Endocrine System Notes

Endocrine System Notes - THE ENDOCRINE SYSTEM: TYPES OF...

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THE ENDOCRINE SYSTEM: TYPES OF HORMONES AND THEIR ACTIONS
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FUNCTIONS OF SELECTED ENDOCRINE GLANDS Most of the target cells’ activities under hormonal control , are concerned with maintaining homeostasis: hypothalamus and posterior pituitary gland function together to release hormones essential for maintaining water balance, and for giving birth and breast feeding anterior pituitary gland secretes hormones that promote growth, and control the hormonal output of several other endocrine glands, including those regulating reproduction thyroid gland secretes hormones which control the basal metabolic rate of the body endocrine pancreas secretes hormones which regulate the metabolism of nutrient molecule parathyroid glands secrete a hormone which is important in calcium homeostasis adrenal glands secrete hormones which are important in the metabolism of nutrient molecules, adaptation to stress, and maintaining salt balance
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TYPES OF HORMONES Classified into 3 categories: peptides - comprise the majority of hormones, including those secreted by the hypothalamus, anterior and posterior pituitary, pancreas and parathyroid amines - derived from the amino acid, tyrosine, and include the hormones secreted by the thyroid gland, and adrenal medulla. (adrenomedullary hormones are catecholamines ) steroids - neutral lipids derived from cholesterol; include hormones secreted by the adrenal cortex, ovaries and testes. Steroid and thyroid hormones are lipid solube (lipophilic) Water-soluble hormones are transported dissolved in the plasma, whereas lipophilic hormones are transported largely bound to plasma proteins
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HOW HORMONES BRING ABOUT THEIR EFFECTS Hormones bind with specific target cell receptors and binding starts a chain of events within the target cell which lead to the effects characteristic of that hormone Based on the location of their receptors, hormones can be classified into 2 groups: hydrophilic peptides and catecholamines, being poorly soluble in lipid, are unable to cross the lipid bilayer and bind to specific plasma membrane receptors lipohilic steroids and thyroid hormones cross the lipid bilayer and bind to specific intracellular receptors
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SPECIFICITY OF HORMONE EFFECTS Interaction between a hormone and its target cell receptor produces a characteristic response in the target cell, which is different for different hormones, and differs between different target cells responding to the same hormone; eg. an adrenal medullary catecholamine, epinephrine, can produce the following effects – contraction of vascular smooth muscle relaxation of respiratory airway smooth muscle breakdown of liver glycogen
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Endocrine System Notes - THE ENDOCRINE SYSTEM: TYPES OF...

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