Thyroid Physiology

Question 1

Describe the general anatomical appearance of the thyroid gland

Answer 1

• 2 lobes usually joined by an isthmus

- sits in front of the trachea

Question 2

What hormones does the thyroid secrete?

Answer 2

T3
T4
Calcitonin

Question 3

What do the parathyroid glands secrete?

Answer 3

Parathyroid hormone

Question 4

What vertebrae does the thyroid sit in front of?

Answer 4

C5-T1

Question 5

What tracheal cartilage rings does the thyroid sit in front of?

Answer 5

2-4

Question 6

The thyroid decreases in size during pregnancy. TRUE/FALSE?

Answer 6

FALSE

It increases in size during pregnancy

Question 7

What nerve has the potential to be damaged during thyroid surgery?

Answer 7

Recurrent Laryngeal Nerve

Question 8

What cells are responsible for synthesising thyroid hormones?

Answer 8

Follicular cells

Question 9

Where can thyroid hormones be stored if the do not need released immediately/

Answer 9

Large Colloid in centre of follicles

Enclosed by follicular cells

Question 10

What cells are responsible for the synthesis of Calcitonin

Answer 10

Parafollicular C cells

Question 11

What ion is required from the bloodstream in order to make thyroid hormones?

Answer 11

Iodine

Question 12

How are thyroid hormones synthesised?

Answer 12

Iodine in from blood
Added to tyrosine molecules
Via pinocytosis and assistance from ribosomes
Hormones then released into bloodstream

Question 13

Explain the naming process when each iodine is added to a tyrosine unit

Answer 13

1 iodine = Monoiodotyrosine
2 iodines = Di-iodotyrosine
3 iodines = Triiodothyronine
4 iodines = Thyroxine

Question 14

Drugs to target HYPERthyroidism (e.g. carbimazole and propyluracil) target what stage of thyroid hormone production?

Answer 14

Creation of mono/di-iodotyrosines

Question 15

What percentage of hormone secreted by the thyroid is T3 and what percentage is T4?

Answer 15

T3  = 10% 
T4  = 90%

Question 16

T4 is a more potent thyroid hormone than T3. TRUE/FALSE?

Answer 16

FALSE

T3 = more potent

Question 17

Which of the thyroid hormones is the most biologically active?

Answer 17

T3

Question 18

If thyroid hormones are hydroPHOBIC, what plasma proteins are required for their transport?

Answer 18

thyroxine binding globulin (70%)
thyroxine binding prealbumin (20%)
Albumin (5%)

Question 19

Unbound thyroid hormones are considered to be biologically active. TRUE/FALSE?

Answer 19

TRUE

Question 20

Give examples of cases where a patient would have increased TBG and therefore increased bound T4?

Answer 20

Pregnancy/Oral Contraceptive
Newborn
Hepatitis
Biliary Cirrhosis
Drug related e.g. clofibrate/heroin

Question 21

Give examples of cases where a patient may have decreased TBG and therefore less bound T4?

Answer 21

Large glucocorticoid dose
Active acromegaly
Chronic Liver Disease
Nephrotic syndrome
Drug related e.g. Phenytoin/Carbamazepine

Question 22

What processes are thyroid hormones known to increase?

Answer 22

• Basal metabolic rate
• Thermogenesis
• Carbohydrate/Lipid/Protein Metabolism

Question 23

What aspects of growth require thyroid hormone?

Answer 23

• Growth hormone releasing hormone (GHRH) production and secretion requires thyroid hormones
• Myelinogenesis and axonal growth in foetus requires thyroid hormones

Question 24

What effect can an under or overactive thyroid have on the CNS?

Answer 24

Hypothyroidism - slow intellectual functions

Hyperthyroidism – nervousness, hyperkinesis and emotional lability

Question 25

What medication can be used to decrease the symptoms of hyperthyroidism?

Answer 25

beta-blocker e.g. PROPRANOLOL

Question 26

Explain the process of thyroid hormone release starting from the hypothalamus

Answer 26

Thyrotrophin releasing hormone (TRH) from hypothalamus
STIMULATES
Thyroid stimulating hormone (TSH) release from anterior pituitary
STIMULATES
T3 and T4 release from thyroid gland

Question 27

What part of the thyroid hormone pathway can T3 and T4 negatively feedback on?

Answer 27

Both TRH and TSH

Question 28

What are the role of de-Iodinases in thyroid hormone activation?

Answer 28

Converts T4 -> T3 or rT3 (reverse T3)

Question 29

What de-iodinases are most important in converting T4 -> T3?

Answer 29

De-iodinase 1 and 2

Question 30

What de-iodinase converts T4 to revers T3 (rT3)?

Answer 30

De-iodinase 3

Question 31

Where is de-iodinase 1 usually found?

Answer 31

liver and kidney

Question 32

Where can de-iodinase 2 be found?

Answer 32

Heart 
Skeletal muscle
CNS
Fat 
Thyroid
Pituitary

Question 33

Where is de-iodinase 3 found?

Answer 33

fetal tissue
placenta
brain (except pituitary)

Question 34

Why may a patient be deficient in thyroid hormones?

Answer 34

Primary (gland) failure – may be associated
with goitre

Secondary to TRH or TSH (no goitre)

Lack of iodine in diet (may be associated with goitre)

Question 35

What are the symptoms of hypothyroidism?

Answer 35

Reduced BMR
Slow pulse rate 
Fatigue, lethargy, slow response times and mental sluggishness
Cold-intolerance
Tendency to put on weight easily

Question 36

What symptom of hypothyroidism in adults is characterised by a puffy face, hands and feet?

Answer 36

Myxoedema

Question 37

What do babies with hypothyroidism sometimes present with?

Answer 37

Cretinism:

- dwarfism and limited mental functioning due to deficiency of thyroid hormones present at birth

Question 38

What is Grave’s disease?

Answer 38

Autoimmune disease
Causes HYPERthyroidism
Thyroid stimulating immunoglobulin (TSI) acts like TSH but unchecked by T3 and T4

Question 39

What can Grave’s disease cause?

Answer 39

Goitre

Exopthalmus - bulging eyes due to water retaining carbohydrate build up behind eyes

Question 40

What are the symptoms of HYPERthyroidism?

Answer 40

• Increased BMR
• Very fast pulse rate
• Increased nervousness and excessively emotional
• insomnia
• Sweating / heat intolerance
• Tendency to lose weight easily