Thyroid Physiology

Question 1

What all does the thyroid gland tissue secrete?

Answer 1

Thyroxine (T4)
Tri-iodothyronine (T3)
Calcitonin

Question 2

What do the parathyroid glands secrete

Answer 2

Parathyroid hormone (PTH)

Question 3

What cells secrete calcitonin

Answer 3

Parafollicular C cells

Question 4

Describe what can be seen under the microscope for thyroid tissue

Answer 4

Follicular cells
Colloid - tyrosine containing thyroglobulin filled spheres enclosed by follicular cells
Parafollicular C cells

Question 5

What does calcitonin play a minor role in

Answer 5

The regulation of Calcium

Question 6

What is the main substance in the colloid

Answer 6

Thyroglobulin

Question 7

What do tyrosine units do?

Answer 7

Convert T3 to T4

Question 8

How is T3 formed

Answer 8

The coupling of MIT and DIT

Question 9

How is T4 formed

Answer 9

coupling of 2 DITs

Question 10

Where is T3 and T4 found

Answer 10

In the colloid thyroglobulin till required

Question 11

Where is iodine taken up

Answer 11

follicle cells

Question 12

How is MIT and DIT formed

Answer 12

Iodine attaches to tyrosine residues on thyroglobulin

Question 13

What do T3 and T4 bind to and why

Answer 13

plasma proteins as they hydrophobic / lipophilic

Question 14

When are T3 and T4 not biologically active

Answer 14

When they are bound - they need to be released by the carrier as they are required into the tissues

Question 15

Is T3 more active than T4 or other way about

Answer 15

T3 is more active than T4

Question 16

How much of thyroid hormones that are secreted are T4

Answer 16

90%

Question 17

What is the more potent Thyroid hormone

Answer 17

T3 - it is around 4 times more potent

Question 18

What converts T4 to T3

Answer 18

Liver and kidneys

Question 19

What do thyroid hormones do to the basal metabolic rate

Answer 19

Increase it:
increase number and size of mitochondria
Increase oxygen use and rates of ATP hydrolysis
Increase synthesis of respiratory chain enzymes

Question 20

What do thyroid hormones do to thermogenesis

Answer 20

Increase it

around 30 % temperature regulation due to thyroid hormone thermogenesis

Question 21

Why is there an increase in blood glucose because of thyroid hormones

Answer 21

Due to stimulation of glycogenolysis and gluconeogenesis as well as an increase of insulin-dependent glucose uptake into cells

Question 22

What do thyroid hormones do to lipid metabolism

Answer 22

Mobilise fats from adipose tissue and increase fatty acid oxidation in tissues

Question 23

What do thyroid hormones do to protein metabolism

Answer 23

Increase protein synthesis

Question 24

Why is the thyroid hormone important in growth and development

Answer 24

It is important in the production and secretion of growth hormone
Development of foetal and neonatal brain
Normal central nervous activity is controlled by this

Question 25

How do thyroid hormones have a permissive sympathomimetic action

Answer 25

They increase responsiveness to adrenaline and sympathetic NS neurotransmitter, noradrenaline, by increasing numbers of receptors

Question 26

What should be used to treat initial stages of hyperthyroidism

Answer 26

Beta blockers such as propranolol

Question 27

How are the release of TRH and TSH controlled

Answer 27

Through negative feedback of T3 and T4

Question 28

What effect does stress have on the thyroid hormone

Answer 28

It inhibits TRH and TSH release

Question 29

How do low temperatures affect thyroid hormone regulation

Answer 29

Stimulation of TRH release which stimulates TSH release and so increases T3 and T4 release from thyroid

Question 30

Describe the levels of thyroid hormones throughout the day

Answer 30

Circadian rhythm | Highest late at night and lowest first thing in the morning

Question 31

What are some symptoms of a deficient thyroid hormone (hypothyroidism)

Answer 31

``` Reduced BMR Slow pulse rate Fatigue, lethargy, slow response times and mental sluggishness cold intolerance tendency to put on weight easily ```

Question 32

What is another symptom for adults with hypothyroidism

Answer 32

Myxoedema (puffy face, hands and feet(

Question 33

What is another symptom for babies with hypothyroidism

Answer 33

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

Question 34

What causes exophthalmos

Answer 34

Water retaining carbohydrate build up behind the eyes

Question 35

What is the main binding globulin for thyroxine

Answer 35

TBG