- Define and explain Hormonal Control in your own words
- Use key terms such as endocrine gland accurately
- Apply what you have learned to new examples and questions
- Avoid the common mistakes learners make with this topic
This lesson focuses on Hormonal Control: compare nervous and hormonal control and explore the glands of the endocrine system.
Compare nervous and hormonal control and explore the glands of the endocrine system.
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 — endocrine gland: A ductless gland that secretes hormones directly into the blood, such as the pancreas, thyroid or adrenal glands.
Compare nervous and hormonal control on speed and duration.
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.
Answer: 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.
- 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.
- Claiming reflexes involve the brain thinking Spinal reflexes are coordinated by relay neurones in the spinal cord; the brain is informed afterwards, which is why you feel the pain after you have already moved.
Practice
Receptor → sensory neurone → relay neurone (in the spinal cord) → motor neurone → effector (muscle).
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.
The arriving impulse triggers release of neurotransmitter into the synaptic gap; it diffuses across and binds to receptors on the next neurone, triggering a new impulse there.
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.
Quick check
Which of these best defines "endocrine gland"?
Why is type 1 diabetes treated with insulin injections?
- Hormonal Control: compare nervous and hormonal control and explore the glands of the endocrine system.
- Hormonal control and homeostasis: Hormones travel in the blood, so hormonal responses are slower but longer-lasting and more widespread than nervous ones.
- negative feedback: A control mechanism in which a change triggers a response that reverses the change, restoring the optimum level.
- Watch out for: saying impulses jump the synapse electrically