About central dogma in biology

Central dogma in biology dates back to 1958, when F. Crick proposed a theory that explained the flow of information within the organism. Moreover, it can be represented in the form of the flow diagram, as you can see right here in the picture, which I borrowed from the book Genetic engineering - dreams and nightmares. The information flow starts from nucleic acids, which are building rocks of DNA, our genetic code. That's all in the nucleus of basically every cell.

 

In there, DNA strand is split apart, and one strand leaves nucleus as messanger RNA, or mRNA. This molecule carries information about how to make various proteins needed for the body. So out of nucleus, and in the cytoplasm, mRNA is processesed and used for protein synthesis.

 

Protein synthesis comes in four structural steps called primary, secondary, tertiary, and quaternary structures. Primary structure consists of the chain of amino acids, and secondary is already building blocks like alpha-helixes or beta-pleated sheets. Those are then used in numerous combinations to create many different proteins. Those are then transported out of the cell into the place where it will be used for building or regenerating the new or existing tissue. And that's how the organism is built up.

 

 

DISCOVERY OF REVERSE TRANSCRIPTASE

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Now we get to the point where this dogma becomes a dogma.This way of information flow was thought to be not revearsable, or simply put, it's only one-way street. But the scientific research and fast progress in genetic engineering proved that the opposite way is also possible. Study of retroviruses like Rous sarcoma virus, or bacteria like Escherichia coli (E. coli), showed that those micro-organisms contain an enzyme, which is able to create brand new DNA code. This enzyme is called reverse transcriptase.

 

In order to do this, it first creates so called complimentary DNA, or shortly cDNA. This is then compared with mRNA, because this serves as a template for reverse transcriptase. Here is where evolution and natural selection will play a part for a while, and the end/best result is then doubled and twisted by DNA polymerase - another enzyme. Well, and the new DNA is ready.

 

The research on viruses and bacteria has been proved to be very beneficial in many ways. For example many enzymes and hormones can be synthetically produced in laboratories using bacteria or viruses. This has been a huge relief from getting all those needed substances by natural ways, that is from people. Pharmacology experienced a big boom since, and is still evolving and developing, along with genetic engineering, as one of the leading research programs to date.    

Glycogen window - the essay on glycogen

Glycogen is the molecule built up from small rings of glucose (see the picture). It's structure is highly branched, which left a lot of space inbetween, and this space needs to be filled up with water. Glycogen reserves are located in the liver, holding 25% of it and the resting 75% is in the muscles.

 

Total amount of glycogen, which the body can produce and store is around 500g in average (meaning untrained) person. With the increase of muscle mass in bodybuilders or athletes, this reserve can add up to 1100g. To imagine this, take for example 1 kg loaf of white bread. That would be something over 500g of complex carbohydrates, which would be the exact amount of glycogen created from eating that whole loaf.

 

Supposing you eat that loaf on 3-4 times during the whole day. Your body needed to cover the energy for that day, and the night that follows. So when you wake up in the mornig, out of those 500g, you can have something less then half left. Plus, if you add up some exercise during the day, the demand of your body for carbohydrates will be even bigger. So here's where the phrase glycogen window start to pick up a proper meaning.

 

Glycogen window metaphorically means eating a lots of carbs and still not having enough of them for the body to process. It's like you would throw them out of window, literally. They disappear somewhere in your stomach, and get soaked into your muscles. That, of course, under the condition that you trained to stimulate growth, and provided sufficient rest for recuperation and restoring all used up nutrients.

 

Muscle growth is not facilitated only by storing extra glycogen. As mentioned earlier, additional mass contain a lots of water, as it's estimated to count 2-3g of water as an addition to every gram of glycogen itself. Plus, after training, muscles stock up on extra fats, and extra creatine phosphate to cover the energy. All together looks as pure muscle on the outside, because all those substances are inside of muscle, or around muscle fibres.

 

Otherwise, after reaching the adulthood, the number of muscle fibres stays the same for the rest of the life for everybody. Muscles are getting bigger only by storing the extra energy. And the volume can be added right into the muscle cells or fibres, or around them in so-called sarcoplasm, as an extra storage.

 

 This flow diagram shows the pathways from glucose to glycogen and back. The whole process take place in the liver cells. Glucose from blood enter liver cells and gets phosphorylated twice before start stacking them into branches of glycogen. The process of creating glycogen out of glucose is called glycogenesis, and the opposite process of breaking it down back to glucose is called glycogenolysis.

