a spontaneous or natural liking for someone or something.

D6 Transport of Respiratory Gases

Affinity

• Protein in red blood cells (RBC)
• Composed of four subunits (4 polypeptide chains)
• Each subunit has a “heme group” (contains iron, Fe)

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D6 Transport of Respiratory Gases

Sea Level = 760mm Hg

Mt Everest = 250mm Hg

• FUNCTION:
• O2 binds to Fe in the heme
• Carries 98% of O2 in the blood
• Grabs O2 when pO2 is high
• Lets go of O2 when pO2 is low

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D6 Transport of Respiratory Gases

SATURATION:

The percentage of hemoglobin binding sites in the bloodstream occupied by oxygen.

D6 Transport of Respiratory Gases

What causes hemoglobin's

affinity for O2 to change?

Body Tissues

Lungs

Higher affinity

Lower affinity

Complete the table by adding high or low to the blanks:

Complete the table by adding high or low to the blanks:

D6 Transport of Respiratory Gases

�

Where in the body will hemoglobin saturation be the highest?

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�

Where in the body will hemoglobin saturation be lower?

�

When Partial Pressure of Oxygen is High, Haemoglobin Saturation is High

D6 Transport of Respiratory Gases

�

Where in the body will hemoglobin saturation be the highest?

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�

Where in the body will hemoglobin saturation be lower?

�

When Partial Pressure of Oxygen is High, Haemoglobin Saturation is High

This occurs in the lungs

When Partial Pressure of Oxygen is Low, Haemoglobin Saturation is Low (Hb lets go of O2)

This occurs in the tissues

Oxygen Dissociation Curve

Hemoglobin affinity for O₂ is high when there is a high pO₂.

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Lots of O₂ around HB →

HB grabs and holds O₂

Oxygen Dissociation Curve

Hemoglobin affinity for O₂ is low when there is a low pO₂.

Not a lot of O₂ around HB →

HB lets go of any O₂ it is holding

D6 Transport of Respiratory Gases

AFFINITY:

A measure of how tightly hemoglobin attaches to oxygen.  

High affinity=  tight hold on O2

Low affinity = gives O2 away

D6 Transport of Respiratory Gases

D6 Transport of Respiratory Gases

Which of these pO2 values will change when exercising?

Atmospheric pO2

pO2 of blood arriving at alveoli

pO2 of blood leaving alveoli

pO2 in blood arriving at tissue capillary

pO2 in body tissues

pO2 in blood leaving tissue capillary

Which of these pO2 values will change when exercising?

Atmospheric pO2

pO2 of blood arriving at alveoli

pO2 of blood leaving alveoli

pO2 in blood arriving at tissue capillary

pO2 in body tissues

pO2 in blood leaving tissue capillary

NO CHANGE

NO CHANGE

NO CHANGE

LOWER. Why?

LOWER.

LOWER. Impact?

D6 Transport of Respiratory Gases

FETAL HEMOGLOBIN

• oxygen binding molecule
• in fetus 
• HIGHER O₂ affinity 

HEMOGLOBIN

• oxygen binding molecule
• after birth
• LOWER O₂ affinity

D6 Transport of Respiratory Gases

D6 Transport of Respiratory Gases

“DARK MEAT”

“LIGHT MEAT”

D6 Transport of Respiratory Gases

Myoglobin

MYOGLOBIN

• oxygen binding molecule
• in muscle
• single polypeptide
• one heme group
• binds one oxygen molecule
• HIGHER O₂ affinity

HEMOGLOBIN

• oxygen binding molecule
• in red blood cells
• four polypeptides
• four heme groups
• binds up to four oxygen molecules
• LOWER O₂ affinity

A small change in pO2 causes a larger change in saturation; Hb will give away O2 rapidly when pO2 drops.

Myoglobin will hold on to O2 even when pO2 drops. It “stores” oxygen until the pO2 is very low (like in exercising tissues).

D6 Transport of Respiratory Gases

Outline the role of myoglobin in muscle fibres [2]

1. binds oxygen when level is high;
2. releases oxygen when level is low;
3. acts as an oxygen store;
4. allows muscles to continue with aerobic respiration for longer;

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D6 Transport of Respiratory Gases

Explain the oxygen dissociation of myoglobin [6]

1. myoglobin is specialized for oxygen storage;
2. myoglobin has a single heme/globin unit/polypeptide chain;
3. found in muscle;
4. myoglobin has a higher affinity for oxygen than haemoglobin; (allow this point if haemoglobin dissociation curve correctly drawn to right of myoglobin curve and labelled)
5. in normal conditions/at rest myoglobin is saturated with oxygen;
6. used during intense muscle contraction when the oxygen supply is insufficient/when muscle is very active its oxygen concentration may fall (below 0.5 kPa);
7. when this happens myoglobin releases oxygen;

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D6 Transport of Respiratory Gases

Exercise

↑ pCO₂

↓ pH

↓ hemoglobin’s affinity for O₂

↓O2 saturation (more O2 for the cells)

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How will the oxygen dissociation curve change?

