Hormones and homeostasis · Grade 10
Homeostasis is keeping the conditions inside the body steady, such as blood glucose, body temperature and water levels, so that cells and enzymes work well. It uses the nervous system and hormones. Hormones are chemicals made by glands of the endocrine system and carried in the blood to their target organs.
Key facts
- Control systems have receptors that detect a change, a coordination centre (the brain, spinal cord or pancreas) and effectors that respond. Many work by negative feedback: a change is reversed.
- Endocrine glands: the pituitary (the “master gland”: ADH, FSH, LH, TSH, growth hormone), thyroid (thyroxine), adrenal glands (adrenaline), pancreas (insulin, glucagon), ovaries (oestrogen, progesterone) and testes (testosterone). Hormones act more slowly than nerves but last longer.
- When blood glucose rises, the pancreas releases insulin: cells take in glucose and the liver and muscles store it as glycogen. When it falls, the pancreas releases glucagon: the liver turns glycogen back into glucose.
- Type 1 diabetes: the pancreas makes too little insulin; it is treated with insulin injections. Type 2 diabetes: cells no longer respond to insulin; it is treated with diet and exercise, and obesity is a risk factor.
- The thermoregulatory centre in the brain monitors body temperature. Too hot: sweating and vasodilation. Too cold: shivering and vasoconstriction.
- Menstrual cycle: FSH makes an egg mature; oestrogen builds up the uterus lining; LH triggers ovulation (about day 14 of a 28-day cycle); progesterone keeps the lining thick. Contraceptive pills use oestrogen and progesterone to stop FSH and LH.