Basics of human metabolism

I found quite good flow diagram in the book Principles of anatomy and physiology, 7-th edition. It covers the  basics of metabolism, mainly the view of certain key molecules involved in it. There could be dozens of similar ones, which would involve different molecules on different pathways, because in the essence, the flow diagram is about the depicting one or more pathways of certain molecules in the body.

The metabolic pathway is defined as a series of chemical reactions that take place somewhere in the body. It can be cyclical or straightforward, and it can be executable in one direction or in both directions. The total sum of all metabolic pathways in the body is called metabolic network. 

So with the pathways, they have their starts and ends, and maybe even some milestones and/or dimension changes along the way. Good flow diagram brings all this information in simple, graphical way of covering the knowledge about human body, and systems involved within it.

This diagram focuses on chemical pathways of food that breaks down to proteins, carbohydrates and fats. Their further broke-down equivalents are amino acids, glucose and triglycerides respectively. But mainly it focuses on three key molecules, which serves as intermediates in human metabolism, and those are Acetyl co-enzyme A, Pyruvic acid, and Glucose 6-phosphate.

The last one is the ring of glucose with addition of phosphate group on sixth carbon in the chain. This altered glucose molecule, also called phosphorylated glucose, can be then used for energy into Krebs cycle, energy for DNA production, or to convert it to Pyruvic acid, the second intermediate molecule.

This one, in turn, can be used for production of alanine amino acid, or by aerobic and anaerobic reactions, to energy (ATP) with lactic acid, or to convert it to another intermediate molecule - Acetyl co-enzyme A. And this molecule can enter Krebs cycle, or to be converted to ketone bodies, cholesterol, or fatty acids. I hope it's all clear from the picture.

Each component or even word in this diagram could be enough to write about for the separate post. In whole, this is the representation of human metabolism, or at least one possible side from which it can be viewed. Plus the metabolism itself could be topic for whole books, and it is. It can be divided by particular substances into fat metabolism, protein metabolism, or carbohydrate metabolism. Or simply the metabolism of any other substance with its own characteristic pathway and chemical changes along the way.

PROCESSES

Some parts of diagram, or words, describe a process, like for example glycolysis, aerobic reactions, or Krebs cycle. So in this case, glycolysis would mean breaking down of glucose rings down to the Pyruvic acid. Aerobic reactions would be those that require oxygen for successful execution, and anaerobic reaction are on the other hand those that don't, and can work without the oxygen.

Krebs cycle represent many different reactions involving many different substances. But just to give you a hint, there is 9 steps or chemical reactions in cyclic manner, which starts and ends with the same substance - Acetyl co-enzyme A. Those then involve 9 different enzymes, 9 substrates and end products for each step. Again, each of these processes could be picked up and fill the text for the whole chapter.

So the topic is complex, and thank God there are such a things as simplifiers of it in the form of flow diagrams. The way I see it, the understanding of processes within our bodies is priceless and irreplaceable. Moreover, it cost nothing these days as there are tons of websites and library books dedicated to bringing the light on the topic. So you can watch, read, think, learn, understand and I'll see you next time around.

Muscle contraction

Muscle contraction is a complex process with one simple objective of enabling the movement to an organism. This complex process can be studied from many different levels, and the knowledge about the musculo-skeletal system reaps benefits in a number of different areas or professions. Generally, the human health during the lifespan is very closely related to normal and effective function of this particular system.

 

D I V I S I O N S

 

Two basic types of muscle contractions are isotonic and isometric. With isotonic, the muscle gets shorter during the contraction, and with isometric, it stays the same lenght. The special type of excercise called isometry is using isometric contractions for developing the strenght of muscles and joints. It's used during the rehabilitations, like for example after having a cast for certain period due the broken bone. The muscle is feeble and significantly smaller so normal exercise is out of question.

 

It's also benefitial for those confined to bed temporarily or long-term. Isometry is basically flexing the muscles without moving or twisting of arms or legs during the contraction. It can be executed by pressing against unmovable object ( for example wall or bed), or simply by pressing two hand against each other. The best thing is that it doesn't require any equipment or skill, and it can be done anywhere and by anyone.  

 

Another special type of involuntary muscle contractions would be cramp or twitching. Stretching and massage are usually very effective in calming down the muscle, as those things usually happen after prolonged exercise or fasting, where the fine balance of electrolytes in the body is disturbed.

 

Muscle contraction works on all-or-none basis as there is no such thing as partial contraction. Plus, it's followed by so-called refractory period, during which the muscle is getting back ready for another contraction.

