Sistema Endocrino

* The nervous and endocrine systems act as a coordinated interlocking supersystem, the neuroendocrine system.
* The endocrine system controls body activities by releasing mediator molecules called hormones.
* hormones released into the bloodstream travel throughout the body
* results may take hours, but last longer
* The nervous system controls body actions through nerveimpulses.
* certain parts release hormones into blood
* rest releases neurotransmitters excite or inhibit nerve, muscle & gland cells
* results in milliseconds, brief duration of effects
* The nervous system causes muscles to contract or glands to secrete. The endocrine system affects virtually all body tissues by altering metabolism, regulating growth and development,and influencing reproductive processes.
* Parts of the nervous system stimulate or inhibit the release of hormones.
* Hormones may promote or inhibit the generation of nerve impulses.
* Help regulate:
* extracellular fluid
* metabolism
* biological clock
* contraction of cardiac & smooth muscle
* glandular secretion
* some immune functions* Growth & development
* Reproduction
* Hormones have powerful effects when present in very low concentrations.
* Exocrine glands
* secrete products into ducts which empty into body cavities or body surface
* sweat, oil, mucous, & digestive glands
* Endocrine glands
* secrete products (hormones) into bloodstream
* pituitary, thyroid,parathyroid, adrenal, pineal
* other organs secrete hormones as a 2nd function
* hypothalamus, thymus, pancreas,ovaries,testes, kidneys, stomach, liver, small intestine, skin, heart & placenta
* Hormones only affect target cells with specific membrane proteins called receptors
* Although hormones travel in blood throughout the body, they affect only specific target cells.* Target cells have specific protein or glycoprotein receptors to which hormones bind.
* Receptors are constantly being synthesized and broken down.
* Synthetic hormones that block the receptors for particular naturally occurring hormones are available as drugs. (Clinical Application)
* Receptors are constantly being synthesized & broken down
* range of 2000-100,000receptors / target cell
* Down-regulation
* excess hormone leads to a decrease in number of receptors
* receptors undergo endocytosis and are degraded
* decreases sensitivity of target cell to hormone
* Up-regulation
* deficiency of hormone leads to an increase in the number of receptors
* target tissue becomes more sensitive to the hormone
* Synthetic drugs may blockreceptors for naturally occurring hormones
* Normally, progesterone levels drop once/month leading to menstruation. Progesterone levels are maintained when a woman becomes pregnant.
* RU486 (mifepristone) binds to the receptors for progesterone preventing progesterone from sustaining the endometrium in a pregnant woman
* brings on menstrual cycle
* used to induce abortion
*Hormones that travel in blood and act on distant target cells are called circulating hormones or endocrines.
* Hormones that act locally without first entering the blood stream are called local hormones.
* Those that act on neighboring cells are called paracrines.
* Those that act on the same cell that secreted them are termed autocrines.
* Lipid-soluble hormones include thesteroids, thyroid hormones, and nitric oxide, which acts as a local hormone in several tissues.
* Water-soluble hormones include the amines; peptides, proteins, and glycoproteins; and eicosanoids.
* Protein hormones circulate in free form in blood
* Steroid (lipid) & thyroid hormones must attach to transport proteins synthesized by liver
* improve transport by making them...