The Thyroid gland Flashcards
What is the Thyroid made up of?
- Follicles - the colloid surrounded by follicular cells
- Parafollicular cells
What lies embedded behind each lobe of the thyroid?
Superior parathyroid gland
Inferior parathyroid gland
Which nerve runs close to thyroid?
Left recurrent laryngeal nerve runs close - supplies vocal cords
How is the thyroid formed? ( Embryology )
- Midline outpouching from floor of pharynx
- Development of Thyroglossal duct
- Divides into 2 lobes
- Duct disappears leaving foramen caecum
- Final position by week 7
- Thyroid gland then develops
What Happens in the Thyroid Gland?
What reactions occur in the colloid?
How do the hormones leave the Thyroid gland?
- TSH binds to TSH-R on follicular cell membrane
- Iodide Ions get transported into follicular cell from Sodium Iodide
The TSH creates TG which going into colloid
The TSH creates TPO (enzyme) which going into colloid
Iodide gets turned into Iodine in colloid ( iodination )
In Colloid:
TPO + hydrogen peroxide acts as an enzyme for the following reaction - Iodine + TG = MIT = DIT
DIT + MIT ( coupling reaction ) also using TPO as enzyme
= T3 / T4
These bind to TG - enter back into follicular cell, they are separated by TG by lysosomes and released into bloodstream
What is Iodination of tyrosine?
Iodine reacted with TG creates MIT (Monoiodotyrosine) and DIT ( 3,5 Diiodotryrosine)
MIT + DIT = T3/T4
DIT + DIT = Thyroxine
What is Deiodination
- Most T3 is made this way
T4 is the main hormone product of thyroid gland
How does T3 alter gene expression?
Can bind and
How does T3 alter gene expression?
Can bind and
What does Thyroid hormone do (Fetal) ?
Fetal growth and development in particular the CNS
What are the characteristics of Cretinism
Congenital hypothyroidism
Baby born without thyroid hormone or gland that functions
How is TSH measured in new born infants?
Heel-prick test on day 5
What does the thyroid hormone to do metabolims?
Increases basal metabolic rate
Increases protein, carb, fat metabolism
Sympathetic N system = cardiac output
Affect GI tract
Maturation of CNS
What controls the thyroid hormone production
Hypothalamic-pituitary-thyroid axis
TRH–>TSH–>Thyroid–> T3+T4
Negative feedback from T3 and T4 turning TRH off in hypothalamus
What is the Wolff-chaikoff effect?
Iodine in large quantities it can inhibit T3 T4 production
Why are women predisposed to thyroid disorders
Autoimmunity tends to affect thyroid
When pregnant women are exposed to antigens and so their immune systems are more likely to develop autoimmune thyroid disorders
What does autoimmune thyroid damage do?
Thyroxine levels decline
TSH levels climbs
( negative feedback )
What is Hypothyroidism
Thyroxine levels decline
TSH levels climbs
( negative feedback )
What disease is linked to hyper
Graves’ disease
What disease is linked to hyperthyroidism?
Graves’ disease
What are the signs and symptoms of hypothryroidism?
- Enlarged thyroid gland
- Fatigue, memory impairment, depression
- Swollen face
- Deepening voice
- Cold intolerance
- Weight gain
reduced appetite - Bradycardia
- Constipation
- Eventual myxoedema coma
What therapeutics can be given to patients with an underactive thyroid?
What is the dosage based on?
Levothyroxine
It mimics the role of the thyroid by producing T4 which gets changed into T3
Dose: according to TSH
( 100 mg )
Side effects - Weight loss and headache – Heart attack
*Sometimes you can give it for hyperthyroidism ( block and replace )
What is hyperthyroidism?
Thyroid makes too much thyroxine
TSH levels drop
Toxic multinodular goitre
Solitary toxic nodule
( causes include Graves disease )
What are the characteristics of Graves’ disease?
Autoimmune disease
Antibodies bind to TSH receptor in thyroid
Smooth Goitre - enlargement of thyroid
Exophthalmos - antibodies bind to muscles behind eyes
: severe eye complications
Antibodies stimulate growth of soft tissue of shins - Pretibial myxoedema
What are the signs and symptoms of hyperthryroidism?
nervousness, Insomnia, Depression Weightloss Hunger Fragile fingernails Warm moist skin Myopathy Mood swings Diarrhoea Tremor of hands Palpitations Sore eyes, goitre Hairloss Increased heart rate High blood pressure
