Hormones and homeostasis

Homeostasis: Two mechanisms: 
                      Positive Feedback                                                                Negative Feedback Loop
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• Application: William Harvey’s investigation of sexual reproduction in deer.

•William Harvey failed to solve the mystery of sexual reproduction because effective microscopes were not available when he was working, so fusion of gametes and subsequent embryo development remained undiscovered.
• Leptin is secreted by cells in adipose (fat) tissue and acts on the hypothalamus of the brain to inhibit appetite.
• Application: Testing of leptin on patients with clinical obesity and reasons for the failure to control the disease.
Watch the short video below several times to understand leptin's effect. 
   Insulin / Glucagon / Regulation of blood glucose /  Diabetes mellitus
Insulin is secreted by β (Beta) cells of the pancreas, and glucagon is secreted by α (Alpha) cells of the pancreas,
to ​control blood glucose concentration.
Glucagon has an a in the middle of the word so think alpha!  Insulin has no a in it, so think beta. 

Application: Causes and treatment of Type I and Type II diabetes
Thyroxin is secreted by the thyroid gland to regulate the metabolic rate and help control body temperature.
Melatonin is secreted by the pineal gland to control circadian rhythms
​Application: Causes of jet lag and use of melatonin to alleviate it.