In physiology, a stimulus (plural stimuli) is a detectable change in the internal or external environment. The ability of an organism or organ to respond to external stimuli is called sensitivity.When a stimulus is applied to a sensory receptor, it normally elicits or influences a reflex via stimulus transduction.he endocrine system is affected largely by many internal and external stimuli. One internal stimulus that causes hormone release is blood pressure. Hypotension, or low blood pressure, is a large driving force for the release of vasopressin, a hormone which causes the retention of water in the kidneys.
Macrophages can be activated by cytokines such as interferon-gamma (IFN-gamma) and bacterial endotoxins, such as lipopolysaccharide (LPS). Activated macrophages undergo many changes which allow them to kill invading bacteria or infected cells.
Macrophages are a type of white blood cell which eat foreign material in the body. These cells are involved in the primary or innate immune response to a number of immune invaders, and they also make up an important part of the body's acquired immune system.acrophages help clean up bacteria and viruses in the body. Macrophages can be co-opted by HIV cells and aid the spread of the virus. A monocyte is the first stage of life for a macrophage. Macrophages are a type of white blood cell that eats foreign material in the body.