Relationship between lymphatic and cardiovascular systems

In this post I will describe the flow between blood vessels and lymphatic vessels, and back. This flow is sort of cyclical as from the end part of capillaries some part of blood get into so-called tissue space. This is the space between (or outside) cells, and the liquid portion of it is called interstitial fluid.

 

Many proteins in the blood are too large to squeeze between the cell that make the blood vessels, so they stay within the cardiovascular system. But many other proteins are really small, so they can get out, and they need to have an extra way to get back to the bloodstream. And that's where the lymphatic system comes very handy.

 

Lymphatic vessels pick up these small proteins from interstitial fluid, and return them back into blood vessels through so-called subclavian vein. Once inside the lymphatic vessels, the fluid is called the lymph. This first picture shows nicely how the fluid flows from blood vessels into tissue space, and then into the lymphatic vessel.

 

 

In the body, there is a number of bacteria, gases, microbes, and metabolic waste, which needs to be drained out of the system. For that purpose, the lymph is full of white blood cells, which fight those substances. They need to be discharged or destroyed, so by the time when the lymph enter the bloodstream, it's clean and purified.

 

The composition of lymph and interstitial fluid are very similar, the main difference is their location. Plus in lymph, there is large number of lymphocytes and macrophages, which are the structures that fight foreign substances like toxins, microbes, and cancer cells.

 

Because the lymphatic system doesn't have a special pump (like the heart is for the cardiovascular system), there is a joint effort of lungs, muscular contrations, and valves inside of them, which support the movement of lymph in one direction, and stop it going the opposite direction. This second picture is another flow diagram showing the flow of lymph and blood, and the interraction between them.

 

Starvation sequence

In this post I'd like to describe the sequence of total stopping of any food intake, providing the water is still available, even if in minimal amounts. To understand the progression, it would be the best to name all the types of nutrients at the beginning, so the further explanation then makes perfect sense.  Three types of nutrients/energy are:

1. carbohydrates (or carbs)

2. fats (or lipids)

3. proteins

Because I couldn't find any flow diagram (anywhere), which would show this sequence of starvation, I was forced to improvise a little. So don't be discouraged by overt simplicity of this flow diagram. Still, (just in case) I want to clarify that symbols between the lines ( | and V ) are supposed to represent the down-pointing arrows. So let's get to it ! 

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Fed state, or so-called postabsorptive state, meaning that
all three energy sources are available for usage
 |
V
after 4 hours - carbs are spent from liver and digestive tract, while
fats and proteins levels are still intact
 |
V
12 - 24 hours - carbs spent from whole body, with
slight increase in usage of fats and proteins
 |
V
2 - 4 days - using fats after converting them into ketone bodies (<100 times of normal level), plus
using proteins in the rate of 90g a day
 |
V
4 - 40 days - further using ketone bodies from fat (100-300 times more then in fed state), plus
decreasing usage of protein each day
 |
V
40 days - 2 months - maximum usage of ketone bodies ( >300 times comparing to normal level), with
usage of proteins in the rate of 20g a day
 |
V
2 - 3 months - Body still have some fat, and ketone bodies for energy, but once the body protein level drops to about half of normal level, the physical death will occur through the infection, because the immune system will fail to work efficiently.

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Now, let's get through the whole process in slowly in the text format. After your meal, the body will be absorbing all nutrients, which is called the absorptive state. Once all the nutrients are absorbed, the next state is called post-absorptive state, signifying that the absorption is finished, and there is nothing else to digest.

Normally, those two state rotate, as with every other meal you get back into the absorptive state, and so on. But in the case, you stop eating and prolong the post-absorptive state, the first stage is called fasting. This is relatively still healthy state as you force your body to use all available (plus all excess) nutrients that are possibly accumulated in your digestive system.

Fasting changes into starvation roughly around 1-2 days after not eating any food. As I mentioned at the beginning, the water intake needs to be still available, otherwise without water, only 2-3 days will lead to dehydration, decrease of sodium levels, muscular spasm, and physical death. But that's the different story, so let's get back to our starvation sequence.

Roughly 4 hours after the end of the absorptive state and basically the beginning of post-absorptive state, all glucose in the form of glycogen in the liver is gone. That would represent about 25% of glycogen reserve in the body. The resting 75% in the skeletal muscles is then gone within 12-24 hours. This range differs with the amount of activity or rest. But basically after about 2 days of not eating, all the glycogen, and therefore the glucose in the body is gone/used.

