_________ constitutes about 80% of circulating antibodies in plasma.
IgG
IgD
IgM
IgE
IgA
The Correct Answer is A
A. IgG: IgG is the most abundant immunoglobulin in plasma, making up approximately 70–80% of circulating antibodies. It provides long-term immunity following infection or vaccination, can cross the placenta to confer passive immunity to the fetus, and is highly effective in opsonization and complement activation.
B. IgD: IgD is present in very low concentrations in the blood and mainly functions as a receptor on immature B cells. It does not constitute a significant portion of circulating antibodies.
C. IgM: IgM is the first antibody produced in an initial immune response and is primarily found in the bloodstream. While important for early defense, it only represents a small fraction of total plasma antibodies compared to IgG.
D. IgE: IgE is involved in allergic responses and defense against parasitic infections, but its plasma concentration is extremely low, making up a negligible portion of circulating antibodies.
E. IgA: IgA is mainly found in mucosal secretions, breast milk, and tears, providing local immunity rather than constituting the majority of plasma antibodies. Its systemic levels are much lower than IgG.
Nursing Test Bank
Naxlex Comprehensive Predictor Exams
Related Questions
Correct Answer is C
Explanation
A. Their secretions may be released onto the body surface:This describes exocrine glands, such as sweat or sebaceous glands, which secrete substances through ducts onto epithelial surfaces. Endocrine glands do not release secretions onto body surfaces.
B. They secrete substances that do not alter the metabolism of their target cells, but have extracellular effects:Endocrine glands secrete hormones that specifically act on target cells to alter their metabolism or function. Substances with only extracellular effects without influencing metabolism are not characteristic of endocrine function.
C. They release their secretions into the blood:Endocrine glands secrete hormones directly into the bloodstream. This allows the hormones to travel throughout the body and act on distant target cells, which is the defining feature of endocrine glands.
D. They secrete their products by way of ducts:Secretion via ducts is a hallmark of exocrine glands, not endocrine glands. Endocrine glands are ductless and rely on the circulatory system to transport their secretions.
E. They have an unusually low density of blood capillaries:Endocrine glands are highly vascularized to facilitate rapid hormone transport into the blood. A low density of capillaries would impede hormone distribution, which is contrary to endocrine physiology.
Correct Answer is A
Explanation
The liver plays a central role in iron metabolism by storing excess iron in the protein ferritin. Ferritin safely binds iron, preventing it from catalyzing harmful free radical reactions, and releases it when the body needs it for processes such as hemoglobin synthesis. This storage mechanism helps maintain iron homeostasis and prevents iron deficiency or overload.
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