How many mEq of potassium chloride are in a 100 mL solution containing 0.5 g of KCl (molecular weights: K = 39; Cl = 35.5)? Round the final answer to the nearest whole number.

Step 1 is to express the percentage concentration as a decimal or ratio

0.005% = 0.005 ÷ 100

Result at this step = 0.00005

Step 2 is to calculate the weight of the active ingredient in grams

Weight (g) = Total weight × Concentration

60 × 0.00005 = 0.003

Result at this step = 0.003 g

Step 3 is to convert grams (g) to milligrams (mg)

mg = 0.003 × 1000

0.003 × 1000 = 3

Result at this step = 3

Step 4 is to round to the nearest whole number

3 = 3

Answer: 3

Cholesterol is an essential sterol synthesized by animal cells to maintain membrane fluidity and serve as a chemical backbone. It is vital for producing steroid hormones and fat-soluble substances. While transported in lipoproteins, it does not function as a fuel source for ATP production. Synthesis primarily occurs via the mevalonate pathway in hepatocytes and enterocytes.

Rationale:

A. Cholesterol serves as the fundamental substrate for the synthesis of bile acids in the liver. These acids are essential for the emulsification and absorption of dietary fats and fat-soluble vitamins within the small intestine. This is a primary metabolic pathway for cholesterol elimination from the human body.

B. Cholesterol is not a storage molecule for lipids; that role is reserved for triacylglycerols. Triacylglycerols are stored in adipose tissue to be hydrolyzed for energy. Cholesterol is a functional and structural molecule and cannot be catabolized by the body to provide caloric energy or fuel.

C. Cholesterol is a critical structural component of eukaryotic cell membranes. It intercalates between phospholipids to modulate membrane permeability and provide mechanical stability across various temperatures. Without cholesterol, cell membranes would be too fluid or too brittle to maintain cellular integrity and proper signaling.

D. Cholesterol acts as the chemical precursor to vitamin D (cholecalciferol). Specifically, 7-dehydrocholesterol in the skin undergoes a photochemical reaction upon exposure to ultraviolet B radiation. This process is the first step in synthesizing the active hormone calcitriol, which is necessary for calcium homeostasis.

E. The human body obtains cholesterol through diet, but the majority is primarily synthesized endogenously. The liver is the central organ for this de novo synthesis, producing approximately 1 gram per day. This ensure a constant supply for hormone synthesis and bile production regardless of dietary intake levels.