|
The
kidney and excretion - Pt 1
Adrian
Whyte and Joanna Johnson, Contributor
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| Students
view the Get Ready For Work career
and education expo at the Hilton
Kingston hotel on June 1, 2005.
- Junior Dowie Photo |
EXCRETION
IS the removal of waste products of
metabolism from the body. If they were
allowed to communicate, they would prevent
the maintenance of a steady state. Secretion
is different from excretion in that
it is usually the release of useful
substances such as hormones from cells.
THE
HUMAN KIDNEY
The
kidney is a major excretory organ.
Its main functions are:
- Removal
of metabolic waste products.
-
Regulations of water content of
body fluids.
-
Regulation of pH of body fluids.
- Regulation
of chemical composition of body
fluids by removal of substances
which are in excess of immediate
requirements.
Since
the kidney has a rich blood supply
where it keeps the composition of
the blood at a steady state, it therefore
contributes to homeostasis.
 HOW
THE KIDNEY FILTERS BLOOD
1.
A large artery brings blood into the
kidney (renal artery).
2.
Tiny blood vessels branch off the
main artery and go through each nephron.
3.
Water, salts urea and glucose are
forced out of the blood into the nephrons.
4.
As these substances flow through the
nephron, most of the water, all of
the glucose, some of the salts and
urea move back into the blood. A concentrated
mixture of waste materials is left
in the nephrons.
5.
The cleaned blood, now with slightly
less water and much less waste material,
leaves the kidney via the large renal
vein.
6.
The yellow fluid that remains in the
nephron is called urine. It is sent
out of the kidney through the ureter
into the urinary bladder to be stored.
7.
Urine leaves the body through the
urethra.
THE
GENERAL STRUCTURE OF THE KIDNEY
There
are three main regions of the kidney,
namely the cortex, medulla, and pelvis.
Cortex - This is the outer part of
the kidney where the blood is filtered
by a process known as ultra-filtration
or high-pressure filtration because
it only works if the blood entering
the kidney in the renal artery is
at high pressure.
Medulla - The inside part of the kidney
where the amount of water and salt
in your urine is controlled.
Pelvis - The region of the kidney
where urine collects.
THE
NEPHRON
This
is the functional part of the kidney.
It is the structure responsible for
filtering the blood and the production
of urine.
*
Adrian Whyte and Joanna Johnson
teach Biology at Ardenne High School
masterbio@gmail.com.
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