What is defined as the process of substances passing through a surface of the body into body fluids and tissues?

The process referred to in the question, where substances pass through a surface of the body into body fluids and tissues, is known as absorption. Absorption specifically describes the movement of nutrients, medications, or other substances from the environment, through the skin or mucosal surfaces, and into the bloodstream or lymphatic system, where they can be delivered to various tissues in the body.

In a healthcare context, understanding absorption is crucial for nursing assistants and other healthcare professionals. For instance, when a patient takes medication, the efficacy of that medication will significantly depend on how well it is absorbed into the body. Factors such as the form of the medication, the patient's age, metabolic rate, and even concurrent food intake can affect absorption rates.

The other options have distinct definitions: ingestion refers to the process of taking substances into the body, typically through the mouth; filtration involves separating substances based on size; and diffusion describes the movement of particles from an area of higher concentration to one of lower concentration, which is a different mechanism than absorption. Thus, absorption is the appropriate term that encapsulates the movement of substances through bodily surfaces into fluids and tissues.