Question

Which of the following would happen to an individual playing a long game of basketball outdoors on a hot afternoon?

• A. The production of thyroxine by the thyroid gland would increase.
• B. The osmotic pressure of the blood would decrease.
• C. The volume of the urine produced would increase.
• D. The secretion of ADH from the pituitary gland would increase.

Answer 1

Answer: (D)

The secretion of ADH from the pituitary gland would increase.

The release of anti-diuretic hormone from the pituitary gland into the bloodstream is controlled by a number of factors. A decrease in blood volume or low blood pressure, which occurs during dehydration or a haemorrhage, is detected by sensors (receptors) in the heart and large blood vessels. These stimulate anti-diuretic hormone release. Secretion of anti-diuretic hormone also occurs if the concentration of salts in the bloodstream increases, for example as a result of not drinking enough water on a hot day. This is detected by special nerve cells in the hypothalamus which simulate anti-diuretic hormone release from the pituitary. If the concentration of salts reaches abnormally low levels, this condition is called hyponatraemia. Anti-diuretic hormone is also released by thirst, nausea, vomiting and pain and acts to keep up the volume of fluid in the bloodstream at times of stress or injury. Alcohol prevents anti-diuretic hormone release which causes an increase in urine production and dehydration.

Therefore, the correct answer is option D.