Mechanics of Breathing

Inspiration: External intercostals muscles contract during

inspiration Diaphragm contracts (downwards and flattens) This pulls the rib cage 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

Expiration 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

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

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

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.

External and Internal Respiration Showing

Changes in O2 and CO2

Oxygen-Haemoglobin Dissociation Curve

Shows us how much haemoglobin is saturated with oxygenSaturated – when haemoglobin is loaded with oxygenDissociation – where oxygen is unloaded from the haemoglobinThe 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 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 EFFECT

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

Myoglobin

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 TrainingReduction 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 musclesTherefore 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. 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 . . .

1. What is the Oxygen-Haemoglobin Disassociation Curve?

2. What happens to the curve during exercise?

3. What causes this to happen?4. What are the effects of the curve

shifting to the right?5. What changes occur to the

respiratory system as a result of training?