To maintain the stable level of glucose in the blood, which is crucial for normal working of nervous system, the body converts fats into the middle-man called ketone bodies. This middle-man looks half the glucose and half amino acid, from which all the proteins are created. Glucose then feed the brain and nervous system, and amino acids are spent for protein synthesis, to save the built-in protein as much as possible.

In this state, the rate of protein usage is about 90g a day, plus with every other day after 2 days, this rate keep decreasing, finally stabilizing at the level of 20g a day in about 40 days. Meanwhile, the level of ketone bodies in the body increase about 100-300 fold. The state called the ketosis is a heavy burden for the organism, especially for the liver and kidneys, which have to take care of it.

Because ketone bodies are slightly toxic substances, they need to be eliminated from the system straight away after they are being used, and therefore, they can't be reused. Because the proteins in the blood, mainly in form of white blood cells incapacitate the toxins in ketone bodies, their level needs to be constantly updated, which is another load for protein usage.

Once the whole body protein level drops to about half, there will not be enough white blood cells for eliminating ketone bodies quickly enough. And at some point, (somewhere between 2 to 3 months), those ketones will overwhelm the immune system, and the result will the that the body will fall prey to the first virus, bacteria, or toxin which will attack the body, and will collapse.

Ironically, even in the time of death, the level of fats will be still at sufficient level to provide more ketone bodies, therefore the energy. But because of the lack of proteins, the immune system will be very frail and inefficient. So technically, the body will never run out of fat, or the energy until the end. It's the infection that will fire that fatal blow, which will result in physical death.

So I hope that this was simple and clear enough to understand the whole sequence. Of course, if at any point the new food intake is provided, the whole process will be postponed, and the cycle will start from beginning. Mainly if all three types of energy are present in fair amount of that particular meal.

Cycle of formation and breakdown of bone tissue

Even in an adult person, the bone tissues undergo the process of constant recycling. The new tissue is usually built at the same rate as the breakdown of the old one. This is achieved by the fact that cells within the bone tissue are going through the process of maturation. Using the analogy of the human life, the babies would be called preosteocytes. To translate that to English, pre means that they are not finished yet, osteo means bone, and cyte means cell.

Those then mature into an adult cell (or person in analogy), called osteocyte, literally meaning the cell of the bone. Those then differentiate into two possible types called osteoblasts and osteoclasts. The former type build new bone tissue, and the later one breakdown of the old tissue.

The flow diagram above shows the whole process nicely in cyclical manner. The vicious cycle is not really that vicious, as it's essential for life and the health. But it indirectly points out that it's going on for the duration of whole life. The old, worn-out tissue  then would be the equivalent of the pensioner (in the analogy). Still important and functioning in certain ways, but sooner or later to be broken down into the separate components, representing the death.

The bone tissue serve a number of functions, one of them is storage, and retrieval system of calcium and phosphorus, along with some other minerals. The form in which those two are stored is the called the calcium phosphate. Calcium is also used as the substance that initiate the muscle contraction (see my other post describing this process), along with some other functions.

If the working speed of osteoblasts and osteoclasts are the same, the same amount of calcium phosphate remains inside of bones. This system is so precise that even the lack or excess of dietary calcium and phosphorus won't affect it. The excess is simply excreted, and the lack is covered by slightly slowing down of osteoblasts, and slightly speeding up of osteoclasts. All this effort is important for keeping the blood levels of calcium and phosphorus within the narrow and healthy range.

The only way to increase the amount of stored calcium phosphate in bones is via vigorous muscular activity, just like the only way to decrease it is via the of the use of muscles. That's why bed-ridden patients show significant reduction in the bone density within months, which can be then reversed by subsequent activity or sport - as it's demonstrated by many athletes and body-builders.

Also, the increase and decrease in bone density goes hand in hand with the increase and decrease of the volume of the muscle tissue. One without the other is not possible, along with many other improvements and declines of efficiency in other tissues and organs throughout the body. The heart efficiency, lung's maximum volume/capacity, the amount of hemoglobin in the blood, total amount/length of blood vessels, total amount of body fat, and the production of certain hormones - would be only a few examples.

So as you can see many processes within the human body are linked and directly influence each other. Pretty basic fact, but quite  fascinating too. The human body is just so full of wonders, so never stop wondering and pondering. See you in next post.

Life cycle of red blood cells

Red blood cells (or RBCs), also medically called erythrocytes, have a lifetime around 120 days, during which they appear and operate at many different places. Then, they undertake the process of breaking them down, once they become old. So it would be the best to start at the beginning, meaning the production of them.

