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Flashcards in Thyroid Gland Deck (23):
1

What are the thyroid hormones?

T3 - tri-iodothyronine (active form)
T4 - thyroxine

2

What is the main function of the thyroid hormones?

Increased metabolic activity

3

On what basis are thyroid hormones secreted?

When TSH is secreted by the follicular cells
TSH is secreted when:
- NIS is upregulated so there is increased intracellular concentration of iodine (iodine trapping)
- Iodination of thyroglobulin
- thyroid peroxidase enzyme

4

What is the NIS?

Sodium iodine symporter
On the basolateral membrane of the follicular cells

5

What is Tg?

Thyroglobulin
Precursor protein of thyroid hormone

6

What is the function of the thyroid peroxidase enzyme?

Oxidises iodide ions to form iodine atoms

7

How are thyroid hormones synthesised?

1) NIS takes up iodide as TSH levels are high and Na+/K+ channels create a suitable gradient
2) Pendrin transporter allows iodide transportation into the colloid whilst follicular cells secrete thyroglobulin
3) Oxidation from iodide to iodine by thyroid peroxidase enzyme
4) Iodine binds to the tyrosine rings of thyroglobulin
5) Molecules will move back into the follicular cells whilst still bound to tyrosine
6) Lysosomes in the follicular cell bind with endosome containing thyroglobulin releasing tyrosine from the structure and so separating T3 and T4
7) MIT and DIT release iodine allowing the process to restart
8) T4 gets converted into T3 by thyroid deiodinase
9) T3 enters the nucleus of target cells and acts on thyroid hormone receptor initiating transcription for specific mRNAs increasing metabolic rate

8

What is the function of the colloid?

Where thyroid hormone synthesis occurs

9

What are MIT and DIT?

MIT - monoiodotyrosine (when 1 iodine binds to tyrosine ring of thyroglobulin)
DIT - di-iodotyrosine (when 2 iodines bind to tyrosine rings of thyroglobulin)

10

What is the function of thyroid deiodinases?

T4 to T3 conversion when it reaches target cells

11

How are thyroid hormones controlled?

- negative feedback so that when iodine levels are higher (iodide is lower) there is a lower rate of hormone production
- intracellular control through D enzymes

12

What is hyperthyroidism?

Hyper function of the thyroid gland

13

What are the causes of hyperthyroidism?

Autoimmune
Grave's disease
HCG
Toxic adenoma
Excess iodine
Toxic multinodular goitre

14

What are the risk factors for hyperthyroidism

Infection
Stress
Female

15

What may hyperthyroidism cause?

Thyrotoxicosis
- when hormone released from a damage gland

16

What are the symptoms for hyperthyroidism?

CR: atrial fibrillation, dissipated excess heat
MET: increased protein and lipid degeneration, increased appetite, heat intolerance, hyperglycemia
NERVOUS SYSTEM: nervousness, seizures
SKIN: plummer's nails, pretibial myxoedema
BONES: accelerated osteoclast activity, hypercalcemia, osteoporosis
HAEMATOLGOICAL: pernicious anaemia, B12 deficiency
EYES: eyelid retraction, inflammation of orbital soft tissue (bulging)
REPRODUCTION: oligomenorrhea, gynecomastia, ED

17

What is the diagnosis for hyperthyroidism?

High serum T3 and T4

18

What is the treatment for hyperthyroidism?

Thionamide drugs - carbimazole, propylthiouracil
Radioactive iodine
Thyroidectomy

19

What are the types of hypothyroidism?

Primary -> permanent loss/destruction of the thyroid
Central/secondary -> insufficient pituitary stimulation of a normal gland (most commonly thyrotroph cell damage from pituitary macroadenoma)

20

What are the causes of hypothyroidism?

Hasiomoto's disease
Infiltrative disease
Hypopituitarism
Cabbage
Lithium

21

What is the diagnosis for hypothyroidism?

Low serum T4, high TSH

22

What is the treatment for hypothyroidism?

Levothyroxine, liothyronine

23

What are the symptoms of hypothyroidism?

ENDOCRINE: delayed puberty, erectile dysfunction
MET: reduced BMR, decreased GLUT4 stimulation
RENAL: reduced GFR, mild hyponatremia
HAEMATOLOGICAL: normocytic anaemia, reduced cutaneous circulation so sensitive to cold, sinus bradycardia
GI: reduced appetite, weight gain
NERVES, MUSCLE, BONE: impaired fetal brain development, dementia, growth retardation