Week 9 - respiratory system, lung volumes Flashcards
Why do we need a respiratory system
It creates an interface between the environment and the tissues (via the blood), which are not very compatible.
Why is dehydration a problem for the respiratory system
For effective diffusion between air and liquid (atmosphere and blood), the surface of the respiratory system must not only be thin, but also must be moist.
Functions of the respiratory system
Gas exchange between environment and blood
Control of the acidity of the body
Filtering of the air that is inhaled
Vocalisation - producing sound
What is special about the lungs
They are large, spongy elastic bags that fill up with air every breath, meaning they can expand and recoil with every breath
The lobes of the lungs
Each lung is divided into compartments called lobes. The right (as you look the left) lung has three lobes but the left lung has only 2.
The left lung has a part missing - where the heart sits
The pleural sac
The pleural sac is a double-walled enclosure of the lungs filled with fluid, the pleural fluid.
Prevents the lungs from collapsing
Layers of the pleural sac
Outer layer is the parietal pleura and the inner layer is the visceral pleura - attaches to lungs
The thoracic cavity turns into a
pump due to the muscles of respiration expanding and contracting the volume of the ribcage
Role of the pleural sac
Reduces friction from movement on the surface of the lungs
Allows lungs to fix on the thoracic wall without having to touch themselves
Bones and muscles in the thoracic cavity
The bones (rib cage and spine) offer rigid protection to sensitive organs (heart and lungs)
The muscles (diaphragm, intercostals abdominals) support the rib cage and turn the chest into a pump that drives air flow
Role of the internal and external intercostals
External intercostals are lifting the ribs and the internal intercostals pull the ribs down
Upper respiratory tract
Nasal cavity
Entry point of the respiratory system
Lower respiratory tract
Trachea - contains the conductive zone or dead space
Bronchial tree
Alveoli - gas exchange
Bronchial tree divisions
The bronchial tree undergoes a number of divisions (23 generations). At the end of the tree the surface area is enormous (100 m2)
Functions of the airways
Warming up of inspired air
Humidification of dry inspired air
Filtration of inhaled foreign materials
Components of the nasal cavity
Turbinates or conchae - bony dividers that increase the surface area of the nasal cavity. The surface of the nasal cavity has a very high blood supply, which helps warm up and humidify the inspired air as it flows over it.
Vestibule - entrance to cavity - first line of airway defence. Small hairs and mucus help trap inhaled particles so they can be blown back out
Cilia blocks unwanted objects from entering - has a stroke and relaxation phase
What cells line the alveoli that allow gaseous exchange to take place
Capillary endothelial cells and a single layer of alveolar epithelial cells
Boyles law
P1 X V1 = P2 X V2
The product of pressure and volume is always the same
Relationship between resistance, airflow and pressure difference
Airflow is inversely proportional to pressure diff / resistance
Airflow is inversely proportional to resistance
Airflow is directly proportional to pressure difference
Relationship between viscosity, length, radius and resistance
Resistance is proportional to length x viscosity / radius^4
Viscosity and airway radius
Viscosity plays a small role in the resistance of the airways to airflow. Viscosity is affected by humidity and the concentration of air (high altitude)
Airway radius is the main factor affecting resistance.
Inspiration
During inspiration, the diaphragm contracts and flattens out, increasing the volume of the thoracic cavity
External intercostal muscles pull ribs up and out
Expiration
Normal expiration doesn’t require the contraction of any muscles
Heavy breathing requires the contribution of the expiratory muscles (internal intercostal and abs) in order to compress the thoracic cavity faster and further than restful breathing
Pneumothorax
A collapsed lung
Happens when intrapleural pressure is equal to atmospheric pressure
Inspiration and expiration occurs when
Inspiration occurs when pressure inside the lungs is below atmospheric pressure
Expiration occurs when pressure inside the lungs is above atmospheric pressure
Law of LaPlace
Pressure = 2 x surface tension / radius
If two bubbles have the same surface tension, the smaller bubble will have the higher pressure
What happens if there would be no surfactant in lungs
In the alveoli, with them being different sizes, contents from the smaller balloon would empty into the larger balloon (same surface tension –> smaller balloon would have greater pressure) therefore some alveoli may collapse, eventually creating one bubble
What does a surfactant do
Surfactant contains proteins that result in a reduction in the surface tension of the alveolar walls
Big alveolus = lower conc of surfacant
Small alveolus = higher conc of surfactant due to greater pressure
Give all of the lung volumes
Tidal volume
IRV
ERV
Residual volume
Functional residual capacity
Vital capacity
Inspiratory capacity
Total lung capacity
Functional residual capacity
The amount of air left in the lungs at the end of a normal expiration
What is different about residual volume and functional residual capacity
They cannot be measured using a spirometer as they stay inside the lungs
Anatomical dead space
Part of the airways where gas exchange does not take place and is a fixed volume (150ml)
Alveolar dead space
Areas of the lungs where gas exchange can take place but that are not properly perfused with blood
Minute ventilation
Amount of air that is moved by the lungs in one minute
Tidal volume x breathing frequency
Average minute ventilation
0.5 L x 12 br/min = 6 L/min
Hyperpnoea
Minute ventilation increases in proportion to metabolic rate
Hyperventilation
Minute ventilation increases more than metabolic rate does
How can volumes of air be measured
Under ambient conditions (ATPS), corrected for body variables (BTPS) or corrected for standard variables (STPD)