On the same graph, add a line for your predicted curve.

and/or ↓ pH

“Bohr Shift”: an increase in blood CO₂ concentration leads to a decrease in blood pH which will result in hemoglobin proteins lowering their affinity for oxygen.

• This mechanism allows for the body to adapt the problem of supplying more oxygen to muscles undergoing strenuous activity.

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• The muscles generate CO₂ and lactic acid which lowers the pH making hemoglobin let go of oxygen.

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Carbonic Anhydrase

CO₂ + H₂O ↔ H₂CO₃ ↔ H+ + HCO₃–

D6 Transport of Respiratory Gases

Effect of Altitude

“As altitude _increases__,

the pO2 _decreases__ and the O2 saturation _decreases_.”

So, less oxygen is being carried by hemoglobin.

Difference in pO2 between air in the lung lung and cell tissues

There is a smaller pO2 difference between the air in the lungs and respiring tissues at altitude. So, diffusion of O2 into the tissues decreases (remember, diffusion depends on pressure gradients). As a result, the tissues get less O2.

air in lungs at sea level

air in lungs at altitude

tissues

Effects of less O2 due to altitude depends on how fast you ascend and let your body acclimate (get used to) the altitude.

Short-term (days):

• Increased respiratory rate leading to increased oxygen in the alveoli of the lungs
• Increased heart rate helping to increase delivery of oxygen to tissues

D6 Transport of Respiratory Gases

How does the body respond to altitude?

Medium-term (weeks):

• Increased urine output leading to reduced plasma volume and concentration of the hemoglobin in the blood (more CO2 = more acidic = more bicarbonate from kidneys = more urine)
• Increased production of hemoglobin so there is more ways to “catch” the O2 that is present in the air

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D6 Transport of Respiratory Gases

How does the body respond to altitude?

This is why athletes will train at altitude

Long-term (months):

• Increased density of capillaries in the tissues so there is more surface area for gas exchange

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D6 Transport of Respiratory Gases

How does the body respond to altitude?

Another reason why athletes will train at altitude

D6 Transport of Respiratory Gases

Outline the changes in the partial pressures of carbon dioxide and oxygen as altitude increases. [2]

1. both pO2 and pCO2 fall with increasing altitude;
2. above certain altitude there is little change in alveolar pO2 / pO2 remains close to 37 mm Hg over a wide range of altitudes;
3. Pco2 changes over the entire range of altitudes;
4. the pO2 is always higher than pCO2;

benefits:

a. improved performance/endurance at lower oxygen levels

b. due to higher concentration erythrocytes/red blood cells/hemoglobin

c. more oxygen transported/ circulating

d. improved metabolic/lung efficiency/gas exchange

e. increase in myoglobin/number of capillaries/mitochondria

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risks:

f. altitude sickness/stroke/lower immunity

g. increased muscle tissue breakdown

h. effects are not immediate/not permanent/extended training at high altitude required

i. may be unfair to competitors who cannot train at high altitude

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D6 Transport of Respiratory Gases

Discuss high altitude training for athletes. [6]

Hypoxia-induced hyperventilation: At high altitudes, the lower oxygen levels (hypoxia) cause the body to increase breathing rate (hyperventilation). This leads to a reduction in carbon dioxide levels in the blood, causing respiratory alkalosis (a more alkaline blood pH). The kidneys respond by excreting more bicarbonate and water through urine to restore the acid-base balance, resulting in increased urine output.

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Reduced plasma volume: As part of acclimatization to altitude, the body reduces plasma volume to concentrate red blood cells, increasing hemoglobin concentration and improving oxygen transport. This reduction in plasma volume is partially achieved by increased urine production.

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Fluid shifts: At altitude, there is a shift in fluid from the intravascular space (inside blood vessels) to the interstitial space (outside blood vessels), which can cause the kidneys to respond by eliminating excess fluid.

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Erythropoietin (EPO) is a hormone primarily produced by the kidneys (and to a smaller extent, the liver) that plays a crucial role in the production of red blood cells. Its primary functions include:

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Regulation of red blood cell production: EPO stimulates the bone marrow to produce more red blood cells (erythropoiesis) in response to low oxygen levels in the blood (hypoxia). This increases the oxygen-carrying capacity of the blood.

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Response to hypoxia: When oxygen levels decrease—such as at high altitudes, during intense exercise, or in cases of anemia—the kidneys sense this and secrete more erythropoietin. The increased EPO levels signal the bone marrow to produce more red blood cells, helping to deliver more oxygen to tissues.

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Acclimatization to altitude: At high altitudes, the body experiences lower oxygen availability (hypobaric hypoxia). In response, the kidneys produce more EPO, which stimulates an increase in red blood cells to improve oxygen transport. This process is a key part of acclimatization to altitude, enabling better performance and endurance in low-oxygen environments.

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Medical uses: Synthetic erythropoietin is used in medical treatments for conditions like chronic kidney disease, anemia in cancer patients, and others where natural EPO production is impaired.

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EPO is also infamously known for its misuse in sports as a performance-enhancing drug to increase endurance by artificially boosting red blood cell count, improving oxygen delivery to muscles.

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