Hemoglobin Affinity

Hemoglobin Affinity

Hemoglobin affinity refers to the love of oxygen by hemoglobinThe oxygen-carrying protein in red blood cells that gives blood its red color..  High affinity means that the conditions are ideal for hemoglobin to love oxygen. It will load up on as much oxygen as it can get.  High affinity also refers to how tightly hemoglobin will hold onto its oxygen.  When hemoglobin has low affinity it hates oxygen.  Hemoglobin will refuse to pick up oxygen and it will also refuse to hold onto any oxygen that does bind. 

 In the lungs, during external or alveolar respirationThe process of gas exchange, including ventilation, external and internal respiration., you want hemoglobin to love oxygen. This way, it picks up a lot of oxygen from the air.  In your tissues, you want hemoglobin to hate oxygen so it drops it off to your cellsThe basic structural and functional units of life..  Fortunately, the lungs and your systemic tissues have really different conditions. These conditions make possible the loading and unloading of oxygen that you are doing right now.  But, if you go to higher altitudes, you will face conditions that are terrible for the oxygen pickup. These conditions are also bad for the oxygen drop off you need.

Saturation

The percent of oxygen saturationThe percentage of hemoglobin molecules carrying oxygen. is how much oxygen is bound to hemoglobin.  Think of this word “saturation.”  You spill your coffee on the carpet and the carpet is saturated with the liquid.  Hemoglobin saturation involves how many hemoglobins are carrying oxygen. It also concerns how many oxygens each hemoglobin is carrying.  Remember, it can hold 4 oxygen moleculesGroups of atoms bonded together. total. 

Let’s start with the simplest idea.  The x axisSecond cervical vertebra; has the odontoid process (dens) for pivoting head (“no” motion). of this graph is partial pressureThe pressure exerted by a single gas in a mixture; drives diffusion in respiration. of oxygen, which is kinda like the concentration of oxygen.  As oxygen concentration or the amount of oxygen in the environment increases, hemoglobin’s love for oxygen grows. Hemoglobin’s saturation of oxygen also increases.  That makes sense.  If there’s more oxygen around, hemoglobin’s gonna try to pick up all that it can.

Hemoglobin is hungy in the presence of oxygen.  It grabs all that it can like a pack animal at feeding time.  But, when oxygen is in a lesser concentration, as in the air high up in the mountains, oxygen affinityThe tendency of hemoglobin to bind to oxygen; affected by pH, temperature, and CO₂ levels. decreases. Oxygen affinity is low.  In high-altitude air, oxygen concentration is lower. This results in low oxygen affinity. It won’t pick up more oxygen and it holds onto whatever oxygen it already has.  That is not good.

Bohr Effect of Exercise

The Bohr effect is simple.  When making ATPThe energy currency of cells used for muscle contraction., you make carbon dioxide.  Carbon dioxide can become a bicarbonate(HCO₃⁻) – A crucial buffer in blood that helps maintain pH balance; formed when carbon dioxide anionA negatively charged ion.. It can also become a hydrogen cation when it hits the waterThe universal solvent essential for life. of the interstitial fluids or the plasmaThe liquid component of blood..  That little hydrogen cation lowers pHA measure of hydrogen ion concentration in a solution. making everything more acidicA solution with a pH below 7, having a higher concentration of H⁺ ions..  This is that acidity that you fight every day to keep in homeostasisThe maintenance of a stable internal environment in the body.!  That hydrogen cation goes up to hemoglobin and pushes it into  releasing some of the oxygen it is carrying.  These little hydrogen cations(H⁺): Protons that influence pH levels in body fluids. are constantly made by the carbon dioxide from your mitochondria. They cause hemoglobin to drop off the oxygen your tissues need.  In your tissues, hemoglobin has a low affinity for oxygen mainly due to that low pH that is created.  This is actually perfect because I definitely want my hemoglobins to drop off oxygen in my tissues. 

This is called the Bohr Effect which says oxygen is unloaded where it is needed.  This, more than anything else, applies to exercise.  During exercise, you create more carbon dioxide as a waste product of the making of ATP.  Your tissues get really acidic quite fast.  But, this is great because you need more oxygen than normal since you are exercising. 

