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 not the only types of cells that function through phagocytosis. There are other important swallowing cells that make up the immune system, such as cells called granulocytes, neutrophils and dendritic cells.acrophages. The macrophage is a vital type of white blood cell. A macrophage is a kind of swallowing cell, which means it functions by literally swallowing up other particles or smaller cells.