 

There are three basic types of muscle tissue in the body:

  a) cardiac - muscle of the heart

  b) smooth - muscle in the gut / involuntary

  c) striated - skeletal / voluntary muscles

 

Striated muscles then divides further into two types:

  a) tonic - slow fibres holding mostly the posture

  b) phasic - twitch fibres of two types:

        1 - slow (red fibres)

        2 - fast (white fibres)

 

Another division could be seen depending on the conditions around the muscle contraction. More specifically, it can be done with the presence or the absence of oxygen.

  a) aerobic - with oxygen / using oxygen

  b) anaerobic - without oxygen / creating oxygen dept

 

This oxygen dept is then compensated in the body by flooding the muscle with toxic compound called lactic acid. Accumulation of this substance in the muscle gives that characteristic feeling of burning in the muscle, during and at the end of very vigorous exercise. Lactic acid needs to be quickly eliminated that's why the burning stops soon after you stop moving. Because it's toxic, it's presence is dangerous to the organism, which is dealing with it three possible ways:

 

a) oxidize to pyruvic acid

b) convert to carbs

c) neutralized and excreted

 

Lactic acid and it's effect will make you stop moving, as any further movement at that precise point is litterally painful. It can flood the blood and liver and destroy the living tissue. Regular aerobic exercise and intake of quality food increase the resistance of body towards lactic acid, and more lean muscle tissue the person possess, longer the person can excercise without being stopped by accumulated lactic acid.

 

This diagram shows nicely how muscle contraction actuallly work on the tissue level. Actin and myosin myofilaments work together to create the complex called actomyosin. This complex is then capable of sliding the actin and myosin against each other, and sort of fold them up, shortening the overall lenght of the muscle fibre. Sarcomeres is a fancy term for the muscle cells, and all this model is called sliding filament hypothesis.

 

For muscle contraction to occur, there is a number of conditions that needs to be met, and there is actually a stream of insights coming from knowing those conditions. For the sake of simplicity, I created a simple list:

 

- the presence of the protein called actin

- the presence of the protein called myosin

- the presence of Ca

- the presence of Mg

- the presence of ATP

- the presence of creatine phosphate

- calcium pumps has enough of Ca pumped in

 

Simply put, calcium pumps located on the plasma membrane, pumps in calcium, which triggers all the other processes. Creatine phosphate is another, alternative source of energy in the muscles. They chip in when there is a shortage of ATP, or the exercise is so vigorous, that all energy sources are in the action.
 

3 FORMS OF ENERGY

On molecular level, the muscle has three big sources of energy to reach for. All three are continously available at all times, what differ is the ratios between them, which correlate with the state or activity of body. Plus they differ in how long they can be available, and the time for their recovery. Three form of energy are:

1. fats - triglycerides
2. glucose - monosaccharides
3. creatine phosphate

Fats are the biggest contributor supplying heart and all energy needed for keeping the posture, along with very slow movement. Fat are continuously used by muscles even if you don't move at all. Technically, fats can never run out completelly from the whole body, but their usage by muscles is limited, because it depends on the oxygen input. And that, in turn, depends on the state of your lungs, heart, and basically the whole body. So to burn more fat than you usually do, you need to improve the state of almost whole body.

Glucose is the type of monosaccharide and serves as main energy source for the brain with whole nervous system, which runs only on glucose. Then, muscles use glucose along with its secret source of it - the glycogen. This is sort of animal version of complex carbohydrates and it can be stored in muscles and liver. From there it can be used at any point, and when you then eat carbs again, you refill it.

Interesting thing is the ratio of fats and glucose in which muscles use them. Supposing you are lying down on the bed without moving. Fat / glucose ration would be about 70/30. But the moment you start moving fat goes down and glucose up. The quicker you will move, further the fats will go down, and glucose up in the ratio. Get the picture?

Creatine phosphate is very interesting substance stored in the muscles only. It start working only when we move very fast, or for longer time. It's the additional source of energy that is available for the muscles in the times of shortage of both fats and glucose. There is quite limited amount of creatine phosphate in muscles, so suppose you start running as fast as you can, it can last for about ten seconds. When you stop, and not move for another 30 seconds, it will be replaced with freshly-new made one.

The storage of this substance can be increased by involving the body or muscles in heavy exercise in short bursts. This is the case of sprinters or bodybuilders for example. They train muscles to develop bigger creatine phosphate stores in order to achive greater performance, or appearance. Those three types of energy can be then combined to bring about the movement or sport we need.

