Multi-functional Structures

Supporters of the Darwinian version of the origin of life are hard-pressed to explain how a new function of the human body, by natural selection, served a new purpose by means of a major alteration of the DNA blueprint of an organic structure which was already equipped to serve an existing purpose.

As explained in The Fundamentals section, it stretches credulity to assume that the 3.2 billion “bits” of the DNA within the human cell were produced without intentional order and arrangement resulting in the organized complexity of a complete body. This complexity is further compounded by multi-functional structures.

Multi-functional Endoplasmic Reticulum

A remarkable configuration within the body of cells is the endoplasmic reticulum. This structure performs many functions:

  • protein synthesis
  • translocation across the membrane
  • integration into the membrane
  • protein folding
  • post-translational modification
  • glycosylation
  • synthesis of phospholipids
  • and the regulation of calcium homeostasis.

No small accomplishment for this labyrinthine structure.

cellsection

Artistic depiction of the cell, showing the labyrinthine arrangement of the
endoplasmic reticulum serving multiple functions within the cell body

Multi-functional Glial Cells

An example of a multi-functional structure of this type is the Radial Glial cell of the human central nervous system. Although these have long known to be specialized cells vital for the developing nervous system, they are now known to perform multiple tasks.

They are characterized by long radial processes that facilitate the guidance of radial migration of newborn neurons from the ventricular zone (the channels of the brain that contain fluid) to the mantle (or pallium) regions, which are the protective layers of the brain analogous to the mantle of the earth. (Incidentally, some brain cell development occurs in what scientists call “inside-out” fashion, where the deeper dependent cells are formed before the cells on which they depend — like watching a tree grow, but the leaves form first, followed by the stems then the branches then the limbs then the trunk!)

The ongoing study of the human brain ensures that new levels of complexity continue to be discovered and form the basis of yet further examination. As Professor Sir Robin Murray, one of the United Kingdom’s leading psychiatrists, said:

“We won’t be able to understand the brain. It is the most complex thing in the universe.”

The late Dr. Isaac Asimov once said:

“The human brain … is the most complicated organization of matter that we know.”

And as physicist Sir Roger Penrose said:

“Consider the human brain. If you look at the entire physical cosmos, our brains are a tiny, tiny part of it. But they’re the most perfectly organized part. Compared to the complexity of a brain, a galaxy is just an inert lump.”

Radial.Glia.Figure_35_01_06

Example of Radial Glial cells (courtesy Openstax College)

Recent data indicate further important roles for the brain’s Radial Glial cells as ubiquitous precursors that generate neurons and glia, provide maintenance tasks for damaged neuronal connections, and also serve as key elements in patterning and region-specific differentiation of the central nervous system. They also at times perform the same signaling functions as neurons. Consequently, these multi-functional cells are very much involved in most aspects of brain development.

Multi-functional Astrocyte Cells

Astrocytes are specialized cells found throughout the entire central nervous system; they are (for the most part) star-shaped glial cells (the name derives from the Greek words aster for star and kutos for container, or cell). They are specialized glial cells that somehow outnumber neurons by more than 5 to 1.

astrocyte

Astrocytes are the most abundant cell type in the central nervous system, and for good reason; they perform many complex functions:

  • assisting in the development of the nervous system (including defining the brain’s overall architecture)…
  • maintaining brain homeostasis (i.e. the brain’s metabolic equilibrium)…
  • controlling concentrations of ions, neuro-transmitters, and metabolites (chemical compounds produced as a result of metabolism or metabolic reactions)…
  • regulating water movements…
  • removing excess (harmful) glutamate…
  • supplying glutamine to maintain glutamatergic neurotransmission (a glutamate–glutamine shuttle service)…
  • facilitating signal transmission…
  • restricting which substances can enter the brain by providing biochemical support of the endothelial cells (the thin layer of cells that lines the interior surface of blood vessels and lymphatic vessels) that form the blood-brain barrier…
  • controlling local blood-flow…
  • delivering nutrients to nervous system tissue…
  • and helping repair the spinal cord after injury.
  • According to the latest research by neuroscientists, the above list is by no means complete. And, as remarked earlier, what is the supporter of Darwin to make of this list?

