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This page is about urine. Recognition and analysis of abnormalities
of this substance expelled from the body can provide information
about the condition of the body - both concerning general health,
and also specific medical conditions.
Biochemical analysis of urine is called "urinalysis",
and is commonly used to diagnose a wide range of diseases. Examples include high levels of urinary gloucose in diabetics,
and high levels of urinary ketone bodies in cases of ketonuria.
Immunological analysis of urine is the basis of most pregancy
tests.
What is a typical normal volume of urine ?
1-2 litres / 24 hours per normal adult.
However, the amount per day varies considerably.
The actual quantity
per person per day is affected by factors such as:
*
recent
fluid intake (water, and other food/drinks that
include water) * diet * temperature * blood
pressure * general health (some disease
states may affect urine volume/time) * mental state.
What are the physical characteristics of normal
urine ?
Volume (as mentioned above) is one of the physical characteristics
of urine. Other physical characteristics that can apply to
urine include colour, turbidity (transparency), smell (odour),
pH (acidity
- alkalinity),
and
density.
- Colour:
Typically yellow-amber but varies according to recent diet
and the concentration of the urine. Drinking more water
generally tends to reduce the concentration of urine, and
therefore cause it to have a lighter colour. (The converse
is also true.)
- Smell: The smell (or "odour", which is the more clinical term, American
spelling "odor") of urine may provide health
information. For example, urine of diabetics may have a sweet
or fruity odour due to the presence of ketones (organic molecules
of a particular structure). Generally fresh urine has a mild
smell but aged urine has a stronger odour, similar to that
of ammonia.
- Acidity: pH is a measure of the acidity
(or alkalinity) of a solution. The pH of a substance (solution)
is usually represented as a number in the range 0 (strong
acid) to 14 (strong alkali, also known as a "base"). Pure
water is "neutal" in the sense that it is neither neither
acid nor alkali, it therefore has a pH of 7. The real significance
of pH in terms of physical chemistry is that pH is a measure
of the activity of hydrogen ions (H+) in a solution.
The pH of normal urine is generally in the range 4.6 - 8,
a typical average being around 6.0. Much of the variation
is due to diet. For example, high protein diets result in
more acidic urine, but vegetarian diets generally result
in more alkaline urine (both within the typical range 4.6
- 8).
- Density: Density is also known as "specific
gravity". This is the ratio of the weight of a volume
of a substance compared with the weight of the same volume
of
distilled water.
Given that urine is mostly water, but
also contains some other substances dissolved in the "water",
its density is expected to be close to, but slightly greater
than, 1.0. This is true - the density of normal urine is
in the range 0.001 to 0.035.
What is contained in normal urine ?
- Approx. 95% of the volume of normal urine is due to water.
- The other 5% consists of solutes (chemicals that are dissolved
in the water).
Some of these solutes are the results of normal
biochemical activity within the cells of the body. Other
solutes may be due to chemicals that originated outside of the
body,
such as pharmaceutical drugs.
Solutes found in urine may
be classified as ions (i.e. single elements
that are positively or negatively charged due to loss or acquisition
of one or more
electrons from/to the outer-levels of the atom), or organic
molecules (i.e. several, sometimes many,
atoms that have joined together to form a group of atoms called
a "molecule"; "organic" molecules are formed from groups, rings,
or chains of carbon atoms and are the "building blocks" of the
living things on the earth - i.e. plants and animals).
As with many topics in first-level anatomy and physiology courses,
there is a "short answer" and a "longer answer". The version required
in an exam will be indicated by the number of marks allocated to
the question (or part of a question).
Identify substances found in normal
urine ...
Short Answer:
The biochemicals found in
urine are predominately the end-products of the nitrogen
metabolism process.
These include urea, uric acid, and creatinine. Other
components of urine include sodium chloride (common salt),
and over 100 other substances that are usually present, but
only in trace (i.e. very small) quantities. |
Identify
substances found in normal urine ...
