Streaming Organism

2006-10-23T03:14:00.000-07:00

Streaming tissues

2006-10-23T02:14:00.000-07:00

The organism is made of cells. Cells aggregate into tissues units, that assemble into tissues. Several tissues make an organ, Nearly all cells live less than the organism does. Epithelia in the gut live two days, skin cells, three weeks. Red blood cells live 120 days, and bone cells, several years. Dying cells are replaced with newly formed cells, a process known as cell turnover.

The entire surface of our skin, known as epidermis, is replaced every three weeks. Skin cell population consists of young , adult and old cells. Just like the human population. One would assume that once a cell is formed it will stay in the place of it birth. Eventually die there, and replaced by a new cell. Yet this is not the case. Cells in the body are formed at one place and literally stream to their graveyard.

Tissue unit

During growth, organism does not pile up cells like bricks. Its building blocks consist of cell clusters, called tissue units.
The epithelial tissue unit is made of five components, embedded in a gel matrix:

-Epithelium cells
-Connective tissue
-Nerve fibers
-Blood vessel
-Lymph vessel

Epithelium cells are responsible for tasks executed by the unit.. Connective tissue cells contribute the scaffold and matrix. Nerve fibers provide communication with other units. Resources arecarried by blood carrying vessels. Lymph vessels drain tissue fluid to other units.

At the base of the tissue unit is a stem cell whose progeny make the unit

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Streaming Proteins

2006-10-17T04:25:00.000-07:00

Changing representation of the organism

Static Organism

Until the beginning of the twentieth century the human organism was conceived as an engine immersed in its own liquid environment. It was assumed that all engine constituents exist as long as the organism does. Only the watery envelope turns over, maintaining a steady state that is called homeostasis.

Random turnover

The first experiments with radioactive isotopes that were introduced in the 1930's revealed that all molecules of the organism continuously turn over and are randomly replaced with new ones. In spite of this, microscopic constituents, e.g. cells and tissues, were assumed to be permanent and replaced only when damaged.

Oriented turnover

The 1950s revealed that molecular turnover is not at all random. Molecules are replaced according to the fi-fo rule (first in, first out). The first that are incorporated are also the first to leave, which was first demonstrated in protein synthesis. The protein starts its existence when its DNA code is translated into RNA that serves as template for the assembly of amino acids into short protein chains that grow with time and stream away from the nucleus. They stream through sub-microscopic cavities of the endoplasmic reticulum toward the cell periphery where they are secreted. The protein is born near the nucleus and ages while streaming. Its age may be read off its position in the cytoplasm, the more distant it is from
the nucleus the older it gets.

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