Tuesday, 8 February 2011

embryology talk

This story starts just after conception.

From Conception to Birth

by Alexander Tsiaras

For the first 3 or 4 days the egg divides, roughly once a day slowing, gathering into a tightly compacted sphere. Within a week it burrows into the lining of the uterus, which after initially swelling to engulf the embryo to dispose of it, suddenly turns receptive, it releases a starch upon which the embryo gorges itself and starts to grow at astonishing speed, doubling daily in size.

A few days after implantation the balled-up cells begin to rearrange and move - migrate. With magnificent speed and co-ordination, sheets of cells stream past each other, some migrating inward, others out, some up, some down - until 3 layers emerge - inner, middle and outer.

Once these layers are established, the cells interact rapidly with each other, rearranging themselves gradually into the complex communities we call organs. Like origami, not in one step, but by folding and pinching and refolding, then refolding again and again, it’s possible to make ever more refined and complex shapes.

It takes just 3 - 6 weeks to lay down the basic body plan. Still less than one-tenth of an inch the round ball of cells curls into a C-shape, a tiny comma. A groove has formed along the length of the back and it closes into a tube. Long stringy cells bundle to form nerves, which connect through the tube to the bulge at the top of the comma. A circulatory system unfolds. Another tube of new highly elastic cells takes shape with the remarkable ability to contract and release. Within 3 weeks from conception they have twisted into an S-shaped loop and have started pumping cells filled with oxygen and nutrients to every other tissue in the body. A heart begins to beat.

Folding and refolding happens everywhere, apace. At 6-7 weeks small bulges morph into limb buds, the head grows swiftly, eye pits deepen, the nasal region expands , the upper limb forms, finger rays appear and nipples.

And then, at about 8 weeks, just as quickly as it all began, the furious shuffling of cells stops. In form the embryo is complete, it is now a fetus.

From the Speech of the Embryo

by Jaap van der Wal

The embryo may be considered as a continuous whole or complete self organized being that seems to fall apart into its bodily constituents and organs. The embryo is maintaining order or centering this process. A kind of tree of cells, tissues and organs can be described which originate out of each other and gradually come to a distinction between each other.

So a fertilized human egg is not just a cell, it represents an organism: it is a complete manifestation of the human organism at that very moment, under the circumstances and environmental conditions that exist one day after conception. Like every living being the human embryo is in every phase of development a coherent whole, a unity of form, shape and function interacting with its environment. It is always itself.

DNA or genes may be considered as the clay for the modeling hands to do their modeling work. Neither the clay nor the hands can come to form on their own. The form and the shape can only come into appearance in the interaction between both conditions. In this way the human embryo is not caused by the genome and environmental factors, it comes into appearance (to manifestation) thanks to these both conditions.

An embryo does not yet, like an adult, have a form that functions, but that the embryo still functions in forms, in growing and changing forms and shapes. It is process in motion.

As an adult human we express ourselves by means of our body: the world is our aim and the body is the instrument for this purpose. The embryo on the other hand still impresses (imprints) itself into a bodily organization. The action, the performance is directed towards itself, inward. An orientation from beyond to here, from periphery to center may be seen in the embryo.

At the end of the first week of embryonic development the entity of the embryo, which at that moment is represented by a small sphere-shaped organism consisting of a few genetically identical cells, is divided. It differentiates into two populations of cells, into a duality. During the first days of development the embryo is divided, split up into a number of smaller cells as if the embryo falls apart into cells. Around the sixth day after conception the embryo is a small vesicle fallen apart into an outer mantle of some hundred cells with fluid within, and into a center or nucleus of only 6 to 8 cells. From that moment on a human organism consists of a peripheral body (mantle body) – and a central body, the body that will become our actual body at birth.

Of course those two bodies will change and metamorphose thoroughly but the duality, stays present and is discernible during our whole prenatal life. The processes in the embryo go from outside to inside. For example in the second and third week from this outer body a stream of blood and nourishment has to be developed in order to assure the existence of the central body. The first appearance of a heart represents the center of this whole entity at that moment. A dangerous threshold has to be taken between the second and third week: the embryo comes from a more peripheral existence to an existence in the center. It so to speak comes more to earth. It is incarnating deeper into the body. Is the whole of embryonic development a process of incarnation, an en-velopment? The dynamics of the embryo show us that the central body is coming forth out of the peripheral body. It emancipates from it in a process of gaining independency.

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