Thyroid Physiology

Question 1

What is secreted from thyroid gland tissue?

Answer 1

Thyroxin
Tri-iodothyronine
Calcitonin

Question 2

What is secreted from the parathyroid glands?

Answer 2

Parathyroid hormone

Question 3

What ion is the parathyroid gland in control of?

Answer 3

Calcium

Question 4

Where does the thyroid sit?

Answer 4

Between the 5th cervical and 1st thoracic vertebrae

Question 5

What is the blood supply to the thyroid gland?

Answer 5

Superior and inferior thyroid arteries from the external caroti
Thyroidea ima in some people

Question 6

What nerve runs alongside the thyroid gland?

Answer 6

Recurrent laryngeal nerve

Question 7

What drains the thyroid gland?

Answer 7

Superior/ middle thyroid vein which drain into internal jugular
Inferior thyroid that drains into braciocephalic vein

Question 8

What are the thyroid producing cells?

Answer 8

Follicular cells

Question 9

What is a colloid?

Answer 9

Tyrosine containing thyroglobulin filled spheres enclosed by follicular cells

Question 10

What cell produces calcitonin?

Answer 10

Parafollicular C cells

Question 11

What is the action of calcitonin?

Answer 11

Opposite of PTH - it reduces calcium levels

Question 12

What ion is needed to make thyroid hormones?

Answer 12

Iodine

Question 13

In what cell is iodine found in inside follicualr cells?

Answer 13

Pinocytosis

Question 14

What is the building blocks of thyroid hormones?

Answer 14

Iodine attached to tyrosine residuces on thyroglobulin

Question 15

Which hormone is more potent - T3 or T4?

Answer 15

T3 is 4x more potent

Question 16

Where is T4 converted to T3?

Answer 16

In the liver and kidneys - but can be converted in any cell in the body

Question 17

Which hormone is the major biologically active thyroid hormone?

Answer 17

T3

Question 18

What does TSH do?

Answer 18

Stimulates the follicualr cell to secrete thyriod hormones

Question 19

How do T3 and T4 travel around the blood?

Answer 19

Bound to plasma proteins due to the hydoophobic nature

Question 20

What are the main plasma proteins that thyroid hormones bind to?

Answer 20

Thyroxin binding globulin
Thyroxine binding prealbumin
Albumin

Question 21

When will the thyroid hormones be biologically active?

Answer 21

When unbound and free in the plasma

Question 22

How is T4 converted to T3?

Answer 22

Removal of an iodine ion

Question 23

What receptors do thyroid hormones bind to at a cellular level?

Answer 23

Hybrid nuclear receptors

Question 24

What do thyroid blood tests measure?

Answer 24

The free levels of T4 and T3

Question 25

What can increase the total T4 but not free T4?

Answer 25

Pregnancy | OCP

Question 26

What effects does thyroxine have?

