Oxygen Dissociation Curves

What is an oxygen-haemoglobin dissociation curve

• how much hb is saturated with oxygen vs partial pressure (conc) of O2 in the blood

• po2 determines the amount of o2 available to bind to Hb

Loading Tension

• po2 when hb is 95% saturated

Unloading Tension

• po2 when hb is 50% saturated

Describe the affinity for O2 at HIGH Partial pressures

• when there are high partial pressures of O2 such as in the alveoli, hb has a high affinity for o2 so it begins to load on oxygen

Describe the affinity for O2 at LOW partial pressures

• at low partial pressures of oxygen such as in the capillaries

• hb looses its affinity for oxygen

• oxygen beings to unbind - unload

Why is the Oxygen-Haemoglobin dissociation curve a sigmoid -s shape

1. at low conc of o2 it is difficult to absorb oxygen bcs the polypeptide chains are packed tightly together

2. once the first molecule binds, haemoglobin’s structure relaxes and the next oxygen molecules are loaded easily

3. then a decrease in oxygenation as hb molecules approach saturation as it is harder for o2 to find an empty binding site

When giving up its oxygen at low Po2 - how does this happen

• the first molecule is given up very slowly but the rest are given up more rapidly

Is the relationship between oxygen saturation and partial pressure of O2 directly proportional

NOT AT ALL!!! AS O2 IS AT IS MAX HB OXYGENATION DECREASES.

how much oxygen is unloaded during rest

• 22%

What purposes does the large reserve of oxygen serve

1. to ensure the blood can supply enough oxygen to cells during excretion and rest

2. to maintain life for 4-5mins even if breathing/heart beat stops

During exercise how much o2 is unloaded - why?

• 62% as more is needed for respiration

Where is myoglobin found

• in the muscle cells

Describe some of the functions and properties of myoglobin

• myoglobin is composed of a single polypeptide chain

• only binds to one o2 molecules

• primary function is to store o2 (while hb is to store and transport)

• myoglobin has a higher affinity for oxygen than hb → only releases it when hb supplies have been exhausted

• myoglobin also helps in extended breath holding, high levels of o2 stored in myoglobin

Briefly Explain the Bohr Effect - High Conc of Co2

• Co2 is a biproduct of respiration

• it produces carbonic acid which disassociates into bicarbonate ion and H+

• Hb has a higher affinity for H+ then o2, so when theres a lot of Co2 (due to respiration) theres a lot of H+, so a lot of unloading happens

• CURVE SHIFTS TO THE RIGHT

Briefly Explain the Bohr Effect - Low Co2 conc

• so less co2 = less h+

• so hb has an increased affinity for oxygen

• hb loads more oxygen

• CURVE SHIFTS TO THE LEFT

Explain the advantage of the Bohr Effect

• in areas where there is a lot of respiration, lots of co2, hb can release more o2

• o2 becomes available during conditions when it is needed most

• when there is a low CO2 conc such as in the lungs, you would want to pick up as much oxygen as possible, so more loading occurs

Describe the Oxygen Dissociation curve for a small animal - mice

• loose more heat - higher metabolic rate

• have to supply more oxygen, so Hb has a lower affinity for oxygen to unload quickly

CURVE SHIFTS TO THE RIGHT

Oxygen Dissociation Curves - Hypoxic Conditions

• reduces PO2 in the air makes it difficult to load HB

• high affinity for o2 → lower release of o2 as means of an O2 reserve

CURVE SHIFTS TO THE LEFT

Effect of temperature on Affinity of Hb for O2

• higher temperature decreases affinity for oxygen → release oxygen more readily

• during exercise, more heat, more respiration → more unloading

CURVE SHIFTS TO THE RIGHT

Double Bohr Effect

• Co2 from the fetus diffuses into the mothers blood

• the mother blood has a higher pco2 - higher conc of H+,

• lower affinity for oxygen releases it more easily

• fetus has less co2, lower conc of h+, higher affinity for O2

• facilitates transfer of oxygen across the placenta from mother to fetus