Endocrine system hormone transport

The circulatory system carries out many important functions that contribute to homeostasis. It obtains oxygen from the lungs nutrients from the gastrointestinal tract and hormones from the endocrine glands and it delivers these substances to the tissues that need them. Furthermore, it removes metabolic waste products, such as carbon dioxide, lactic acid, and urea, from the tissues. Finally, it contributes to the actions of the immune system by transporting antibodies and leukocytes to areas of infection. Overall, the circulatory system plays a vital role in maintenance of optimal conditions for cell and tissue function. 

Molecular communication is the characteristic information system in the bioinformation networks. The endocrine system, which is one of intermolecular information networks, may represent the feature of molecular communication. The gland is a collection of specialized cells that synthesize, store, and release hormones. A hormone, molecular information, is released into the extracellular fluid and transported via the blood to two types of cells target cells where the hormone acts, and other cells that degrade the hormone as schematically presented in Fig.l. In some systems the target cell and the degradation site are in the same organ or even the same cell. Both activities may even be located on the same plasma membrane. The receptor for the hormone is located on the surface of the plasma membrane. 

The endocrine system is an anatomically diverse assemblage of organs, united by the common fnnetion of secreting hormones. Organs, with qnite different fnnetions, inclnding the kidney, liver and intestine, also secrete hormones and, in this sense, they too are part of the endocrine system. In a functional sense, the endocrine system also inclndes the blood which transports hormones to their target cells, tissues or organs. 

The conventional definition of the endocrine system is the collection of ductless glands that secrete small amounts of hormones directly into the blood of vertebrates. The hormones are transported to other parts of the body where they have a profound effect on biological processes. Perhaps the best examples are the sex hormones oestrogen and testosterone, but there are many others. Hormones are also produced by invertebrates (e.g. moulting hormones) and even by plants (e.g. growth hormones). 

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.

Xenobiotics can adversely affect the normal functions of the cells/organs of the reproductive system. These agents may induce a variety of outcomes, including prevention of ovulation and impairment of ovum transport, fertilization, or implantation. Endocrine disruptors may mimic endogenous hormones as well as directly destroy cellular components, leading to cell death. More indirect effects may include inhibition of key enzymes involved in steroid synthesis. 

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