Final answer:
Hyperthyroidism occurs when the thyroid gland secretes excessive amounts of thyroid hormones, resulting in symptoms like an increased metabolic rate, weight loss, and increased heart rate.
Step-by-step explanation:
Hyperthyroidism, also known as hyperactivity of the thyroid, occurs when the thyroid gland secretes excessive amounts of thyroid hormones. The most common cause of hyperthyroidism is Graves' disease, an autoimmune disorder in which abnormal antibodies stimulate the thyroid to produce excessive quantities of hormones. This condition is characterized by an increased metabolic rate, excess body heat, sweating, diarrhea, weight loss, and increased heart rate.