Breathing and respiration

In everyday life, we commonly use the words 'breathing' and 'respiration' interchangeably, but they are actually very distinct processes. We will be looking at them in detail in this section.
Key definitions
Be clear that you understand the differences between these key words:
Breathing
This is the mechanical process whereby air is moved into and out of the lungs, and from there the exchange of carbon dioxide for oxygen in the blood. Breathing is also known as ventilation
Respiration
This is a set of metabolic reactions by which cells convert glucose to energy. There are 2 forms of respiration:
  • aerobic respiration - occurs in the presence of oxygen
         Glucose + oxygen = carbon dioxide + water + energy
  • anaerobic respiration - occurs in the absence of oxygen 
          Glucose = lactic acid and (less) energy

See below for more details and specifics about respiration
Picture
Anatomy of the respiratory system

Lungs - the lungs are found in your chest (or thorax to give it its proper name). There are two of them. They are bordered by the rib cage above and around the sides, and below by the diaphragm. The lungs are where gaseous exchange takes place
Diaphragm - strong sheet of muscle which separates the thorax from the abdomen. It is domed upwards in shape, and contracts and relaxes during breathing to 
                                                                                   move air into and out of the lungs (see below)
Trachea - the tubes which carries air from the mouth to the entrance of the lungs. It divides into two bronchi as it enters the lungs, and is strengthened by horseshoe-shaped rings of cartilage
Bronchi (singular = bronchus) - two tubes which branch from the lower end of the trachea. These tubes take air into the lungs before dividing further
Bronchioles (singluar = bronchiole) - tiny tubes which branch from the bronchi and which carry air to and from the alveoli
Alveoli (singular = alveolus) - tiny air sacs at the end of the bronchioles. They look like bunches of grapes (see below for details of how these structures are adapted). Oxygen is absorbed and carbon dioxide is lost by the blood here. Thus they are the site of gaseous exchange
Capillaries - the smallest of the blood vessels. These form a mesh covering the alveoli and allow for gaseous exchange from the lungs to the blood to take place
Intercostal muscles - the muscles between your ribs. These contract and relax during breathing to move the rib cage up and down, respectively
The mechanics of breathing
As mentioned above, breathing (or ventilation) is the mechanical process of moving air into and out of the lungs so that gaseous exchange can take place (more about this below). Here I have indicated the physical changes that take place during breathing. It is movements of the rib cage and diaphragm which bring about ventilation. These movements result in pressure changes in the lungs. It is the changes in pressure in the lungs that causes air to move into and out of the lungs. Relate this to the Particle Model, and remember that pressure and volume are inversely proportional.

Remember, it is easy to work out the changes that are occurring if you can't recall them: sit with your hands on your rib cage and take a deep breath in and then release it. You will feel the movements of your body and this will allow you to answer any questions on breathing. 
Breathing in (inhalation)
  • Intercostal muscles contract (shorten)
  • This causes ribcage to move UP and OUT
  • The diaphragm contacts, resulting in it flattening out from its normal domed position
  • All of these changes result in an increase in volume of the thorax
  • Increased volume = decrease in air pressure (because the same amount of gas now has more room to more about in)
  • Internal pressure is now lower than atmospheric pressure (pressure of gas outside of body)
  • Thus, air moves into the lungs
Breathing out (exhalation)
  • Intercostal muscles relax 
  • This causes ribcage to move DOWN and IN
  • The diaphragm relaxes, resuming its normal domed position
  • All of these changes result in an decrease in volume of the thorax
  • Decreased volume = increase in air pressure (because the same amount of gas now has less room to more about in)
  • Internal pressure is now higher than atmospheric pressure (pressure of gas outside of body)
  • Thus, air is squeezed/forced out of the lungs
When a person stops breathing naturally due to disease or injury,  mechanical ventilators are used. Find out more about these machines by visiting these sites:
For more information about lung conditions and the fight against lung disease, go to the British Lung Foundation website
So, what is gaseous exchange?
Gaseous exchange is the movement of oxygen from the lungs into the blood supply, and the movement of carbon dioxide from the blood to the lungs. It occurs in the alveoli (air sacs)
Picture
Adaptations of the lungs for efficient gaseous exchange include:
  • large surface area of alveoli
  • extensive blood supply
  • moist surface of alveoli
  • thin walls of alveoli and capillaries

How do you think these adaptations make the lungs efficient? You should know this!
For a lovely animation on gaseous exchange visit the BBC Bitesize website

Respiration

There are two types of respiration: aerobic and anaerobic. You need to know the differences between each, and when each might be occurring in your body, and also in other organisms.
PictureA mitochondrion
Aerobic respiration
  • one of the most important enzyme-controlled processes
  • occurs in all living organisms (that's animals, plants, yeast, bacteria)
  • takes place in the mitochondria (infact, the number of mitochondria in a cell will give you an indication of how active that cell is. For example, a muscle cell will have many mitochondria as it needs lots of energy for contraction)
  • provides the cells with ENERGY from glucose and oxygen
Energy from respiration is used:
  • to keep warm (mammals and birds)
  • to carry out the basic functions of life, such as building large molecules from small ones, or breaking down molecules during digestion
  • to contract muscles
  • to move minerals into plant cells from the soil
Picture
Anaerobic respiration
  • this type of respiration takes place in the absence of oxygen
  • mainly occurs in the cytoplasm of the cell
  • occurs in animal cells when insufficient oxygen is being supplied to them (for example, during bouts of strenuous exercise)
  • In animals: glucose → lactic acid (+ little energy) 
  • occurs in yeast cells too. This provides us with useful waste products (see below)
  • In yeast: glucose →ethanol and carbon dioxide (+ little energy). We can use the ethanol (alcohol) in brewing, and the carbon dioxide in baking to make bread rise
Effect of exercise
When we exercise:
  • our muscles contract more
  • this means the rate of respiration increases (in order to provide the muscles with more energy)
  • we breathe faster and heavier to increase the supply of oxygen needed for respiration
  • our heart beats faster in order to pump the blood which is carrying oxygen and glucose to the cells that need it. The blood also removes the carbon dioxide (waste product of respiration)
  • glycogen stored in the muscles is converted back to glucose, providing more fuel for respiration 
  • the arteries that supply the muscles dilate (get wider) in order to increase the supply of blood to the cells
  • to prevent overheating, the blood vessels in the skin dilate, allowing heat to be lost by radiation. We also sweat which acts to cool us down


Visit the BBC Bitesize site for revision, an activity and a test