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 The macrophage is one of the most important cells of the immune system. For many years it has been known as the main phagocyte of the immune system. Macrophages eat and destroy pathogens, such as bacteria, viruses and fungi, thus they are a critical part of the body's defense against microorganisms.acrophages are produced in the bone marrow, where red blood cells, platelets and granulocytes are made. In the bone marrow, macrophage precursor cells are called promonocytes. Promonocytes eventually mature and migrate into the blood, where they are called monocytes. Monocytes are only found in the blood.