How does histamine affect blood
vessels near an injured area? (A) It dilates blood vessels and
decreases capillary permeability. (B) It dilates blood vessels and
increases capillary permeability. (C) It dilates blood vessels but
does not affect capillary permeability. (D) It constricts blood vessels but
does not affect capillary permeability. Or (E) it constricts blood vessels
and increases capillary permeability.
When we injure ourselves, the
affected area quickly becomes red, swollen, painful, and hot. Although this is pretty unpleasant
for us, it’s actually a sign that the body is reacting to the injury and beginning
to repair itself. It does this through a nonspecific
immune response known as inflammation.
Inflammation, which is sometimes
called the inflammatory response, is initiated by a special type of white blood cell
called a mast cell. Mast cells detect injury or
infection and respond by releasing a chemical called histamine. This is what the question is asking
us about. Histamine has two important effects
on the blood vessels near the site of injury. The first is that it causes them to
dilate, allowing more blood to flow to the injured area. This is known as vasodilation, and
it’s what causes the redness and heat. As answer options (D) and (E) say
the blood vessels constrict, which means that they become narrower, these options
must be incorrect.
The second effect of histamine is
that it increases the permeability of capillaries near the site of injury. This allows more fluid to enter the
injured area from the blood, bringing with it specialized white blood cells, such as
phagocytes, which can help to clear any infection. This is what causes the
swelling. We have therefore determined how
histamine affects blood vessels near an injured area. The correct answer is (B). It dilates blood vessels and
increases capillary permeability.