Welcome to the Respiratory System: The Body at Work
Ever wondered why you start puffing and panting within seconds of sprinting for a ball or swimming a lap? Your body is working hard behind the scenes to supply your hard-working muscles with energy! In this chapter, we will look at how your respiratory system takes in oxygen, gets rid of carbon dioxide, and helps you perform at your best in sports and physical activities.
Don't worry if the names of muscles and pathways seem tricky at first! We will break everything down into clear, manageable steps.
1. Core Functions of the Respiratory System
In physical education and sport, the respiratory system has three primary jobs:
• Transporting air into the lungs: Taking in atmospheric air containing the oxygen needed to release energy in working muscles.
• Diffusion of oxygen into the bloodstream: Allowing oxygen to cross from your lungs directly into your blood so it can be carried to active muscles.
• Removing carbon dioxide and other gases from the blood: Collecting waste gases produced during exercise and expelling them out of the body.
Key Takeaway for Athletes: Without efficient transport, diffusion, and waste removal, your muscles would quickly run out of energy and fatigue, forcing you to slow down or stop.
2. The Pathway of Air: Structure and Function
When you take a breath during exercise, air travels through a dedicated pathway. Here are the specific parts you need to know:
A. Mouth, Nose, and Nasal Cavity
• Function: Warms, filters, and moistens incoming air.
• Why it matters: Warming and moistening protects delicate lung tissue, while filtering traps foreign debris so clean air enters your body.
B. Trachea (Windpipe)
• Function: Carries air from the throat down into the lungs.
• Special Feature: Lined with tiny, hair-like structures called cilia. These catch particles of dust, which are then swept upward and removed through coughing.
C. Bronchi (Singular: Bronchus)
• Function: The trachea divides into two tubes called bronchi, which branch off into the left and right lungs to distribute air.
D. Bronchioles
• Function: Inside each lung, the bronchi split into smaller and narrower tubes called bronchioles, which lead directly to the alveolar sacs.
E. Alveoli (Singular: Alveolus)
• Function: Individual, hollow cavities contained within the alveolar sacs where gaseous exchange takes place.
• Analogy: Picture a bunch of grapes at the end of a stem. The stem is the bronchiole, and the individual grapes are the alveoli!
F. The Diaphragm
• Function: A broad band of muscle that sits directly underneath the lungs. It is attached to the lower ribs and sternum, forming the base of the thoracic cavity (chest cavity). It powers your breathing by moving up and down.
Quick Memory Aid for the Pathway of Air:
"No Tired Boxer Breathes Air"
Nose/Mouth \(\rightarrow\) Trachea \(\rightarrow\) Bronchi \(\rightarrow\) Bronchioles \(\rightarrow\) Alveoli
3. The Mechanics of Breathing (Inspiration and Expiration)
Breathing is divided into two phases: inspiration (breathing in) and expiration (breathing out). Notice how the muscles involved change when you move from resting to exercising!
Breathing at Rest
• Inspiration at Rest:
The external intercostal muscles and the diaphragm contract. This expands the chest (thoracic) cavity, pulling air into the lungs.
• Expiration at Rest:
The external intercostal muscles and the diaphragm relax. The chest cavity becomes smaller, gently pushing air out.
Breathing During Exercise
During physical activity, your body demands faster and deeper breaths. Extra muscles are recruited to speed up the process:
• Inspiration During Exercise:
To expand the chest cavity even further and faster, the following muscles all contract:
1. External intercostal muscles
2. Diaphragm
3. Sternocleidomastoid (neck muscle)
4. Scalenes (neck muscles)
5. Pectoral minor (chest muscle)
• Expiration During Exercise:
Expiration is no longer passive; it becomes active and forceful. The following muscles contract to pull the ribs down and push the diaphragm up quickly:
1. Internal intercostal muscles
2. Abdominals
Common Mistake to Avoid: Remember that external intercostals work during normal inspiration, while internal intercostals contract during forced expiration in exercise!
4. Gaseous Exchange and Diffusion
Once air reaches the alveoli, oxygen must enter the blood, and carbon dioxide must leave. This happens via diffusion.
• Definition of Diffusion: The process where gases diffuse down a concentration gradient from an area of high concentration to an area of low concentration.
• How it works in the lungs:
- Oxygen: There is a high concentration of oxygen in the alveoli and a low concentration in the blood capillaries. Oxygen diffuses across into the blood.
- Carbon Dioxide: There is a high concentration of carbon dioxide in the blood arriving at the lungs and a low concentration in the alveoli. Carbon dioxide diffuses out of the blood and into the alveoli to be exhaled.
5. Lung Volumes and Measurements
Two essential terms you need to master for the exam are vital capacity and minute ventilation:
A. Vital Capacity
• Definition: The maximum amount of air exhaled after a maximal inspiration (the biggest breath in followed by the biggest breath out).
• Impact on Sport: Vital capacity varies between individuals. Exercise training can improve vital capacity by expanding the lungs further to take in extra oxygen, boosting endurance performance.
B. Minute Ventilation
• Definition: The total volume of air breathed in or out in one minute.
• Formula:
\(\text{Minute ventilation} = \text{Tidal volume} \times \text{Respiratory rate}\)
(Tidal volume is the amount of air breathed in or out per normal breath; respiratory rate is the number of breaths taken per minute.)
• Impact on Sport: Minute ventilation increases during exercise because your breathing rate quickens and each breath becomes deeper.
6. Short-Term vs. Long-Term Effects of Exercise
A. Short-Term (Immediate) Effects of Exercise
As soon as you start exercising, your body responds immediately:
1. Increased breathing rate: Changes are detected in the concentration of carbon dioxide and oxygen in the body, which triggers an immediate increase in breathing rate.
2. Muscles work harder: The intercostal muscles and diaphragm work harder to expand the thoracic cavity to draw in more air.
B. Long-Term Effects of Optimal Training
After weeks and months of regular training, your respiratory system adapts permanently:
1. Stronger respiratory muscles: The respiratory muscles (the diaphragm and intercostal muscles) increase in strength.
2. Increased vital capacity: An increase in vital capacity allows for a greater intake of air with each large breath.
3. Increased capillarisation: An increase in the number and diameter of capillaries surrounding the alveoli allows for more efficient gaseous exchange of oxygen and carbon dioxide.
Quick Summary Review
• Pathway: Mouth/Nose \(\rightarrow\) Trachea \(\rightarrow\) Bronchi \(\rightarrow\) Bronchioles \(\rightarrow\) Alveoli.
• Breathing at Rest: Diaphragm and external intercostals contract for inspiration; relax for expiration.
• Breathing in Exercise: Inspiration uses extra muscles (sternocleidomastoid, scalenes, pectoral minor); expiration is forced using internal intercostals and abdominals.
• Diffusion: Movement of gases from high concentration to low concentration.
• Formula: \(\text{Minute ventilation} = \text{Tidal volume} \times \text{Respiratory rate}\).
• Long-term benefits: Stronger diaphragm/intercostals, increased vital capacity, more and wider capillaries around alveoli.