<unk> s are a large group of signaling molecules that do not circulate within the blood.<unk> s are produced by nerve and gland cells and bind to either neighboring cells or the same type of cell that produced them.<unk> s are activated and inactivated quickly. They are released during physical work and exercise. They mainly control smooth and vascular muscle dilation. Strength of response is dependent upon the concentration of receptors of target cell and the amount of ligand ( the specific<unk> . Eicosanoids (ī′kō-să-noydz; eicosa = twenty, eidos = formed) are a primary type of<unk> . These<unk> s are formed by a chain of 20 amino acids and fatty acids from phospholipids in the cell membrane. Eicosanoids initiate either autocrine stimulation or paracrine stimulation. There are two main types of eicosanoids: prostaglandins and leukotrienes, which initiate either autocrine stimulation or paracrine stimulation. Eicosanoids are the result of a ubiquitous pathway which first produces arachidonic acid, and then the eicosanoid product. Prostaglandins are the most diverse category of eicosanoids and are thought to be synthesized in most tissues of the body. This type of<unk>  stimulates pain receptors and increases the inflammatory response. Nonsteroidal anti-inflammatory drugs stop the formation of prostaglandins, thus inhibiting these responses. Leukotrienes are a type of eicosanoids that are produced in leukocytes and function in inflammatory mediation. Paracrines (para- = beside or near) are<unk> s that act on neighboring cells. This type of signaling involves the secretion of paracrine factors, which travel a short distance in the extracellular environment to affect nearby cells. These factors can be excitatory or inhibitory. There are a few families of factors that are very important in embryo development including fibroblast growth factor secreted them. Juxtacrines (juxta = near) are<unk> s that require close contact and act on either the cell which emitted them or on adjacent cells.
Local hormone
Xenohormone
Hormone
Neurohormone
Gastrointestinal hormone
Sex hormone
Prohormone
Lymphokine