Transport of Oxygen in Body Fluids

- mito need more O2 if exercise fueled aerobically - PO2 100----80 mmHg - PO2 60----40 mmHg - PO2 40----20 mmHg - O2 extraction increases from 25% to ~ 65% - this is approximately constant over wide range of exercise states, because rate of blood flow increases, not because extracting more O2/vol blood

Effects of Exercise

A measure of the tendency of hemoglobin to bind oxygen and release oxygen.

Effects of Exercise Affinity Each of the red arrows signify a 5 mL decrease in oxygen concentration in the blood (e.g. 20 to 15, 15 to 10). If you start off at really high oxygen concentrations at the far right side of the curve, in order to unload 5 mL of oxygen (plateau), partial pressure has to decrease from 90 to 40. In order to unload another 5 mL of oxygen (relatively steep part of curve), partial pressure only has to decrease by 15 mmHg. In order to unload another 5 mL (steepest part of the curve), you only have to decrease partial pressure by 8-9 mmHg. This

1. Activity (tissue use of O2) 2. Rate of blood flow 3. PO2 in blood - If PO2 in the blood when it gets to a particular tissue is already lower, we are on a different part of that curve. 4. Hb concentration varies - We may unload the same relative amount of oxygen but if we have a higher concentration of hemoglobin the absolute amount of oxygen unloaded will be greater.

Effects of Exercise: At Rest There is enough of a gradient in an individual at rest and enough of a demand for oxygen at rest that there is about a 25% decline in oxygen concentration in the blood in the blood leaving the tissue compared to blood leaving the lungs. In the lungs, concentration is about 20 mL O2 per 100 ml blood. After it is leaving the systemic tissues, it is about 15 mL O2 per 100 mL blood. There is a 5 mL decrease (25% of oxygen bound to hemoglobin in the lungs is unloaded to the systemic tissues). What factors might make the amount of oxygen unloaded in the tissues either higher than 25% or less than 25%?

At PO2 100-80 mmHg, a little O2 unloaded. At PO2 60-40 mmHg, a good amount of O2 is unloaded. At PO2 40-20 mmHg, a lot of O2 is unloaded because of the sigmoidal cooperative relationship, you are moving down this curve from the plateau to the steep part of this curve where oxygen gets unloaded more easily. During exercise, a whole lot more oxygen is unloaded from the hemoglobin (65% compared to 25% at rest). Blood is moving faster. How much time blood spends passing by something (e.g. alveoli, muscle cells) affects gas exchange.

Effects of Exercise: Exercise The mitochondria need more O2 if exercise fueled aerobically. As PO2 decreases from 100-80 mmHg, how much oxygen is unloaded? As PO2 decreases from 60-40 mmHg, how much oxygen is unloaded? As PO2 decreases from 40-20 mmHg, how much oxygen is unloaded? Why do you think the top of the big arrow at rest is higher than the big blue arrow for exercise?The percent saturation in the blood of someone exercising as it leaves the lungs is lower than the percent saturation of blood leaving the lungs in a person at rest. What might explain this small decrease?

It relates to the effect of CO2 and Hydrogen ion concentration (PH) CO2 + H20 (arrow) HCO3- + H+ You will have a higher concentration of CO2 in the muscle compared to the lungs. It reduces the PH (more acidic conditions). In an actively contracting bed of muscles, LA will contribute to a decrease in PH when you have to rely on anaerobic metabolism (producing LA). Compared to the lungs, the conditions that the Hb in the blood experiences shifts the curve to the right. By shifting to the right, we are decreasing the affinity of hemoglobin for oxygen making it easier for the hemoglobin to unload the oxygen. By the time the blood gets back to the lungs, PH is higher and CO2 concentration is lower. This will shift the curve back to the left and increase the affinity of hemoglobin for oxygen and it will load up with oxygen more easily. Decrease PH, Right Shift, Increase P50, Decrease Hb O2 affinity. This will cause oxygen to be unloaded more easily and get to the mitochondria. You can have situations where CO2 concentration changes in the absence of a H+ ion concentration which is why we see a fixed acid bore effect (e.g. pH doesn't change but CO2 concentration changes).

