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  • the endocrine system is one of the two systems that are responsible for

  • communication and integration between various body tissues the other being the

  • nervous system endocrine communication is achieved by means of chemical

  • messengers called hormones hormones are produced in endocrine glands and

  • secreted into the bloodstream to reach body tissues a hormone can travel

  • wherever the blood goes but it can only affect cells that have receptors for it

  • these are called target cells there are two major types of hormones steroid

  • hormones derived from cholesterol and are lipid soluble and non steroid

  • hormones derived from peptides or amino acids and are water-soluble lipid

  • soluble steroid hormones can cross the cell membrane to bind to their receptors

  • inside the cells either in the cytoplasm or nucleus steroid hormone receptors are

  • typically transcription factors upon forming the hormone receptor complex

  • binds to specific DNA sequences to regulate gene expression and thus

  • mediating cellular response on the other hand water-soluble non steroid hormones

  • are unable to cross the lipid membrane and therefore must bind to receptors

  • located on the surface of the cell the binding triggers a cascade of events

  • that leads to production of cAMP, a second messenger that is responsible for

  • cellular response to hormone it does so by changing enzyme activity or ion

  • channel permeability major endocrine glands include the hypothalamus

  • pituitary gland pineal gland thyroid and parathyroid glands thymus adrenal gland

  • islets of the pancreas and testes in men or ovaries in women

  • the endocrine system also includes hormone secreting cells from other

  • organs such as kidneys and intestines except for the hypothalamus and the

  • pituitary different endocrine glands are involved in different more or less

  • independent processes for example the pancreas produces insulin and glucagon

  • that keep blood sugar levels in check the parathyroid glands produce hormones

  • that regulate calcium and phosphorus thyroid hormones control metabolic rates

  • while the ovaries and testes are involved in reproductive functions on

  • the other hand the hypothalamus and pituitary gland play a more central

  • integrative role the hypothalamus is also part of the brain it secretes

  • several hormones called neuro hormones which control the production of other

  • hormones by the pituitary thus the hypothalamus links the nervous system to

  • the endocrine system the pituitary is known as the master gland because it

  • controls the functions of many other endocrine glands

  • a major role of the endocrine system is to maintain the body's stable internal

  • conditions or homeostasis such as blood sugar levels or serum calcium levels to

  • do this it utilizes negative feedback mechanisms which work very much like a

  • thermostat the heater is on when the temperature is low off when it's high

  • for example when blood glucose level is high such as after a meal glucose

  • induces insulin release from the pancreas insulin helps body cells

  • consume glucose clearing it from the blood low blood glucose can no longer

  • act on the pancreas which now stops releasing insulin another example is the

  • regulation of thyroid hormone levels which are induced by a pituitary hormone

  • called thyroid stimulating hormone TSH TSH in turn is under control of

  • thyrotropin-releasing hormone trh from the hypothalamus when thyroid hormone

  • levels are too high they suppress the secretion of TSH and trh consequently

  • inhibiting their own production

the endocrine system is one of the two systems that are responsible for

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B2 中高級 美國腔

內分泌系統、概述、動畫 (The Endocrine System, Overview, Animation)

  • 27 1
    Amy.Lin 發佈於 2021 年 01 月 14 日
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