Thank you for allowing me to answer your interesting question.
As an example, on average a normal, healthy individual who donates a
unit of blood (about 450 ml or ¾ pint) will fully recuperate from the
blood loss in four to six weeks.
The issue is a bit more complicated than that though. You see, our
blood is made up of a variety of things:
Red blood cells that carry oxygen from the lungs to all other tissues in the body.
White blood cells that provide the body's defenses against disease.
Platelets, specialized cells that plug damaged blood vessel walls and
join other elements in the blood in the production of clots to stop
Plasma, a yellow fluid made up of about 92% water and 7% vital
proteins such as albumin, gamma globulin, and antihemophilic and other
And other elements consisting of mineral salts, sugar, fats, hormones,
Red blood cells, white blood cells, and platelets account for about
45% of the volume of blood in the body. The remaining 55% is plasma
including the other extraneous elements I mentioned. The four to
six-week period I indicated a moment ago is the time necessary to
replace ALL these factors, though our bodies actually replace some of
the individual components faster than others. For example, the fluid
(mostly water) lost in a blood donation, is replaced in only a few
hours, provided the donor drinks a moderate amount of water or
healthy, non-alcoholic liquids to replenish the loss. The other
components of the blood, such as platelets and red cells begin to
replenish immediately but take a bit longer to complete; usually
within a few days or weeks depending on how much blood is lost.
Generally speaking, after donating a unit of blood, the body replaces
the fluid and white cells within 24 hours, and platelets and plasma
proteins within 48-72 hours. The red blood cells are completely
replaced in 4-6 weeks.
It would be safe then to say that a blood ?sample? (rather that a
whole unit) or a small amount of loss due to a very minor scrape or
bleed could conceivably be fully replaced in a healthy individual
within hours. How fast the entire blood loss is replenished obviously
depends on the amount of blood lost, the size of the individual (for
every 12-15 pounds of body weight, a human being has about one pint of
blood) and the health of the individual from whom the blood is
removed. If the body is functioning normally and there are no
extenuating circumstances (interfering medication, unhealthy lifestyle
or diet, etc) age alone should have little or no impact on the natural
replacement of blood. A poor diet or sedentary lifestyle can however
have an impact on how fast the body replaces blood because of the
necessary nutrients in a proper diet that enable the cell replacement.
Lack of exercise, for example, can lead to obesity (and ultimately the
need for more blood than normal) and can certainly cause
arteriosclerosis or other venous constrictions than can complicate
blood flow, adding to difficultly or delayed replacement. This of
course is just one hypothetical situation, but there are others.
Replacement is also relative to size and exercise (or lack thereof) If
a pint of blood is a significant portion of a person?s entire blood
volume (as in a newborn for example) it will take longer for the body
to replace half the blood volume. In a 500lb man, a pint of blood is
not that much in terms of overall blood volume, BUT his body may have
a difficult time replacing that pint in the normal range of
expectations because of his morbid obesity and other health factors.
So you can easily see how diet and excercise can affect blood
As a rule though, if you are relatively healthy, eat right more often
than not, and even moderately exercise you can expect a fairly
predictable and complete replacement of a non-life threatening blood
loss within the time frame I specified regardless of your age.
I hope you find that my research exceeds your expectations. If you
have any questions about my research please post a clarification
request prior to rating the answer. Otherwise I welcome your rating
and your final comments and I look forward to working with you again
in the near future. Thank you for bringing your question to us.
Tutuzdad-ga ? Google Answers Researcher
BLOOD DONATION Q&A
AMERICAN RED CROSS
WIKIPEDIA: BLOOD TRANSFUSION
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