Thyroid

Question 1

Diet

Answer 1

1mg of iodine required in diets per week

1/5th of this used for thyroid hormone synthesis

Question 2

TSH

Answer 2

From anterior pituitary

Stimulates expression of NIS, TOP, Tg –> increase formation of T3 relative to T4

Question 3

Thyroid hormone synthesis

Answer 3

Iodide taken up by NIS (sodium-iodine symporter on basolateral membrane) of thyroid follicular cell in response to TSH increase
Iodide transported into colloid via pendrin transporter
Follicular cell also releases thyroglobulin

Question 4

Thyroid hormone synthesis part 2

Answer 4

Iodide oxidised to iodine
Iodine binds to tyrosine rings of thyroglobulin
One iodine binds= MIT
Two iodine binds= DIT

Question 5

Thyroid hormone synthesis part 3

Answer 5

MIT and DIT can bind together forming T3

DIT and DIT can bind together forming T4

Question 6

Thyroid hormone synthesis part 4

Answer 6

T3 and T3 molecules move back into follicular cells
Contains lysosomes- bind together with endosome containing thyroglobulin
–> release tyrosine molecule from structure
T3 and T4 separate
DIT + MIT release iodine to restart process

Question 7

T3 (converted from T4)

Answer 7

Enters nucleus and enters target cells
In nucleus= thyroid hormone receptor, initiates transcription for specific mRNAs
–> increase metabolic rate

Question 8

T4 –> T3

Answer 8

T3 is active form

Converted when reaches target cell by thyroid deiodinases -D1, D2, D3

Question 9

D1

Answer 9

rT3 –> T4 –> T3
Liver, kidney, muscle, thyroid
Upregulated in hyperthyroidism
Downregulated to hypothyroidism

Question 10

D2

Answer 10

Provide T3 to nucleus, especially in brain
If T4 levels fall, D2 upregulated –> T3 maintained
Excess T4= decrease D2 to protect from excess thyroid hormone

Question 11

D3

Answer 11

Activated by hypoxia/ischaemia
Slow down metabolism of affected tissues by reducing T3 levels
Upregulated in hyperthyroidism

Question 12

Control of thyroid function

Answer 12

Negative feedback
The higher the iodine level, the lower the rate of hormone formation
Control at intracellular level through D enzymes

Question 13

Hyperthyroidism

Answer 13

May cause thyrotoxicosis
Causes AF
Increased appetite, protein + lipid degradation
Heat intolerance
Hyperglycaemia
Eyelid retraction
Plummer's nails
Osteoporosis
Pernicious anaemia
B12 deficiency
Bulging eyes
Pretibial myxoedema
Oligomenorrhea

Question 14

Grave’s disease

Answer 14

Autoimmune
Positive antibodies against TPO, thyroglobulin + TSH receptor
hyperthyroidism
Thyroid stimulating immunoglobulin (an antibody) is produced, and has similar effects to TSH –> causes body to produce too many thyroid hormones

Question 15

Graves RF

Answer 15

Infection
Stress
Female

Question 16

Other causes hyperthyroidism/thyrotoxicosis

Answer 16

Toxic multinodular goitre
Toxic adenoma
Excess iodine
HCG

Question 17

Hyperthyroidism diagnosis

Answer 17

High T3 and T4

Question 18

Hyperthyroidism treatment

Answer 18

Thionamide drugs
---> propylthiouracil
---> carbimazole
Radioactive Iodine I131
Thyroidectomy

Question 19

Primary hypothyroidism

Answer 19

Permanent loss or destruction of thyroid

Question 20

Central or secondary hypothyroidism

Answer 20

Caused by insufficient pituitary stimulation of a normal gland
Most commonly caused by damage to thyrotroph cells from pituitary macroadenoma

Question 21

Hypothyroidism effects

Answer 21

Cold- hypothermia
Bradycardia
Weight gain
Dementia
Growth retardation
Delayed puberty
Erectile dysfunction
Reduced GFR
Mild hyponatremia
Normochromic normocytic anaemia
Decreased GLUT4 stimulation (decreased glucose delivery to tissues)

Question 22

Hypothyroidism causes

Answer 22

Hashimoto's disease
Endemic goitre
lithium
Cabbage
Infiltrative disease

Question 23

Recommended iodine intake

Answer 23

pregnant or lactating- 250 u thingy g per day

Question 24

Hashimoto’s thyroiditis

Answer 24

Lymphocytic infiltration

Question 25

Hypothyroidism diagnosis

Answer 25

High TH

Low T4

Question 26

Hypothyroidism treatment

Answer 26

Levothyroxine