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  • >> NARRATOR: Our body is always in flux:

  • when we are cold our body shivers;

  • when we are hot our body sweats.

  • Our body engages in these activities to keep to keep our internal temperature constant.

  • This is an example of homeostasis, which is defined as

  • the ability of the body to maintain a constant internal state.

  • One major way the body maintains homeostasis is through the endocrine system.

  • The endocrine system is the system of glands that produce hormones

  • to regulate and control bodily activities.

  • The endocrine system controls a number of important functions throughout the body,

  • including growth and development, metabolism, and homeostasis.

  • There are many different hormones in the body,

  • and each is responsible for different functions.

  • Estrodiol, testosterone, insulin, growth hormone, and epinephrine are just a few examples of hormones.

  • Although they are involved in different functions of the endocrine system,

  • hormones work in a similar manner.

  • First, a gland in detects a change in the body's internal environment.

  • This gland then increases the secretion of hormones, which enter the bloodstream.

  • Hormones travel through the blood and can have potential effects throughout the body.

  • However, hormones will not act on every cell.

  • Hormones activitate target cells by binding to specific receptors

  • on the outside or inside the target cells.

  • When a hormone binds to a receptor, the receptor sends a signal throughout the cell.

  • Just like a megaphone amplifies the volume of a person's voice,

  • a hormone's message is amplified inside the cell.

  • This signal goes a long way. Just a few hormones can induce great change.

  • Once hormones have succeeded in sending their message to their target cells,

  • and, in this case, homeostasis is achieved, the gland decreases the secretion of hormones.

  • The mechanism by which the gland stops secreting hormones is called negative feedback.

  • What exactly is negative feedback?

  • Negative feedback allows a system to self regulate a response or output.

  • The following example may help explain.

  • A house regulates its temperature using negative feedback.

  • When a thermostat detects a decrease in temperature,

  • it sends a message to the furnace to produce heat.

  • When the thermostat detects that the room temperature has returned to the correct level,

  • it stops sending its message to the furnace.

  • A furnace will turn on and off several times a day to keep the temperature relatively constant.

  • Now lets look at a specific example of homeostasis

  • using a hormone that many of you may have already heard of: insulin.

  • Lets say a person eats a meal.

  • As the food is digested and glucose is absorbed into the bloodstream, blood glucose levels begin to rise.

  • It is important for this glucose to be removed from the blood,

  • otherwise it may cause damage to important organs such as the liver, brain, and kidneys.

  • Thus, to maintain blood glucose levels,

  • insulin is released from an endocrine gland: the pancreas.

  • The pancreas senses increased blood glucose and releases insulin into the blood.

  • Insulin travels through the blood and binds to receptors on muscles, fat tissue, and as shown here, the liver.

  • Upon binding to receptors, insulin causes an increase in glucose transporters,

  • allowing excess glucose to be taken from the blood and stored in the liver for future use.

  • This uptake of glucose by the liver and other organs for storage,

  • restores blood glucose levels back to a balanced state.

  • Homeostasis has been achieved!

  • Because blood glucose levels have reached homeostasis,

  • the pancreas will stop secreting insulin.

  • This is just one type of hormone involved in the endocrine system.

  • Remember, the glands of the endocrine system send messages to the body in a similar manner.

  • A gland senses a change in the body...

  • and secretes a hormone.

  • Hormones travel through the blood.

  • Hormones are receptor specific.

  • A hormone's signal is amplified.

  • And finally, hormones are regulated by feedback --

  • many times, negative feedback.

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B2 中高級 美國腔

內分泌系統 (The Endocrine System)

  • 13 1
    Amy.Lin 發佈於 2021 年 01 月 14 日
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