I know that your blood carries oxygen to distribute to cells, but if the red blood cells and hemoglobin never leave the blood cells, how do the body cells receive oxygen from these cells? How is oxygen transferred?
In: Biology
Hemoglobins affinity for oxygen is different in the lungs vs the body’s tissues and the tissues (especially muscle) have a protein called myoglobin which is even better at binding oxygen than hemoglobin. In the capillaries of the body’s tissue the hemoglobin has lower afinity for the O2 so it falls off and can diffuse from the RBC to the cells that need it (think of it like hemoglobin pushing it off and myoglobin acting as a vacuum sucking it in).
[This curve](https://en.m.wikipedia.org/wiki/File:Oxyhaemoglobin_dissociation_curve.png) shows how hemoglobin’s affinity for oxygen changes. On the bottom is the partial pressure of oxygen, more O2 present means more will bind hemoglobin. But also pH, temperature and metabolites will affect hemoglobins binding. These all add up to conditions which strongly favor O2 to bind hemoglobin in the lungs, but then change so that it will dissociate from hemoglobin in the tissues (where there is lower O2 partial pressure, lower pH, higher temperature and more DPG).
all thing naturally move from where there is a lot of it to where there is little of it – this is called diffusion. think of putting colouring in water. even if you don’t stir it, it will still eventually spread out across all the water. there is a lot of oxygen in your blood and less oxygen in your cells, so the oxygen will diffuse out of the red blood cells, and into cells near the vessel. i’m pretty sure cells can be up to 1~2 centimeters away from a blood vessel before it can’t get enough oxygen or other nutrients from diffusion.
The oxygen is carried bound up in the molecules of hemoglobin that are in your red blood cells. As they move through smaller and smaller arteries, then capillaries, they eventually get into very, very small capillaries and spaces between tissues and fibers. The chemistry of your body tissues tries to be homeostatic in regards to oxygen and other cellular inputs and also carbon dioxide and other cellular waste. The hemoglobin molecules chemically release the oxygen into depleted spaces and tissues and similar processes cause your cells to take up carbon dioxide to ferry back to your lungs. It’s actually a process of chemistry as opposed to some sort of “physical” process. Also, while we have a circulator system, the easily observable parts – veins, arteries and many capillaries – are just then big parts, like freeways and major streets. Most of your tissues are filled with very small, even invisible capillaries where the red blood cells actually go to release their oxygen and pick up waste products, similar to how you take a freeway to the store and back, then take a major street to get to your neighborhood, and then a small surface street to get to your house. The veins and arteries are just transport systems for blood, they’re not where the blood is doing it’s work. There are a few other steps in the process of how the oxygen actually moves in and out of cells, but ultimately its a process of chemical diffusion.
Several excellent and completely correct answers here already, so I’ll try to do the 5 year old version…
Your body has these red colored blood cells that are built to act like dump trucks. When they’re in your lungs, they know to pick up oxygen, when they get to your cells (the guys that ordered oxygen) they know to unload. That’s because they’ve been built to know the difference between lungs and the cells that need the oxygen.
If I understand your question, you’re asking how the oxygen molecule physically gets from the haemoglobin in the vascular compartment to the cells in the extra vascular compartment. The answer is blood plasma. The fluid that cells are surrounded by is the same fluid that is in blood vessels because capillaries are permeable to plasma. The oxygen is in solution in the plasma. When it is used up by cells, it is replenished by the oxygen bound to haemoglobin.
You may wonder why then have haemoglobin at all? Why not only have plasma circulating with oxygen in solution? The answer is that very little oxygen can be stored in solution. Haemoglobin evolved to increase the oxygen carrying capacity of blood.
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