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. 

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