Longer Answer:
Urine is aprox. 95% water.
The other components of normal urine
are the solutes that are dissolved in the water component of
the urine. These solutes can be divided into two categories according
to their chemical structure (e.g. size and electrical
charge).
Organic molecules are
electrically neutral and can be relatively large (compared with
the 'simpler' ions - below).
These include:
- Urea - Urea is an organic (i.e. carbon-based)
compound whose chemical formula is: CON2H4 or (NH2)2CO. It is also known as carbamide. Urea is derived from ammonia
and produced by the deamination of amino acids. The amount of urea in urine is related to quantity of dietary protein.
- Creatinine - Creatinine is a normal (healthy)
constituent of blood. It is produced mainly as a result of
the breakdown of creatine phosphate in muscle tissue. It
is usually produced
by the body at
a fairly constant rate (which depends on the muscle
mass of the body).
- Uric acid - Uric acid is an organic (i.e.
carbon-based) compound whose chemical formula is: C5H4N4O3.
Due to its insolubility, uric acid has a tendency to crystallize, and is a common part of kidney stones.
- Other substances/molecules - Example of other substances that may be found in small amounts in normal
urine include carbohydrates, enzymes, fatty acids, hormones,
pigments, and mucins (a group of large, heavily glycosylated
proteins found in the body).
Ions are
atoms or groups of atoms that have either, lost some
outer electrons, hence have a positive electric charge,
or have gained some outer electrons (to the atom or
group of atoms), and hence have a negative electric
charge. Even in the cases of ions formed by groups of atoms (they
are ions due to the few lost or gained electrons), the groups
are formed from only a small number of particles and therefore
tend to be relatively small.
These include:
Individual elements: |
- Sodium (Na+) : Amount
in urine varies with diet and the amount of aldosterone
(a steroid hormone)
in the body.
- Potassium (K+) : Amount
in urine varies with diet and the amount of aldosterone
(a steroid hormone)
in the body.
- Chloride (Cl-) : Amount
in urine varies with dietart intake (chloride is a part
of common salt, NaCl).
- Magnesium (Mg2+) : Amount
in urine varies with diet and the amount of parathyroid
hormone in the body. (Parathyroid
hormone increases the reabsorption of magnesium by the
body, which therefore decreases the quantity of magnesium
in urine.)
- Calcium (Ca2+) : Amount
in urine varies with diet and the amount of parathyroid
hormone in the body. (Parathyroid hormone increases
the reabsorption of calcium by the body, which
therefore decreases the quantity of calcium in
urine.)
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Small groups formed from a few different elements: |
- Ammonium (NH4+)
: The amount of ammonia produced by the kidneys may vary
according to the pH of the blood and tissues in the body.
- Sulphates (SO42-)
: Sulphates are derived from amino
acids. The quantity of sulphates excreted in urine
varies according to the quantity and type of protein
in the person's diet.
- Phosphates (H2PO4-,
HPO42-, PO43-)
: Amount
in urine varies with the amount of parathyroid
hormone in the body - parathyroid hormone increases
the quantity of phosphates in urine.
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Note: This page is about the normal characteristics
and constituents of urine. Abnormal components of urine are
another topic.
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Quick Summary: The
Properties and Composition of normal human urine
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- Recognition and analysis of abnormalities of urine
can provide information about the
condition of the body.
Biochemical analysis of
urine is called "urinalysis",
and is commonly used to diagnose a wide range of diseases
- Typical volume of urine: 1-2
litres / 24 hours per day (normal adult).
Variations due to : recent fluid intake, diet, temperature,
blood
pressure,
general health, mental state.
- Physical characteristics include: volume, colour, smell,
acidity, density.
- Constituents of urine include: approx. 95% water, approx.
5% other solutes (incl. organic molecules such as urea,
creatinine and uric acid, and ions derived from amino acids,
hormones, and other biochemicals).
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