Answer 26

``` Metabolism Growth Development Reproduction Behaviour ```

Question 27

What will an overactive thyroid do to the skin?

Answer 27

Increased sweat

Question 28

What will an overactive thyroid have to the heart?

Answer 28

Increased HR | Palpitations

Question 29

What can increased thyroxine do in gynae?

Answer 29

Reduced periods

Question 30

For what organ is thyroxine particularly important for in a developing foetus?

Answer 30

Brain

Question 31

What do thyroid hormones do the basal metabolic rate?

Answer 31

Increased basal metabolic rate Increase number and size of mitochondria Increase oxgen use and rates of ATP hydrolysis Increased synthesis of resp chain enzymes

Question 32

What effect do thyroid hormones have on thermogenesis?

Answer 32

Increased

Question 33

What effect do thyroid hormones have on carbohydrate metabolism?

Answer 33

Increase blood glucose | Increase insulin-dependent glucose uptake into cells

Question 34

What effect do thyroid hormones have on lipid metabolism?

Answer 34

Mobilise fats from adipose tissue | Increase fatty acid oxidation in tissues

Question 35

What effect do thyroid hormones have on protein metabolism?

Answer 35

Increased protein synthesis

Question 36

What effect do thyroid hormones have on growth?

Answer 36

Growth hormone releasing hormone (GHRH) production and secretion requires thyroid hormones Glucocorticoid induced GHRH release also dependent on thyroid hormones

Question 37

What effect do thyroid hormones have on developement of foetal and neonatal brain?

Answer 37

Myeliongenesis and axonal growth require thyroid hormones | Particularly imporant in 1st trimester as foetus doesn't have thyroid gland yet

Question 38

What effect do thyroid hormones have on normal central nervous system activity?

Answer 38

Hypothyrodism - slow intellectual function | Hyperthyrodism - nervousness, hyperkinesis, emotional lability

Question 39

What neurotransmitters are affected by thyroid hormones?

Answer 39

Thyroid hormones increase the responsivness to adrenaline and sympathetic neurotransmitter noradrenaline by increasing the number of receptors

Question 40

What happens in the heart in increased thyroid production?

Answer 40

Increased force and rate of contraction

Question 41

What drug can be used to treat the inital symptoms of hyperthyrodism?

Answer 41

Beta blockers such as propanolol

Question 42

What is the effect of stress on thyroid hormone regulation?

Answer 42

Inhibitis TRH and TSH release

Question 43

How does the circadian rhythm affect thyroid hormone regulation?

Answer 43

Highest late at night and lowest in the morning

Question 44

How do low temps affect thyroid hormone regulation?

Answer 44

In babies and young children, expsoure to cold environments stimualtes TRH release, stimulating TSH release increasing T3 and T4 release

Question 45

What is the function of throtrophin releaseing hormone (TRH)?

Answer 45

Formed in the hypothalamus and stimulates TSH release from the anterior pituitary

Question 46

What type of feedback is utilised in thyroid hormone regulation?

Answer 46

Negative feedback control of release of TRH and TSH

Question 47

What is the function of deiodinase enzymes?

Answer 47

Activate and deactivate thyroid hormones via the addition or removal of an iodine atom in the outer ring

Question 48

What is the most important deiodinase enzyme?

Answer 48

Type 2 - D2

Question 49

What does D2 do?

Answer 49

Converts T4 to T3

Question 50

Where it D1 found?

Answer 50

Liver and kidneys

Question 51

Where is D2 found?

Answer 51

Heart and skeletal muscle, CNS, fat, thyroid and pituitary

Question 52

Where is D3 found?

Answer 52

Fetal tissue and placenta, brain (except pituitary)

Question 53

What can cause hypothyrodism?

Answer 53

Primary gland failure - may be associated with goitre - autoimmune disease Secondary to TRH or TSH (no goitre) Lack of iodine in diet

Question 54

What are the symptoms of hypothyrodism?

Answer 54

``` Reduced BMR Slow pulse rate Fatigue Cold-intolerance Tendency to put on weight easily ```

Question 55

What is myxoedema?

Answer 55

Puffy face, hands and feet

Question 56

What is cretinism?

Answer 56

Dwarfism and limited mental function due to deficiency of thyroid hormones at birth

Question 57

What is the most common cause for hypothyrodism?

Answer 57

Autoimmune disease

Question 58

What is the most common reason for hyperthyrodism?

Answer 58

Graves disease - autoimmune disease where thyroid stimulating immunoglobulin acts like TSH

Question 59

What is exopthalmos?

Answer 59

Bulging eyes due to water retaining carbohydrate buld up behind eyes

Question 60

What are the common symptoms of hyperthyrodism?

Answer 60

``` Increased BMR Vert fast HR Increased nervousness and excessively emotional Insomnia Sweating and heat intolerance Tendency to lose weight easily ```

Question 61

What is the average weight of the thyroid gland in adults?

Answer 61

25-30g

Question 62

What is the main regulator of thyroid hormone release?

Answer 62

TSH

Question 63

What is the main binding globulin for thyroxine?

Answer 63

TBG - thyroxine binding globulin

Question 64

What effects can thyroxine have on the heart?

Answer 64

Cardiomyopathy | AF