Monday, March 29, 2010

Glycogen.


Glycogen is stored in Liver and Muscle


After absorption into a cell, glucose can be used immediately for release of energy to the cell, or it can be stored in the form of glycogen, which is a large polymerof glucose.All cells of the body are capable of storing at least some glycogen, but certain cells can store large amounts,
especially liver cells, which can store up to 5 to 8 percent of their weight as glycogen, and muscle cells, which can store up to 1 to 3 per cent glycogen. The glycogen molecules can be polymerized to almost any molecular weight, with the average molecular weight being 5 million or greater; most of the glycogen precipitates in the form of solid granules.
This conversion of the monosaccharides into a highmolecular- weight precipitated compound (glycogen) makes it possible to store large quantities of carbohydrates without significantly altering the osmotic pressure of the intracellular fluids. High concentrations of low-molecular-weight soluble monosaccharides would play havoc with the osmotic relations between intracellular and extracellular fluids.

Monday, March 8, 2010

What is Passive Immunity?


Passive Immunity
Thus far, all the acquired immunity we have discussed
has been active immunity. That is, the person’s own
body develops either antibodies or activated T cells in
response to invasion of the body by a foreign antigen.
However, temporary immunity can be achieved in a
person without injecting any antigen. This is done by
infusing antibodies, activated T cells, or both obtained
from the blood of someone else or from some other
animal that has been actively immunized against the
antigen.
Antibodies last in the body of the recipient for 2 to
3 weeks, and during that time, the person is protected
against the invading disease. Activated T cells last for
a few weeks if transfused from another person but
only for a few hours to a few days if transfused
from an animal. Such transfusion of antibodies or T
lymphocytes to confer immunity is called passive
immunity.

Innate Immunity


The human body has the ability to resist almost all
types of organisms or toxins that tend to damage the
tissues and organs. This capability is called immunity.
Much of immunity is acquired immunity that
does not develop until after the body is first
attacked by a bacterium, virus, or toxin, often
requiring weeks or months to develop the immunity. An additional portion of
immunity results from general processes, rather than from processes directed
at specific disease organisms. This is called innate immunity. It includes the
following:
1. Phagocytosis of bacteria and other invaders by white blood cells and cells
of the tissue macrophage system,
2. Destruction of swallowed organisms by the acid secretions of the stomach
and the digestive enzymes.
3. Resistance of the skin to invasion by organisms.
4. Presence in the blood of certain chemical compounds that attach to
foreign organisms or toxins and destroy them. Some of these compounds
are (1) lysozyme, a mucolytic polysaccharide that attacks bacteria and
causes them to dissolute; (2) basic polypeptides, which react with and
inactivate certain types of gram-positive bacteria; (3) the complement
complex that is described later, a system of about 20 proteins that can be
activated in various ways to destroy bacteria; and (4) natural killer
lymphocytes that can recognize and destroy foreign cells, tumor cells, and
even some infected cells.
This innate immunity makes the human body resistant to such diseases as
some paralytic viral infections of animals, hog cholera, cattle plague, and distemper—
a viral disease that kills a large percentage of dogs that become
afflicted with it. Conversely, many lower animals are resistant or even immune
to many human diseases, such as poliomyelitis, mumps, human cholera, measles,
and syphilis, which are very damaging or even lethal to human beings.

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