only kicks in only when PaO2 is really low
47
What is the main clinical significance of hypoxic drive in a person with chronic hypercapnia and hypoxia
- Chronically retains CO2 --> central chemoreceptors become desensitised so depends on low O2 as a respiratory trigger
- if too much O2 given it wipes out the only active stimulus therefore leads to respiratory failure or apnea
- So in chronic CO2 retainers like COPD patients make sure to not correct the PaO2 to a normal all at once
48
What is meant by the breaking point
point at which the body's ability to remove carbon dioxide (CO2) through ventilation becomes overwhelmed, leading to a rapid increase in arterial CO2 levels
(body can no longer eliminate CO2 fast enough to keep up with how much is being produced)
49
When does the body reach the breaking point
1. Strenuous exercise
2. Metabolic stress
3. Respiratory compromise
50
What happens to cause breaking point
- CO2 builds up
- Arterial PCO2 increases rapidly
- Blood pH drops (acidosis)
- ventilatory demand exceeds more than what lungs can deliver
- Tissue oxygenation drops
51
CHEYNE-STOKE BREATHING:
Description
- Occurrence of waxing (increasing in depth) & waning (decrease in depth) type of respiration with a period of apnea in between
- (lasts for few seconds to few minutes& then the cycle repeats)
52
CHEYNE-STOKE BREATHING:
causes
- after hyperventilation,
- Congestive Cardiac Failure ,
- increased intracranial tension (ICT)
- brainstem stroke or metabolic encephalopathy
53
BIOT’S BREATHING:
description
- Regular deep respirations
- interspersed with periods of apnea
54
BIOT’S BREATHING:
causes
- Caused by damage to the pons due to stroke, trauma, or uncal herniation
55
Bezold - Jarisch reflex defintion
A cardiovascular reflex initiated in response to certain stimuli in the heart.
56
Bezold - Jarisch reflex:
Mechanism:
* Triggering factors stimulate cardiopulmonary chemoreceptors & mechanoreceptors in left ventricular (LV) wall
* → Signal via unmyelinated vagal afferent type C fibers
* → Inhibits medullary vasomotor center
* → Leads to ↑ parasympathetic tone
57
Bezold - Jarisch reflex:
Mechanism:
- Bradycardia
- Hypotension
- Peripheral vasodilation
58
Afferent Impulses from Proprioceptors
Source:
* Proprioceptors → stimulate inspiratory neurons (I neurons)
* → Result: Increased rate and depth of respiration
- Active/passive joint movements stimulate proprioceptors in:
- muscles,
- tendons,
- joints.
59
Afferent Impulses from Proprioceptors:
Pathway:
- Proprioceptors → stimulate inspiratory neurons (I neurons)
- → Result: Increased rate and depth of respiration
60
Afferent Impulses from Irritant Receptors
Location:
Reflex effects based on zone:
* Conducting Zone:
○ → Cough reflex
○ → Sneeze reflex
* Respiratory Zone:
○ → Bronchoconstriction
→ Tachypnoea
- Below mucosa of entire respiratory tract
- Innervated by myelinated vagal fibers
61
Afferent Impulses from Irritant Receptors:
Reflex effects based on zone:
- Conducting Zone:
○ → Cough reflex
○ → Sneeze reflex
- Respiratory Zone:
○ → Bronchoconstriction
→ Tachypnoea
62
Control by higher brain centres
- Afferents from:
- Pathway:
- Limitation:
Afferents from:
* Limbic system & hypothalamus
* Cerebral cortex
Pathway:
* Signals from neocortex → respiratory muscles
(🛑 Bypass medullary neurons)
Limitation:
* Voluntary control cannot override strong chemical stimuli like:
○ ↑ PCO₂
○ ↑ H+ concentration
