Control of breathing Flashcards
Describe the purpose of controlled breathing
To maintain a blood pH between 7.35-7.45, a PaO” of 13.kPa. PaCO2 of 5kPa
Describe the alveolar
ventilation equation
AV= (tidal volume- anatomic dead space) x respiratory rate
Va= VCO2/ PaCO2
Describe odines curse
Also known as central congenital hypoventilation syndrome, a rare disorder that disrupt the ability to breathe automatically
Trouble sensing low O2 levels or high CO2 in their blood during sleep, the brain does not trigger the automatic urge to breathe during sleep, so they need to consciously breathe or use a ventilator during sleep e.g. CPAP
This condition is normally genetic and presents itself in childhood or adolescence
Describe the cortical & limbic factors that allow us to override our breathing
Cortical (cerebral cortex)
- laughing
- smiling
- speaking
-holding a breath
Limbic
- fear
- anxiety
- Pain
- Anger
Describe the central controller
This is made of the medulla & pons, it controls rate, depth & rhythm of breathing, automatic & voluntary control. The central controller adjusts breathing in response to changes in activity, environment, and even emotions.
It ensures that the body maintains homeostasis by adjusting breathing in response to fluctuations in blood gases and pH.Basic rhythm is generated via repeating cycles of inspiration & expiration
Describe the location, function and role of the medulla in the central controller
Medulla is responsible for involuntary breathing, it contains the DRG & VRG.
Medulla is highly responsive to changes in pH, if CO2 rises the medulla will signal the respiratory muscles to increase breathing rate to expel excess CO2, to ensure blood pH remains within range
Describe the location, function and role of the Pneumotaxic centre in the central controller
(upper pons) It is responsible for the control of inspiration, it inhibits inspiration to prevent over-inflation of lungs. This shortens the duration of each breath. Limiting inspiration allows time for sufficient expiration, maintaining time spent inspiring & expiring. The PC sets the respiratory rate by determining how frequently the breathing cycle repeats.
Describe the location, function and role of the Apneustic centre in the central controller
(lower pons) This area promotes prolonged inspiration, enabling depth of breathing. It signals the DRG to prolong inspiration to make breaths deeper, this is important during exercise.
It is regulated via PC to avoid excessive inspiration, without this breathing could become uncontrollable. It recieves feedback via vagal nerve
Describe the function of the DRG
DRG: dorsal respiratory group, is needed for basic rhythm, located in the dorsal medulla, close to vagal & glossopharyngeal nerve which transmit signals to respiratory centre.
Describe the function of the VRG & the 4 nuclei
VRG is involved in inspiration & expiration, it is dormant during quiet breathing. Consists of 4 nuclei:
1. Botzinger nuclei complex which controls expiration
2. Pre-Botzinger complex which sets the pace of respiration
3. Nucleus ambiguous which has inspiratory neurons
4. Nucleus retro ambiguous has inspiratory & expiratory neurons
These nuclei are active during forced expiration & exercise
Describe the inspiratory ramp signal
This refers to the gradual increase of neural signals that stimulate the muscles involved in inspiration, ramp ensures the breathing is smooth & gradual, avoiding sudden forced inhalations. Initiation of the respiratory muscles allow air to be drawn into the lungs, the signal then stops for 3 seconds once it reaches it’s peak, this marks the end of inspiration & triggers the beginning of expiration. This triggers relaxation of resp muscles resulting in recoil of lungs
Describe the role of the pneumotaxic center in the inspiratory ramp
The PC modulates the length of the ramp signal & helps coordinate the transition from inspiration to expiration. It prevents inspiration from lasting too long by inhibiting it.
