PhysioEx 4/1

Which of the following statements about metabolism is false?

All of the energy from metabolism is ultimately stored in the chemical bonds of ATP.

Why didn't any of the rats develop a goiter after thyroxine injection?

In all cases, TSH levels were not elevated by the thyroxine injection.

How would you treat a thyroidectomized animal so that it functions like a "normal" animal?

Provide the animal T4 supplements.

Make a prediction about the basal metabolic rate (BMR) of the remaining rats compared with the BMR of the normal rat you just measured.

The BMR of both remaining rats will be lower than the normal rat's BMR.

What was the effect of TSH injections on the hypophysectomized rat's BMR? How does the BMR in this case compare with the normal rat's BMR? Was the dose of TSH in the syringe too large, too small, or just right?

The Hypox rat became hyperthyroidic and developed a goiter, which is similar to the normal rat. The dose was too large.

What was the effect of thyroxine injections on the hypophysectomized rat's BMR? How does the BMR in this case compare with the normal rat's BMR? Was the dose of thyroxine in the syringe too large, too small, or just right?

The Hypox rat was hyperthyroidic, as was the normal rat. The dose of thyroxine was too large.

Why did the normal rat develop a palpable goiter with the TSH injection?

The TSH receptors on the thyroid gland were excessively stimulated.

What was the effect of PTU injections on the thyroidectomized rat's BMR? How does the BMR in this case compare with the normal rat's BMR? Why was this effect observed?

The Tx rat became hypothyroidic, as did the normal rat. These results were similar to no injection, since the rat is missing the thyroid gland and already cannot produce thyroxine.

What was the effect of thyroxine injections on the thyroidectomized rat's BMR? How does the BMR in this case compare with the normal rat's BMR? Was the dose of thyroxine in the syringe too large, too small, or just right?

The Tx rat was hyperthyroidic after injection of thyroxine. This is similar to the normal rat's results after the injection, so the dose was too large.

What was the effect of TSH injections on the thyroidectomized rat's BMR? How does the BMR in this case compare with the normal rat's BMR? Why was this effect observed?

The Tx rat was hypothyroidic and did not develop a mass, which is the opposite of what happened to the normal rat. This was observed because the Tx rat is missing the thyroid. TSH stimulates the thyroid to secrete thyroxine, however, since there was no thyroid, there was no thyroxine.

If an animal has been hypophysectomized, what effect would you expect to observe in the hormone levels in its body?

The hormones would be low, because the pituitary gland is important to stimulate the thyroid to secrete thyroxine.

Propylthiouracil (PTU) is a drug that inhibits the production of thyroxine by blocking the attachment of iodine to tyrosine residues in the follicle cells of the thyroid gland (iodinated tyrosines are linked together to form thyroxine). What do you think will happen after you inject PTU into the three rats?

The hypophysectomized rat will become hypothyroidic and develop a goiter.

Which of the following statements is true?

The hypothalamus primarily secretes tropic hormones that stimulate the secretion of other hormones.

What was the effect of PTU injections on the hypophysectomized rat's BMR? How does the BMR in this case compare with the normal rat's BMR? Why was this effect observed?

The hypox rat was hypothyroidic, as was the normal rat. This was observed because no TSH was produced to stimulate the thyroid, since the pituitary gland is gone. That is why no goiter was found, whereas the normal rat developed a goiter.

Why did the normal rat develop a palpable goiter with the propylthiouracil injection?

The injection decreased the negative feedback mechanism on TSH.

Why did the metabolic rates differ between the normal rat and the surgically altered rats? How well did the results compare with your prediction?

The metabolic rates were not the same as the normal rat because the other rats were missing key glands that ended up producing thyroxine. The Tx rat was missing the thyroid gland and could therefore, not produce thyroxine, and the Hypox rat was missing the pituitary gland, and was therefore unable to produce TSH to stimulate the thyroid gland into producing thyroxine.

What was the effect of thyroid-stimulating hormone (TSH) injections on the normal rat's BMR?

The normal rat became hyperthyroidic and developed a goiter.

What was the effect of thyroxine injections on the normal rat's BMR?

The normal rat became hyperthyroidic but it did not develop a goiter.

Which rat had the fastest basal metabolic rate (BMR)?

The normal rat had the fastest metabolic rate.

What do you think will happen after you inject TSH into the three rats?

The normal rat will become hyperthyroidic and develop a goiter.

What do you think will happen after you inject thyroxine into the three rats?

The normal rat will become hyperthyroidic but will not develop a goiter.

What was the effect of propylthiouracil (PTU) injections on the normal rat's BMR? Why did this rat develop a palpable goiter?

The rat was hypothyroidic and developed a goiter. The goiter developed because the thyroid became overstimulated with TSH but was unable to secrete thyroxine.

If an animal has been thyroidectomized, what hormone(s) would be missing in its blood?

Thyroxine would be missing because the thyroid is missing.

As a result of the missing hormone(s) in the hypophysectomized rat, what would be an expected symptom?

decreased basal metabolic rate.

An injection of TSH to an otherwise normal animal will cause which of the following?

goiter development.

An injection of propylthiouracil to an otherwise normal animal will cause which of the following?

goiter development.

An injection of thyroxine to an otherwise normal rat will cause which of the following?

hyperthyroidism.

Thyroid-stimulating hormone (TSH) is

produced in the pituitary gland.

Thyrotropin-releasing hormone (TRH) is

secreted by the hypothalamus.

Thyroxine is

the most important hormone for maintaining the metabolic rate and body temperature.

Which of the rats did not develop a goiter after injection with TSH?

the thyroidectomized rat.