Week 7 - Respiration during exercise (Part 1) Flashcards
Whats the primary function of the respiratory system
Maintain arterial blood-gas homeostasis
How is the maintenance of arterial blood-gas homeostasis done
- Pulmonary ventilation
- Alveolar gas exchange
- Gas transport
- Systematic gas exchange
Structural and Functional organisation
The epiglottis separate the upper and lower respiratory tracts.
The lungs are encolsed within membranes called pleura - intrapleural pressure < atmospheric pressure, which prevents the alveoli from collapsing
Airways
There are 23 main airways
The main bronchi is Z1 - conducting zone extends to terminal bronchioles (Z16)
Gas exchange occurs in the respiratory zone (Z17-23)
Alveolar (pulmonary) gas exchange
Pulmonary gas exchange takes place across the pulonary capillary
Oxygen and co2 move between blood and air by simple diffusion (high to low partial pressure)
What are the 2 types of alveolar cell
(ON SHEET)
Type 1 - cover 95% of the internal surface of the alveoli and are critical for gaseous exchange
Type 2 - release surfactant which is a molecule that lowers the surface tension
Fick’s law of diffusion
Volume of gas passing through a sheet is dependent on:
- surface area
- thickness
- diffusion coefficient
- pressure gradient
Blood gas barrier interface
The diffusion path from alveolar gas to the erythrocyte includes 5 layers:
1. Surfactant
2. Alveolar epithelium
3. Interstitium
4. Capilary endothelium
5. Plasma
The blood/gas barrier is very thin and has vast surface area 950-1000m2(make it ideal for gas exchange/diffusion)
Mechanics of breathing
Mechanics of brathing are concerned with the movement air into and out of the lungs by changes in pressure, flow and volume.
During inspiration the volume of the thoracic cavity increases as the respiratory muscles contract.
Whats the bucket handle motion
(ON SHEET)
The bucket handle motion of the ribs increases the transverse diameter of the thorax during inspiration
What is the pump handle motion of the ribs
(ON SHEET)
The pump handle motion of the ribs increases the anteroposterior diameter of the thorax during inspiration
Muscles of respiration
(ON SHEET)
At rest diaphragm contraction is responsible for the majority of pulmonary ventilation - expiration is passive
During exercise the diaphragm is assisted by external intercostal muscles, scalenes, sternocleidomastoid and others to increase pulmonary ventialtion 10-20 fold above resting levels
Ohm’s Law
Current = voltage/resistance
this can be applied to breathing as airflow is dependent on a pressure gradient and airway resistance
Poiseuille’s Law
Resistance is dependent on length and radius. Radius is raised to the fourth power thus the major determinent of airway resistance
What is dead space
The volume of air not participating in gaseous exchange
Obstructive airway disease
(ON SHEET)
Spirometry can be used to diagnose pulmonary disease such as COPD (chronic obstructive pulmonary disease)
Forced vital capacity (FCV) is the maximum volume air that can be forcefully expired after a maximal inspiration, COPD is characterised as an increased airway resistance and a reduced FEV/FCV
Exercise hyperpnoea
(ON SHEET)
PaCO2 regulation due to proportional changes in alveolar ventialtion and metabolic rate
Incremental exercsie
Ventilation increases linearly with exercise intensity until a certain point ventilatory threshold (lactate/anaerobic threshold) tVent. Once Tvent is reached ventilation increase exponentially resulting in hyperventilation
Exercise induced arterial hypoxaemia (EIAH)
(ON SHEET)
EIAH is defined as a reduction in Paco2 of >10mmg from rest. Occurs in higly trained males and the majority of females regardless of fitness or exercise intensity.
Theorised to occur because ventilatory demand exceeds capacity.
Causes are believed to be due to:
Diffusion limitation
V/Q mismatch
Relative hyperventilation
Control of ventilation
Neural control of breatthing is very complex
There are 3 main groups of neurons:
1. Ventral respiratory group (inspiratory and expiratory)
2. Dorsal respiratory group (inspiratory)
3. Pontine respiratory group (modulatory)
Control of ventilation 3 compartmental model
Central controller (pons, medulla, other brain parts) output information to the effectors (respiratory muscles) then transferred to the sensors (chemoreceptors, lung and other receptors) then input this back to the central controller to control ventilation
Peripheral chemoreceptors
Located at the aortic arch and carotid of the body.
They detect changes in Po2 of blood perfusing systemic and cerebral circulation
Relay sensory information to the medulla via vagus and glossopharangeal nerves
Decreased Pa02 = increased Expired volume.
Other factors can also stimulate peripheral chemoreceptors such as temperature, adrenaline and CO2
Central chemoreceptors (pco2 sensors)
Located primarily in the ventral surface of the medulla known as the retrotrapezoid (RTN).
The RTN is sensitive to change is Paco2/h+
Chemoreceptor feedback
- Detect error signals (disturbances to blood-gas homeostasis)
- Central and peripheral chemoreceptors increase afferent input to the brainstem in response to Paco2 increase or decrease paO2 or pH.
- Premotor neurons in the dorsal respiratory group are activated
- Inspiratory muscle contract Increasing expiratory volume
- Changes in expiratory volume elicit changes in paO2, paCO2 and pH thus restoring blood-glucose balance
