Name: 內分泌系統、概述、動畫 (The Endocrine System, Overview, Animation)
Uploaded: 2021-01-14T08:07:10.000Z
Duration: 4 min 52 s
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關係子句

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