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Respiratory System. Exchange of oxygen and carbon dioxide between the blood and the muscle tissues Exchange of oxygen and carbon dioxide between the lungs and blood The breathing of air into and out of the lungs. Mechanics of Breathing. Inspiration:

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respiratory system
Respiratory System

Exchange of oxygen and carbon dioxide between the blood and the muscle tissues

Exchange of oxygen and carbon dioxide between the lungs and blood

The breathing of air into and out of the lungs

mechanics of breathing
Mechanics of Breathing


  • External intercostals muscles contract during inspiration
  • Diaphragm contracts (downwards and flattens)
  • This pulls the rib cage upwards and outwards
  • These actions cause the thoracic cavity size to increase
  • This decreases the pressure inside the thoracic cavity
  • Gases move from areas of high pressure to low pressure areas
  • Therefore oxygen moves from the atmosphere (higher pressure) into the lungs (now low in pressure)
  • During exercise, a more forceful inspiration is required so extra muscles are involved in this process – sternocleidomastoid and pectoralis minor
  • Usually a passive process
  • As the intercostals muscles relax the rib cage moves downwards
  • The diaphragm relaxes and returns to its dome shape
  • This decreases the size of the thoracic cavity
  • This causes the pressure to increase in the thoracic cavity (smaller volume)
  • Therefore gases move out of the lungs (high pressure) into the atmosphere (lower pressure)
  • During exercise breathing rate is increased, expiration is aided by the internal intercostal muscles and the abdominal muscles,
  • This pulls the rib cage down more quickly and with greater force
gaseous exchange
Gaseous Exchange

Key Terms:

Gaseous Exchange – the process of exchanging O2 and CO2

Partial Pressure - the pressure a gas exerts in a mixture of gases

Diffusion - The movement of gases from areas of higher partial pressure to lower partial pressure

Diffusion Gradient - The difference between high and low pressure of gases. The bigger the gradient the greater the diffusion.

external respiration
External Respiration

Involves the movement of oxygen and carbon dioxide between the alveoli of the lungs and capillaries surrounding the alveoli.

The aim of external respiration is to oxygenate the blood returning from the tissues

As blood circulates through the capillaries surrounding the alveoli oxygen is picked up and carbon dioxide is dropped off to be expired

internal respiration
Internal Respiration

Involves the movement of O2 and CO2 between the capillaries surrounding the muscles and the muscle tissues

The aim of internal respiration is to oxygenate the muscles and collect CO2 to return it to the alveoli

These processes can only happen if a diffusion gradient is present.

oxygen haemoglobin dissociation curve

Oxygen-Haemoglobin Dissociation Curve

Shows us how much haemoglobin is saturated with oxygen

Saturated – when haemoglobin is loaded with oxygen

Dissociation – where oxygen is unloaded from the haemoglobin

The higher the partial pressure of oxygen, the higher percentage of oxygen saturation to haemoglobin

Oxygen associates with haemoglobin at the lungs and dissociates at the muscles (because PP of O2 is high at lungs and low at muscles)
  • During exercise a greater amount of dissociation of O2 at the muscles is required, therefore less saturation at the muscles has to occur
  • Four factors happen in our bodies during exercise to allow this to occur
factors affecting the saturation of oxygen to haemoglobin
Factors Affecting the saturation of oxygen to haemoglobin
  • Increase in temperature – in the blood and muscles during exercise
  • Decrease in PP of O2 – within the muscles during exercise, therefore creating a greater diffusion gradient
  • Increase in PP of CO2 – therefore causing a greater CO2 diffusion gradient
  • Increase in acidity – lowering the pH of the blood through production of lactic acid (more hydrogen ions produced). This is known as the BOHR SHIFT

All four of these factors (which occur during exercise) increases the dissociation of oxygen from haemoglobin, which increases the supply of oxygen to the working muscles and therefore delays fatigue.

Exam Style Question:
  • What happens to the oxygen-Haemoglobin Dissociation Curve during exercise? (6 marks)
  • It shifts to the right
  • Because during exercise there is an increase in blood/muscle temperature
  • Decrease in PP of O2 in the muscles
  • Increase in PP of CO2 in muscles
  • Increase in acidity (more lactic acid)
  • Known as Bohr Effect/Shift
  • Has a higher affinity for O2 than haemoglobin
  • Therefore acts as a store of O2
  • Even at very low partial pressures of 02 (the muscles when exercising) it remains saturated
  • This means that myoglobin still has O2 available to supply the working muscles.
respiratory adaptations to training

Respiratory Adaptations to Training

Reduction in breathing rate during sub-maximal exercise,

System is more efficient therefore less

breaths required,

No changes in lung volumes except. . . .

Vital capacity – amount of air that can be forcibly expired after maximal inspiration – increases slightly, largely due to stronger respiratory muscles

Therefore spirometer traces are not good predictors of training or fitness because lung size/volume do not determine fitness (these are largely genetic and not adapted due to training)

Gaseous exchange becomes efficient
  • External Respiration - increased capilliarisation surrounding alveoli – more opportunity for gaseous exchange to occur, more O2 enters the blood
  • Internal Respiration – increase in myoglobin within the muscles (this carries O2 to mitochondria), therefore leading to improved efficiency of energy production.
describe the chemical physical and neural changes that cause a change in our breathing rate
Describe the chemical, physical and neural changes that cause a change in our breathing rate.

Chemical –

Increase in CO2, increase in acidity

Detected by chemoreceptors

Physical –

Movement of muscles and joints

Detected by proprioreceptors

Also stretch receptors in lungs, temperature receptors detect changes

Neural –

Nervous control

Messages sent to the medulla (respiratory control centre)

Messages to send respiratory muscles via sympathetic nervous system.

respiratory system so far
Respiratory System so far . . .

What is the Oxygen-Haemoglobin Disassociation Curve?

What happens to the curve during exercise?

What causes this to happen?

What are the effects of the curve shifting to the right?

What changes occur to the respiratory system as a result of training?

effects of exercise on volumes
Effects of Exercise on Volumes
  • At rest, lungs are ventilated at approx. 6 Litres per minute
  • During “steady state” endurance exercise maximal ventilation is about 80-100 Litres per minute (males) and 45-80 Litres per minute (females) – smaller lungs!
  • Brief maximal exercise (800m race) rates may increase to 120-140 Litres per minute
  • BREATHING RATES – rise from 12 per minute to 45 per minute during strenuous exercise
  • Depth of respiration can increase from 0.5 litres per breath to 2.5 litres per breath

Training will usually result in little or no change in pulmonary function. However, swimmers may experience some increase in vital capacity and maximal breathing capacity (breathing against resistance of the water)

Comparison of marathon runners and sedentary subjects showed no difference in actual lung functions (FEV1, etc)

  • The respiratory system functions to deliver O2 to the lungs and remove CO2
  • The system consists of the nose, trachea, larynx, bronchial tree and lungs
  • Inspiration occurs when air is drawn into the lungs by the reduction of the pressure caused by an increase in the size of the thoracic cavity
  • Expiration occurs when the pressure increases as the size of the thoracic cavity decreases and air is forced out
  • During normal breathing inspiration is produced by the activity of the diaphragm and intercostal muscles
  • During exercise both the rate and depth of breathing increase
  • Respiration is controlled by the MEDULLA of the brain
  • Total Lung Capacity = Tidal Volume + Inspiratory Reserve Volume + Expiratory Reserve Volume and Residual Volume (6000ml)