Which of the following is a normal skin change associated with aging?

A. While phagocytes move to areas of infection or damage, their primary role is not clumping together and adhering to tissues but rather engulfing and digesting foreign particles.

B. Phagocytes, such as neutrophils and macrophages, are white blood cells that ingest and digest foreign pathogens, dead cells, and debris in damaged tissues. This is their primary function in the immune response.

C. Releasing histamine is the function of mast cells, not phagocytes. Histamine is involved in initiating inflammation, but phagocytes are focused on clearing pathogens and debris.

D. Transporting oxygen is the function of red blood cells, not phagocytes. Phagocytes are involved in immune defense, not in the transport of oxygen.

A. GABA (gamma-aminobutyric acid) is an inhibitory neurotransmitter in the central nervous system, meaning it generally reduces neuronal excitability and does not play a role in excitatory neuromuscular transmission.
B. Glycine is also an inhibitory neurotransmitter, mainly in the spinal cord, and works to prevent over-excitation of neurons, not directly involved in neuromuscular transmission.
C. Acetylcholine is the primary neurotransmitter responsible for neuromuscular transmission. It binds to receptors on muscle cells, causing depolarization and triggering muscle contraction, thus playing an excitatory role.
D. Serotonin primarily functions in the brain to regulate mood, appetite, and sleep but does not play a direct role in neuromuscular transmission.