The correct answer is A. a protein substance found in the blood of some people.
The Rh factor is a protein found on the surface of red blood cells. It is named after the rhesus monkey, in which it was first discovered. About 85% of people have the Rh factor, and are said to be Rh-positive. The remaining 15% do not have the Rh factor, and are said to be Rh-negative.
The Rh factor is important in blood transfusions. If an Rh-negative person receives Rh-positive blood, their body may produce antibodies against the Rh factor. This can lead to a serious condition called hemolytic disease of the newborn, if the mother is Rh-negative and the baby is Rh-positive.
The Rh factor is also important in pregnancy. If an Rh-negative woman is pregnant with an Rh-positive baby, there is a risk that the baby’s blood cells will cross the placenta and enter the mother’s bloodstream. This can cause the mother to produce antibodies against the Rh factor. If this happens, the mother’s antibodies can attack the baby’s blood cells, which can lead to serious problems for the baby.
To prevent this, Rh-negative women who are pregnant with Rh-positive babies are given an injection of RhoGAM (anti-D immunoglobulin) during pregnancy and after delivery. RhoGAM helps to prevent the mother’s body from producing antibodies against the Rh factor.
Options B, C, and D are incorrect.
Option B is incorrect because a hormone is a chemical substance produced by an endocrine gland that travels in the bloodstream to another part of the body, where it affects a specific cell or organ. The Rh factor is not a hormone.
Option C is incorrect because the ratio of red corpuscles to white corpuscles in the blood is called the hematocrit. The Rh factor is not the hematocrit.
Option D is incorrect because a process that speeds up the clotting of blood is called coagulation. The Rh factor is not coagulation.