Thyroid & parathyroid

Question 1

What is the single most important determinant of basal metabolic rate (BMR)?

Answer 1

thyroid hormone

Question 2

Which is the active form and which is the secretory form? (T3, T4)

Answer 2

T4 is major secretory product but T3 is most active form of hormone

Question 3

What are the components of thyroid hormones?

Answer 3

iodide, tyrosine, thyroglobulin

Question 4

Describe the multi-level control of thyroid hormone release.

Answer 4

TRH is released from hypothalamus; stimulates release of TSH from anterior pituitary; stimulates release of T3/T4 from thyroid gland.

Plasma thyroid hormone inhibits release of TRH and of TSH.

Question 5

What is ‘permissiveness’?

Answer 5

Hormone-hormone interaction required for full strength of effectiveness.

E.g. Thyroid hormone stimulates synthesis of adrenergic receptors

Question 6

A hyperthyroid individual has symptoms similar to a person with an adrenal medullary tumor.

T/F

Answer 6

True

Question 7

Uncontrolled growth of the thyroid gland can result from:

A. hyperthyroid

B. hypothyroid

C. neither

D. both

Answer 7

both

Question 8

What causes cretinism?

Answer 8

• Insufficient dietary iodine during pregnancy (maternal thyroid hormones limited)
• Fetal thyroid cannot manufacture sufficient T3 and T4
• Impact on CNS development (cretinism) –Formation of myelin, axon terminals, dendritic spines

Question 9

What is this disease?

• Hyperthyroidism via autoimmune disease
• Produces antibodies that bind TSH receptor stimulating & not destroying receptor
• Not influenced by negative feedback from thyroxine levels

Answer 9

Graves disease

Question 10

Acidemia is associated with high or low serum free/ionized calcium?

Answer 10

HIGH (more H+ bound to albumin = less spots available for calcium to bind, so more calcium in serum)

Question 11

Alkalemia is associated with high or low serum free/ionized calcium?

Answer 11

LOW (less H+ bound to albumin = more spots available for calcium to bind, so less calcium in serum)

Question 12

What are the three action sites of parathyroid hormone?

Answer 12

• Bone: indirect stimulation of osteoclasts
• Kidney: inhibit phosphate reabsorption & stimulates calcium reabsorption
• Intestine: indirectly stimulates calcium & phosphate absorption via stimulating renal enzyme to hydroxylate vitamin D

Question 13

Which bone cells have PTH receptors?

Answer 13

Receptors are located on osteoblasts NOT osteoclasts

Question 14

What is the effect of chronic hyperparathyroidism?

Answer 14

Chronic elevation of PTH leads to net bone resorption

Question 15

What stimulates PTH release?

Answer 15

~PTH secreting cells are equipped with calcium sensors

~Hormone release usually associated with ↓ in calcium

Question 16

All of calcium ingested is absorbed.

T/F

Answer 16

False

• Large part of calcium ingested is not absorbed
• Calcium absorption is under hormonal control
• Thus, hormonal control of absorption is major means for regulating total body calcium
• Active form of vitamin D induces synthesis of vitamin D-dependent Ca2+ binding protein

Question 17

Where is calcitonin secreted from?

Answer 17

•Peptide hormone secreted by parafollicular cells within thyroid gland

Question 18

What stimulates calcitonin secretion?

Answer 18

•Secretion stimulated by increased plasma Ca2+

Question 19

What is the effect of calcitonin?

Answer 19

•Calcitonin inhibits activity of osteoclasts