arachidonic acid pathway

(noun)

The pathway by which the fever regulator prostaglandin E-2 and several inflammatory mediators are produced by pyrogen activity with phospolipids and COX-2, usually in the brain or liver.

Related Terms

Examples of arachidonic acid pathway in the following topics:

  • Fever

    • PGE2 release comes from the arachidonic acid pathway, which also produces inflammatory mediators such as thromboxane and leukotriene.
    • This pathway is mediated by the enzymes phospholipase A2 (PLA2), cyclooxygenase-2 (COX-2), and prostaglandin E2 synthase.
    • Exogenous factors s lipopolysaccharide toxin (from gram negative bacteria) which can activate a number of innate immune activation pathways.
    • These pathways induce the expression of endogenous pyrogens, including a variety of cytokines such as IL1α, IL1β, IL6, TNFα, TNFβ, IFNα, INFβ, and INFγ.
    • When TNFα or any of these cytokine factors bind to cells in phospolipids in the brain, the arachidonic acid pathway is activated and PGE2 released to act on the hypothalamus and cause the fever response.

  • Eicosanoids

    • In biochemistry, eicosanoids are signaling molecules made by oxidation of 20-carbon essential fatty acids (EFAs).
    • An excess of ω-6 to ω-3 fatty acids is common in western diets and is thought to encourage certain inflammatory disorders such as arthritis, cardiovascular disease, and cancers of the digestive system.

  • Chemistry of Hormones

    • Peptide hormones consist of short chains of amino acids, such as vasopressin, that are secreted by the pituitary gland and regulate osmotic balance; or long chains, such as insulin, that are secreted by the pancreas, which regulates glucose metabolism.
    • Lipid and phospholipid-derived hormones are produced from lipids such as linoleic acid and arachidonic acid.
    • Eicosanoids are also lipid hormones that are derived from fatty acids in the plasma membrane.
    • Monoamine hormones are derived from single aromatic amino acids like phenylalanine, tyrosine, and tryptophan.

  • Platelet Plug Formation

    • Thromboxane is an arachidonic acid derivative (similar to prostaglandins) that activates other platelets and maintains vasoconstriction.

  • Antigenic Determinants and Processing Pathways

    • A conformational epitope- is composed of discontinuous sections of the antigen's amino acid sequence.
    • A linear epitope is formed by a continuous sequence of amino acids from the antigen, which forms a "line" of sorts that builds the protein structure.
    • T cells do not recognize polysaccharide or nucleic acid antigens.
    • There are two different pathways for antigen processing:
    • The Exogenous Pathway- occurs when MHC class II molecules present fragments derived from extracellular (exogenous) proteins that are located within the cell.

  • Gastric Phase

    • The gastric phase is a period in which swallowed food and semidigested protein (peptides and amino acids) activate gastric activity.
    • ACh is secreted by parasympathetic nerve fibers of both the short and long reflex pathways.
    • All three of these stimulate parietal cells to secrete hydrochloric acid and intrinsic factor.
    • Small peptides also buffer stomach acid so the pH does not fall excessively low.
    • Below pH of two, stomach acid inhibits the parietal cells and G cells: a negative feedback loop that winds down the gastric phase as the need for pepsin and HCl declines.

  • Gastrointestinal Reflex Pathways

    • The enterogastric reflex is stimulated by the presence of acid levels in the duodenum at a pH of 3-4 or in the stomach at a pH of 1.5.
    • In turn, this inhibits gastric motility and secretion of gastric acid (HCl).

  • Chemoreceptor Regulation of Breathing

    • The action potential is sent along nerve pathways to parts of the brain, which are the integrating centers for this type of feedback.
    • Because most carbon dioxide is converted to carbonic acid (and bicarbonate) in the bloodstream, chemoreceptors are able to use blood pH as a way to measure the carbon dioxide levels of the bloodstream.
    • Without that carbon dioxide, there will be less carbonic acid in blood, so the concentration of hydrogen ions decreases and the pH of the blood rises, causing alkalosis.
    • As bicarbonate levels decrease while hydrogen ion concentrations stays the same, blood pH will decrease (as bicarbonate is a buffer) and become more acidic.
    • Conversely, vomiting removes hydrogen ions from the body (as the stomach contents are acidic), which will cause decreased ventilation to correct alkalosis.

  • Phenylketonuria (PKU)

    • PAH enzyme is necessary for the metabolism of the amino acid phenylalanine (Phe) to the amino acid tyrosine.
    • Excessive phenylalanine can be metabolized into phenylketones through the minor route, a transaminase pathway with glutamate.
    • Phenylalanine is a large, neutral amino acid (LNAA).
    • LNAAs compete for transport across the blood–brain barrier (BBB) via the large neutral amino acid transporter (LNAAT).
    • The mainstream treatment for classic PKU patients is a strict PHE-restricted diet supplemented by a medical formula containing amino acids and other nutrients.

  • The Role of the Basal Ganglia in Movement

    • In the basal ganglia, however, the great majority of neurons uses gamma-aminobutyric acid (GABA) as the neurotransmitter and have inhibitory effects on their targets.
    • The + and - signs at the point of the arrows indicate whether the pathway is excitatory or inhibitory, respectively, in effect.
    • Green arrows refer to excitatory glutamatergic pathways, red arrows refer to inhibitory GABAergic pathways and turquoise arrows refer to dopaminergic pathways that are excitatory on the direct pathway and inhibitory on the indirect pathway.