 

 This very nice flow diagram describes the muscle contraction cycle in four steps. The diagram is pretty much self-explanatory, so it's all the question of reading and trying to understand. First I recommend to map out the symbols from the key in the grey box, and then reading the steps should make easily a lot of sense on closer observation and study. Good luck and enjoy.
 

ATP - cell's rechargeable battery

ATP, or adenosine triphosphate, could be put in an analogy of a mini rechargeable battery that cells are using to feed the energy for many different processes within the body. It contains three basic parts.  The adenine molecule, sugar molecule (ribose), and three phosphate groups - which are really one phosphorus atom surrounded by four oxygen atoms.

The energy we talk about here is in the form of high-energy bond between those phosphate groups. When they separate, the energy is released, and then used. To put back on that last phosphate group, and therefore recharging it, it requires the energy which the body needs to get from the food we eat. This principle is explained on this picture.

 

When you take away that last phosphate group, you create the molecule called ADP - adenosine diphosphate (only 2 phosphate groups). That would be the representation of empty battery in this analogy. Rotating those two chemical reactions, then provides the means of an empty and full battery, which are moving from the place of using up to the place of recharging it. And back again and again cyclically.

 

For example, one molecule of glucose can bring up the production of as much as 38 ATPs, provided there is an oxygen present in the process. This is called an aerobic respiration. In the absence of oxygen, however, only two ATPs can be made - the process called anaerobic respiration. For more detailed view of how and where ATPs are made in the body, this flow diagram does a great job.

 

Here you can see that some ATPs are made in mitochondrion, some in the cytosol, and some in the gut - where happens the basic breaking down of food from the meals we eat. In the gut, the proteins, complex carbohydrates, and lipids are digested into the final products, which are in form of amino acids, glucose, fatty acids, and glycerol respectively.

 

First round of freshly made ATPs is happening in the cytosol, where the glucose and the glycerol are used for creating it. Cytosol is semi-fluid matrix inside of the cells, in which all the organelles are suspended. Mitochondrion is a special organelle for making ATPs and many other functions. There in the middle, there is a cyclical sequence of chemical reactions called TCA, or Krebs cycle (or citric acid cycle). This represents the biggest system for ATP production in the body.

 

Stress response

The stress response, commonly known as the fight-or-flight reaction, is the first part of so-called General Adaptation Syndrome (GAS). It's a short lasting physical reaction of the body (or organism) towards the real (or even any imagined) threat. This response can be seen from multiple of levels - molecular, cellular, anatomic or atomic. It can be defined by physical or/and chemical processes which are triggered by it, or by any physical symptoms on the perception level. Or by some other means.

Three phases of GAS are:

1. stress response (fight-or-flight reaction)
2. resistance
3. exhaustion

So in the hypothetical situation where your life is in danger and you are forced to run away, the first part is very explosive and effective accumulation of energy at your disposal. If the threat persists, the next phase called resistance, is much longer sustainable state of increased level of disposable energy, but decreasing with time. After a while, depending on physical condition of that particular person, the third phase called exhaustion will follow. This is the state where the most of the energy is already spent, and the body is no longer in a position to fight or flight anymore. 

But from those three phases the first one is by far most interesting, so let's go deeper into particular physiological and chemical changes that are triggered by the stress response. It's all happening in real time, so the stress response is occurring on the observable level (to a certain degree of course). The consequences of the stress response could be put into two broad categories:

a) short-term consequences

b) long-term consequences

and those two differ substantially, so let's elaborate both of them.

SHORT-TERM

In the short-term, the stress response can be useful and helpful by presenting some information (a lesson learned), the impulse for the body to improve, or get stronger. In the short-term, it can be even perceived as a pleasurable event, providing it's happening within well-known boundaries (like for example in adrenalin sports). But it can be harmful in the case when the impulse is too strong to handle, and it slips the person into any negative experience of stress. And in the big proportions we talk about trauma (on mental level) or the injury (on physical level).

The principle behind the stress response in the short-term is to provide the organism the opportunity to improve, or strengthen itself in some way. Providing there is the sufficient and quality recovery time, and handling the stress is still manageable (to the comfortable level), the result should be the improvement of the body in dealing with that particular type of stress or condition.

The analogy could be used of learning how to drive the car. The frustration and stress associated with handling new circumstances evoke the stress response on the number of occasions. But if handled, it leads into the ability of driving the car, which in turn becomes a very useful skill in life.

