Signaling endocrine

Myometrium of pregnancy is a unique example of visceral smooth muscle. Essentially quiet for the majority of gestation, a burst of rhythmic contractile activity is responsible for delivery of the human fetus. Endocrine signals originating from the fetus are likely responsible for the events that begin labour (McLean Smith 2001), but the mechanisms of intra- and intercellular signalling during the course of labour are not fully resolved. 

In endocrine signaling, a hormone moves from a gland to a distant target cell by direct secretion into the bloodstream. 

In endocrine signaling the hormone is synthesized in specific signaling, or endocrine, cells and exported via exocytosis into the extracellular medium (e.g. blood or lymphatic fluid in animals). The hormone is then distributed throughout the entire body via the circulatory system so that remote regions of an organism can be reached. 

Fig. 3.5. Endocrine, paracrine and autocrine signal transduction, a) endocrine signal transduction the hormone is formed in the specialized endocrine tissue, released into the extracellular medium and transported via the circulatory system to the target cells, b) paracrine signal transduction the hormone reaches the target cell, which is found in close juxtaposition to the hormone producing cell, via diffusion, c) autocrine signal transduction the hormone acts on the same ceU type as the one in which it is produced.

Figure 17.2 The hypothalamic-pituitary-gonadal axis. Endocrine signaling cascades provide multiple sites for regulation and ensure optimum signaling.

Figure 17.5 Endocrine signaling pathway involving steroid hormone, sex hormone binding globulin (SHBG), and the SHBG receptor.

Walker C, Amed SA, Brown T, Ho SM, Hodges L, Lucier G, Russo J, Weigel N, Weise T, Vandenbergh J (1999) Species, interindividual, and tissue specificity in endocrine signaling. Environ Health Perspect, 107(Suppl 4) 619-624. 

In endocrine signaling, the signaling molecules, called hormones, act on target cells distant from their site of synthesis by cells of the various endocrine organs. In animals, an endocrine hormone usually is carried by the blood or by other extracellular fluids from its site of release to Its target. 

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