Factors can Alter Affinity: Bohr Effect What does the Bohr Effect relate to? Compared to conditions in the lungs, think about an actively working muscle group/tissue. What is the CO2 concentration likely to be in those two areas? Where are you likely to have a higher CO2 concentration?

a) As temp increase, rightward shift. In an exercising muscle, temperature increases (Higher CO2, higher H+ concentration, lower pH). Increases P50 and lowering oxygen. b) Plays an important role in the continuous modulating of the affinity of hemoglobin molecules for oxygen. We see important changes in 2,3 BPG concentrations in people who are anemic (e.g. don't have enough red blood cells and enough hemoglobin in bodies) and in people who are acclimating to high altitudes when they are moving to areas where the partial pressure of oxygen is lower. An increase in 2,3 BPG shifts the curve to the right, there is a decrease in affinity. c) Inorganic ions can affect the affinity of hemoglobin for oxygen (e.g. Ca2+ and oxygen)

Factors can Alter Affinity: Root Effect Other Factors: a) Temp b) Organic compounds, e.g. 2, 3 - BPG inside RBC c) Inorganic ions

Hemoglobin in certain fish species. It can lead to a shift to the left or right (e.g. change in P50) but it can also lead to a decrease in percent saturation. If pH decreases, you shift to the right but there is also a downward shift. 100% saturation is not up here where it was for that curve. 100% saturation is now down here. When you see a decrease in pH, it lowers the point at which the hemoglobin is fully saturated (decreases carrying capacity). Left/Right shift depending on pH and there is also an up/down shift because of the way hemoglobin molecules in certain species of fish respond to changes in Hydrogen ion concentrations. It helps oxygenate the retina (e.g. where the photoreceptors cells are located in the eyes of the fish). This tends to not be a well vascularized part of the eye. By shifting the curve to the right and down, hemoglobins can release more oxygen. It helps fill a fish's swim bladder. It is a balloon inside the animal where they can add gas to it or take gas away from it in order to keep them neutrally buoyant at different depths. Having this fancy version of hemoglobin helps regulate the amount of gas in the swim bladder which helps regulate buoyancy and helps regulate part of the eye where the photoreceptor cells are located.

Factors can Alter Affinity: Root Effect What is the Root Effect apply to? What is the point of all this?

Fetal hemoglobin. You want the fetus to be able to grab the oxygen from the maternal hemoglobin. Maternal Hb O2 affinity < fetus Different subunits. In an adult or young child, you have alpha and beta subunits. In a fetus, you have alpha and gamma subunits. You have different subunits in the embryonic stages. Alpha and gamma subunits in the hemoglobin has an effect on the hemoglobin oxygen affinity. Opposing Bohr effects affects the mother, maternal blood in the placenta, and fetal blood in the placenta. CO2 is going into the mothers circulatory system. The placenta is a mix of eternal and embryonic tissue. Increasing P50, decreasing affinity, shifting it to the right. It is giving up CO2. Curve shifts to the left. A decrease in P50 = increase in affinity. The fetal hemoglobin has a higher affinity as a result of the Bohr shift than the maternal hemoglobin does.

Fetal Hb Generally, fetus has Hb with lower P50 than mother. The individual is giving their oxygen from the placenta and delivering their CO2 to the placenta. Do you want to have a higher affinity for oxygen in fetal hemoglobin or maternal hemoglobin? What is the difference between fetal hemoglobin and adult hemoglobin? What is that doing to the oxygen dissociation curve of the mother's blood? What is that doing to oxygen dissociation curve to the fetus' blood?

We want a low P50 in the lungs and a high P50 in the body. The partial pressure of oxygen that you need in order to have your hemoglobin molecules 50% saturated. Your P50 is less than it was before. You need a lower partial pressure of oxygen in order to 50% saturate your hemoglobin. It is an indicator of a molecule with a higher affinity for oxygen. If you need a lower partial pressure of oxygen to achieve 50% saturation (the same degree of saturation), that tells you that your hemoglobin has a stronger affinity for oxygen. You have a higher P50. It is an indicator of a hemoglobin molecule with a lower affinity for oxygen. You have to have a higher partial pressure to achieve the same degree of saturation.

