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 develop from white blood cells called monocytes. Monocytes are the largest type of white blood cell. They have a large, single nucleus that is often kidney-shaped. Monocytes are produced in bone marrow and circulate in the blood anywhere from one to three days.acrophage Phagocytosis. Phagocytosis allows macrophages to get rid of harmful or unwanted substances in the body. Phagocytosis is a form of endocytosis in which matter is engulfed and destroyed by a cell. This process is initiated when a macrophage is drawn to a foreign substance by the presence of antibodies.