LONG-TERM

By the long-term consequences of stress response I don't mean cyclical and continual short-term stress response with recovery time on day-to-day basis. But mainly it means some degree of continual residue of stress, which hasn't been handled within the manageable (or comfortable) level. Or, in the case when there isn't sufficient recovery time provided to the organism, even if the impulse itself is handled well. This stress is not really used for an improvement of the organism, but instead it builds up as some form of toxic substances within the body, or it can manifest as the lack of useful (energy) substances in the body.

Now here, we really talk about quite negative consequences of the stress response. Those can be recognizable on physical level, as well as on the perception level. It's roughly summarized in the flow diagram bellow:

Noise, heat, infection, isolation, aggression, and many more other factors persisting in the experience of the individual, can lead into some sort of negative long-term consequences of the stress response. Concrete physical symptoms then follow, for example the memory loss, the rapid (unhealthy) weight loss, ulcers, heart diseases, loss of sexual function, and many many others.

DISSECTION OF STRESS RESPONSE:

Once we have cleared the function of it, and the differences between long-term and short-term, we can now go deeper into many particular changes within the body. For easier grasping of so many processes, I created a simple list of direct physical and/or chemical processes that follow immediate stress response. In brackets, I present the particular hormone, which is responsible for that particular physical response - even if only in those cases (of course) where it can be determined. So simply put, the stress response causes:

- increased heart rate (adrenalin)
- increased blood pressure (noradrenalin)
- decreased pain sensitivity (endorphines)
- stopped/slowed down the activity of digestive system (cortisol)
- stopped/slowed down the activity of reproductive system (cortisol)
- alerted mind (adrenalin)
- enriched blood with:
    a) glucose  (glucagon)
    b) fatty acids (cortisol)
- started up/kicked in of the immune system (ACTH)
- started up the proliferation (building up) of T-cells
- inhibited production of GH (growth hormone)
- stimulated release of CRH from hypothalamus into blood
- stimulated anterior pituitary to release ACTH
- stimulated cortisol synthesizing from cholesterol in adrenal cortex
- increased carbohydrate metabolism (glucagon, cortisol)
- stopped/slowed down the tissue repair (less GH)
- increased rate of blood circulation (adrenalin+noradrenalin)
- enhanced memory formation (adrenalin)
- increased signalling of sympathetic part of nervous system
- suppressed signalling of parasympathetic part of nervous system
- prepared body to deal with challenges (adrenalin)
- inhibited inflammatory response (cortisol)
- suppressed stomach activity
- reduced secretion of digestive acids
- decreased blood flow to the walls of the stomach
- slowed down epithelial cell replacement in the gut
- reduced thickness of mucous membrane in the gut
- reduced production of reproductive hormones
- loss of sexual desire (less testosterone)
- disruption of sexual performance (less testosterone)
- enhanced brain activity - agility - learning
- more relaxed lung muscles - prepared for more oxygen getting in
- increased volume of lungs / their effectiveness

ADH negative feedback

And just as I promised to you in my last post, I'm bringing here nice flow diagram that very nicely explains how the body regulates the amount of water in the blood and therefore the body itself. It comes from GCSE book on Human biology (Letts, 1994).  The diagram is pretty much self explanatory, so I don't have to say very much about it.

Maybe only that on the most left and most right sides of the picture the text says: "Norm with just the right amount of water". It's the same text on both sides. Just wanted to make sure that you know, because it came out a bit blurry on sides. Otherwise, the picture describe so-called negative feedback loop. It's called negative because it negates any too big alteration from the constant norm level of certain molecule or hormone in the blood. If it goes too up, something happen to make it go down, and vice versa.

In this case, ADH goes up when body's reserves of water are going short, and no new water is getting into system. ADH means anti-diuretic hormone, which could be translated that it goes against of(anti) the loss of water in the urine (diuretic). That happens the way that kidney increases the process of reabsorbtion to the level that is needed, in order to save the water that is already in the system (or in this case in the blood). When ADH goes down, kidney decrease reabsorbtion of water, so more of the water in the blood end up in the urine.

The content of water in the body is controlled by Hypothalamus. This very small part of the brain regulates the content of the water by measuring the osmolarity of the blood. Osmolarity could be simply described as the amount of dissolved particles in the water. It can be solid particles or gases. To give you a clearer picture, imagine two pint glasses of water. One would be filled by pure water and in the other, there will be a lots of salt, sugar, or some other stuff in it. So the difference between those two pints would be the amount of empty space between water molecules, despite of the same volume, or even the mass of the content in the pint glass.

