# Units, Definitions and O2 Availability

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Units, Definitions and O2 Availability
OXYGEN Units, Definitions and O2 Availability

Units Barometric Pressure (mmHg)
760 mmHg = 1 atmosphere (atm) = 100 kPa Partial pressure= Pgas a = Gasa X Ptotal Gasmix Usually given as a percentage

Calculate partial pressure of O2 at Sea level
Pgas a = Gasa X Ptotal Gasmix What’s in our air? Nitrogen 78.08% Oxygen 20.95% Water Vapor 0 to 4 % Argon 0.93% Carbon Dioxide 0.036% Neon 0.0018% Helium 0.0005% Methane % Hydrogen % Nitrous Oxide % Ozone % Atmospheric pressure is 1 atm at sea level O2 content ~ 21% If you go up in elevation (X ft elevation is 0.5 atmosphere), what happens to the partial pressure? O2 is still 21% of the atmosphere, but there are less air molecules per area. So 21% * 0.5 = 10.5

The respiratory pigments…
Why are they important? 100X increase!

The respiratory pigments…
Why are they important? Greatly increase O2 carrying capacity of blood 100X increase!

Hemoglobin (Hb) 4 heme units: = 1 iron-porphyrin + 1 protein
“heme” “globin” (1 Hb can carry 4 oxygen molecules)

Hb binds oxygen reversibly…
Hb + O HbO2 Hemoglobin Oxyhemoglobin Why is reversible binding important? what happens when O2 concentration is high? respiratory surface) what happens when O2 concentration is low? systemic tissues)

O2-Hb dissociation curves:
Describe activity of Hb at different PO2 % saturation PO2 % of Hb binding sites bound

O2-Hb dissociation curves:
Describe activity of Hb at different PO2 % saturation PO2 % of Hb binding sites bound

O2-Hb dissociation curves:
Describe activity of Hb at different PO2 % saturation PO2 @ systemic tissues @ respiratory surface

O2-Hb dissociation curves:
Describe activity of Hb at different PO2 % saturation PO2 @ systemic tissues @ respiratory surface

Hb and O2…. “Affinity”- how tightly two molecules bind together
Do you want your hemoglobin to have really High or really Low affinity for O2?

* Hemoglobin’s affinity for O2 determines which of these is favored

O2-Hb dissociation curves:
P50 is a measure of O2 affinity % saturation PO2 (mmHg) 20 40 60 80 100 30 90 = PO2 at which pigment is 50% saturated with O2 P50

There are many different forms of hemoglobin
=The product of different selective pressures (i.e., an example of adaptation) based on differences in protein portion Show different affinities for O2

O2-Hb dissociation curves:
P50 is a measure of O2 affinity Hb with a high affinity has a lower P50 Animals that have Hb with high affinity: Hb is saturated when O2 concentrations are relatively low b/c Hb will not release O2 unless O2 levels are very low this kind of Hb favors O2 uptake (loading) % saturation PO2 (mmHg) 20 40 60 80 100 30 90 P50

O2-Hb dissociation curves:
P50 is a measure of O2 affinity Hb with a low affinity has a higher P50 Animals that have Hb with low affinity: Hb is only saturated when O2 concentrations are relatively high b/c Hb is more likely to “let go” of O2, even if O2 levels are pretty high this kind of Hb favors O2 delivery (offloading) % saturation PO2 (mmHg) 20 40 60 80 100 30 90 P50

Animals native to high altitudes
% saturation P50 PO2 (mmHg) 40 60 80 100 30 90 20 Bar-headed goose

Animals native to high altitudes
Favors O2 loading 100 80 Bar-headed goose 60 % saturation Hb has higher O2 affinity 40 P50 20 30 60 90 PO2 (mmHg)

One more respiratory pigment…
Myoglobin (Mb) essentially identical to Hb but only 1 heme unit always in muscle cells very high O2 affinity

Comparing dissociation curves…
myoglobin % saturation PO2 (mmHg) hemoglobin 20 40 60 80 100 30 90 P50 P50

What is the function of myoglobin?
May serve as an O2 reserve or store Facilitates diffusion of O2 into muscle Very common in animals that live in periodically low O2 environments

What I want you to know about respiratory pigments…
Draw Hb-O2 dissociation curve and explain why it has that shape Define and locate P50 on a Hb-O2 dissociation curve Draw dissociation curve for Hb’s with different affinities and give physiological and ecological relevance of difference in affinity. Compare dissociation curves for Hb and myoglobin and give physiological relevance.

DIVING PHYSIOLOGY

Diving Physiology- marine mammals
Cetaceans (whales, dolphins and porpoise) Pinnipeds (seals, sea lion, walrus) Sirenia (manatee, dugong) Mustelidae (sea otter) Carnivora (Polar Bear)

Some diving records… Southern Elephant Seal Northern Elephant Seal
2 hours! Sperm Whale 2000 m! It is pretty astounding what diving mammals can do Even with scuba gear humans are far behind. Not sure if this record is current Dr. Sylvia Earle 375 meters, 1230 ft (with scuba gear)

Free Diving (no scuba tank)
“no limits” record = 171 m ( ft) “unassisted constant ballast” record = 65 m ( ft)

Where can an organism “store” O2?
How do diving mammals deal with hypoxia? -need to be able to store O2 for use when holding breath. Where can an organism “store” O2? Lungs Blood Muscle If you are going to hold your breath you need a reserve supply of Oxygen to use until you can breath again We are going to talk about the relative importance and adaptations on each of these stores

Major internal O2 stores: Lungs
Big lungs? - no…let lungs collapse! - many deep divers exhale before diving ( % capacity) When you are asked to hold your breath what do you do? What do you predict about the lungs of diving mammals? Chest wall WHY wouldn’t you want to store air there if you can?

Lung O2 stores vs. Blood O2 stores
Describe axes, Q: what is the point that this graph makes? Q: Compare shallow divers to deep

Major internal O2 stores: Blood
Deep Divers have more blood for their body size than non-divers More blood holds more oxygen! So Blood appears to be more impt than lungs in deep divers Deep divers actually have more blood (for their body size) than shallow or non-divers Percent fat inc this relationship

Major internal O2 stores: Blood
Oxygen carrying capacity (Hb) - more Hb per red blood cell (RBC) - more RBC’s per ml blood (higher Hematocrit) Weddell Seal Harbor seal Human Blood has different properties- it can hold more Oxy- see graph 1 Describe graph

Comparing Total O2 Stores:
Along x -axis depth of diving (diving ability) increases

 What about our favorite curve?… Hb-O2 dissociation
Left shift or right shift? Shallow divers that rely more on lungs Deeper Divers that rely more on blood stores of O2  % saturation What shift do you predict in diving mammals? WHY- How does it change affinity? What does it favor? PO2

Why??? Divers that rely on O2 stores in lungs need high affinity Hb that will pull O2 into blood even when the partial pressure of O2 left in lungs has gotten really low. Divers that rely on blood stores of O2 need lower affinity Hb that will allow O2 to move into tissues even when partial pressure of O2 in blood is really low.