 

They are created in red bone marrow, meaning inside of bones. For their production, there is a need of certain nutrients and conditions to be present. Those are the molecule of iron (3 atoms of Fe joined together), vitamin B12, Folic acid, hormone erythopoietin, and protein globin. I will get to the explanation of each of those as I go along in the post.

 

First let's look at the RBC from the structural level. One such a cell is filled up with a lots of proteins called the hemoglobin (about 280 millions). This hemoglobin consists of two basic parts - the heme and the globin. Already mentioned globin is a protein created from two (alpha and beta) polypeptide chains, which is basically many amino acids (building blocks) connected to each other into long, but at many points twisted chains. The precise sequence of different amino acids in that chain is dictated by DNA.

 

Every molecule of hemoglobin has 2 of these chains and 4 hemes, the parts in the middle of which resides the molecule of iron. So once the RBC is finished in the red bone marrow, it enters the bloodstream, where it does its job for already mentioned 120 days. Now would be a good time to say something about that job they do.

 

The job of RBCs

 

In the lungs, the hemoglobin picks up oxygen, super nitric oxide (SNO), along with some other gases. Then it carries them to the tissues, where they are being used as the fuel, and many other functions. Once those gases are unloaded, the space is straight away filled up with carbon dioxide, nitric oxide (NO), and some other gases. Those are then carried back to lungs to get rid of them by breathing out, as they represent the waste products of metabolism and many other functions.

 

I think that it's worth to mention that all this loading and unloading is happening by the process called the diffusion, which is very fast system. During those 120 days, they undergo certain changes, and become "sort of" worn out. And they need to be broken down into their initial components, so let's go to explaining that.

 

Breaking down of RBCs

 

Firstly, in the liver or spleen, they split into those two basic parts - the heme and the globin. Each of them then follow separate routes. The globin is broken down back into amino acids, which enter the bloodstream, and are further being used for the synthesis of another proteins. So no wasting in here.

 

The heme part, which is much, much smaller then the globin, splits into the molecules of iron and biliverdin, which is the green pigment, that is straight away converted into bilirubin - the yellow pigment. Both parts (iron and bilirubin) then enter the bloodstream and then they get to the liver. The liver then sends the iron back to the red bone marrow using the transport protein called transferrin, which grabs the iron molecule and looks after the safe delivery of it throughout the bloodstream.

 

Once the iron is back in bones, it's used again for creating a brand new RBC. It only has to add the missing parts - the globin, vitamin B12 and Folic acid (which both serve as catalysts), and the hormone erythopoietin, which function as signalling molecule, produced by kidneys. This hormone basically brings the information about how many of new RBCs are needed to be done.

 

Ok so that was the iron part, now let's get back to the bilirubin part, which is slighly more complex. Hopefully not too much. The liver sends this bilirubin into the small intestine via the bile, from where it moves down to the large intestine. There, some friendly bacteria convert it into the urobilinogen, which can get out by two possible ways.

 

It's either converted to stercobilin, still in the large intestine, and go out with feces. Stercobilin is basically the brown pigment, giving feces their characteristic color. Or the other way is that they are moved from the large intestine to kidneys, where it's converted into urobilin, and get out in the urine.

 

So this is it. The whole life cycle of one RBC. Probably sounds as a long and complicated journey on the first reading, but I'm sure that on the second one, it might just make sense easily. I prepared two flow diagrams, which I present one above the other, partly because I couldn't decide which one is better (they are both brilliant). But mostly, because this way, you can actually see a lots of small details in which they differ, giving you even bigger picture, and easier understanding.

 

 

 

 

Still some important info needs to be said. The production and breaking down of RBCs are normally at the same rate, so the number of them in the body stays constant. The only two (still healthy) exeptions would be:

 

1. going and staying in the area of higher altitude then usually, where the concentration of oxygen is lower, so the body will have to conpensate this change by making and keeping more RBCs, or

2. after some heavy-duty exercise, the oxygen consumption can be go up even to 20 times higher, so the deficit is then made up by making some extra RBCs.

 

I said still healthy, because there is a number of unhealthy ways, meaning diseases, in which this balance can be broken. Plus, there is a dangerous procedure called Blood Doping, in which some athletes inject extra RBCs before the sporting event, giving them extra power and energy. This procedure is, of course, banned by the International Olympics Committee, as it presents a number of risks to the person's health.

 

See you next time.