Hb affinity for O2 When it is at the lungs, we want hemoglobin to have high affinity so that it can grab the oxygen from inside the alveoli, respiratory bronchioles, terminal bronchioles. We want hemoglobin to have a lower affinity when it gets to the body tissues so that it will give up that oxygen to the cells and make its way to the mitochondria. Conflict: We want a molecule that has a high affinity for oxygen and also a low affinity for oxygen so that it unloads the oxygen readily. Q1. Do we want a low or high P50 in the lungs? Body? Q2. What happens when we shift the oxygen dissociation curve to the left? Q3. What happens when we shift the oxygen dissociation curve to the right?

The heart would have to work 50 times harder. We have a lot of oxygen bound to hemoglobin means that your heart does not have to work as hard.

Hb in Blood What are implications for having a larger amount of oxygen bound to hemoglobin in the heart? What if we didn't have hemoglobin?

- Small amount of oxygen dissolved in the blood (4 ml oxygen/L blood in dissolved form) - Larger amount of oxygen bound to hemoglobin (200 ml oxygen/L blood) e.g. human blood leaving lungs - 4 ml dissolved/L blood and 200 ml bound to Hb/L blood - plays role in blood buffering (e.g. bind hydrogens and carbon dioxide molecules) and CO2 transport (myoglobins - specialized Hb's in muscle cells) 1. Store oxygen 2. Nitric Oxide production/breakdown (e.g. regulation of mitochondrial respiration of the cell)

Hb in blood

It has decreased it. The movement left (mitochondria in muscles cell are taking up oxygen) is going to cause the oxygen that is bound to hemoglobin in the red blood cells to move into the blood. From there, they go into the mitochondria. The movement of dissolved oxygen in the blood into nearby tissues is going to cause oxygen to be unloaded from the hemoglobin in the RBC's because we are decreasing the percent saturation of the hemoglobin because the partial pressure is going down. Summary: The dissolved oxygen is diffusing through making its way to the mitochondria. Because the partial pressure is decreasing in the capillary, the oxygen bound to the hemoglobin is going to be unloaded from the hemoglobin molecule. There is a decrease in PO2 in the blood because oxygen is diffusing into the mitochondria and that lowers the hemoglobin oxygen affinity (shifts to the left) which causes Hb unloading O2. There is a decrease in the percent saturation of hemoglobin because oxygen that is bound to the hemoglobin diffuses into the blood.

Here's a capillary. Here's a nearby muscle cell. We have some oxygen bound to hemoglobin inside RBC's. We have a small amount of oxygen dissolved in the blood itself. A mitochondrion is inside the muscle cell. PO2 in the blood is greater than PO2 in the tissues. There is a partial pressure gradient that is going to favor the diffusion of oxygen dissolved in the blood into the muscle cell and it will bind to a myoglobin for a bit and will eventually get to the mitochondria. What has the arrow done to the partial pressure of oxygen in the blood? What happens when blood reaches the systemic tissues? PO2 blood cf PO2 mito?

- Specific binding site for oxygen (e.g. oxygen binds weakly due to non covalent bonds formed) - Specific binding sites for other molecules such as hydrogen ions and carbon dioxides (affect oxygen binding ability) - oxygenated and deoxygenated forms - non covalent bond between oxygen and heme - HB changes shape when oxygenated (e.g. just like enzymes when oxygen binds to hemoglobin it changes the shape of hemoglobins - Shows "cooperativity" (The binding of an oxygen molecule influences the binding of other oxygen molecules. The release of one oxygen molecule influences the release of other oxygen molecules) - Carried in RBC (RBC synthesized in bone marrow, very high turnover rate (2 million degraded and produced in one second), under hormonal control)

Key Characteristics of Hb

Molecule is produced in the kidneys and it increases the production of RBC's. It increases the oxygen carrying capacity of the blood.

Key Characteristics of Hb Erythropoietin

Adult 2 alpha-globin 2 beta-globin In human embryo and fetus, we see different globin proteins - There are alpha-globin proteins (red line). There are also epsilon and zeta proteins. Epsilon and zeta proteins disappear early on in development and are replaced by gamma-globin proteins which decline shortly after birth and is replaced by beta-globin proteins.

