Module 9.1 Thyroid Gland

Question 1

What are the two types of endocrine cells contained in the thyroid gland?

Answer 1

The thyroid gland contains two types of endocrine cells:

1. follicular cells and
2. C cells

Question 2

The follicular cells are

• arranged into ____\_-like structures (called _____)
• that are filled with _____\_ and
• are involved in the secretion of the ______\_

Answer 2

The follicular cells are

• arranged into sphere-like structures (called follicles)
• that are filled with colloid and
• are involved in the secretion of the thyroid hormones

Question 3

The C cells are interspersed between the ____\_and are responsible for the secretion of ____\_

Answer 3

The C cells are interspersed between the follicles and are responsible for the secretion of calcitonin

Question 4

Calcitonin is a _____\_hormone involved in __________\_

Answer 4

Calcitonin is a peptide hormone involved in calcium metabolism

Question 5

What are the two thyroid hormones?

Answer 5

1. tri-iodothyronine (T3) and
2. tetraiodothyronine (T4 or thyroxine)

Question 6

The amino acid _____\_ is used to synthesize thyroglobulin inside the follicular cells.

Answer 6

The amino acid tyrosine is used to synthesize thyroglobulin inside the follicular cells.

Question 7

The amino acid tyrosine is used to synthesize _____\_ inside the follicular cells.

Answer 7

The amino acid tyrosine is used to synthesize thyroglobulin inside the follicular cells.

Question 8

Thyroglobulin, along with iodine obtained from the diet, is transported into the ____\_, where the iodine is then attached to the ____\_ within the _____\_

Answer 8

Thyroglobulin, along with iodine obtained from the diet, is transported into the colloid, where the iodine is then attached to the tyrosine within the thyroglobin

Question 9

When one iodine is attached to the tyrosine in the thyroglobin, this produces a____________ molecule.

Answer 9

When one iodine is attached, this produces a monoiodotyrone (MIT) molecule.

Question 10

When two iodines are attached to the tyrosine within thyroglobin, this produces a __________molecule

Answer 10

When two iodines are attached to the tyrosine within thyroglobin, this produces a di-iodotyrosine (DIT) molecule

Question 11

Coupling between one MIT and one DIT molecule yields ____\_, whereas coupling between two DIT molecules yields __\_.

Answer 11

Coupling between one MIT and one DIT molecule yields T3, whereas coupling between two DIT molecules yields T4.

Question 12

Secretion of the thyroid hormones involves phagocytosis of the _____\_-containing __\_ by the ____\_ cells

Answer 12

Secretion of the thyroid hormones involves phagocytosis of the thyroglobulin-containing colloid by the follicular cells

Question 13

Once inside the follicular cell, fusion of the phagocytosed vesicle with a lysosome releases the __\_and __\_, as well as any uncoupled ___\_and __\_ molecules, from the thyroglobin

Answer 13

Once inside the follicular cell, fusion of the phagocytosed vesicle with a lysosome releases the T3 and T4, as well as any uncoupled MIT and DIT molecules, from the thyroglobin

Question 14

T3 and T4 diffuse out of the ____\_cell and into the ____\_, and iodine is removed from the remaining _____and ___\_molecules and transported back into the ___\_ for reuse.

Answer 14

T3 and T4 diffuse out of the follicular cell and into the plasma, and iodine is removed from the remaining MIT and DIT molecules and transported back into the colloid for reuse.

Question 15

Synthesis, storage and secretion of thyroid hormone: (1) _____\_ produced within the thyroid follicular cells by the endoplasmic reticulum and Golgi complex is exocytosed into the colloid.

(2) _____\_ is carried by transport proteins across both membranes of the follicular cells and into the colloid.
(3a) Attachment of one iodine to tyrosine within the TGB molecule yields _____\_.
(3b) Attachment of two iodines to tyrosine within the TGB yields _____\_.
(4a) The coupling of two DITs yields _____\_.
(4b) The coupling of one MIT and one DIT yields _____\_.
(5) _____\_ colloid enters into the follicular cells through phagocytosis.
(6) Lysosomes separate the ________from the _____\_.
(7a) _____\_and _____\_ diffuse into the blood.
(7b) The iodine is removed from _____\_and _____\_ and moved back to the colloid for synthesis of more _____\_.

Answer 15

Synthesis, storage and secretion of thyroid hormone: (1) Thyroglobulin (TGB) produced within the thyroid follicular cells by the endoplasmic reticulum and Golgi complex is exocytosed into the colloid.

(2) Iodine is carried by transport proteins across both membranes of the follicular cells and into the colloid.
(3a) Attachment of one iodine to tyrosine within the TGB molecule yields monoiodotyrosine (MIT).
(3b) Attachment of two iodines to tyrosine within the TGB yields diodotyrosine (DIT).
(4a) The coupling of two DITs yields tetraiodothyronine (thyroxine or T4).
(4b) The coupling of one MIT and one DIT yields triiodothyronine (T3).
(5) TGB-containing colloid enters into the follicular cells through phagocytosis.
(6) Lysosomes separate the iodinated products from the TGB.
(7a) T3 and T4 diffuse into the blood.
(7b) The iodine is removed from MIT and DIT and moved back to the colloid for synthesis of more thyroid hormone.