Now, once the Hypothalamus detect the change in the osmolarity in the blood (up or down), it signals the pituitary gland to secret more or less of ADH hormone. This hormone then travels by blood into kidneys, and those interpret it as the signal to reabsorb more or less water, respectively. The mechanism by which this is done, is the inserting the special proteins called aquaporins into the cell membranes. Those proteins work as a channel for the water to be able to cross the membrane, as the name itself suggest - the pore for the water. The more aquaporins, the more water is reabsorbed. So the less ADH hormone means less aquaporins, which means less water reabsorbed and let go into the urine. Simple as that. 

3-tier system of hormones

In this post, I will get into closer examination of endocrine or hormonal system. It's called 3-tier, because the secretion of hormones comes in three sort of "waves". The first one comes from hypothalamus, which release so-called relasing hormones, or in some older literature you can see it by the name releasing factors. Apart of those, there are release-inhibiting factors, which are hormones that act as having an opposite effect to releasing hormones.

 

Hypothalamus releases hormones into two ways. Either through the pituitary stalk into anterior pituitary lobe, or straight into posterior pituitary lobe. And those two lobes are already second wave or tier, from which series of another hormones are secreted. That would be ADH and oxytocin from posterior pituitary lobe and TSH, FSH, LH, PrL, GH, ACTH, beta-lipotropin, and beta-endorphin enkephalins from anterior pituitary lobe. All those hormones are directed towards gland or other organs, which become third tier in the system, and react to the signal by further secreting of another set of hormones.  

 

Those glands and organs could be thyroid gland or mammary gland, or liver, or nerves. For better illustration of what I have just written,  here is a picture I took from Open University course book on Human biology.  It summarizes all pathways I mentioned in nicely color flow diagram. In this case another proper example of human body flow diagram.

 

 

 

So let's start nicely to explain main hormones.

ADH is anti-diuretic hormone, which gives signal to kidney to start reabsorbing more water. When the level of water in the body is adequte, ADH will stop coming to kidney, because hypothalamus will stop releasing first set of hormones. I'll bring nice flow diagram in some future post, as this particular negative feedback deserves more attention in a separate post.

 

TSH stands for thyroid-stimulating hormone, which clearly means that thyroid gland will become stimulated for prodution and secretion its hormones thyroxin and tri-iodothyronine. Those than go out and have the effect on their target cells.

 

FSH is follicle-stimulating hormone, which means the follicle in the ovary and testes. Those produce and secrets their own hormones. For testes it's testosterone and for ovary it's progesterone and oestrogen. Those two organs are further stimulated by LH (luteinizing hormone), and ovary also with PrL (prolactin), which affects mammary gland too (for producing a milk).

 

Then we have here a growth hormone (GH), which gives signal to liver that it's time to build some more tissue - hence the growth promotion. Liver reacts by releasing IGF-1 (insulin-like growth factor), which starts the action by bringing more glucose from bloodstream into the cells, where it can be used as energy for building new tissue, or repairing the old one.

 

ACTH stands for adrenocorticotropic hormone, because it stimulates adrenal glands, and it further release the group of hormones called corticosteroids. So that would be all abbreviations from the picture above, but there is still more to come as I didn't mention no examples or releasing hormones yet. So here it is. There are two types of hormones coming from hypothalamus to anterior pituitary lobe, also called neurohormones:

 

Releasing hormones (or factors):

GnRH - gonadotropin-releasing hormone

CRH - adrenocorticotropic hormone-releasing hormone

TRH - thyroid-stimulating hormone-releasing hormone

GRH - growth hormone-releasing hormone

 

and release-inhibiting factors:

SIF - somatostatin - inhibits secretion of GH and TSH

(also known as GIF - growth hormone release-inhibiting factor)

PIF - prolactin release-inhibiting factor

 

So now I hope you have some idea about what hormonal system is. Of course, there is much more to be said about any particular hormnone or pathway, but that would be loads of pages about each one. This post serves for a rough summary, accompanied with nice flow diagram for better imagination of what is being written. Only time will tell if I expand this post in the future, but so far I think that it's deep enough. See you later. 

Level of glucose in the blood

In this post I'm bringing here one of the most typical representative of the flow diagram. This one explains the process of working on the steady level of glucose ( type of simple sugar) in the blood. This is achieved by so-called negative feedback loop. Negative, because it negates any bigger changes from the balance, and restore the level towards the stable position - within the norm. The mechanism is two-fold.

