Controlling blood glucose
| English | Chinese | Pinyin |
|---|---|---|
| glucagon | 胰高血糖素 | yí gāo xuè táng sù |
| insulin | 胰岛素 | yí dǎo sù |
| glycogen | 糖原 | táng yuán |
| G-protein | G蛋白 | G dàn bái |
| second messenger | 第二信使 | dì èr xìn shǐ |
| cyclic AMP | 环腺苷酸 | huán xiàn gān suān |
| enzyme cascade | 酶级联反应 | méi jí lián fǎn yìng |
| glucose oxidase | 葡萄糖氧化酶 | pú táo táng yǎng huà méi |
Keeping sugar in check
- Blood glucose is held steady by two hormones working against each other.
- The hormone glucagon 胰高血糖素 also shows how a signal gets into a cell.
- That signalling amplifies a tiny message into a big response.
Insulin 胰岛素 and glucagon
- When glucose is high, insulin makes muscle and liver cells take in glucose and store it as glycogen 糖原 — lowering the level.
- When glucose is low, glucagon makes liver cells break glycogen back into glucose — raising the level.
- Two opposing hormones = negative feedback.
Insulin and glucagon hold blood glucose steady
Controlling blood glucose
insulin ↓ · glucagon ↑
Drag the disturbance. High glucose → insulin lowers it; low glucose → glucagon raises it, back to ~90 mg/dl.
When blood glucose is high, insulin:
Insulin lowers blood glucose by promoting uptake and storage as glycogen.
When blood glucose is low, glucagon:
Glucagon raises blood glucose by breaking down glycogen into glucose in the liver.
Match each situation to the hormone and its effect.
Two opposing hormones from the pancreas hold glucose steady: insulin down, glucagon up.
The hormone that LOWERS blood glucose, by making cells store it as glycogen, is ______.
Insulin lowers blood glucose; its opposite, glucagon, raises it.
The glucagon cascade (cell signalling)
- glucagon binds a receptor on the liver cell, changing its shape.
- this activates a G-protein G蛋白, which switches on adenylyl cyclase.
- adenylyl cyclase makes a second messenger 第二信使, cyclic AMP 环腺苷酸 (cAMP).
- cAMP activates protein kinase A, starting an enzyme cascade 酶级联反应 (each enzyme switches on the next).
- because each step activates many, the signal is greatly amplified.
- the final enzyme breaks glycogen into glucose.
Glucagon triggers a cAMP cascade that amplifies the signal
In the glucagon cascade, the second messenger inside the cell is:
Adenylyl cyclase makes cAMP, the second messenger that activates protein kinase A.
In an enzyme cascade, each enzyme activates many of the next, so a small signal becomes a large response.
This amplification means a few hormone molecules can release a huge amount of glucose.
Measuring glucose
- Test strips and biosensors use the enzymes glucose oxidase 葡萄糖氧化酶 and peroxidase.
- They react with glucose to give a colour change (or an electrical signal) showing how much is present.
Ultrafiltration keeps blood cells and proteins in the blood
Glucose test strips and biosensors detect glucose using the enzyme:
Glucose oxidase (with peroxidase) reacts with glucose to give a colour change or electrical signal.
You've got it
- insulin (high glucose) → store as glycogen; glucagon (low glucose) → break glycogen → glucose
- glucagon cascade: receptor → G-protein → adenylyl cyclase → cAMP (second messenger) → protein kinase A → enzyme cascade
- the cascade amplifies the signal hugely
- glucose measured with glucose oxidase (test strips / biosensors)