CFB Lungs 2 Flashcards
Describe the basic mechanism of ventilation
- O2 inhaled, passes into alveoli, diffuses through capillaries into arterial blood
- During exhalation, CO2 released into alveoli from venous blood
What components are involved in ventilaion?
Upper respiratory tract
Lower respitatory tract
Muscles
Skeletal elements
State the functions of the respirtatory sysem
- Ventilation of lungs
- Extract O2 from air, transfer to blood
- Remove CO2 from blood
- Maintain Acid base of blood
What is absolute pressure?
Atmospheric pressure
If alveolar pressure = 0, what does this tell us?
Alveolar pressure = atmospheric pressure
Describe Boyle’s law
Gas law
As vol of gas increases, pressure of gas decreases, in closed system
Describe the process of inspiration
Active process
Activated by respiratory centre, medulla
Causes diaphragm + external intercostal muscles contract
Diaphragm contracts + moves downwards
External intercostal muscles contract + cause adjascet ribs to move upwards + forwards
These 2 processes increase vol in thoracic cavity
Lower pressure in thoracic cavity
Air flows down pressure gradient into lungs
AIR FLOW CONTINUES UNTIL ALVEOLAR PRESSURE = PRESSURE ATAIRWAY OPENING
Describe the process of expiration
Passive
Diapghragm + intercostal muscles relax
Diaphragm = curved / “dome”
Ribs = inwards + downwards
Reduce vol of thoracic cavity
Increase pressure
Atm pressure lower than pressure in lungs
Air moves out
Describe how expiration can become a passive process
If airways narrow too much (asthma)
Or if it is needed to get rid of a vas quantity of air quickly, during exercise
INTERNAL INTERCOSTAL MUSCLES CONTRACT
ANTERIOR ABDOMINAL MUSCLES CONTRACT
ACCELERATE EXPIRATION, RAISE AIR PRESSURE IN LUNGS FASTER
Control of breathing
Involunary process controlled by respiratory centre in medulla oblongata in brainstem
Controls depth + rate
Important for NORMAL LEVELS of PCO2 and PO2
What are the 3 regions involved in control of respiration?
- Central controller
- Respiratory muscels
- Strategically placed sensors
What is the central controller?
Respiratory centre:
- Medullary respiratory centre (dorsal + ventral respiratory neurones)
- Pons respiratory centre (pneumotaxic + apneustic centres)
Describe the role of dorsal neurones in the medullary respiratory centre
Dorsal medullary respiratory neurones - INSPIRATION
when activated, send electrical impulses to RETICULO-SPINAL TRACT in spinal cord + intercostal nerves to stimulate respiratory mucles
(maintain basic rythm of breathing)
Describe the role of ventral neurones in the medullary respiratory centre
Expiration
But only forced expiration
To increase depth + rate of expiration
How are these neurones activated?
Deep breathing, increases activity of dorsal neurones, which activates ventral neurones
When ventral neurones are stimulated, this inhibits dorsal neurones, so inhibiting inspiratory centre
Describe why respiratory movements are symmetric
Dorsal + ventral neurones are bilaterally paired, this allows cross communication, which means they are synchronous
Describe the role of the apneustic centre
LOWER PONS
Exact function unknown
Stimulates insipratory centre
Without, breathing becomes shallow, IRREGULAR
Pathological lesions= increased freq of apnoea
Describe the role of the of the pneumotaxtic centre
Found in pons respiratory centre
Its neurones inhibit the dorsal neurones in the respiratory medullary centre and also inhibit apneustic centre
Therefore, inhibit inspiration
Lesions lead to PROLONGUED DEEP INSPIRATION + shorter expiration due to continuous activation of inspiratory centres
INVOLVED IN REGULATING
-VOL
-RATE
of respiration
Describe volunary control of ventilation
This is known as cortical influence
Cerebral cortex overrides autonomic meduallary respiratory centre (e.g. when you want to hold breath)
However, if you hold breath for too long, autonomic medullary respiratory centre overrides cerebral cortex.