 

The pancreas creates two hormones called the insulin and the glucagon, and they act in antagonistic way, meaning they function in contrast. Insulin takes glucose from bloodstream into the cells that need it, and this way lower the level of glucose in the blood. Glucagon, on the other hand, supress the action of insulin, so the glucose in the blood starts accumulating again. If I may offer an analogy, they work just like the gas pedal and the break pedal in the car.

 

But this is all pretty basic knowledge. I took this picture out of the GCSE book on Human biology (Letts, 1994)  and technically, we talk the language of sixteen years old pupils. So let's go a bit deeper. The healthy blood glucose level is within the range of  4 to 6 mmol/l. Of course, that level fluctuates during the day as the reflection of having meals containg carbohydrates.
 

After such a meal, the level tends to rise, because the food needs to be digested and all micronutrients (results of digestion) go into the bloodstream. This is the signal for pancreas to release the insulin, which takes the glucose molecules across the cell membrane into the cells. Glucose molecule is too big to cross the plasma (cell) membrane by itself, so it needs the insulin to help widen a gap a little bit.

But then, when you don't eat for a while, the level goes down, and this is a signal for pancreas to release the glucagon, which stops the insulin from doing its job. This way the glucose can't get inside anymore, and stays in the blood. By this mechanism, the relatively stable level is achieved, falling in the healthy range of 4-6 mmol/l. This could be translated as 4-6 milimole per litre of blood, in which one milimole (or thousanth of one mole) is 180 mg of glucose.

I know that this is probably really hard to imagine, so I put it into the perspective. Fluctuation during the day within this healthy range is ok, but hit the level of 10 mmol/l, and you'll be diagnosed with hyperglycemia - which basically means having too much of glucose (sugar) in the blood. Or on the other hand, if your level sinks under 3 mmol/l, then you'll be diagnosed with hypoglycemia - which means not enough glucose in the blood.

So why is so important for the body to have always a stable supply of glucose? Well, many reasons, but probably the biggest one is that the glucose is the only food for the brain, and the whole nervous system. And you probably want those parts to work all the time, and properly. Plus the glucose is used as a fuel for movement. Fat is also a fuel, but glucose is much more readily available for immediate actions and reactions. Lipids chips in mostly when you move very slowly, or not at all (holding the position of the body). But all rapid movements, including your fingers, eyes, or ankles, are down to glucose, so without it (or with low level of it), the body would be pretty slow and stiff. That's why.

Nicely from beginning - embryology

... and that's how I became interested in embryology. Well, sort of. As soon as I saw this diagram in this Dictionary of biology (Penguin, 2004)  straight away started the process of deep study of basic terminology when it comes to development of an embryo:

blastocyst - single-layered inner cell mass (see pic.)
blastula - name of the stage of development
blastocoele - cavity in the middle of blastocyst
blastoderm - first (outer) row of cell in a blastocyst
blastomere - name of one cell in a blastocyst
blastopore - transitory opening for injecting ES cells

ES cells stands for embryonic stem cells, which are the ones that are still not differenciated into specific type. First type of cells produced in the brainstem are unspecified, or "sort of" universal, and they grow to produce a cluster of cells called morula. This is a stage prior to blastula, in which the basic cleavage (or division) of those cells occur.

One cell becomes two, four, eight, sixteen, and so on, and that's how morula is created. Then the outer layer and inner cavity is formed, and this is already second stage called blastula. Diagram shows roughly this stage, when an artificial injection of ES cells can occur. 

After that blastula follows another stage called gastrula - the stage where first differentiation happen. Firstly, cells are divided into three main categories - germ layers:

- ectoderm - outermost cells
- mesoderm - middle layer inbetween
- endoderm -  innermost cells

The ectoderm leads to development of skin, nervous system (neurons and glia), and gland cells. Mesoderm leads to bones, muscles, kidneys and gonads. Endoderm developes into yolk cells and alimentary canal (mainly epithelials in liver, lungs, stomach, pharynx, and intestine).

Mesoderm further divides into dorsal and ventral, which in layterms means the one at the back and the one in front respectively. Ectoderm further divides into three types - neural plate (neurons and glia) on one side, neural crest (cartilage) in the middle, and epidermis (skin, gland cells) on the other side. All these processes of differentiation are collectivelly named gastrulation movements, and once they are finished, the new stage called neurula will start.

