Hormones are chemical messengers made by endocrine glands and carried in the blood. They act more slowly than nerves but their effects last longer. The pituitary gland in the brain is a master gland that controls others. Adrenaline from the adrenal glands prepares the body for fight or flight. Thyroxine controls metabolic rate.
The pancreas controls blood glucose. After a meal, glucose rises, and the pancreas releases insulin, which makes liver and muscle cells take in glucose and store it as glycogen. If glucose falls, the pancreas releases glucagon, which converts glycogen back into glucose. In Type 1 diabetes the pancreas makes too little insulin, so patients inject insulin. In Type 2, cells stop responding to insulin; it is linked to obesity and is treated with diet, exercise and medicines.
Worked example
What happens to blood glucose after eating pasta, and how is it corrected?
- Starch is digested into glucose, so blood glucose rises.
- The pancreas releases insulin.
Answer:Cells take in glucose and the liver stores it as glycogen, so the level falls back.
Key words
- hormone
- a chemical messenger carried in the blood
- insulin
- lowers blood glucose
- glucagon
- raises blood glucose
- glycogen
- stored form of glucose in liver and muscles
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NGSS-referenced: HS-LS1-3