Topic 6.6: Homoeostasis

Secreted by the thyroid gland . Regulates metabolic rate Thyroxin: Key Points Secreted by the thyroid gland . Regulates metabolic rate Helps control body temperature. Correct functioning of the thyroid requires IODINE in the diet. Lack of dietary iodine causes GOITRE Lack of thyroxin causes: lack of energy Depression Weight gain despite appetite loss Feeling cold

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Secreted by the adipose tissue cells. Acts on the hypothalamus Leptin: Key Points Secreted by the adipose tissue cells. Acts on the hypothalamus Inhibits appetite Leptin is a protein hormone that targets the appetite centre of the hypothalamus. Food intake triggers Leptin secretion which in turn inhibits appetite which reduces food intake. This is an example of negative feedback.

Spot the mouse treated with Leptin blockers. Leptin and Obesity: should GM Leptin be made available as a treatment for obesity?

Secreted by the pineal gland . Helps control circadian rhythms. Melatonin: Key Points Secreted by the pineal gland . Helps control circadian rhythms. High levels of MELATONIN cause feeling of drowsiness and promote sleep. Falling melatonin levels encourage waking at the end of the night. Melatonin also promotes a drop in core temperature and probably causes the night time body temperature drop. Melatonin is sometimes advertised as a treatment for Jet Lag why do you think it might work?