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Module 203 Reproduction & endocrinology > T1 L7 Thyroid hormones and physiology > Flashcards

T1 L7 Thyroid hormones and physiology Flashcards

1
Q

Describe the tissue of the thyroid gland

A

Composed of follicles consisting of monolayer of epithelial cells enclosing a large core of viscous homogenous colloid

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2
Q

What does the colloid do?

A

Thyroid hormones are stored here

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3
Q

What are the 3 primary hormones secreted by the thyroid gland?

A

T3
T4
Calcitonin

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4
Q

What does T3 stand for?

A

Triiodothyronine

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5
Q

What does T4 stand for?

A

Tetraiodothyronine

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6
Q

What is calcitonin involved in?

A

Calcium homeostasis

Secreted independently of other thyroid hormones

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7
Q

Where does iodine come from?

A

The diet

Vegetables and meat providing the animals have been fed on vegetables containing iodine

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8
Q

What can affect thyroid function?

A

Pollution
Contamination
Iodine deficiency
Iron deficiency

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9
Q

What degrades MIT & DIT to free the iodide?

A

Halogenases

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10
Q

What happens when T3 and T4 leave the follicular cells?

A

Enter blood stream and are distributed to target tissues

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11
Q

What percentage of thyroid hormone leaving the thyroid gland is T4?

A

95%

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12
Q

Why can’t we be certain that T3 and T4 inhibit TRH release in humans?

A

We can’t measure TRH in humans

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13
Q

What happens if you are iodine deficient?

A

1) Thyroid hormone decreases
2) Lose negative feedback
3) Increased TSH
4) Enlarged thyroid gland

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14
Q

How are thyroid hormones carried round the body?

A

Bound to plasma proteins and transported in the blood

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15
Q

Describe the binding of T4

A

75% to thyronine-binding globulin (TBG)
15-20% to thyroxine
5-10% to albumin

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16
Q

What happens after a thyroid hormone has interacted with its intracellular receptor?

A

Influence gene transcription to influence protein synthesis

17
Q

What is the main effect of thyroid hormones?

A

Increase basal metabolic rate

18
Q

How do thyroid hormones increase the basal metabolic rate?

A

Increase in carbohydrate metabolism
Increase in synthesis, mobilisation and degradation of lipids
Increase in protein synthesis

19
Q

How is carbohydrate metabolism increased by thyroid hormones?

A

Glycogenesis and glucose uptake by muscle and adipose cells
Potentiation of effects of insulin
Potentiation of effects of catecholamines
Increase in glucose absorption by GI tract

20
Q

What organs does thyroid hormone not increase the basal metabolic rate of?

A 
Brain
Uterus
Testes
Spleen
Thyroid gland
Anterior pituitary gland
21
Q

What happens to the growth of an individual who is thyroid hormone deficient?

A

They won’t grow and will continue looking like a child after puberty

22
Q

What happens to the growth of an individual who is growth hormone deficient?

A

They won’t grow but they will undergo normal changes of ageing so they look like a short adult

23
Q

What is levothyroxine used for?

A

Treat thyroid deficiency

Suppress TSH secretion in treatment of some thyroid tumours

24
Q

How is levothyroxine administered?

A

Mouth

Injection

25
Q

What are the adverse effects of levothyroxine?

A 
palpitations
arrhythmias
diarrhoea
insomnia
tremor
weight loss
26
Q

What drugs affect thyroid function?

A 
Carbimazole and methimazole
Propythiouracil
Potassium perchlorate
Radioactive iodine 
Lithium
Iodides
27
Q

What drugs can induce goitre?

A

Lithium

Iodides

28
Q

What does potassium perchlorate do?

A

Competes with iodide for active iodide uptake pump

29
Q

Describe prophylactic administration of iodine

A

Injection or incorporation into table salt or flour
Reduced incidence of endemic goitre
Carries risk of Jod-Basedown phenomena

30
Q

What is carbimazole used for?

A

Hyperthyroidism

31
Q

What are the adverse effects of carbimazole?

A

Rashes and pruritus
Neutropenia
Agranulocytosis
Teratogenic

32
Q

How is carbimazole a pro drug?

A

After absorption it is converted into active form methimazole which prevents peroxidase iodinating the tyrosine residues on thyroglobulin which reduces production of thyroid hormones T3 and T4

33
Q

What is propylthlouracil used for?

A

Hyperthyroidism including Graves disease

Drug of choice in first trimester

34
Q

What are the adverse effects of propylthouracil?

A

Rashes and pruritus
agranulocytosis
Serious liver injury

Module 203 Reproduction & endocrinology (52 decks)

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