Thyroid Physiology Flashcards Preview

The Endocrine System > Thyroid Physiology > Flashcards

Flashcards in Thyroid Physiology Deck (50)
Loading flashcards...
1

Which three hormones does the thyroid produce? 

  1. Thyroxine (T4)
  2. Triiodothyronine (T3)
  3. Calcitonin

2

The parathyroid glands are responsible for regulation of what in the body?

Calcium

3

How much does the thyroid gland weigh?

25-30g

(adults)

4

How can the thyroid gland be imaged?

  1. USS
  2. Iodine uptake (it is highly vascular)

5

Describe the cells involved in the structure of the thyroid gland

Follicular cells surround colloid

Parafollicular C cells are dispersed rarely

6

What is a colloid?

Mixture of substances

Contains thyroglobulin

7

How are T3 and T4 synthesised?

Iodine is taken up by follicle cells and attaches to tyrosine residues forming monoiodotyrosine (MIT) and di-iodotyrosine (DIT) units.

Coupling of units occurs with MIT + DIT forming T3 and DIT + DIT forming T4

8

Where are T3 and T4 stored until they are required?

Colloid thyroglobulin

9

Which two drugs are used most to treat hyperthyroidism?

  1. Carbimazole
  2. Propylthiouracil (PTU)

10

How do carbimazole and PTU function?

Inhibits binding of iodine to tyrosine residues preventing formation of T3 and T4

11

Which thyroid hormone comprises around 90% of all secreted thyroid hormones?

T4

12

Which thyroid hormone is more potent?

T3

13

Which enzyme is responsible for the conversion of T4 to T3?

Deiodinase enzyme

14

Where does the conversion of T4 to T3 largely occur?

Liver and kidneys

15

Why do do pharmacotherapies for hyperthyroidism not work instantly?

They inhibit formation of T3/4

There is a large reservoir of these hormones already built up in the colloid

To have an effect these hormone stores must first be used up

16

What induces T3/4 release from follicle cells?

TSH binding

17

Which plasma proteins can T3/T4 bind to?

  1. Thyroxine binding globulin (70%)
  2. Transthyretin (20%)
  3. Albumin (5%)

18

Since T3 is the biologically active form, where does it act upon?

Nuclear receptors

19

What effect does T3 have when bound to nuclear receptors?

Alters transcription of certain genes

20

Metabolic state correlates most directly with what?

Free T3/T4

(moreso that total concentration)

21

Why do thyroid hormones increase basal metabolic rate? (3)

  1. Increase no. and size of mitochondria
  2. Increase O2 use and rates of ATP hydrolysis
  3. Increase synthesis of respiratory chain enzymes

22

In which two ways is carbohydrate metabolism increased by thyroid hormones?

  1. Blood glucose levels increase as glycogenolysis and gluconeogenesis are stimulated
  2. Insulin-dependent glucose uptake into cells is increased

23

How is protein metabolism impacted by thyroid hormone release?

There is increased protein synthesis

24

How do thyroid hormones increase responsiveness to adrenaline and sympathetic neurotransmitters?

Increasing no. of receptors

25

In hyperthyroidism, there is cardiovascular responsiveness to rasied thyroid hormones. How can this be treated pharmacologically?

Propranolol

26

Why is propranolol the preferred beta blocker for cardiovascular responsiveness to thyroid hormones?

It reduces the symptoms of cardiovascular responsiveness

It has inhibitory action upon deiodinase enzymes blocking conversion of T4-T3 which provides a minimal but added therapeutic benefit

27

The thyroid stimulating hormone receptor is which type of receptor?

G protein coupled

28

When are thyroid hormones

a) Highest

b) Lowest

a) Late at night

b) In the morning

29

How many type of deiodinase enzymes are there?

3

30

Where is type I deiodinase enzymes found?

Liver and kidney