What is the primary effect of histamine?

A. An increased pulse is a later symptom of dehydration, as the body attempts to maintain blood pressure and circulation when fluid levels are low.

B. Poor skin turgor is a sign of more advanced dehydration and is usually detected when skin remains tented after being pinched.

C. Decreased urinary output typically occurs as dehydration progresses and the body conserves water, but it is not usually the first sign.

D. Thirst is one of the earliest and most common symptoms of dehydration, as the body signals the need for water intake to restore fluid balance. This is the correct answer.

A. Natural passive immunity occurs when antibodies are passed from mother to child, either during pregnancy or through breast milk. This is not related to having the disease.

B. Artificial passive immunity is the transfer of antibodies from an external source, such as through antibody-containing blood products, to provide immediate protection against a disease.

C. Natural active immunity is acquired when an individual is exposed to a pathogen and the immune system responds by producing antibodies and memory cells. This type of immunity occurs after contracting the disease.

D. Artificial active immunity is gained through vaccination, where a person is exposed to a harmless form of the pathogen (such as inactivated or attenuated form), prompting the immune system to create a defense without causing illness.