______ are secreted by cells infected with viruses, alerting neighboring cells and protecting them from becoming infected.

A. Digestion: This physiological process involves both mechanical mastication and chemical hydrolysis to convert complex food into absorbable molecules. It begins in the oral cavity and continues through the stomach and small intestine. It is the specific term for the multi-modal breakdown of nutritional matter.

B. Ingestion: This term refers specifically to the act of taking food or liquid into the body via the oral cavity. It is the entry phase of the nutritional process rather than the breakdown mechanism itself. Digestion follows ingestion but represents a distinct set of biochemical and physical actions.

C. Compaction: This process occurs primarily in the large intestine where water is absorbed from indigestible residue. It converts liquid chyme into consolidated feces for eventual excretion. It involves the dehydration of waste products rather than the constructive breakdown of food for nutrient extraction.

D. Absorption: This stage involves the movement of digested nutrients from the lumen of the gastrointestinal tract into the blood or lymph. It occurs after the mechanical and chemical breakdown of food is largely complete. It describes the uptake of molecules, not the process of breaking them down.

E. Extraction: In a biological context, this word is often used generally for the removal of specific substances from a mixture. It is not the standard clinical term used to describe the integrated digestive functions of the alimentary canal. It lacks the specificity required to describe human gastrointestinal physiology.

A. Trachea: The trachea, or windpipe, marks the beginning of the lower respiratory tract. It is located inferior to the larynx and serves as the conduit to the primary bronchi. Including the trachea within the upper respiratory tract contradicts standard clinical and anatomical classification systems.

B. Pharynx: The pharynx is a muscular funnel that connects the nasal cavity to the larynx. While it is a critical component of the upper respiratory system, the tract extends further down to include the vocal apparatus. Classification ends at the transition point between the larynx and the trachea.

C. Larynx: The upper respiratory tract encompasses the nasal cavity, pharynx, and the larynx. The larynx serves as the anatomical boundary before the air enters the tracheobronchial tree. Structures located from the trachea downwards are categorized as the lower respiratory tract in medical anatomy.

D. Alveoli: Alveoli are the microscopic sites of gas exchange located at the terminal ends of the bronchial tree. They are the deepest structures within the lower respiratory tract. Defining them as part of the upper respiratory system ignores the vast anatomical distance from the nose.

E. Lungs: The lungs are the primary organs of the lower respiratory system, containing the bronchi, bronchioles, and alveolar sacs. They are situated within the thoracic cavity, protected by the rib cage. The upper respiratory tract is limited to the structures superior to the thoracic inlet.