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SM Endocrine > Thyroid Physiology > Flashcards

Thyroid Physiology Flashcards

1
Q

What all does the thyroid gland tissue secrete?

A

Thyroxine (T4)
Tri-iodothyronine (T3)
Calcitonin

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2
Q

What do the parathyroid glands secrete

A

Parathyroid hormone (PTH)

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3
Q

What cells secrete calcitonin

A

Parafollicular C cells

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4
Q

Describe what can be seen under the microscope for thyroid tissue

A

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

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5
Q

What does calcitonin play a minor role in

A

The regulation of Calcium

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6
Q

What is the main substance in the colloid

A

Thyroglobulin

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7
Q

What do tyrosine units do?

A

Convert T3 to T4

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8
Q

How is T3 formed

A

The coupling of MIT and DIT

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9
Q

How is T4 formed

A

coupling of 2 DITs

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10
Q

Where is T3 and T4 found

A

In the colloid thyroglobulin till required

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11
Q

Where is iodine taken up

A

follicle cells

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12
Q

How is MIT and DIT formed

A

Iodine attaches to tyrosine residues on thyroglobulin

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13
Q

What do T3 and T4 bind to and why

A

plasma proteins as they hydrophobic / lipophilic

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14
Q

When are T3 and T4 not biologically active

A

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

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15
Q

Is T3 more active than T4 or other way about

A

T3 is more active than T4

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16
Q

How much of thyroid hormones that are secreted are T4

A

90%

17
Q

What is the more potent Thyroid hormone

A

T3 - it is around 4 times more potent

18
Q

What converts T4 to T3

A

Liver and kidneys

19
Q

What do thyroid hormones do to the basal metabolic rate

A

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

20
Q

What do thyroid hormones do to thermogenesis

A

Increase it

around 30 % temperature regulation due to thyroid hormone thermogenesis

21
Q

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

A

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

22
Q

What do thyroid hormones do to lipid metabolism

A

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

23
Q

What do thyroid hormones do to protein metabolism

A

Increase protein synthesis

24
Q

Why is the thyroid hormone important in growth and development

A

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

25
Q

How do thyroid hormones have a permissive sympathomimetic action

A

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

26
Q

What should be used to treat initial stages of hyperthyroidism

A

Beta blockers such as propranolol

27
Q

How are the release of TRH and TSH controlled

A

Through negative feedback of T3 and T4

28
Q

What effect does stress have on the thyroid hormone

A

It inhibits TRH and TSH release

29
Q

How do low temperatures affect thyroid hormone regulation

A

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

30
Q

Describe the levels of thyroid hormones throughout the day

A

Circadian rhythm

Highest late at night and lowest first thing in the morning

31
Q

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

A 
Reduced BMR 
Slow pulse rate 
Fatigue, lethargy, slow response times and mental sluggishness 
cold intolerance 
tendency to put on weight easily
32
Q

What is another symptom for adults with hypothyroidism

A

Myxoedema (puffy face, hands and feet(

33
Q

What is another symptom for babies with hypothyroidism

A

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

34
Q

What causes exophthalmos

A

Water retaining carbohydrate build up behind the eyes

35
Q

What is the main binding globulin for thyroxine

A

TBG

SM Endocrine (27 decks)

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