The colors on the background of this graph reflect the Bohr effect.  Here in yellow, exercising tissues need oxygen and hemoglobin has low affinity for it in these tissues.  Perfect, then hemoglobin will drop off oxygen.

Here in the lungs, hemoglobin’s affinity for oxygen is really high.  Perfect, I definitely want my hemoglobins to pick up oxygen in the lungs.

On Mt. Everest

This is why I am fascinated at attempt to climb Mt Everest.  First, there is less oxygen per volume of air.  Every breath you take contains less oxygen than the air you breath at a low elevation.  Your lungs are not operating over here in the blue area.  They are experiencing low oxygen, which puts your lungs here where hemoglobin has a low affinity for oxygen.  This is bad.  You want hemoglobin to love oxygen in your lungs so it picks it up.  At lower partial pressures of oxygen, hemoglobin’s affinity is low.

It’s cold.  Hemoglobin loves oxygen when it’s cold.  Hemoglobin holds on to oxygen really tightly when it’s cold.  In factA statement based on direct observation that is repeatedly confirmed., when it’s cold, this entire graph shifts to the left to make this blue line here.  Your systemic tissues are probably not really at 98.6F anymore.  Not good.  You want hemoglobin to drop off the oxygen it holds into your tissues.  But, it won’t because you are colder than normal. 

You are shivering all the time because it is cold.  This causes you to generate ATP and carbon dioxide at a faster rate than normal.  This decreases the pH in your systemic tissues.  This shifts this entire curve to the right or the green line on the graph.  This affects external respirationThe exchange of gases between the lungs and the blood in the pulmonary capillaries..  Now, your hempglobins have a reduced affinity for oxygen and refuse to pick it up in the lungs. What is the lesson here? Humans start dying at a high altitude. 

On Mt. Everest

There are people called sherpas who can be guides to Everest. However, most sherpas are tasked with simply carrying gear up Mt Everest.  That sounds simple, but it’s not.  The increase in altitude places significant demands on the body. Carrying an extra 40 pounds of stuff is harder than you think.  I used to use an article for another class of mine on the website Understanding Evolution.  This article was about how sherpas might be adapted to life in higher altitudes.  It proposed first that sherpas seem to have thoracic cages that are larger than the general population.  Sherpas are capable of achieving a higher volume and lower pressureThe force exerted by gases in the respiratory system, affecting airflow and gas exchange. in inhalation.  They can decrease the intrapulmonary pressureThe pressure within the alveoli; fluctuates during breathing and equalizes with atmospheric pressure more than other people.  This increases the value of the gradient on the top of the equation for air flowThe movement of air into and out of the respiratory tract, driven by pressure differences between th.  If the numerator increases, so does air flow.   This is similar to the case study patient with asthmaA chronic condition characterized by airway inflammation, narrowing, and excessive mucus production,.  Our patient has complained of neckNarrow region just below the head; common fracture site. and side pain.  Most likely, our patient is using their accessory muscles unconsciously to increase the volume of their thoracic cavityThe body cavity housing the heart and lungs. in inhalation.  This would allow them to overcome the resistanceThe opposition to airflow in the respiratory tract, influenced by airway diameter. in the denominator of the fraction.  In both situations, the volume of the thoracic cavity increases, increasing the numerator of the fraction and increasing air flow.

The article suggested blood differences for sherpas, but this was not able to be verified with evidence.  It was just proposed that sherpas may have more hemoglobin per erythrocyte or more erythrocytes(RBCs): Red blood cells responsible for oxygen transport. in their whole blood.  Either quality would increase the oxygen carrying capacity of blood.  This principle involves training at high altitudes. Athletes may also use a low pressure mask or chamber when working out.  If you are consistent in working out at lower atmosphere pressures, you will start making EPO. You will naturally increase your RBC count or hematocritThe percentage of blood volume occupied by red blood cells. over the course of about 2 to 3 weeks.  For climbers on Mt Everest, they spend weeks acclimatizing in Nepal. Then, they acclimatize at baseA substance that accepts hydrogen ions (H⁺) or releases hydroxide ions (OH⁻). camp and during a few partial climbs. Only after all these stages do they make the trek to the summit.  This allows them to increase EPO production.