Human Breathing

• the human respiratory system is located in the thorax
• the diaphragm is a sheet of involuntary muscle that separates the thorax from the lower abdominal cavity.
• the ribs and intercostal muscles form the walls of the thorax
• breathing in through the nose is beneficial as air is:

  • flitered and cleaned by hairs and mucus
  • moistened
  • warmed as it passes through the nasal passages

  moist warm air diffuses more easily
• The pharynx is the throat and contains the larynx which is the voice box
• In the pharynx a flap of tissue called the epiglottis closes over the trachea, preventing food and drink from passing into the trachea.
• In the larynx (voice box) two vocal cords vibrate to produce sound. Our tongue and lips convert the sound to speech.
• Trachea and many of it's subdivisions such as bronchi and bronchioles are made of muscles and elastic fibres with rings of cartilage. Cartilage prevents the tubes from closing when air is drawn through them. The lower, smaller bronchioles do not contain cartilage, which become narrow during an asthma attack. All tubes are lined with mucus and cilia.
• Mucus

  • mucus is sticky and traps small particles such as dust and bacteria.
  • Cilia beat and create an upward movement which pushes the mucus upwards and past the epiglottis and down into the stomach.
• Lungs are where gas exchange takes place. They are enclosed by a pair of pleural membranes.

  • outer pleura lines the chest wall and diaphragm
  • inner pleura lines the lungs
• The pleural cavity is the gap between the two pleura which contains a liquid to lubricate the membranes and reduces friction during breathing.
• Alveoli are adapted for gas exchange as:

  • they are numerous which provide a huge surface are for gas exchange
  • they are one cell thick which allows for fast diffusion
  • they have moist surfaces
  • and are enclosed in blood capillaries
• Carbon dioxide and water pass out of body cells by diffusion. They diffuse from blood plasma into the alveoli in the lungs to be exhaled.
• Oxygen passes from the alveoli into the red blood cells in the plasma. It then passes from red blood cells into body cells.

  Oxygen is transported by combining with haemoglobin in red blood cells to form oxyhaemoglobin
• Breathing is an involuntary process. An adult breathes at an average of 15 times per minute.
• Inhalation

  1. The medulla oblongata controls the rate of breathing by monitoring Carbon dioxide levels.
  2. the brain sends a signal to the intercostal muscles and diaphragm.
  3. these muscles use ATP to contract as inhalation is an active process.
  4. the ribs move up and out and the diaphragm curves down
  5. the volume in the chest (thoracic) cavity increases
  6. the pressure inside the chest cavity decreases
  7. the external air pressure is greater than the internal air pressure.
  8. air is then forced into the lungs
• Exhalation

  1. the intercostal muscles and the diaphragm relax, no energy is needed as exhalation is a passive process
  2. the ribs move in and the diaphragm curves up
  3. the volume of the chest cavity decreases
  4. the pressure in the chest cavity increases
  5. the internal pressure is now greater than the external pressure.
  6. Air is now forced out of the lungs
• exercise increases the rate of respiration and breathing rate as a result of excess carbon dioxide. Exhalation becomes an active process to get rid of carbon dioxide when strenuously exercising. In addition, extra muscles are used to increase the depth in breathing
• Name examples where we can control our breathing

  • singing
  • swimming
  • speaking
• Composition of air when at rest

  oxygen = inhaled - 21%, exhaled - 14%

  carbon dioxide = inhaled - 0.04%, exhaled - 5.6%

  water = inhaled - low amount, exhaled - high amount
• Asthma

  • Symptoms - wheezy breathing, breathlessness
  • Cause - (external) allergens e.g. pollen, animal hair, dust, (internal) lower bronchioles narrowing and becoming inflamed due to no cartilage
  • Prevention - avoiding allergens or preventative inhalers
  • Treatment - drugs that force the bronchioles to widen and reduce inflammation such as bronchodilators (inhalers)
• Controlling human breathing

  The rate of human breathing is controlled by the medulla oblongata by monitoring carbon dioxide levels. When carbon dioxide dissolves in water it makes a weak acid called carbonic acid, this acid lowers the pH slightly in the blood from 7.4. The brain detects this drop in pH and sends signals to the diaphragm and intercostal muscles which causes us to breathe.
• Our brain does not respond to low levels of oxygen but to higher levels of carbon dioxide.
• Carbon dioxide operates as a controlling factor in gas exchange in both plants and animals.
• Effect of exercise on breathing rate experiment

  • count your number of breaths per minute at rest. Repeat three times and get your average. This is used as a control to compare the rest of the results after walking and exercising.
• after exercise, the rate of breathing often falls below the resting rate. This is due to deeper breathing.