Pathway of air
- Nasal cavity
-Pharynx
-Epiglottis
-Larynx
-Trachea
-Bronchus
-lungs
-Bronchioles
-alveoli
Inspiration
during inspiration, the thoracic cavity increases in size allowing the lungs to expand and the pressure within them to drop compared to outside. Inspiration causes air to enter the lungs
Expiration
during expiration, the thoracic cavity decreases in size, reducing the size of the lungs so the pressure increases in the lungs, compared to outside. Expiration causes air to leave the lungs.
Thoracic cavity
Is the area inside the chest from the base of the neck to the diaphragm. It contains the heart and lungs, protected by the ribs and sternum.
Gaseous Exchange
Gaseous exchange happens in the alveoli, where oxygen diffuses into the blood and carbon dioxide diffuses out, due to differences in concentration and thin walls for efficient diffusion.
Oxygen moves from high concentration in the alveoli to low concentration in the blood.
Carbon dioxide moves from high concentration in the blood to low concentration in the alveoli.
Minute Ventilation
The volume of air breathed in and out per minute
Tidal Volume- include volume
Is the amount of air inspired or expired in a normal breath when the person is at rest. It is the amount of air the person can breath in or out without forcing their breathing.
On average this is 0.5 litres
Vital capacity- include volume
Is the volume of air that cab e inspired it expired per breath, including forced breathing. Vital capacity can be as much as 4.8 litres
Residual Volume- inculde Volume
is the amount of air left in the lungs even after forced breathing out. This volume of air cannot be breathed out. It prevents the lungs from collapsing. The average residual volume is approximately 1.2 litres.
Total Lung volume- include volume
Is vital capacity and residual volume, therefore on average 6.0 litres
Neural control of breathing
- Breathing is largely involuntary
- Inspiration is active process, expiration a passive process
- Process controlled by neurones in the brain stem
Two areas in the medulla oblongata are critical in this – the Dorsal Respiratory group (DRG) and Ventral Respiratory Group (VRG)
Chemical control of breathing
- Sensors (chemoreceptors) respond to fluctuations in levels of oxygen and CO2 in the blood and signal the medulla to change breathing rate
- Found in the medulla, the aortic arch and carotid arteries
Also detect changes in bloody acidity
- Found in the medulla, the aortic arch and carotid arteries
How is incrased breathing rate and depth is achived
-Chemorecpors
-impulse set to the medualla oblongata
- Nerve impule are sent via the phrenic nerve to the inspiratory muscule (diaphragm & intercostals)
-Breathing rate and depth are increased
- Detect an increase in carbon dioxide in the blood
-Sympthtic nervous system is stimulated
Medulla Oblongata
- Is found in the brain stem, just above the spinal cord
- Contains nerve fibres
- Is responsible for autonomic nervous activity(i.e. things we do not consciously control such as breathing rate and sneezing)
- Is the respiratory centre transferring messages to and from the spinal cord and the brain
These messages control the action of the diaphragms and intercostal muscles and therefore the rate of breathing.
