Thyroid

Question 1

What are the dimensions and weight of an adult thyroid?

Answer 1

Each lobe is 2.5 – 4 cm long, 1.5 – 2 cm wide and 1 - 1.5 cm thick Adult gland weighs 10 – 20 g

Question 2

When is the thyroid usually enlarged?

Answer 2

During adolescence
During pregnancy
During lactation
During later portion of menstrual cycle

Question 3

What is the blood supply to the thyroid gland?

Answer 3

Blood supply from SUPERIOR and INFERIOR THYROID ARTERIES
These Arise from EXTERNAL CARATOID ARTERY SUBCLAVIAN ARTERY
- Blood flow 4 – 6 ml/min/g tissue

Question 4

What are the main roles of the thyroid gland?

Answer 4

Neural development in foetus
Growth in the young child
Controls basal metabolic rate (BMR)
Concentrates iodine for incorporation into thyroid hormones Contains 60 – 65% of body iodine

Question 5

What are the direct effects of a thyroid hormone-receptor complex binding to DNA (hormone responsive element TRE)?

Answer 5

Increased mRNA production
Increased protein synthesis
Increased Na+/K+-ATPase levels, Increased ATP turnover Increased O2 consumption
Increased number of adrenoceptors

Question 6

What are the physiological effects of thyroid hormones?

Answer 6

Increased O2 consumption and heat production
Increase cardiac muscle contractility
Increased sensitivity to catecholamines
Maintenance of hypoxic and hypercapnic drive in respiratory centre respiratory centre
Increase gut motility
Increase erythropoeisis
Increase bone turnover
Increase protein turnover – decrease in muscle mass
Increase cholesterol degradation
Increase metabolic turnover of hormones and drugs

Question 7

What are the causes of hypothyroidism (non-dietary causes)?

Answer 7

HASHIMOTO’S THYRODITIS - Affects about 3% of population - autoimmune disease - antibodies to thyroglobulin or thyroid peroxidase

Radiotherapy or surgery for hyperthyroidism

Question 8

What are the treatments for hypothyroidism?

Answer 8

Thyroxine (T4) - T1/2: 6 days, effects last 14 days

Liothyronine (sodium salt of T3) - T1/2: 2-4 days, effects last 8 days

Question 9

What is the daily requirement for iodine intake?
Below what level does hypothyroidism (myxedema) occur?
What type of goitre develops

Answer 9

Dietary iodine requirement 150microg/day
Iodine deficiency<50microg/day
non-toxic goitre

Question 10

What are goitrogens and what are they found in/caused by?

Answer 10

• GOITROGEN suppresses hormone secretion
• increases TSH secretion – goitre
  iodine in kelp (seaweed), brassicae (cabbage), cassava, lithium some local drinking water, cough mixtures

Question 11

What is Graves’disease?

Answer 11

GRAVES’ DISEASE (diffuse toxic goitre) autoimmune disease TSAb (LATS) - produces prolonged stimulation of TSH receptors

Question 12

What are the feature of Graves’ disease?

Answer 12

Thyrotoxicosis - weight loss, sweating, tremor, tachycardia, nervous, diarrhoea
Goitre, Exophthalmos and upper lid retraction. Pretibial myxoedema thickening of skin over tibia due to deposition of glycosaminoglycans

Question 13

2 antithryroid drugs?

Answer 13

CARBIMAZOLE (converted to methimazole in body) PROPYLTHIOURACIL - both inhibit thyroid peroxidase and propylthiouracil also prevents peripheral conversion of T4 to
- 4-8 weeks to become euthyroid .
Reduce dose to maintenance dose
Treat for 12-18 months
Side effect: Neutropenia and angranulocytosis - Report sore throat etc

Question 14

How is radioiodine (131I) used to treat hyperthyroidism?

Answer 14

Taken up into follicular cells and irradiates them. Beta and gamma emitter.
Beta particles kill cells, gamma pass through without causing damage.
T1/2 8 days, 2 months completely decayed

Question 15

What are the causes of a raised free T4?

Answer 15

Graves' Disease
Toxic nodular disease (non-autoimmune)
Thyroxine treatment
Sub acute viral thyroiditis
Iodine ingestion
Struma ovarii 
Cancer of the thyroid

Question 16

What is the ratio of hyperthyroidism in females to males?

Answer 16

6:1

Question 17

Two types of benign thyrotoxicosis?

Answer 17

Toxic Diffuse Goitre (Grave’s Disease)

Toxic Nodular Goitre (Plummer’s Disease)

Question 18

What are the 3 pathological mediators in Graves’ disease?

Answer 18

TSH Receptor Antibody (TSHRA)
Thyroid Stimulating Immunoglobulin (TSI)
Long Acting Thyroid Stimulator (LATS)

Question 19

Conditions in which TSHRAb are found?

Answer 19

• Graves’ Disease
• Hashimoto’s Thyroiditis
• Thyroid Cancer
• Sub-acute thyroiditis
• Juvenile Diabetes

Question 20

What should you do if a cold nodule presents in the thyroid ofa Grave’s disease patient when you do a technetium study with a gamma camera?

Answer 20

Ultrasound and FNA to rule out thyroid cancer

Question 21

Does severe dysthyroid eye disease require urgent attention?

Answer 21

Yes - immediate referral to an ophthalmologist.

The affected muscle can affect the cranial nerves

Question 22

What a about a country increases the number of toxic nodular goitre (Plummer’s disease) cases it has?

Answer 22

Low dietary iodine - eg. Switzerland

Question 23

Prominence of veins on upper chest is a sign of what thyroid disease?

Answer 23

Toxic Nodular

Goitre Plummer’s Disease

Question 24

What are the causes of IODINE INDUCED THYROTOXICOSIS?

Answer 24

• Contrast media ( CT)
• Kelp
• Amiodarone