presence or absence of Rh factor in red blood cells
people determines their belonging to the Rh-positive
(Rh +) or Rhesus negative (Rh-) group.
found that 86% of people caucasian (white)
races have Rh-positive (99% Indians and Asians),
and 14% - rhesus negative factor (7% of Africans).
Rhesus affiliation does not change during the life
rights.
"Rh-positive" blood properties due to
the influence of a dominant gene, and "Rhesus negative" - a recessive
gene.
Blood "Rh positive" and "Rh negative"
people is not compatible. Since when released into the blood, "Rh negative"
individual Rh factor antigen causes the formation of antibodies
(Immune response), which can lead to such a severe state of
as anaphylactic shock.
"Rhesus negative" patients may be transfused
only "Rh negative" blood, "Rh-positive -
as "Rh positive" and "Rh negative".
When married man with Rh-positive
factor, and women with Rh-negative factor most probably
Conception Rh-positive "fasit.
antigens of the fetus during gestation in a small
number are able to penetrate into the bloodstream through the placenta to the mother
and cause the formation of antibodies (especially if there is a pathology
child seat). At first pregnancy (and sometimes on second)
their concentration in blood is relatively low and the embryo develops,
without experiencing harmful effects of these antibodies.
picture changes dramatically in subsequent pregnancies:
concentration of antibodiesmoreandmoreincreasing, due to the small
size, they are able to freely cross the placenta into the bloodstream
fetus and damage its Rh-positive red blood cells (hemolysis)
and blood-forming organs. The result is the emergence of
hemolytic disease of the child.
At an early manifestation of the disease Rhesus-conflict
can cause premature birth or miscarriage, as well as
stillbirth. Analysis of Rh-conflict produce
usually at the eighth week of pregnancy and determine the presence of Rh antibodies
in the blood. This is especially important if in the past have abortions, miscarriages
or was a blood transfusion.
Now medicine has ways
anti-hemolytic disease in the form of rapid transfusion
infant rhesus negative blood or the introduction of anti-Rh-antibodies
to prevent the immunization of the mother.
If the Rh-negative, "a woman wants to give birth
second or third child from the "Rh-positive" men,
then she should consult with their doctor and be screened
the presence of Rh antibodies in the blood.
details physiology of blood here
something interesting
a bit further, I can inform you
that the Rh factor is only one of the many antigens
up the system Rh. Ie erythrocytes of each person
contain a complex of Rh antigens, consisting of three pairs of antigens.
Different combinations of these six antigens form 27 groups of
Rh. But in everyday medical practice, the definition of these
groups (which in itself is important for a blood transfusion donor recipient)
impossible because of extreme rarity antisera (some of
They are even hypothetical).
Therefore, amorerealistic definition of three antigens
which may be in human erythrocytes together or separately,
form 7 different combinations, which including a possible lack of
in red cells of all 3 of these antigens are 8 major groups
rhesus system.
And more. With regard to natural selection during
evolution. Now, scientists believe that the death of newborn
as a result of hemolytic disease (if no medical
assistance) is a form of natural selection (performing
stabilization fund and the maintenance of genetic inheritance
diversity).
Thus y "Rh negative" mother "of a Rhesus positive"
fasit is always the heterozygote, ie, has both recessive (Rh-)
and dominant (Rh +) allele. This means that with the death
such person is removed from the gene pool of population equal to the number of
locus "Rh."
selection in this case is directed against heterozygotes.
And asmoredominant genes than recessive in a population
that such selection gradually leads to a decrease in the share of the rarer
(Rh-). It is estimated that the decline in its share from 14% (Europeans) to
1% by selection against heterozygotes would require 600 generations,
or about 15000 years.