Homeostasis and the liver · ⁨稳态与肝脏⁩

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.

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.

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.

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.

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