The transport of oxygen When oxygen from the alveoli diffuses across the alveolar capillary membrane, it enters the bloodstream. It is the function of the blood to transport oxygen and does it in two ways: 1. 97% is carried in haemoglobin 2. 3% is dissolved in the blood plasma When oxygen combines with haemoglobin, it forms oxy-haemoglobin Hb(haemoglobin) + O2 (oxygen) = HbO2 (oxy-haemoglobin)

GAS TRANSPORT GAS TRANSPORT ACROSS THE RESPIRATORY MEMBRANE oxygen diffuses from alveolus across the alveolar wall, respiratory membrane, and capillary wall towards red blood cells carbon dioxide diffuses in the opposite direction from the red blood cell and from blood plasma to the alveolus

What happens when we exercise? Task: complete flow diagram Page 74 Fig. 4.20 Putting it all together Increases in Lactic Acid Increases in CO2 Increases in blood and muscle temperature Decreases in pH thus acidity levels increase. These changes mean that the body needs oxygen quickly.

Haemoglobin Haemoglobin has a very high affinity for oxygen The most important factor that determines how much oxygen combines with haemoglobin is the partial pressure of oxygen. When the pO2 of blood is high, such as in the alveolar capillaries of the lungs, haemoglobin readily combines with large amounts of oxygen until it becomes almost fully saturated.

When the pO2 of blood is low, such as in the capillaries of the contracting muscles, oxygen is released by the haemoglobin. This O2 can now be used by the muscle tissues. This is represented by the oxy-haemoglobin dissociation curve.

Dissociation curve shifts to the RIGHT The Bohr Effect During exercise muscles need more oxygen so the dissociation (release) of oxygen from Hb happens more readily This is known as the Bohr effect and frees up more oxygen = used by working muscles Dissociation curve shifts to the RIGHT

Animation http://www.getbodysmart.com/ap/respiratorysystem/physiology/gases/hbsaturation/animation.html

1. Increase in blood and muscle temperature Factors shifting the dissociation curve to the right are: 1. Increase in blood and muscle temperature 2. Decreases in PP oxygen within muscle increasing the oxygen diffusion gradient. 3. Increase in PP of carbon dioxide increasing carbon dioxide gradient. 4. Bohr effect – increase in acidity (lower pH)

The effect is that the working muscles: Generate more heat when working Use more oxygen to provide energy, lowering the PP oxygen Produce greater carbon dioxide as a by-product Increase lactic acid levels which increase muscle/blood acidity Collectively all four factors increases the dissociation of oxygen from haemoglobin that increases the supply of oxygen to the working muscles.

Transport of oxygen 3% dissolves in plasma. 97% combines with haemoglobin to form oxyhaemoglobin One further method the body has of ensuring the muscles are constantly supplied with adequate amounts of oxygen is through myoglobin. It is only found in the skeletal muscles.

Myoglobin Iron based protein Similar to Hb In the muscle oxygen is transported by myoglobin. Myoglobin has a high affinity for oxygen. It stores oxygen and transports it from the capillaries to the mitochondria. Mitochondria are the centres in the muscle where aerobic respiration takes place. Much higher affinity For 02 than Hb

Arterial-venous oxygen difference (a-vo2 diff) This represents how much oxygen is actually extracted and used by the muscles Measured by: Analysing the difference in oxygen content of the blood in the arteries leaving the lungs and that in the mixed venous blood returning to the lungs

Exam Questions 1. Explain how oxygen is taken up by haemoglobin from the lungs and released at the muscle site. (3 marks) 2. Explain why aerobic training improves the performer’s ability to transport oxygen. (2 marks)

Mark scheme 1. A. Forms oxyhaemoglobin/Hb O2 B. At lungs - high partial pressure of O2/ blood – low partial pressure of O2; C. Haemoglobin becomes saturated; D. At muscles - low partial pressure of Oxygen/ O2/ blood - high partial pressure of O2; E. Hence oxygen dissociates from haemoglobin; F. Mention of myoglobin.

Mark scheme 2. A. More blood volume/haemoglobin/Hb/red blood cells; B. Increased a-VO2 diff/more oxygen extracted by muscles; C. Increased capilliarisation/more capillaries.