Completed Chapter 17 - Chapter 17 17.1 Overview of the...

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Chapter 17 17.1 Overview of the Endocrine System 4 Principle avenues of communication from cell-cell: 1. Gap Junctions- join smooth and cardiac muscle, epithelial and other cells to each other Allow cells to pass nutrients, electrolytes and signaling molecules directly from the cytoplasm of one cell to another via pores in plasma membrane 2. Neurotransmitters- released by neurons, diffuse across a narrow synaptic cleft and bind to receptors on the surface of the next cell 3. Paracrines (local hormones)- secreted by one cell, diffuse to nearby cells in the same tissue and stimulate their physiology 4. Hormones- chemical messengers Transported by the bloodstream and lymph Stimulate physiological response in cells of another tissue/organ (often a far distance away) Endocrine system- glands, tissues and cells that secrete hormones Endocrinology- the study of the endocrine system and the diagnosis and treatment of its disorders Endocrine glands- pituitary, thyroid, parathyroid, adrenal, and pineal Hormones are also secreted by organs and tissues-adipose cells, thymus, cells in the wall of the small intestine Endocrine/Exocrine Glands Exocrine glands- secretes products by ducts into an epithelial surface (ex. Skin) o Extracellular effects (ex. Digestion of food) Endocrine glands- ductless and release secretions into the blood stream o Intracellular effects- alter cell metabolism o Have an unusually high density of blood capillaries – pick up and carry away hormones Permeable type called fenestrated capillaries- patches of large pores in their walls allow for easy uptake of matter Some glands and secretory cells defy simple classification as endocrine or exocrine - examples: liver cells o Secrete bile into ducts (exocrine) o Secrete hormones into blood (endocrine) Nervous and Endocrine Systems Both serve for internal communication but are not redundant o They compliment each others functions The 2 systems differ in means of communication o Nervous- Both electrical and chemical o Endocrine- Solely chemical Differ in how quickly they start and stop o Nervous- responds within a few milliseconds and stops responding almost immediately 1
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Chapter 17 o Endocrine- takes several seconds to days to respond and some effects persist for several days to weeks Under long term stimulation o Most neurons quickly adapt and their response declines o Endocrine system shows more persistent responses Another difference: o Nervous- effects are precisely targeted and relatively specific o Endocrine- Hormones circulate throughout the body Some hormones – GH, epinephrine, and TH have more widespread effects than the output of an one nerve fiber Several chemicals function as both neurotransmitters and hormones o Norepinephrine, dopamine, TRH and ADH Some hormones like oxytocin and epinephrine are secreted by neuroendocrine cells- neurons that release their secretions into the bloodstream
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