Controlling blood glucose
Introduced| English | Meaning |
|---|---|
| glucagon/ˈɡluːkæɡən/ | A hormone from pancreatic alpha cells that helps raise blood glucose concentration. |
| insulin/ˈɪnsjuːlɪn/ | A hormone produced by pancreatic beta cells that helps lower blood glucose concentration. |
| glycogen/ˈɡlaɪkədʒn/ | A highly branched glucose polysaccharide used for energy storage in animals and fungi. |
| G-protein/dʒiː ˈprəʊtiːn/ | A protein that binds guanine nucleotides and acts as a molecular switch in cell signalling. |
| second messenger/ˈsekənd ˈmesɪndʒə/ | An intracellular molecule or ion that carries a signal onward after a receptor is activated. |
| cyclic AMP/ˈsaɪklɪk ˌeɪ em ˈpiː/ | A cyclic nucleotide that acts as an intracellular messenger in many signalling pathways. |
| enzyme cascade/ˈenzaɪm kəˈskeɪd/ | A sequence in which activation of one enzyme triggers activation of others, often amplifying a signal. |
| glucose oxidase/ˈɡluːkəʊs ˈɒksɪdeɪs/ | An enzyme that catalyses oxidation of glucose using oxygen, producing hydrogen peroxide and a gluconolactone product. |
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:
Difficulty 1/5 · 100 coins + a small bonus on first completion today
Insulin lowers blood glucose by promoting uptake and storage as glycogen.
When blood glucose is low, glucagon:
Difficulty 1/5 · 100 coins + a small bonus on first completion today
Glucagon raises blood glucose by breaking down glycogen into glucose in the liver.
Match each situation to the hormone and its effect.
Difficulty 2/5 · 140 coins + a small bonus on first completion today
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 ______.
Difficulty 1/5 · 100 coins + a small bonus on first completion today
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:
Difficulty 1/5 · 100 coins + a small bonus on first completion today
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.
Difficulty 1/5 · 100 coins + a small bonus on first completion today
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:
Difficulty 1/5 · 100 coins + a small bonus on first completion today
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)