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Local hormones are a large group of signaling molecules (communicate amongst each other), a metabolic product that communicates with others to send signals throughout the body for functioning and do not circulate within the blood. Local hormones are produced by nerve and gland cells and bind to either neighboring cells or the same type of cell that produced them. Local hormones 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 local hormone). There are about fifty known local hormones. Factors within the body that local hormones can impact include muscle growth, heart rate, menstrual cycles, and hunger.

Eicosanoids (ī′kō-să-noydz; eicosa = twenty, eidos = formed) are a primary type of local hormone. These local hormones 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 local hormone 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 local hormones that act on neighboring cells. This type of signaling involves the secretion of paracrine factors, which travel a short distance in the extracellular environment (institial fluid, fluid between the cells) 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 (FGF), the Hedgehog family, the Wnt family, and the TGF-β superfamily.

Autocrines (auto- = self) are local hormones that act on the same cell that secreted them. Furthermore, they direct processes/secretions on the same cells from which they were released originally.

Synaptic are more unique local hormones. This local hormone occurs between neurons and muscle cells. They allow neurons to communicate amongst each other as well as with muscle cells.

Juxtacrines (juxta = near) are local hormones that require close contact and act on either the cell which emitted them, adjacent cells, or extracellular matrix surrounding.

Classification
According to structural and functional similarity, many local hormones fall into either the gastrin or the secretin family.

Gastrin family
The Gastrin family is a group of peptides evolutionarily similar in structure and function. Commonly synthesized in antroduodenal G-cells. Regulate gastric function along with gastric acid secretion and mucosal growth. The gastrin family serves as regulators in the diigestive processes. The gastrin family is also known as the gastrin and cholecystokinin family (CCK). These hormones can be found throughout the nervous system.


 * 1) Gastrin
 * 2) Cholecystokinin (CCK)

Secretin family
The Secretin family is also referred to as the pituitary adenylate cyclase-activating peptide (PACAP) family. The Secretin family are peptides that act as local hormones which regulate activity of G-protein coupled receptors. Most often found in the pancreas and the intestines. Secretin was discovered in 1902 by E. H. Starling. It was later linked to chemical regulation and was the first substance to be deemed a hormone.


 * 1) Secretin
 * 2) Glucagon
 * 3) Glicentin (GLI)
 * 4) Vasoactive intestinal peptide (VIP)
 * 5) Gastric inhibitory polypeptide (GIP)