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Gas Exchange 4: Blood summarized lectures notes along with relevant pictures and notes from the assigned readings

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Biology 2601A/B
Brent Sinclair

Organismal Lecture 18 Gas Exchange 4: Blood Gases Dissolve in Liquids  He same as having air bubbles  Pressure of the liquid (Pliquid) is proportional to pressure of the ai) (P  The amount of gas in a solution is dependent upon o 1. Temperature o 2. Salinity o 3. Type of gas  Gases that have reacted chemically will not contribute to partial pressure in a solution Blood Must be Thicker than Water  The solubility of O₂ in water (especially warm salty water) is not enough to provide O₂ to active tissues  Most organisms have to, therefore, use respiratory pigments to reversibly bind O₂ and have them transport it to the tissues o An example of a respiratory pigment is haemoglobin o By taking this O₂ out oof solution, O₂ carriers help to maintain the PO₂ gradient across the respiratory surface, improving O₂extraction  At the tissues, mitochondrial O₂ consumption ↓’s the PO₂ of the blood, causing O₂ to dissociate from the oxygen carrier, and allowing it to then diffuse down its PO₂ gradient into the cells Respiratory Pigments  diffusion will be dependent upon the properties of the solution as well as the [O₂] of the air  ↓ed partial pressure in the blood allows for ↑ of O₂ diffusion from the air  Once the O₂ molecules are bound to the respiratory pigment they are no longer considered part of the solution What it Means to have a Respiratory Pigment  In comparison to water, there is much more carrying capacity of the respiratory pigments to carry O₂, allowing the organism to better pull O₂ out of the water/air and deliver large amounts to the tissues Respiratory Pigments  Most are proteins; can either be in solution or enclosed in red blood cells (usually for vertebrates)  Hematocrit is the proportion of total blood volume that is occupied by red blood cells  We can use Hematocrit to measure O₂ carrying capacity in the blood  This is done by centrifuging the whole blood and measuring the proportion of solids (cells) o This is a pretty good measure of blood O₂ carrying capacity in vertebrates Components of a Respiratory Pigment  When considering haemoglobin, it is made up of 4 subunits (2 α and 2 β subunits = tetramer)  Within each subunit, heme groups are non covalently bound to the molecule and contain a iron ion at the centre  Haemoglobin plays a role in O₂ transport and storage Kinds of Respiratory Pigments (**ON EXAM***)  1/ Fe means these pigments require 1 iron ions to bind to 1 O₂ molecule  1/ 2Fe mean these pigments require 2 iron ions to bind to 1 O₂ molecule Chlorocruorins  Found in 4 polychaete (annelid worm) families o 1. Serpulidae; 2. Sabellidae; 3. Chlorhaemidae; 4. Ampharetidae Hemerythrins  Found in the following invertebrate phyla o 1. Sipunculida; 2. Priapulida; 3. Brachiopoda Hemocyanins  Found in some arthropods and many molluscs Hemoglobin  Many organisms contain hemoglobin  Although our hemoglobin is tetrameric, other organisms can have monomeric or polymeric (extracellular – almost cell size) hemoglobin  If look at phylogeny of animal groups, we see that many derived families have evolved some form of hemoglobin in at least one of more of their members Hemoglobin Oxygen Association Curve  O₂ equilibrium curves can be either hyperbolic or sigmoidal  Myoglobin will exhibit a hyperbolic curve (each O₂ binds independently of one another), while hemoglobin exhibits a sigmodial one  Unbound hemoglobin has a low affinity for O₂; however as soon as one O₂ binds to any of the heme groups, the affinity of the heme for O₂ ↑’s a lot (Subunit interaction) o Oxygen affinity ↑’s progressively as each O₂ molecule binds; this is known as cooperative binding, and causes a sigmoid curve  As seen in the diagram, as PO₂ ↑’s, so does the proportion of hemoglobin loaded with O₂  Is a very efficient way to get O₂ off hemoglobin and into blood  The lower the partial pressure in the blood, the less O₂ will be bound to hemoglobin  just showing the comparison between the
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