Question 16

Secretion of the thyroid hormones is regulated through a _______-______________-_______ pathway

Answer 16

Secretion of the thyroid hormones is regulated through a hypothalamus-anterior pituitary-thyroid gland pathway

Question 17

___\_ is the most abundant thyroid hormone produced, but it is the least active form.

Answer 17

T4 is the most abundant thyroid hormone produced, but it is the least active form.

Question 18

Most of the T4 in the plasma is converted by the ___\_and ____\_ into the more active _\_ form before the T4 can exert its physiological actions

Answer 18

Most of the T4 in the plasma is converted by the liver and kidney into the more active T3 form before the T4 can exert its physiological actions

Question 20

Thyroid hormones are the primary determinant of the

• _______
• exert _______ and _______ effects,

and

• alter _______ and _______ function.

Thyroid hormones are also essential for normal growth and development of the _______

Answer 20

Thyroid hormones are the primary determinant of the

• metabolic rate,
• exert calorigenic and sympathomimetic effects,

and

• alter fuel metabolism and cardiac function.

Thyroid hormones are also essential for normal growth and development of the nervous system.

Question 21

Hypothyroidism (______\_) can result from

• an abnormality in the _______\_,
• a deficiency of ________\_and/or ________\_
• or an inadequate supply of ______\_

Answer 21

Hypothyroidism (underactive thyroid) can result from

• an abnormality in the thyroid gland,
• a deficiency of thryotropin-releasing hormone (TRH) and/or thyroid-stimulating hormone (TSH),
• or an inadequate supply of iodine

Question 22

Symptoms of hypothyroidism include

• ______ (a swelling of the ______, ______, and ______),
• decreased ______,
• ______,
• ______,
• ______,
• decreased ______, and
• poor tolerance of ______

Answer 22

Symptoms of hypothyroidism include

• myxedema (a swelling of the face, hands, and feet),
• decreased metabolic rate,
• weight gain,
• fatigue,
• weak pulse,
• decreased mental functioning, and
• poor tolerance of cold

Question 23

What are two treatment options for hypothyrodism?

Answer 23

Hypothyroidism can be treated by

• thyroid hormone replacement therapy

or

• dietary iodine

Question 24

What is Cretinism?

What happens if it is left untreated?

Answer 24

• Cretinism is the medical condition resulting from hypothyroidism present from birth.
• If untreated, cretinism results in retardation of both physical growth and mental development.

Question 25

Hyperthyroidism (____\_ thyroid) can result from

• ______\_
• an excess of ___\_and/or __\_,
• a hypersecreting ______\_

Answer 25

Hyperthyroidism (overactive thyroid) can result from

• Graves’ disease,
• an excess of TRH and/or TSH,
• a hypersecreting thyroid tumour

Question 26

What is the most common form of hyperthyroidism?

Answer 26

Graves’ Disease

Question 27

What is Graves’ disease?

Answer 27

An autoimmune disease resulting from immunoglobulin stimulation of TSH receptors

Question 28

Graves’ disease, an _____\_disease resulting from ____\_ stimulation of ______\_, is the most common form of hyperthyroidism

Answer 28

Graves’ disease, an autoimmune disease resulting from immunoglobulin stimulation of TSH receptors, is the most common form of hyperthyroidism

Question 29

A classic symptom of Graves’ disease is ______\_, in which the eyes bulge forward due to fluid retention behind the eyes

Answer 29

A classic symptom of Graves’ disease is exophthalmos, in which the eyes bulge forward due to fluid retention behind the eyes

Question 30

Symptoms of hyperthyroidism include

• increased _______\_,
• poor tolerance of _____,
• increased _______,
• decreased ______,
• _______ abnormalities, and
• altered ______ functioning

Answer 30

Symptoms of hyperthyroidism include

• increased metabolic rate,
• poor tolerance of heat,
• increased appetite,
• decreased weight gain,
• cardiovascular abnormalities, and
• altered mental functioning

Question 31

What are two treatment options for Hyperthyroidism?

Answer 31

Hyperthyroidism can be treated by

• surgically removing part of the oversecreting thyroid gland or
• by destroying part of it by applying radioactive iodine

Question 32

A ____\_ is an enlarged thyroid gland and can result from hypothyroidism or hyperthyroidism

Answer 32

A goiter is an enlarged thyroid gland and can result from hypothyroidism or hyperthyroidism

Question 33

An appropriate level of TSH is necessary to maintain the _______ of the thyroid gland

Excess TSH will stimulate both

• _______ (increased cell ___\_) and,
• _______ (increased cell _______) of the thyroid gland

Answer 33

An appropriate level of TSH is necessary to maintain the structural integrity of the thyroid gland

Excess TSH will stimulate both hypertrophy (increased cell size) and hyperplasia (increased cell numbers) of the thyroid gland

Question 34

How does hypothyroidism result in a goiter?

Answer 34

low levels of the thyroid hormones decrease the negative feedback to the anterior pituitary and, in consequence, increased amounts of TSH are produced

Question 35

How does hyperthyroidism result in a goiter?

Answer 35

Either Graves’ disease or increased synthesis of TSH leads to excessive stimulation of the growth of the thyroid gland.