Strong PC signal: reduces ramp to 0.5s compared to 2s, reduces expiration rate therefore leading to an increased respiratory rate
Weak PC: Increases duration of inspiration & expiration therefore reduces the respiratory rate
Describe effectors involved in controlled breathing
They are controlled via the central controller (medulla & pons)
Resp muscles are the effectors, e.g., diaphragm, intercostal, accessory, abdominal muscles
Describe the sensors involved in controlled breathing
These refer to resp receptors e.g., central chemoreceptors, peripheral chemoreceptors, J receptors, Stretch receptors, muscle & joint receptors & irritant receptors
Describe the location and function of central chemoreceptors in breathing
Located: ventral surface to the medulla,
Function: maintain homeostasis by regulating rate & depth of breathing in response to changes in pH & blood gases
Chemoreceptors are not sensitive to PaO2, they are responsible for 80% of response to CO2, this response is quite slow
Describe the response of central chemoreceptors in changes to pH
- When CO2 rises in the blood (hypercapnia), CO2 diffuses across the blood-brain barrier into the CSF
- Carbonic acid forms from CO2 & H2O in CSF, which then dissociates in H+ & HCO3-, this lowers pH which is detected via C Chemoreceptors
- Signals are sent to the respiratory centres in the medulla, these signals stimulate increased rate of breathing & depth, to expel more CO2 from the body in attempt to restore normal pH levels in the blood & CSF
Describe peripheral chemoreceptors in breathing
Located: carotid bodies & aortic body (aortic arch)
In carotid small clusters of chemoreceptors are found at the bifurcation site of common carotid arteries
Aortic body: A smaller group of peripheral chemoreceptors is in the aortic bodies, which are found along the aortic arch
Account for 20% of response to CO2 & work faster than central chemoreceptors
They respond to PCO2, PO2 & pH changes
Describe the response of peripheral chemoreceptors to changes in pH, PO2,PCO2
O2 sensing:
1. P chemoreceptors respond to low O2 (hypoxia) where PaO2 drops below 60mmHg, P chemoreceptors become activated & signal is sent via glossopharyngeal nerve & vagus nerve
2. The brain responds by increasing rate & depth of breathing to bring in more O2 & restore O2 in blood
pH & PaCO2:
1. P chemoreceptors are activated & respond to changes in CO2 & pH, when pH drops due to hypercapnia.
2. Peripheral chemoreceptors send signals to the brain to increase the rate of breathing to expel excess CO₂ and restore normal blood pH.
Describe the function of stretch receptors
Located: smooth bronchial walls
Function: prevent over-inflation of lungs, allow smooth/coordinated breathing
The primary stretch receptors are slow-adapting pulmonary stretch receptors (also known as Hering-Breuer stretch receptors),
Stimulating these receptors results in shortening of inspiration, shallow breaths & delay before next breath
Describe the Hering-Breuer Reflex
Located: Hering-Breuer stretch receptors found in bronchial walls of large bronchi & bronchioles
REFLEX: triggered when the lungs are stretched to a certain point, which signal DRG to inhibit inhalation & trigger exhalation by switching off inspiratory ramp
This prevents the lungs from becoming excessively inflated and helps regulate the breathing cycle. The Hering-Breuer reflex is especially important in newborns and during forced or deep breathing. This reflex is weak in normal breathing, but is needed when tidal volume increases during excercise
Describe J receptors
(juxtaposition/ C fibre receptors)
Located: in alveolar walls, near the capillaries, the junction between the alveolar epithelium & pulmonary capillaries
Function: Regulate breathing & Detect changes in the pulmonary environment, e.g., inflammation, congestion oedema etc
When activated it results in dyspnea, decreased HR & BP & restriction of the larynx. The response to J receptor activation is typically characterized by rapid, shallow breathing, a pattern known as dyspnea.
Describe irritant receptors
Located: in the ciliated epithelium of large airways e.g., trachea & bronchi.
Function: To detect chemical, physical or mechanical irritants e.g. smoke, dust, that enters the airways, they initiate refelxes that aim to protect the lungs & airways from damage.
This reflex can involve coughing & sneezing via restriction of the larynx or taking a deep sigh every 5-20 minutes
Describe the purpose of the coughing reflex
Irritant receptors send signals to the medulla via the vagal nerve. The brain then coordinates the motor response for forceful exhalation (coughing), Coughing serves to expel foreign particles, irritants or mucus from the airways to maintain hygiene of respiratory tract
Describe the function & location of proprioceptors
Located: Muscle spindles, Golgi tendon organs & joints
Function: monitor & adjust respiratory efforts based on movement of the body, helps maintain synchronized breathing during movement.
During excercise: Proprioceptors in muscles and joints provide signals to adjust the breathing rate and depth to match the body’s increased oxygen demand.
Proprioceptors in the muscles and joints of the chest and abdomen provide feedback about changes in posture and the position of the rib cage. This helps the brain adapt the breathing pattern to accommodate the new body position.
They help achieve optimum tidal volume & frequency, stimulated by increased load e.g., excercise and respiratory muscle contraction.
Describe other receptors involved in breathing
Other receptors:
1. pain receptors: stimulate apnea followed by hyperventilation
2. Arterial baroreceptors: detect pressure changes in blood, stimulated via increased BP, signals to decrease rate & depth of breathing
Describe the homeostatic response of decreased ventilation
A decrease in ventilation causes arterial pressure of CO2 to build up, this causes a drop in pH as H+ concentration increases, this is detected via chemoreceptors that signal the medulla. The medulla that stimulates the respiratory centres to expel excess CO2 to ensure blood pH stays within 7.35-7.45, this signals a negative feedback mechanism resulting in a increase in ventilation to remove extra CO2
