botanist pfeffer discovered that all organisms are made of cells.
who discovered that all organisms are made of cells?
botanist pfeffer
in biology, cell theory is the historic scientific theory, now universally accepted, that living organisms are made up of cells, that they are the basic structural/organizational unit of all organisms, and that all cells come from pre-existing cells. cells are the basic unit of structure in all organisms and also the basic unit of reproduction. with continual improvements made to microscopes over time, magnification technology advanced enough to discover cells in the 17th century. this discovery is largely attributed to robert hooke, and began the scientific study of cells, also known as cell biology. over a century later, many debates about cells began amongst scientists. most of these debates involved the nature of cellular regeneration, and the idea of cells as a fundamental unit of life. cell theory was eventually formulated in 1839. this is usually credited to matthias schleiden and theodor schwann. however, many other scientists like rudolf virchow contributed to the theory. it was an important step in the movement away from spontaneous generation.
cell theory
through most of its early period of study, acute inflammatory responses were regarded as self-limiting innate immune system reactions to invading foreign organisms, tissue injuries, and other insults. these reactions were orchestrated by various soluble signaling agents such as a) foreign organism-derived n-formylated oligopeptide chemotactic factors (e.g. n-formylmethionine-leucyl-phenylalanine); b) complement components c5a and c3a which are chemotactic factors formed during the activation of the host's blood complement system by invading organisms or injured tissues; and c) host cell-derived pro-inflammatory cytokines (e.g. interleukin 1s), host-derived pro-inflammatory chemokines (e.g. cxcl8, ccl2, ccl3, ccl4, ccl5, ccl11, cxcl10), platelet-activating factor, and pufa metabolites including in particular leukotrienes (e.g. ltb4), hydroxyeicosatetraenoic acids (e.g., 5-hete, 12-hete), the hydroxylated heptadecatreineoic acid, 12-hht, and oxoeicosanoids (e.g. 5-oxo-ete). these agents functioned as pro-inflammatory signals by increasing the permeability of local blood vessels; activating tissue-bound pro-inflammatory cells such as mast cells, and macrophages; and attracting to nascent inflammatory sites and activating circulating neutrophils, monocytes, eosinophils, gamma delta t cells, and natural killer t cells. the cited cells then proceeded to neutralize invading organisms, limit tissue injury, and initiate tissue repair. hence, the classic inflammatory response was viewed as fully regulated by the soluble signaling agents. that is, the agents formed, orchestrated an inflammatory cell response, but then dissipated to allow resolution of the response. in 1974, however, charles n. serhan and his renowned colleagues, mats hamberg and bengt samuelsson, discovered that human neutrophils metabolize arachidonic acid to two novel products that contain 3 hydroxyl residues and 4 double bonds viz., 5,6,15-trihydroxy-7,9,11,13-icosatetraenoic acid and 5,14,15-trihydroxy-6,8,10,12-icosatetraenoic acid. these products are now termed lipoxin a4 and b4, respectively. while initially found to have in vitro activity suggesting that they might act as pro-inflammatory agents, serhan and colleagues and other groups found that the lipoxins as well as a large number of newly discovered metabolites of other pufa possess primarily if not exclusively anti-inflammatory activities and therefore may be crucial for causing the resolution of inflammation. in this view, inflammatory responses are not self-limiting but rather limited by the formation of a particular group of pufa metabolites that counteract the actions of pro-inflammatory signals. later, these pufa metabolites were classified together and termed specialized pro-resolving mediators (i.e. spm).
specialized pro-resolving mediators