1.) Compared to the baseline metabolic rate of the normal rat, which rat(s) bene

Question

1.) Compared to the baseline metabolic rate of the normal rat, which rat(s) benefited from thyroxine injections? Why is this benefit seen with one, both, or none of the rats?

2.) Compared to the baseline metabolic rate of the normal rat, which rat(s) benefited from TSH injections? Why is this benefit seen with one, both, or none of the rats?

Effect of Hormones of Metabolic Rate (mL O2/kg/hr) Normal Rat Thyroidectomized Rat Hypophysectomized Rat Baseline with Thyroxine with TSH 1680 2016 1920 1542.86 1934.69 1542.86 1542.86 1910.2 1934.69

Explanation / Answer

thyroidectomized = thyroid gland was removed, source of thyroxine

hypophysectomized rat = hypophysis or pituitary gland was removed, source of TSH

1) With thyroxine, the metabolic rate has increased in all the three rats because thyroxine is the active hormone and increases the body's metabolism by inducing insulin release, breakdown of sugar, increase in respiration, BMR etc.

2) The increase is not seen in thyroidectomized rat because TSH (thyroid stimulating hormone) acts on the thyroid gland to stimulate it to produce thyroxine. No thyroid gland, no stimulation by TSH to release thyroxine

Pituitary---------> Thyroid---------------> Increase in metabolism.

TSH thyroxine

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