Too high blood pH
Chemoreceptors override cortical influence, you gasp take a deep breath (inspiration)
State the strategically placed sensors
- Mechanoreceptors
- Chemoreceptors
State the role of mechanoreceptors in regulation of breathing
Stretch receptor, sensory receptor, activated in response to distortion + pressure
Located in walls of bronchi + bronchioles
Prevent over-inflation of lungs
Activated in response to inflation of lungs
When activated, send APs via VAGAL NERVE FIBRES which inhibit inspiratory centres + activate pneumotaxic centre
Describe the Hering-Breuer Reflex
Happens more commonly in infants
In adults, when tidal vol is larger than normal e.g. when exercising
When lungs inflated, mechanoreceptors activated, send APs via vagal nerve fibres to inhibit insipratory centre + stimulate pneumotaxic centre
When expiration starts, activation of mechanoreceptor decreases…
State the role of chemoreceptors in the control of breathing
Sensory receptors, detect changes in blood pH
Detect O2 levels in body, CO2 levels in brain
2 types:
- Peripheral
-Central
Describe the role of peripheral chemoreceptors
- Found at birufication of carotid artery + aortic arcfh
- Repond to changes in O2 levels mainly, but sometimes CO2 levels
- Connected to respiratory centre via cranial nerves IX and X
-chemoreceptors in carotid artery detect levels of O2 in arterial veseels
-chemoreceptors in aortic arch detect levels of O2 close to heart
-composed of two types of cells: Type I: glomus cells Type II: Glia-like cells
-activated during hypoxia (low O2 levels)
-electrical impulses sent from chemoreceptors to brainstem
-hypoxic drive
-ventilation
Describe the role of central chemoreceptors
Found at medulla in brainstem
Exposed to local blood flow, metabolsim, CSF
Activated when pCO2 = low
When pCO2 low, high conc of H+ in CSF
Detected by receptors, send APs, to inspiratory centre, stimulate alveolar hyperventlation, therefore, low pCO2 in CSF + blood
As pCO2 decrerases, reduces AP sent, less stimulation of inspiratory centre, hypoventilatiojn
Central chemoreceptors directly respond to H+ conc CSF
Indirectly to blood CO2
These values are linked because arterial CO2 crosses BBB + enters CSF
Explain why central chemoreceptors play a more prominent role in cemical regulation of ventilation compared to peripheral chemoreceptors
PCO2 = major regulator of respiration, more than PO2
State the Respiratory muscles involved in regulation of breathing
- Diaphagm
- Intercostal muscles
- Accessory muscles
- Abdominal muscles
Describe the role of the diaphragm in the control of breathing
MOST IMPORTANT COMPONENT
When contract, increases intra-thoracic vol significantly
This decreases pressure
Atmospheric pressure higher than intra-thoracic pressure
Air moves in down pressure gradient
When relaxes, reduces intra-thoracic vol significantly
Increases pressure
Atmospheric pressure lower than intrathoracic pressure
Air moves out, down pressure gradient
What method is used by the lungs to expel air?
Elastic recoil
Describe the role of the intercostal muscles in the control of breathing
External intercostal muscles
Have antero-inferior fibres
When they contract, the fibres pull ribcage upwards + outwards + forwards
Increases the intra-thoracic vol, allowing inspiration
Internal intercostal muscels
Have postero-superior fibres
When contract, fibres pull ribcage down
Forced expiratin / active expiration
Describe the role of accessory muscles in the control of breathing
Two main accessory muscles:
Sternocleidomastoid + scalene
INSPIRATION
Scalane: first 2 ribs upwards (quiet breathing)
Sternocleidomastoid: sternum upwards (heavy breathing)
Describe the role of the abdominal muscles during breathing
Muscles in abdominal wall:
-Rectus abdominus
-Transversus abdominus
-Internal + external obliques
