Hormonal Control of Metabolic Rate PDF

## Hormonal Control of Metabolic Rate ### Adrenalin * Adrenaline is a hormone that is released from the adrenal glands. * In normal conditions, very little adrenaline is released into the blood. * In frightening or exciting situations, an increase in impulses from neurones reaching the adrenal gla...

## Hormonal Control of Metabolic Rate ### Adrenalin * Adrenaline is a hormone that is released from the adrenal glands. * In normal conditions, very little adrenaline is released into the blood. * In frightening or exciting situations, an increase in impulses from neurones reaching the adrenal glands from the spinal cord triggers the release of large amounts of adrenalin into the blood. * Adrenaline has many target organs, including the liver in which it causes the breakdown of a storage substance called glycogen. * Glycogen is a polymer made of glucose molecules. * When glycogen is broken down, the glucose molecules can be released into the blood providing additional glucose for respiration. * Some of the other target organs and effects of adrenalin are as follows: * Heart muscle cells contract: * more rapidly, which increases heart rate * more strongly, which increases blood pressure * Diameter of blood vessels leading to muscles widens, which increases blood flow to muscles * Liver cells change glycogen to glucose and release it into the blood, which increases blood sugar concentration. * Diameter of blood vessels leading to other organs narrows, which reduces blood flow to those organs and increases blood pressure. ### Thyroxine * Your metabolic rate is the rate at which the energy stored in your food is transferred by all the reactions that take place in your body to keep you alive. * Resting metabolic rate is measured with the body at rest, in a warm room and long after the person last had a meal. * Name two processes that require the transfer of energy when the body is fully at rest. * Explain why these processes need a source of energy. * Explain why resting metabolic rate is measured in a warm room and not in a cold room. * One hormone that affects metabolic rate is thyroxine, which is released by the thyroid gland. * Thyroxine is taken into, and affects, many different kinds of cell. * It causes heart cells to contract more rapidly and strongly, and it also increases the rate at which proteins and carbohydrates are broken down inside cells. * The amount of thyroxine produced by the thyroid gland is controlled by hormones released by two other glands, as shown in diagram C. * The control of thyroxine concentration in the blood is an example of negative feedback. * This is because an increase in thyroxine concentration directly causes changes that bring about a decrease in the amount of thyroxine released into the blood, and vice versa. * Negative feedback of the blood concentration of thyroxine involves two other hormones. * TRH is thyrotropin-releasing hormone. * TSH is thyroid-stimulating hormone. ### Diagram C - Hormonal Control of Thyroxine Concentration | | | | |---|---|---| | **Higher than normal blood concentration of thyroxine** | Hypothalamus --> TRH --> Pituitary --> TSH --> Thyroid gland --> Thyroxine --> Target organs | **Lower than normal blood concentration of thyroxine** | **Key** * Stimulates (makes more active) * Inhibits (makes less active) **Gland** * Hormone