Thoughts on the growth of tissues in embryology

Embryology has always fascinated me.  I’m particularly fascinated with the growth of tissues and how they develop into the shapes and forms they do.  What do I mean by this?  When something grows the cells of the tissues have to divide so its mass will get larger and grow into the correct shape.  This must all be done with precision so that the growth happens in the right place.  Otherwise, there will be a ‘distortion’ of the tissue.  These create birth defects and other malformations.  This is true even later in life as cells that continue to grow without the correct shape create tumors and cancers which can be life threatening.  The controlled growth of tissues is very critical in living things, not only in their development and growth but in later years, that the shapes and forms are kept the way they are intended.

How is tissue growth done with such precision?  How is it controlled?  What are the mechanism of tissue growth?  It’s difficult to say.

All organisms begin with one cell, which divides into two, which divides again.  Everything begins with one undifferentiated cell.  Of course, this means that the ‘blueprint’ for its division and growth are all found in that single cell.  Everything is already found within the cell, all shapes, all organs, etc.  That single cell must have the means to create all subsequent growth. 

The first cell division is simple:  they just divide.  If they keep going a big glob of circular-like mass of cells will be created . . . but it doesn’t.  The cells start to grow in a controlled way.  More is grown on one area, less on another to create all sorts of shapes and configurations.  Only in this way are tissues, organs, and organisms created.  This requires controlled growth.  Somehow the cells must be controlled as a mass to achieve a shape. 

Controlled growth seem to entail two process:

  1. Cell division.  This is the controlling of the number, shape, and organization of cells.  The controlling of cell division gives tissues shape and mass.  The cells grow as a mass.  That is to say, it’s as if they are growing ‘in concert’.  Cells are working with the cells next to it, not as independent cells.
  2. Cell differentiation.  Here the cells change to achieve qualities and functions different from the cells about it.  The cells differentiated become a separate tissue (like a lung, or heart) and grow as a separate unit, creating the shape needed for that organ.

How is cell division performed?  It seems some requirements are needed:

  • In order for there to be a controlled cell division there must be a start, a beginning.  The cells need an axis to base its divisions on.  It probably creates this at random.  There seems to be two forms of axis:  an ‘axis as a point in space’ or a ‘linear axis’.  Both of these axis create a symmetrical growth pattern (see below).  In order for any axis to work there must be an ‘understanding’, so to speak, of the surrounding cells as to where this axis is at.  The cells must ‘know’ where the axis is in order to grow properly. 
  • It seems that cell division needs to be controlled spacially.  That is to say, cells don’t just start to divide to create a shape.  They must know where its location is in space and in relation to other cells. 

 Once this axis is created the cells divide spacially in a number of ways:

SYMMETRICALLY GROWTH

  • Spherically.  This means the cells grow in an organized way so it creates something spherical. 
  • Radially.  This means that the cells grow outward from a central ‘axis’.  All the growth is identical in all directions.  This growth can be in three dimensions, as something growing in all directions, or in two dimensions, growing outward like the points of a flat star.
  • Planar.  This is cell growth in two dimensions – a plane – creating something like a sheet of cells.
  • Bilaterally.  This means growing identically on either side of an axis.  It’s sort of like a mirror image of one another.  It requires a linear axis for this to take place.

NON-SYMMETRICAL GROWTH

  • A ‘protuberance’.  This means a cell grows in one direction from a mass of cells.  It is not copied anywhere else.  As a result, it is a ‘one of a kind’.
  • ‘Special’ growth.  This is a special growth pattern that starts at a certain point.  Typically, it does not follow any symmetrical pattern but its location is established by a symmetrical growth pattern (such as a hand).

It seems to me that symmetrical growth patterns are the first growths to grow.  It is with the symmetrical growth that the ‘foundation’ or ‘layout’ of the organism is built upon.  The later non-symmetrical growths (such as the thumb in relation to the fingers) come after symmetrical growth is established, helping to give the organism unique features.  This means that all life is based on symmetrical patterns. 

Often, these forms of growth are as if ‘blended together’.  For example, spherical growth, in a way, is a radial growth in three dimensions.  Radial growth, if it is constant in all directions, is really planar growth, the development of a ‘sheet’ of cells.  What this means is that there is often no fine line between cell growth types.  They often blur together.

I tend to believe that the first controlled growth of the cells, which create the tissues, is spherical.  This establishes the organism in a  three-dimensional plane.  It establishes axes to begin further growth.

Once spherical growth is established, then it goes to radial growth.  From a central axis cells divide outward from a central point.    This often creates a planar growth, like a ‘sheet’ of cells, a ‘canvas’ for further cell growth.

Once radial or planar growth happens an axis is probably randomly created on the ‘sheet’ which develops into bilateral growth.  Now, identical growth, a mirror image, is created on either side of the axis on the ‘sheet’.  These grow and grow slowly developing into the organism.   

Cell growth creates shapes and forms for the organism.  But, take a look at the shapes of tissues.  Look at your skin for example.  The cells had to divide the right amount, in the right place, in the right form, to create a ‘tight fitting skin’.  If there weren’t enough cells or too much, or in the wrong location, then our skin would be a mess.  But they’re not.  The controlled cell division required to create a tissue, such as skin, requires great precision.  It’s amazing.

When the embryo forms, shapes are created and formed.  But take a longer look at shapes.  They aren’t just shapes.  They are controlled shapes, with gradual curves, inclines, depressions, etc.  And, more importantly, they are identical on both sides of a bilateral axis – every curve, every depression, every protuberance.  Nothing is random here.  Each curve, each surface has a direction and a form.  Seldom are shapes just standard shapes – lines, flat surfaces, spheres, etc.  They are unique, unstandard shapes.  In any shape each point is at a different spot in relation to the any other point.  If they are not in the correct spot then the shape is not ‘perfect’.  This requires great control and organization.  In embryology, how is this type of control achieved? 

I have always found it very unbelievable that this is all ‘chemistry’, that every cell, every shape, every division is created by chemicals.  The theory being that the chemicals originate from the DNA strand.  The perfect and unique shapes shown in embryology, it seems to me, can’t be just a ‘chemical reading’ originating from the DNA.  How can each point be controlled by DNA?  There must be more to it than that.  But, I cannot say how such control is achieved.

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