Hormones and Blood Glucose Control
AdvancedHormones are chemical messengers secreted by endocrine glands and carried in the blood. They act more slowly but last longer than nerve signals. Blood glucose is controlled by two opposing hormones from the pancreas: insulin lowers it, glucagon raises it — maintained by negative feedback.
- Hormones travel in blood — slower but longer-lasting
- Insulin lowers glucose; glucagon raises it
- Negative feedback = automatic correction back to normal
§Text Passage
1Besides the nervous system, the body runs a second messaging system — the endocrine system. Hormones are secreted by endocrine glands straight into the blood and carried around the body, acting only on particular target organs. They respond more slowly than nerves but act longer and more widely, managing growth, metabolism and blood glucose in cooperation with the nervous system.
2Take blood glucose control: after eating, sugars are digested into glucose and absorbed by the small intestine into the blood, and the level rises above its fasting value. The pancreas detects the rise and secretes insulin, which makes the liver and muscles take up glucose faster and store the excess as glycogen, so the level falls back into the normal range.
3Conversely, exercise makes the muscles burn through glucose and hunger brings no fresh supply, so the level drops; too low causes dizziness, trembling and weakness, and in severe cases coma. The pancreas then switches to glucagon, telling the liver to break stored glycogen down into glucose and release it back into the blood, and the level climbs again. The two hormones pull in opposite directions, checking each other and taking turns in charge.
4This 'correct the deviation' mechanism is negative feedback: pulled down when high and pushed up when low, blood glucose stays steady at about 4-7 mmol/L over the long term, giving organs such as the brain a stable energy supply. If insulin is secreted in too small an amount, or the body's cells respond poorly to it, glucose cannot be stored effectively and stays chronically high — diabetes — managed with diet, medication or insulin injections.
1Summary 重點摘要
Hormones are chemical messengers secreted by endocrine glands and carried in the blood. They act more slowly but last longer than nerve signals. Blood glucose is controlled by two opposing hormones from the pancreas: insulin lowers it, glucagon raises it — maintained by negative feedback.
2Vocabulary cards Vocabulary
A chemical messenger secreted by an endocrine gland, carried in the blood.
Released when blood glucose rises; makes the liver store glucose as glycogen, lowering blood glucose.
Released when blood glucose falls; makes the liver break down glycogen and release glucose.
When a value drifts from normal, a corrective mechanism automatically brings it back.
A gland secreting hormones straight into the blood, e.g. the pancreas.
The gland secreting insulin and glucagon — it monitors blood glucose.
Glucose stored in the liver, broken down to release glucose when needed.
The organ that stores glucose as glycogen and releases it on demand.
A disease where insulin is lacking or ineffective, leaving blood glucose chronically high.
3Step by step Steps
- After a meal: glucose risesSugars in food are digested into glucose, absorbed by the small intestine into the blood, and blood glucose rises from its fasting level of about 4-6 mmol/L. Glucose is the main fuel for cellular respiration, and blood glucose is one of the indicators the body works hardest to keep steady; too high a concentration damages blood vessels and nerves, so the level must be brought back to normal quickly — and hormones are the gatekeepers in charge.
- Insulin respondsThe pancreas detects the rise and secretes insulin, which travels in the blood around the body and acts mainly on the liver and muscles: cells take up glucose faster and the excess is stored as glycogen, so the level falls again. Careful: insulin STORES glucose — it does not break it down. Exam questions love swapping those two verbs, so stay alert when answering.
- Hungry or exercising: glucose fallsDuring exercise the muscles burn through glucose, and when you are hungry no new glucose is arriving from the digestive tract, so the level falls from its peak and may even dip below normal. Too low causes dizziness, trembling and weakness, and in severe cases coma — just as dangerous as being too high; the body therefore keeps a second mechanism ready to push the level back up. Control in both directions is indispensable — a double safeguard for staying alive.
- Glucagon respondsWhen blood glucose runs low, the pancreas switches to glucagon, which travels to the liver and makes it break stored glycogen down into glucose, releasing it back into the blood; the level climbs again and the cells regain their fuel. Glucagon works in exactly the opposite direction to insulin — the two hormones check each other and take turns in charge, pulling the level back into the normal range whether it is too high or too low, and keeping the body stable.
- Negative feedback loopHigh glucose is pulled down by insulin; low glucose is pushed up by glucagon. This 'correct any deviation' mechanism is called negative feedback: the correction always opposes the deviation, so blood glucose stays steady at about 4-7 mmol/L over the long term and organs such as the brain receive a stable energy supply. Negative feedback is the basic principle by which organisms keep their internal conditions stable, and glucose control is its classic example.
- Other hormones: adrenalineHormones do far more than control glucose. In an emergency the adrenal glands quickly secrete adrenaline, which speeds up the heart and breathing and raises blood glucose, delivering more oxygen and fuel to the muscles so the body has the reserves to act — escaping danger or handling a sudden event, for example. It shows how nerves and hormones share the work: nerves handle split-second responses, hormones handle longer-lasting, body-wide regulation, and the two complement each other.
4Diagrams Diagrams
5Worked example Example
Why is blood glucose high in diabetes?
- Type 1: the pancreas secretes too little insulin
- Type 2: the body responds poorly to insulin
- Result in both: glucose stays in the blood instead of being stored
- So glucose stays high after meals
- Answer: Because insulin is secreted in too small an amount (Type 1) or the body's cells respond poorly to it (Type 2), blood glucose cannot be pulled back to normal after meals: glucose stays in the blood and remains chronically high. Failure of the negative feedback loop is the core of the disease, so patients must control their diet and take medication or insulin injections as directed. In your answer, distinguish Type 1 and Type 2 first, then give the consequences and the management.
6Common mistakes Mistakes
7Quick check Quick check
Q1When blood glucose rises, which organ secretes which hormone?
Q2What does negative feedback mean? Use blood glucose as an example.
Q3Hormones vs nerve signals: which is faster? Which lasts longer?
Q4What happens to the body when blood glucose is too low?
Q5What role does the liver play in blood glucose control?
8Recap Recap
- Hormones travel in blood — slower but longer-lasting
- Insulin lowers glucose; glucagon raises it
- Negative feedback = automatic correction back to normal
- High glucose: pancreas secretes insulin; the liver stores glucose as glycogen
- Low glucose: glucagon makes the liver break glycogen down and release glucose