Applied Anatomy and Physiology - Respiratory system - A-Level Physical Education

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Applied Anatomy and Physiology - Respiratory system

infoWhy this? Ventilation, gaseous exchange, and respiratory control explain how the body supplies oxygen and removes carbon dioxide at rest, during exercise, and throughout recovery. Analysing breathing responses and oxygen unloading helps us explain physiological influences on performance.

scheduleWhy now? Following the cardiovascular system allows us to connect the movement of air and diffusion of gases with their transport in the blood. Together, these units establish the oxygen-delivery knowledge needed for later work on training, aerobic energy provision, and exercise at altitude.

Tidal volume is the volume of air inhaled or exhaled in one breath, breathing frequency is the number of breaths taken per minute, and minute ventilation is the total volume of air ventilated per minute.
Minute ventilation is calculated using `V_E = f \times V_T`, where `V_E` is minute ventilation, `f` is breathing frequency and `V_T` is tidal volume.
Typical resting values are a breathing frequency of about 12–16 breaths per minute, a tidal volume of about 0.5 litres and a minute ventilation of about 6–8 litres per minute.
During sub-maximal exercise, breathing frequency and tidal volume increase, causing minute ventilation to rise in proportion to the increased demand for oxygen and removal of carbon dioxide.
As exercise approaches maximal intensity, tidal volume begins to plateau, so further increases in minute ventilation are mainly produced by a rapid increase in breathing frequency.
During recovery, breathing frequency, tidal volume and minute ventilation gradually return towards resting values as carbon dioxide, temperature and acidity decrease and oxygen stores are restored.
At rest, inspiration is active because the diaphragm contracts and flattens while the external intercostal muscles contract to lift the ribs upwards and outwards.
At rest, expiration is mainly passive because the diaphragm and external intercostal muscles relax and elastic recoil reduces the volume of the thoracic cavity.
An increase in thoracic volume lowers pressure inside the lungs below atmospheric pressure so air enters, whereas a decrease in thoracic volume raises pressure so air leaves.
During sub-maximal exercise, the diaphragm and external intercostal muscles contract more forcefully, increasing the depth and frequency of breathing.
During maximal exercise, the sternocleidomastoid assists forced inspiration, while the internal intercostal and rectus abdominis muscles actively force expiration.
As tidal volume increases during exercise, it uses more of the inspiratory and expiratory reserve volumes, but residual volume and total lung capacity change very little during a single exercise session.
The respiratory control centre in the medulla oblongata regulates breathing by sending neural impulses to the respiratory muscles.
At the start of exercise, anticipatory signals from the motor cortex and feedback from receptors in moving muscles and joints rapidly increase breathing before major chemical changes occur.
Chemoreceptors detect changes associated with increased carbon dioxide, increased hydrogen ion concentration and reduced blood pH, causing the respiratory control centre to increase ventilation.
Thermoreceptors detect increased body temperature and baroreceptors detect changes in arterial blood pressure, providing additional information to the respiratory control centre during exercise.
Gaseous exchange occurs by diffusion down partial-pressure gradients, from an area where a gas has a higher partial pressure to an area where it has a lower partial pressure.
External gaseous exchange occurs at the alveoli: oxygen diffuses from alveolar air into the blood, while carbon dioxide diffuses from the blood into the alveoli.
Internal gaseous exchange occurs at the muscles: oxygen dissociates from oxyhaemoglobin and diffuses from the blood into muscle cells, while carbon dioxide diffuses from the muscle cells into the blood.
The oxyhaemoglobin dissociation curve is sigmoid-shaped; high oxygen partial pressure in the lungs favours oxygen association, while lower oxygen partial pressure in active muscles favours dissociation, and increased carbon dioxide, temperature and acidity produce a rightward Bohr shift that increases oxygen unloading.

rocket_launchYou must be able to

Calculate minute ventilation using `V_E = f \times V_T`, giving the answer in litres per minute.
Rearrange the minute-ventilation equation to calculate breathing frequency using `f = V_E \div V_T` or tidal volume using `V_T = V_E \div f`.
Interpret respiratory data or graphs to compare changes in breathing frequency, tidal volume and minute ventilation at rest, during sub-maximal and maximal exercise, and throughout recovery.
Explain inspiration and expiration as linked sequences involving respiratory-muscle action, thoracic volume, lung pressure and airflow direction.
Compare the muscles recruited during resting, sub-maximal and maximal breathing, distinguishing passive expiration from active forced expiration.
Explain how neural signals and feedback from chemoreceptors, baroreceptors and thermoreceptors alter the activity of the respiratory control centre during exercise and recovery.
Use partial-pressure gradients to explain the direction of oxygen and carbon dioxide diffusion at the alveoli and active muscles.
Interpret an oxyhaemoglobin dissociation curve to identify association and dissociation, and predict how a rightward Bohr shift affects oxygen delivery during exercise.

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