NUTR 313: Final Exam Questions and
All Correct Answers Graded A+.
What are the food sources of iodine? - Answer Seafoods and iodized salt
Food content is variable based on soil
How is iodine absorbed? - Answer Organic bound iodine is freed and converted to iodide
within the gastrointestinal tract
What is the single main function of iodine? - Answer The synthesis of thyroid hormones
How is thyroid hormone synthesized from iodine? - Answer Thyroid peroxidase, a membrane-
bound glycoprotein, catalyzes the oxidation of the iodide to the active form I2. The binding of
this active form to the tyrosine in the thyroglobulin to form MIT or DIT (monoiodotyrosines or
diiodotyrosines).
MIT or DIT then condense to form thyroid hormones.
DIT+DIT = T4
MIT+DIT = T3
How is thyroid hormone status regulated? - Answer Stimulation of the thyroid gland causes
the release of the hormones into circulation.
The releasing of thyroid hormone is controlled by the thyroid stimulating hormone (TSH) from
pituitary, which in turn is controlled by thyroid releasing hormone (TRH) from the
hypothalamus.
This hypothalamic-pituitary-thyroid axis is responsible for producing the appropriate amounts of
thyroid hormones, but thyroid status can also be regulated by altering the rate of T4 to T3
conversion by deiodinases.
What is the function for selenium containing 5'-, and 5-deiodinase? - Answer 5'-deiodinase
catalyzes the deiodination (removal) of iodine from the 5' position of T4. This forms active T3.
5-deiodinase catalyzes the deiodination (removal) of iodine from the 5 position of T4. This forms
inactive T3.
What are some of the selected physiological function for thyroid hormone? - Answer
Enhances lipolysis in adipose tissue
Enhances contraction of muscle
Promotes anabolism of bone
Increases the heart rate
, Stimulates nutrient digestion and absorption
Stimulates metabolic rate and cellular oxygen consumption in metabolically active tissues
How does thyroid hormone act on regulating gene expression thereby regulating physiological
functions? - Answer On a target gene promoter, TR forms a heterodimer with RXR (retinoid X
receptor). In the absence of T3, this dimer is associated with a co-repressor, which has histone
deacetylase activity.
This complex also interacts with TFIIB basal transcriptional machinery, and inhibits transcription.
In the presence of T3, a co-activator replaces co-repressor. This results in histone acetylation
and initiation of transcription.
What are the deficiencies associated with iodine? - Answer Goiter
Iodine deficiency disorders (IDDs)
Cretinism
Goiter - Answer Enlargement of the thyroid gland
Caused by over stimulation of TSH
Iodine deficiency disorders (IDDs) - Answer An insufficient supply of iodine during pregnancy
is associated with an increased occurrence of spontaneous abortions, stillbirths and congenital
abnormalities, as well as prenatal and infant mortality
Cretinism - Answer The lack of maternally supplied thyroid hormones at a time when very
active fetal brain development occurs (1st trimester)
Neurological: mental retardation, deaf-mutism, and spastic displegia - paralysis of the legs
Myxedematous: less severe neurological symptoms, more clinically hypothyroid and growth
retarded; concurrent selenium deficiency may lead to the greater thyroid damage associated
with this form of cretinism
What are the toxicities associated with iodine? - Answer Can cause problems with the thyroid
gland
What is hyperthyroidism? - Answer Most often caused by Grave's disease
Results in a continuous stimulation of the thyroid gland and overproduction of the hormone by
antibodies against self TSH receptor
Can also result from adenomas or thyoiditis
Symptoms: palpitations, heat intolerance, nervousness, insomnia, fatigue, increased bowel
movements, light or absent periods, trembling hands, weight loss, warm moist skin, hair loss,
staring gaze
All Correct Answers Graded A+.
What are the food sources of iodine? - Answer Seafoods and iodized salt
Food content is variable based on soil
How is iodine absorbed? - Answer Organic bound iodine is freed and converted to iodide
within the gastrointestinal tract
What is the single main function of iodine? - Answer The synthesis of thyroid hormones
How is thyroid hormone synthesized from iodine? - Answer Thyroid peroxidase, a membrane-
bound glycoprotein, catalyzes the oxidation of the iodide to the active form I2. The binding of
this active form to the tyrosine in the thyroglobulin to form MIT or DIT (monoiodotyrosines or
diiodotyrosines).
MIT or DIT then condense to form thyroid hormones.
DIT+DIT = T4
MIT+DIT = T3
How is thyroid hormone status regulated? - Answer Stimulation of the thyroid gland causes
the release of the hormones into circulation.
The releasing of thyroid hormone is controlled by the thyroid stimulating hormone (TSH) from
pituitary, which in turn is controlled by thyroid releasing hormone (TRH) from the
hypothalamus.
This hypothalamic-pituitary-thyroid axis is responsible for producing the appropriate amounts of
thyroid hormones, but thyroid status can also be regulated by altering the rate of T4 to T3
conversion by deiodinases.
What is the function for selenium containing 5'-, and 5-deiodinase? - Answer 5'-deiodinase
catalyzes the deiodination (removal) of iodine from the 5' position of T4. This forms active T3.
5-deiodinase catalyzes the deiodination (removal) of iodine from the 5 position of T4. This forms
inactive T3.
What are some of the selected physiological function for thyroid hormone? - Answer
Enhances lipolysis in adipose tissue
Enhances contraction of muscle
Promotes anabolism of bone
Increases the heart rate
, Stimulates nutrient digestion and absorption
Stimulates metabolic rate and cellular oxygen consumption in metabolically active tissues
How does thyroid hormone act on regulating gene expression thereby regulating physiological
functions? - Answer On a target gene promoter, TR forms a heterodimer with RXR (retinoid X
receptor). In the absence of T3, this dimer is associated with a co-repressor, which has histone
deacetylase activity.
This complex also interacts with TFIIB basal transcriptional machinery, and inhibits transcription.
In the presence of T3, a co-activator replaces co-repressor. This results in histone acetylation
and initiation of transcription.
What are the deficiencies associated with iodine? - Answer Goiter
Iodine deficiency disorders (IDDs)
Cretinism
Goiter - Answer Enlargement of the thyroid gland
Caused by over stimulation of TSH
Iodine deficiency disorders (IDDs) - Answer An insufficient supply of iodine during pregnancy
is associated with an increased occurrence of spontaneous abortions, stillbirths and congenital
abnormalities, as well as prenatal and infant mortality
Cretinism - Answer The lack of maternally supplied thyroid hormones at a time when very
active fetal brain development occurs (1st trimester)
Neurological: mental retardation, deaf-mutism, and spastic displegia - paralysis of the legs
Myxedematous: less severe neurological symptoms, more clinically hypothyroid and growth
retarded; concurrent selenium deficiency may lead to the greater thyroid damage associated
with this form of cretinism
What are the toxicities associated with iodine? - Answer Can cause problems with the thyroid
gland
What is hyperthyroidism? - Answer Most often caused by Grave's disease
Results in a continuous stimulation of the thyroid gland and overproduction of the hormone by
antibodies against self TSH receptor
Can also result from adenomas or thyoiditis
Symptoms: palpitations, heat intolerance, nervousness, insomnia, fatigue, increased bowel
movements, light or absent periods, trembling hands, weight loss, warm moist skin, hair loss,
staring gaze
