- Define and explain Homeostasis: Blood Glucose in your own words
- Use key terms such as negative feedback accurately
- Apply what you have learned to new examples and questions
- Avoid the common mistakes learners make with this topic
This lesson focuses on Homeostasis: Blood Glucose: explain the negative-feedback control of blood glucose by insulin and glucagon.
Explain the negative-feedback control of blood glucose by insulin and glucagon.
Key ideas
Hormonal control and homeostasis
Hormones travel in the blood, so hormonal responses are slower but longer-lasting and more widespread than nervous ones. Blood glucose is controlled by negative feedback: after a meal, rising glucose triggers insulin release from the pancreas, which lowers blood glucose by promoting uptake into cells and conversion to glycogen; when glucose falls, glucagon triggers the liver to convert glycogen back to glucose. In type 1 diabetes the pancreas produces little insulin, so blood glucose must be managed by injection.
Neurones and synapses
A neurone carries an electrical impulse along its axon, insulated by a myelin sheath that speeds transmission. At the synapse, the impulse triggers release of neurotransmitter, which diffuses across the gap and binds to receptors on the next neurone, starting a new impulse. Because transmission is one-way and chemical, synapses introduce a tiny delay but allow impulses to be directed and integrated.
Key term — negative feedback: A control mechanism in which a change triggers a response that reverses the change, restoring the optimum level.
After eating a meal rich in carbohydrate, blood glucose rises above the normal range. Describe the sequence of events that returns it to normal.
Receptors in the pancreas detect the rise in blood glucose concentration. Beta cells of the pancreas secrete the hormone insulin into the blood. Insulin binds to receptors on liver and muscle cells, increasing glucose uptake and stimulating conversion of glucose to glycogen. As cells take up glucose, blood glucose concentration falls back towards normal. The fall is detected and insulin secretion is switched off — negative feedback.
Answer: Insulin lowers blood glucose by driving uptake into cells and glycogen formation in the liver and muscles; negative feedback then halts insulin release once levels are normal.
- Mixing up insulin and glucagon Insulin lowers blood glucose (after a meal); glucagon raises it (between meals). Remember: insulin in, glucagon up.
- Saying impulses jump the synapse electrically The impulse travels electrically along the axon but crosses the synapse chemically, by diffusion of neurotransmitter. The gap cannot be jumped electrically.
Practice
When blood glucose falls, the pancreas releases glucagon, which stimulates the liver to convert stored glycogen back into glucose and release it into the blood.
In type 1 diabetes the pancreas produces little or no insulin, so blood glucose cannot be lowered after meals; injected insulin replaces the missing hormone.
Nervous responses are very fast and short-lived, travelling as electrical impulses along neurones to specific targets. Hormonal responses are slower and longer-lasting, travelling in the blood to widespread targets.
The impulse travels only to the spinal cord via short relay neurones and does not travel up to the brain for conscious processing, so the pathway is shorter and the response quicker.
Quick check
Which of these best defines "negative feedback"?
Describe how an impulse crosses a synapse.
State the five stages of a spinal reflex arc in order.
- Homeostasis: Blood Glucose: explain the negative-feedback control of blood glucose by insulin and glucagon.
- Hormonal control and homeostasis: Hormones travel in the blood, so hormonal responses are slower but longer-lasting and more widespread than nervous ones.
- endocrine gland: A ductless gland that secretes hormones directly into the blood, such as the pancreas, thyroid or adrenal glands.
- Watch out for: mixing up insulin and glucagon