Homeostasis and the liver
Introduced| English | Meaning |
|---|---|
| homeostasis/ˌhəʊmiːəˈstɑːsiz/ | Maintaining a relatively stable internal environment despite external or internal changes. |
| stimulus/ˈstɪmjʊləs/ | A change in the internal or external environment that can be detected and produce a response. |
| endocrine system/ˈendəʊkraɪn ˈsɪstəm/ | The glands and tissues that release hormones into the blood to coordinate body functions. |
| hormone/ˈhɔːməʊn/ | A chemical messenger released by a cell or gland that affects target cells with suitable receptors. |
| effector/ɪˈfektə/ | A muscle, gland or other structure that carries out a response to a stimulus. |
| negative feedback/ˈneɡətɪv ˈfiːdbæk/ | A control process in which a change triggers responses that oppose that change. |
| urea/juːˈrɪə/ | A nitrogen-containing compound formed from excess amino groups in mammals and excreted mainly in urine. |
| deamination/ˌdiːmɪˈneɪʃn/ | The removal of an amino group from an amino acid or another molecule. |
Keeping the inside steady
- Homeostasis 稳态 means keeping the conditions inside the body steady, even when outside changes.
- Steady temperature, water and glucose let enzymes and cells work properly.
- Almost all homeostasis follows the same plan — and corrects itself.
Homeostasis is:
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Homeostasis keeps internal conditions (temperature, water, glucose) steady so cells work well.
Removing the amino group from excess amino acids in the liver is called ______.
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It produces ammonia, which the liver converts to urea for the kidneys to excrete.
The principle
- A change (a stimulus 刺激) is detected by a receptor.
- A coordination system carries the message — the nervous system (nerve signals) or the endocrine system 内分泌系统 (hormones 激素).
- An effector 效应器 (a muscle or gland) makes a response that corrects the change.
- This is negative feedback 负反馈: a change away from normal triggers a response that pushes it back to normal.
Negative feedback: a receptor detects a change and an effector corrects it, back toward the set point
A blood glucose meter: homeostasis keeps blood glucose within narrow limits.
Homeostasis
negative feedback to a set point
Drag the disturbance. A change is corrected back to the set point — the basis of all homeostasis.
Put the homeostatic control steps in order.
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A stimulus is detected by a receptor, the message is coordinated, and an effector responds to correct it.
Negative feedback works by:
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Negative feedback opposes the change, returning the condition toward its normal level.
Match each part of a control system to its job.
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Receptor → coordination → effector, with negative feedback always pushing the condition back to normal.
In negative feedback, a change away from the set point triggers a response that reverses it.
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This self-correcting loop is what keeps temperature, glucose and water steady.
The liver and urea 尿素
- The body cannot store extra amino acids.
- In the liver, deamination 脱氨基作用 removes the amino group from excess amino acids.
- This is turned into urea, carried in the blood to the kidneys to be removed.
Excess amino acids are dealt with in the liver by:
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Deamination removes the amino group from surplus amino acids; the product is converted to urea for excretion.
The liver's many jobs
- The liver also detoxifies substances such as alcohol and drugs.
- It carries out deamination — removing the amino group from excess amino acids to form urea.
You've got it
- homeostasis = keeping internal conditions steady so enzymes/cells work
- the loop: stimulus → receptor → coordination (nerve/hormone) → effector → response
- negative feedback pushes any change back towards normal
- the liver removes excess amino acids by deamination → urea → kidneys