Paracrine in the context of "Cellular communication (biology)"

Prostaglandins (PG) are a group of physiologically active lipid compounds that have diverse hormone-like effects in animals. They are a subclass of eicosanoids and of the prostanoid class of fatty acid derivatives. Prostaglandins have been found in almost every tissue in humans and other animals. They are derived enzymatically from the fatty acid arachidonic acid. Every prostaglandin contains 20 carbon atoms, including a 5-carbon ring.

The structural differences between prostaglandins account for their different biological activities. A given prostaglandin may have different and even opposite effects in different tissues in some cases. The ability of the same prostaglandin to stimulate a reaction in one tissue and inhibit the same reaction in another tissue is determined by the type of receptor to which the prostaglandin binds. They act as autocrine or paracrine factors with their target cells present in the immediate vicinity of the site of their secretion. Prostaglandins differ from endocrine hormones in that they are not produced at a specific site but in many places throughout the human body.

A neurohormone is any hormone produced and released by neuroendocrine cells (also called neurosecretory cells) into the blood. By definition of being hormones, they are secreted into the circulation for systemic effect, but they can also have a role of neurotransmitter or other roles such as autocrine (self) or paracrine (local) messenger.

The hypothalamus releasing hormones are neurohypophysial hormones in specialized hypothalamic neurons which extend to the median eminence and posterior pituitary. The adrenal medulla produces adrenomedullary hormones in chromaffin cells, cells which are very similar in structure to post-synaptic sympathetic neurons, even though they are not neurons they are derivatives of the neural crest.

A myokine is one of several hundred cytokines or other small proteins (~5–20 kDa) and proteoglycan peptides that are produced and released by skeletal muscle cells (muscle fibers) in response to muscular contractions. They have autocrine, paracrine and/or endocrine effects; their systemic effects occur at picomolar concentrations.

Receptors for myokines are found on muscle, fat, liver, pancreas, bone, heart, immune, and brain cells. The location of these receptors reflects the fact that myokines have multiple functions. Foremost, they are involved in exercise-associated metabolic changes, as well as in the metabolic changes following training adaptation. They also participate in tissue regeneration and repair, maintenance of healthy bodily functioning, immunomodulation; and cell signaling, expression and differentiation.