Key Characteristics of Hb In the blood of humans, Hb is usually a 4 unit molecule. In a mammalian adult, how many types of hemoglobin are there in our red blood cells?

Sigmoidal curve - Hemoglobin molecule shows a sigmoidal relationship between partial pressure of oxygen and the degree to which it is saturated. - Sigmoidal relationship is a consequence of the cooperativity that as one oxygen binds to a heme group in a hemoglobin, it easier for another one to bind.

O2 Binding to Heme Describe the shape of this curve. (Graph on the left)

Hb is oxygenated when it has oxygen bound to it (oxy Hb). Hb is deoxygenated when it does not have oxygen bound to it (deoxy hb). Hb is not oxidized or reduced.

O2 Binding to Heme What distinguishes hemoglobin from being oxygenated and deoxygenated?

Hemoglobin is insensitive to changes in partial pressure in terms of how much oxygen is going to bind to it. There is not a huge difference in percentage of heme groups that have oxygen from 80 mmHg of partial pressure on up (Relatively Insensitive). Sensitivity increases as partial pressure decreases

O2 Binding to Heme What happens at higher partial pressures of oxygen? What happens to sensitivity as partial pressure goes down?

- Oxygen bound to Hb varies with PO2 - Oxygen dissociation curve (oxygen equilibrium curve) - Hb saturated if all O2 binding sites occupied - Note plateau in dissociation curve at high PO2 - When blood leaves lungs, Hb is mostly saturated When blood flows past the lungs, it picks up as much oxygen as it can because the PO2 in the alveoli is high. When it gets to the systemic tissues (e.g. muscles, liver), the partial pressure of oxygen in the blood is higher than the partial pressure of oxygen in the tissue. - Decrease of PO2 in blood - Decrease of Hb O2 affinity and Hb unloads O2 25% 1. Activity (tissue use of O2) 2. Rate of blood flow 3. PO2 in blood 4. Hb concentration varies

O2 Binding to Heme What happens when blood reaches systemic tissues? PO2 blood cf PO2 mito? On average, what percent of oxygen in the blood is unloaded? Individuals tissues vary in terms of the amount of O2 that they take up... 1. 2. 3. 4.

- PO2 in alveoli is 90-100 - 100% (The PO2 of oxygen in the alveoli is high enough that when the blood leaves the lungs it is 100% saturation with oxygen)

O2 Binding to Heme What is the partial pressure of oxygen in the alveoli? What is our percent saturation of hemoglobin molecules in the blood that pass by the alveoli?

Concentration of oxygen in per 100 ml of blood - When oxygen is fully saturated at these higher partial pressures, it has 20 ml of oxygen per 100 ml of blood - Fifty fold difference (200 ml per liter of blood)

O2 Binding to Heme Graph on the Right

There is a relationship between the partial pressure of O2 in the blood and the percentage of heme groups that are oxygenated. At higher partial pressures, we get close to having 100% saturation (e.g. all 4 heme groups, every hemoglobin, and every RBC has an oxygen bound to it).

O2 Binding to Heme Graph on the left

0.4 ml of oxygen per 100 ml of Blood. This is the oxygen involved in the blood. It shows a linear relationship. Linear Relationship

O2 Binding to Heme Line for dissolved oxygen (Graph on the right). Describe the relationship.

- Bind reversibly with oxygen and then release oxygen - Variety of metalloproteins, e.g. Hb (heme groups + global proteins) in verts, inverts, protists, plants - The respiratory pigments that are transporting oxygen will bind oxygen and pick up the oxygen in the lungs and deliver it in the circulatory system and unload it or drop it off.

Respiratory Pigments

1. Heme is surrounded by a complex globin protein. 2. Myoglobin is a monomer found in muscle cells and it binds oxygen. Hemoglobin is a tetramer found inside red blood cells in the circulatory system. They differ in how they bind oxygen.

Respiratory Pigments 1. In figure B, what is heme surrounded by? 2. Where is myoglobin found? Where is hemoglobin found?

Respiratory pigments are often compared to enzymes because they share functional similarities to enzymes

Respiratory Pigments What are respiratory pigments often compared to?

