the thyroid gland

Question 1

describe the structure of the thyroid

Answer 1

in neck below thyroid cartilage
made of 2 lobes (left and right) and an isthmus joining them
some people have a pyramidal lobe

Question 2

describe the cellular arrangement of a thyroid

Answer 2

follicular cells surround the colloid creating a follicle

parafollicular cells scattered about

Question 3

what nerve runs close to the thyroid

Answer 3

left recurrent laryngeal nerve

Question 4

what glands are embedded in the thyroid

Answer 4

parathyroid glands

Question 5

outline the embryology of the thyroid gland

Answer 5

1: midline outpouching from the floor of the pharynx(originates from the base of the tongue)
2: development of the thyroglossal duct
3: divides into 2 lobes
4: duct disappears leaving the foramen caecum
5: week 7 is at its final position and gland develops

Question 6

explain what happens when thyroid stimulating hormone binds to thyroid stimulating receptor

Answer 6

1: Na+ and I- enter follicular cell. thyroglobulin(TG) is also produced
2: I- , TG and TPO diffuse into the colloid
3: TG is iodinated
4: coupling reactions between MIT and DIT occur
5: the TG with T3/T4 attached go into the follicular cell into a lysosome
6: T3 and T4 released into the blood

Question 7

what does MIT and DIT stand for?

Answer 7

Mono/Di Iodo Tyrosine

Question 8

what is T3 comprised of?

Answer 8

a DIT and MIT ( 3,5,3’-tri-iodothyronine)

Question 9

what is T4 (thyroxine) comprised of?

Answer 9

2 DIT ( 3,5,3’,5’-tetra-iodothyronine)

Question 10

what happens when T4 is deiodinated in target tissues?

Answer 10

produces T3 or reverse T3( inactive) depending on which iodine is removed

Question 11

outline what happens when TRH is released and how it is controlled

Answer 11

TSH levels rise from pituitary to thyroid
T4 and T3 levels rise
T4 provides negative feedback to hypothalamus and pituitary and is also converted into T3
T3 is active in target tissues
iodide also reduces thyroid output(wolff-chaikoff effect)

Question 12

what are the names of the plasma proteins that transport thyroid hormones in he blood?

Answer 12

thyroid-binding globulin
albumin
prealbumin(transthyretin)

Question 13

what is the effect of binding to thyroid receptors?

Answer 13

gene expression is altered

Question 14

what is the action of thyroid hormones?

Answer 14

fetal growth and development (especially CNS)
increases basal metabolic rate
protein, carbohydrate and fat metabolism increase
potentiate action of catecholamines( tachycardia, lipolysis)
growth and bone maturation
increased cardiac output

Question 15

how is thyroid hormone levels measured in babies?

Answer 15

heel prick test

Question 16

who are thyroid diseases more common in?

Answer 16

women (4:1)

Question 17

what are the main causes of hypothyroidism?

Answer 17

autoimmune damage
(hashimoto's thyroiditis)

Question 18

what are the symptoms and signs of hypothyroidism?

Answer 18

deepening of voice
depression and tiredness
cold intolerance
weight gain and reduced appetite
constipation
bradycardia(slow heart rate)
eventual myxoedema coma
shaggy hair/ hair loss
memory impairment
swollen face, eye socket
dry rough skin
muscle cramps
paraesthesia(tingling)
diminished potency and fertility
low sex drive
menstrual cycle disorders

Question 19

what medication can be used for hypothyroidism?

include common dose and complications

Answer 19

levothyroxine oral tablets 100micrograms( dose is adjusted)
minor side effects- weight loss and headache
major complications- heart attack/ rapid heart rate

Question 20

what is the issue with giving liothyronine(T3) tablets?

Answer 20

no more effective than T4

combination tablets of T4 and T3 may cause toxicity(palpitations, tremor, anxiety) TSH is often supressed by this

Question 21

what are the main causes of hyperthyroidism?

Answer 21

grave’s disease
toxic multinodular goitre
solitary toxic nodule

Question 22

what are signs of grave’s disease?

Answer 22

diffuse goitre of thyroid
eyes stick out exophthalmos
growth of soft tissue shins- pretibial myxoedema

Question 23

what are the signs and symptoms of hyperthyroidism?

Answer 23

heat intolerance
weight loss with increased appetite
myopathy
mood swings
diarrhoea
tremor of hands
palpitations
sore eyes
goitre
broken hair/ hair loss
nervousness
insomnia
depression
fragile nails
arrhythmia(irregular heart rate)
increased heart rate
high blood pressure
warm moist skin
muscle cramps and weakness
menstrual cycle disorders