Thyroid Gland

Question 1

What are the 2 physiologically active thyroid hormones?

Answer 1

T3

T4

Question 2

What are the 2 types of cells in the thyroid?

Answer 2

C (clear cells)

Follicular cells

Question 3

What do clear cells secrete?

Answer 3

Calcitonin

Question 4

What does calcitonin regulate?

Answer 4

Calcium

Question 5

What tends to dominate the action of calcitonin?

Answer 5

PTH

Question 6

What are thyroid follicles?

Answer 6

Structures surrounded by follicular cells

Question 7

What is the centre of thyroid follicles filled with?

Answer 7

Colloid

Question 8

What type of hormone are thyroid hormones?

Answer 8

Amine derived from tyrosine `

Question 9

What do follicular cells manufacture?

Answer 9

The enzymes that make thyroid hormones as well as thyroglobulin

Question 10

Where are thyroid hormone and thyroglobulin exported to?

Answer 10

The colloid

Question 11

What do follicular cells concentrate?

Answer 11

Iodide

Question 12

What does iodide combine with?

Answer 12

Tyrosine residues to form TH

Question 13

Which enzyme catalyses the formation of TH>

Answer 13

Thyroid peroxidase

Question 14

How does iodide enter follicular cells from the plasma?

Answer 14

via a Na+/I- transporter (symport they both travel in the same direction). The coupling to Na+ enables the follicular cells to take up iodide against a concentration gradient.

Question 15

How is iodide transported to the colloid?

Answer 15

Via the pendrin transporter

Question 16

How is iodide transport inhibited?

Answer 16

by thiocyanates

Question 17

What does the addition of one iodine to tyrosine form?

Answer 17

MIT (monoiodotyrosine)

Question 18

What does the addition of two iodine to tyrosine form?

Answer 18

DIT

Diiodothyrosine

Question 19

What does DIT + DIT form?

Answer 19

tetraiodothyronine or Thyroxine T4

Question 20

What does DIT + MIT form?

Answer 20

triiodothyronine or T3

Question 21

What happens in response to TSH?

Answer 21

Portions of the colloid are taken back up into the follicular cell by endocytosis. Within the cells they form vesicles which contain proteolytic enzymes that cut the thyroglobulin to release thyroid hormones.

Question 22

Are T3 and T4 lipid soluble?

Answer 22

Yes

Question 23

What do T3 and T4 bind to in the plasma?

Answer 23

Thyroxine-binding globulin

Plasma proteins

Question 24

Where do T3 and T4 circulate?

Answer 24

In the plasma

Question 25

What is the movement of TH from the colloid to the plasma under the control of?

Answer 25

TSH release from the PG

Question 26

Where is TSH released from?

Answer 26

PG

Question 27

How much TH circulates bound to plasma proteins?

Answer 27

99.8%

Question 28

Which hormone is released from the hypothalamus to stimulate TSH production?

Answer 28

TRH

Question 29

Why does T4 have a longer half life?

Answer 29

Because it has a higher affinity for thyroxine binding globulin

Question 30

Does bound hormone exert an inhibitory effect on TSH and TRH?

Answer 30

no only free hormone does

Question 31

What do TH receptors have a higher affinity for?

Answer 31

T3

Question 32

Which TH is more physiologically active?

Answer 32

T3

Question 33

Where do thyroid hormones bind?

Answer 33

To nuclear receptors in target cells

Question 34

What is the effect of TH binding to receptors?

Answer 34

Change transcription and translation to alter protein synthesis

Question 35

What are the effects of TH in the body?

Answer 35

Raises metabolic rate and promotes thermogenesis increase hepatic gluconeogenesis net increase in proteolysis net increase in lipolysis critical for growth (lack of TH results in retarded growth) anabolic required for foetal brain development

Question 36

What is congenital hypothyroidism?

Answer 36

Thyrodism from birth

Question 37

How does TH affect growth?

Answer 37

Stimulates GH receptor expression

Question 38

What happens to growth when TH is not present?

Answer 38

Receptors are not in adequate numbers and normal growth cannot occur

Question 39

What can cause hyperthyroidism?

Answer 39

Graves disease | Thyroid adenoma

Question 40

What causes graves disease?

Answer 40

(common) antibodies produced that bind mimic TSH and continually activate the thyroid gland. Increased release of TH switches off TSH release from anterior pituitary so [TSH] plasma is very low

Question 41

What are the symptoms of hyperthyroidism?

Answer 41

Increased metabolic rate and head production - weight loss Increased protein catabolism - muscle weakness Altered nervous system function - hyper excitable reflexes Elevated CVS function - increased HR/contractile force

Question 42

What is a main causes of hypothyroidism?

Answer 42

Hashmoto's disease Iodide deficiency Idiopathic

Question 43

What causes Hashmoto's disease?

Answer 43

Autoimmune attack of thyroid gland

Question 44

What are the symptoms of hypothyroidism?

Answer 44

1. Decreased metabolic rate and heat production - weight gain/cold intolerance 2. Disrupted protein synthesis - brittle nails/thin skin 3. Altered nervous system function - slow speech/reflexes, fatigue 4. Reduced cardiovascular function - slow heart rate/weaker pulse

Question 45

What is Goitre?

Answer 45

Enlargement of the thyroid gland

Question 46

What is primary Thyroid disease?

Answer 46

When the TG is not working

Question 47

What is secondary thyroid disease?

Answer 47

When the problem is with the PG

Question 48

What is tertiary thyroid disease?

Answer 48

When the problem is in the hypothalamus