American Society for Clinical Pathology (ASCP) Histotechnician Certification Practice Exam

What is the principal component of plasma?

1. Protein

2. Water

3. Fats

4. Glucose

The correct answer is: Water

Water is the principal component of plasma, constituting approximately 90-92% of its volume. Plasma serves as the liquid matrix in which various blood components, such as red blood cells, white blood cells, platelets, proteins, electrolytes, nutrients, hormones, and waste products, are suspended. The high water content in plasma is essential for maintaining blood volume and pressure, facilitating the transport of nutrients and waste, and ensuring proper physiological function. While proteins play a significant role in plasma, including important functions such as coagulation and immune response, they make up a smaller percentage compared to the water content. Fats and glucose are also present in plasma but are not the primary constituents; fats are usually carried as lipoproteins and glucose is a metabolic product. The predominance of water in plasma highlights its critical role in maintaining homeostasis and supporting the various functions of the circulatory system.