1. Determine hormones with external and internal secretion. 2. The nervous system and the hormonal system control the sending of messages to different organs of the body, describe the difference between them.
3. Explain the role of thyroxine in the metabolic processes of our body.
4. Describe the role of insulin in regulating blood sugar. What are the effects of adrenaline in the body?
5. Distinguish the role of testosterone and estrogen in human sexual development.​

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Explanation:

Thyroxine is the main hormone secreted into the bloodstream by the thyroid gland. It plays vital roles in digestion, heart and muscle function, brain development and maintenance of bones.

Alternative names for thyroxine

T4; tetraiodothyronine; thyroxin

What is thyroxine?

Thyroxine is the main hormone secreted into the bloodstream by the thyroid gland. It is the inactive form and most of it is converted to an active form called triiodothyronine by organs such as the liver and kidneys. Thyroid hormones play vital roles in regulating the body’s metabolic rate, heart and digestive functions, muscle control, brain development and maintenance of bones.

How is thyroxine controlled?

The production and release of thyroid hormones, thyroxine and triiodothyronine, is controlled by a feedback loop system that involves the hypothalamus in the brain and the pituitary and thyroid glands. The hypothalamus secretes thyrotropin-releasing hormone which, in turn, stimulates the pituitary gland to produce thyroid stimulating hormone. This hormone stimulates the production of the thyroid hormones, thyroxine and triiodothyronine, by the thyroid gland.

This hormone production system is regulated by a feedback loop so that when the levels of the thyroid hormones (thyroxine and triiodothyronine) increase, they prevent the release of both thyrotropin-releasing hormone and thyroid stimulating hormone. This system allows the body to maintain a constant level of thyroid hormones in the body.

What happens if I have too much thyroxine?

The release of too much thyroxine in the bloodstream is known as thyrotoxicosis. This may be caused by overactivity of the thyroid gland (hyperthyroidism), as in Graves' disease, inflammation of the thyroid or a benign tumour. Thyrotoxicosis can be recognised by a goitre, which is a swelling of the neck due to enlargement of the thyroid gland. Other symptoms of thyrotoxicosis include intolerance to heat, weight loss, increased appetite, increased bowel movements, irregular menstrual cycle, rapid or irregular heartbeat, palpitations, tiredness, irritability, tremor, hair