Neurula, is called this way, because it signified the presence of neural plate at the begining of this stage. Neural plate is rising from ectodermal tissue, and further develop into so-called neural tube, which is the begining of the formation of spine.
 

So that would be about the embryo. In human, the embryo becomes a foetus at about seven weeks from beginning, which is marked by the appearance of first bone being formed. If you notice the blue color underlined sentence, you will probably realize that there are probably not sufficiently defined limits, where exactly the human life starts. Some would place it exactly inbetween an embryo and feotus, some at the conception, still some would go even further.

 

Many people would place it even before that - the intention of conception. So this topic and the debate remains still open, as I read here and there. What do you think?  

Introduction

Hello everyone who is into any information about the human body. Be it a biochemistry, human biology, or physiology, flow diagrams are here to interpret some very complex information flow within our bodies in the simplest possible terms. As the saying goes, seeing once is better than hearing a hundred times, I found flow diagrams very useful tools for remembering things I want to remember, and understand the thing I want to understand.

 

Because human body is so complex and delicate at the same time, informations about it could be seen as layered into many dimensions. So many flow diagrams are here trying to reflect as many of those dimensions working together, and plus present the picture that shows links between them. For example, some flow diagrams are purely about endocrine system (or hormones), some purely about nervous system (or nerves). But some are about interconnected cooperation of those systems, and that's where it starts to be interesting.

 

Seeing a bigger picture is very important, as it gives a many ideas about connections between different parts of body. So here in this blog, I'll try to collect and comment many of those flow diagrams I found across various literature and internet. This blog is the result of my dedication to pursuing the understanding of many complex processes that are happening inside us. I only hope that you will find useful my explanations along with those diagrams. I'll try go as simple as possible, as the basics are usually most important, so every new or seemingly complicated term will be explained in simple laymen terms.

So how would you translate for your self the human body flow diagram mania? It doesn't have to be necessarily a set of flow diagrams about human body, like you found plenty in biochemistry books. But rather see it as a collection of diagrams concerning human body, which represents flow of molecules, substances, time, energy, information (you name it) in the human body. As I said, the bigger picture must be seen, and that's my motto, so here is the flow diagram to illustrate my point.

 



 This flow diagram basically represents the biggest picture possible. The ultimate structure of reality or the existence, mainly on the planet earth, but possibly not only here. Technically, all is composed with very small parts called atoms, even if those has its component too - protons, neutrons, and electrons. Either two or more atoms put together create so-called inorganic molecules, or commonly called inorganic compounds.

 

By the definition, those are very small, with very simple structure, and not containing the carbon atom. The only two exceptions are carbon dioxide, and bicarbonate ion, which contain carbon, but are still classified as inorganic - mainly due to simple structure. Other examples are water, salts, bases, acids, and separate ions called electrolytes. In the body, there's about 55-60% water, and 1-2% of all other inorganic molecules.

 

Once a lots of those are put together, the organic molecule is created. Those are big, complex, and contain carbon, or a lots of carbon atoms. The resting 40% of the body is built with those organic molecules. Types of those are carbohydrates, lipids, proteins, nucleic acids (building blocks of DNA), and ATP - the energy molecule of the body.

 

So once those already big and complex organic compounds (or molecules) start to react with each other, even bigger molecules are created. If big enough to start fulfilling some particular function, they become an organelles - like mitochondria, nucleus, ribosome, lysosome, plasma membranes, centrosomes, etc, etc. Those are the functional parts of the cells, the building units of every living organism.

 

On cellular level there is about 200 different types of cells in the body. Those close to each other, and with similar (or the same) function group together and make a functional unit called the tissue. Different tissues which are working on the same basic function create an organ, and different organs working on the same basic function create a system.

 

Altogether 12 systems in the body make the whole organism, in our case, the human body. Two basic types of body (male and female) can create a so-called breeding pair, and bring about another organism into the existence. This way populations are created leading to represent certain species, differenciating themselves from many other species on the planet. So that would be the flow diagram above put into the words.

 

Levels of structural organization

 

Still there is a number of dimensions within an organism, or human body, which I'd like to list nicely from the smallest to the biggest:

 

1. chemical level - atoms and molecules (e.g. water, oxygen, protein, ...)

2. cellular level - different types of cells (nerve, sperm, muscle, goblet, ...)

3. tissue level - different types of tissues (adipose, bone, connective, ...)

4. organ level - different types of organs (heart, brain, kidney, spleen, ...)

5. system level - 12 different systems (skeletal, digestive, urinary, ...)

6. organismal level - whole human body, or some other organism