Thyroxine: Metabolism and Feedback Control Revision Notes | GCSE OCR Foundation Biology

What this lesson covers

Discover how thyroxine from the thyroid gland controls basal metabolic rate and supports growth and development, and understand how thyroxine levels are...

• Explain the role of thyroxine in controlling basal metabolic rate
• Describe how thyroxine affects growth and development
• Analyse how negative feedback controls thyroxine levels
• Compare the effects of high and low thyroxine levels on the body

Key ideas to keep in view

Use this lesson to stay inside B3.2 Coordination and control - the endocrine system while connecting the detail back to the wider B3: Organism level systems topic.

• B3: Organism level systems
• B3.2 Coordination and control - the endocrine system
• GCSE OCR Foundation Biology

Lesson notes preview

Read the core explanations from Thyroxine: Metabolism and Feedback Control before testing yourself from memory.

• Right now, your body is burning energy just to keep you alive. Your heart beats, your brain thinks, your cells repair themselves. This constant energy use has a name — your basal metabolic rate. But what controls how fast or slow this energy burning happens?
• Meet thyroxine — the hormone that acts like a thermostat for your entire body's energy system. Too little, and everything slows down. Too much, and your body goes into overdrive.
• A hormone produced by the thyroid gland that controls basal metabolic rate and is important for growth and development.
• Trap: Many students think thyroxine only affects weight. Actually, it controls the speed of nearly every chemical reaction in your body — from how fast your heart beats to how quickly your hair grows.
• Think of thyroxine as your body's accelerator pedal. When thyroxine levels are normal, your metabolism runs at the right speed. But what happens when levels go wrong?
• High thyroxine levels: Everything speeds up. Heart rate increases, body temperature rises, weight loss occurs even with normal eating, and people feel restless or anxious.
• Low thyroxine levels: Everything slows down. Heart rate decreases, body temperature drops, weight gain occurs, and people feel tired and sluggish.
• The minimum rate of energy expenditure needed to maintain basic body functions at rest, measured in kilojoules per day.
• But thyroxine doesn't just control energy use. It's crucial for growth and development, especially in children. Without enough thyroxine, children don't grow properly and brain development is affected.
• 3. The Feedback Loop That Keeps You Balanced

Continue through the topic

Move to the related lessons or back to the topic page when you need the wider sequence before exam-style practice.