Given the closely-related studies of other components of the central nervous system, and their own levels of complexity, how is the Darwinian system to explain the converging, mutually-dependent, yet disparate functions of these systems?

The Multi-functional Liver

The liver is very much a multi-functional organ. It performs, among other things, the following functions:

(1) It converts food into energy,

(2) makes extensive use of water to cleanse the body from pollutants such as alcohol, drugs, poisons, and airborne mephitic chemicals;

(3) it uses water again when manufacturing bile, even increasing production in the event of gall bladder failure; it stores

(4) vitamins

(5) minerals, and

(6) energy for use by other cells and organs of the body when needed.

liver

The multi-purpose liver (illustrated by Gerry Fey)

Additional articles in this series will deal with the multilayered dependency relationships that the complexity of this organ contrives at the atomic, molecular, DNA, and organ levels.

Multi-purpose Neurovascular Development

A further example involves independent neurovascular growth; that is, nerve fibers and blood vessels (both being multi-attribute structures) during embryonic development.

Growth cones of nerves and endothelial cells of blood vessels are closely analogous in the way they extend and branch out, and they both perform similar tasks during the early development of a limb or organ. Both must invade the mesenchyme, the plexus of embryonic connective tissue in the mesoderm (one of the three primary cellular layers of the developing embryo), which form the connective tissues of the blood and lymphatic vessels to produce complex networks of nerves and vessels. Both structures (blood vessels and nerve fibers) must extend into regions of the developing limb such as muscles and both form dense subcutaneous plexuses at precisely the same depth. Also, adult tissues show many examples of neurovascular bundles in which nerves and blood vessels give evidence of having developed in close parallel and have branched out in filial fashion in a manner that well illustrates the “dependency links to multiple lines of the complex latticework” described above.

The embryo continues to grow in size as nerve fiber and blood vessel growth continues; however, the density of both remains the same throughout the growth period until near the end of development. Moreover, during the early stages of neurovascular growth, scientists see no obvious signs of symbiotic (mutually dependent) development. They do observe, though, that blood vessels tend to be in place generally before nerve fibers. However, during the mature stages of neurovascular branching, nerve fiber and blood vessel growth is closely correlated, so much so that nerve fibers are either very closely paralleled by blood vessels to within 10 micron distance, or up to 4 blood vessels form a tight sheath around the nerve fibers ensuring an adequate supply of blood at this microscopic level. Once tissue growth is complete for the organ or limb and branching has reached its maximum twig level, neurovascular growth ceases.

The behavior of these systems throughout embryonic and fetal development is an highly complex. How does each filament of fiber or blood vessel branch out (for example, cascading to twig level at appropriate density nearing the end-points) and where? How do they determine when to stop branching out? How does the branching density respond when organ or limb growth has stopped? Why does branching density reach “twig” level near the completion of branching at the perimeter of every organ or limb? Only when the tissue and organ growth is complete does the intended pattern become obvious.

Considering the quantity of both blood vessels and nerve fibers that migrate to the nethermost regions of the human body (in fact, in one body alone, placed end-to-end these structures would each stretch about four-times around the earth — not counting the more prolific lemniscus of the brain (the pathways that carry sensory information), which have more than the entire body combined — and neurosurgeons estimate that blood vessel quantities probably match those of nerve fibers, despite the fact that the average length of capillaries in the human body is only about half a millimeter!)

blood.vessel.branchingFractal branching of blood vessels in the foot
(picture courtesy of Scielo, Chile)

The above image shows the visible fractal branching of the blood vessels; lesser capillary branching is too small for the unaided eye to observe.

So, what conclusion do we draw? Did the multiple inter-related, mutually dependent layers of design features — from tiny atomic particles to body organs — arrange themselves into their complicated, exquisite formations?

Advertisements

Published by:

Michael A. Barber

IT Consultant, Technical Author, Certified Data Scientist. Over 30 years experience in consultancy and writing. See my personal web site: michaelbarber.co.uk

1 Comment

One thought on “Multi-functional Structures”

Thank you for your interest !

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google+ photo

You are commenting using your Google+ account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

This site uses Akismet to reduce spam. Learn how your comment data is processed.