Revision lecture thyroid

Question 1

Where is the thyroid located?

Answer 1

Inferior to the laryngeal prominence and the thyroid cartilage

Question 2

Describe the histology of the thyroid

Answer 2

Follicular cells arranged in spheres around extracellular colloid

Question 3

What is colloid?

Answer 3

A deposit of thyroglobulin (precursor to thyroxine)

Question 4

Describe the synthesis of thyroxine

Answer 4

Thyroglobulin is synthesised in the epithelia cells
Exocytosis of the thyroglobulin into the follicle lumen
Iodide is actively transported into the epithelial cell
Iodide is oxidised into iodine
You get iodination of the thyroglobulin to make monoiodothyroglobulin and diiodothyroglobulin

MIT +DIT–>T3
DIT+DIT–>T4

Question 5

How is thyroxine transported in the blood?

Answer 5

Bound to thyroxine binding globulin and albumin

Question 6

Describe the negative feedback loop of the synthesis of thyroxine

Answer 6

Hypothalamus releases TRH
Anterior pituitary releases TSH
Thyroid produces thyroxine
Has negative feedback on anterior pituitary–>less TSH production
Has negative feedback on hypothalamus–> Less TRH production

Question 7

four actions of thyroxine?

Answer 7

Increased metabolic rate
Increased glucose uptake
Increased fatty acid breakdown
Increazsed protein synthesis

Question 8

What receptors does thyroxine act on?Effect does it have? Describe how it has this effect

Answer 8

Intracellular ones
Affects transcription of genes
Thyroxine enters the cell, binds to hormone response element on the DNA, which relieves repression of gene transcription

Question 9

What is the most common form of hypothyroidism?

Answer 9

Hashimoto’s disease

Question 10

Whats the most common form of hyperthroidism?

Answer 10

Graves Disease

Question 11

Describe Hashimoto’s disease

Answer 11

Hypothroidism

Its an autoimmune disease where antibodies block TSH receptors on the thyroid. Leads to a destruction of follicles

Question 12

Symptoms of Hashimotos? (6)

Answer 12

Cold intolerance
Reduced BMR
Tiredness
Bradycardia
Goitre
Voice deep and husky

Question 13

Describe Graves Disease

Answer 13

Autoimmune disease

You get an antibody that stimulates TSH receptors

Question 14

Symptoms of Graves disease

Answer 14

Heat intolerance
Increased BMR
Hyperactivity
Tachycardia
Goitre
Exothalmos- Bulging eyes

Question 15

What is exothalmos? Why does it occur?

Answer 15

Bulging eyes
You get increased lipid deposit
esp behind the eyes
pusshes eyes out

Question 16

A 45 year old woman comes into your GP clinic, with hot
flushes and an increased appetite. She has also noticed
some weight loss. Differential diagnosis? (3)

Answer 16

Hyperthyroidism (Grave’s)
● Parasite infection
● Pre-menopausal?

Question 17

Are autoimmune conditions more common in males or females?

Answer 17

2.5x more common in females

Question 18

With graves and hashimotos disease, in terms of T4 and TSH levels, what would you see?

Answer 18

Graves–> High T4, low TSH

Hashimotos–>Low T4, high TSH

Question 19

How do you treat overactive thyroid? How does it work?

Answer 19

Carbimazole

Blocks formation of thyroid hormone