They combine a metallic group with a protein. The metal in the metalloprotein is iron (Heme).

Respiratory Pigments Why are respiratory pigments known as metalloproteins?

They are increasing it. Increasing their layer of insulaiton.

Thermoneutral Zone (TNZ) When organisms with a lot of fur or feathers get cold, they fluff themselves up. What are they doing to their insulation area? If you are thinking of an arctic fox whose hair is laying flat, its external layer is this thick. When it fluffs itself up, it is larger. This changes the rate at which heat energy is lost to the environment. The lower limit of an arctic fox thermoneutral zone is below 0 degrees celsius. A sloth has a much narrower and much higher thermoneutral zone.

Ambient temperature Body temperature (left y axis) Metabolic rate (right y axis) The heat energy that is used to determine the animals body temperature is largely derived externally. Humans, birds, fish. Most of the heat that is used to determine body temperature is produced internally as a result of a high metabolic rate. Anytime you make ATP heat is produced. Directly proportional. A lizard at this ambient temperature and therefore this body temperature has a higher metabolic rate than a lizard at that temperature. The lines track each other. A warm lizard is faster than a cold lizard because metabolic rate is positively related to temperature so also is muscle contraction.

Thermoneutral Zone (TNZ): Ectotherms What does Ta represent? What does Tb represent? In the absence of any kind of behavioral thermoregulation, you expect to see it in a lizard that is an ectotherm. What is an ectotherm? Endotherms? Given the relationship between body temperature and ambient temperature, what is the relationship between ambient temperature and metabolic rate in this lizard?

A range of ambient temperatures over which body temperature is constant and metabolic rate is constant.

Thermoneutral Zone (TNZ): Endotherms In humans, body temperature does not track ambient temperature. We are able to maintain a constant body temperature over a wide range of ambient temperature. We can expand that range by putting on more clothes/taking off clothes. There is some point at which ambient temperatures are so low that you become hypothermic (e.g. body temperature drops). There are high temperature where your body temperature increases (e.g. hyperthermia). Definition: Thermoneutral zone

37.5 degrees Celsius 21-30 degrees Celsius. Our thermonetural zone/range of ambient temperatures over which body temperature is constant and metabolic rate is constant is lower than our body temperature. We are always losing heat to the environment. In the absence of doing anything, the rate at which you are losing heat to the environment is increasing because the gradient is increasing. You are losing more heat to the environment on the left side of the TNZ. You are still able to maintain body temperature constant. Within that thermoneutral zone (e.g. in order to keep that body temperature constant, it is not metabolically more expensive than it is when you are at rest. Your fingers get cold. Vasoconstriction helps keep your core body temperature at 37.5 degrees celsius. Flapping your arms, putting on more clothings (e.g. reducing the amount of surface area that is exposed) are things that allow us to keep constant body temperature without increasing our metabolic rate even though we are losing more heat to the environment. Beyond that, exercise, shivering (e.g. things that are metabolically expensive) allows our body temperature to continue to stay constant until things get too low where body temperature drops and you become hypothermic. Because of the relationship between metabolic rate and temperature, your metabolic rate goes down and you are losing more heat to the environment and it becomes bad. If you want to keep a constant body temperature even above your thermoneutral zone, you need to do things that increase your metabolic rate. Our explanation for this is that the net effect of those things that lead to an increase in metabolic rate is a net loss of heat. This includes panting, sweating, etc.

Thermoneutral Zone (TNZ): Endotherms What is the body temperature of a non-hyperthermic human? What is the TNZ for humans? What does that mean in terms of losing heat or gaining heat to the environment? As you move from the upper temperature to lower temperature, what happens to the rate at which you are losing heat to the environment? As we move downward toward cooler temperatures in the thermoneutral zone, despite the fact that we are losing more heat to the environment, we don't have to do things like shivering which is metabolically expensive, because our metabolic rate is constant. As soon as temperatures drop below an organism's thermoneutral zone, in order to keep body temp constant, it has to do things that are metabolically expensive so that metabolic rate goes up (e.g. exercise, shivering). What physiological things are going on that allow you to keep body temperature constant even though ambient temperature is dropping (e.g. things that don't metabolically cost)?