Thyroid Flashcards
What makes up mono-iodotyrosine
Tyrosine with one iodine
What is the proper name for T3
Liothyronine
What is the proper name for T4
Levothyroxine
Describe the dimensions of the thyroid gland
2cm thick and 4cm long
Right lobe is usually larger
Which gland has the highest blood supply per g in the body
Thyroid
Are the thyroid or parathyroid glands more anterior
Thyroid
What is meant by thyroid follicle
Lots of thyroidal epithelium surrounding each colloid
Describe the epithelium of the thyroid follicles
Cuboidal when inactive
Columnar when active
How many follicles are there per lobule
20-40
How many arteries are there per lobule
1
VERY briefly state how thyroid works to release thyroid hormones
Traps iodine and attaches it to protein
Protein can then be broken down
Hormones can then be released
What receptor receives signals from the pituitary gland
TSH receptor
What protein is used to oxidise the iodide int he thyroid
Thyroid peroxidase (TPO)
What is the oxidising agent for iodide in the thyroid? How is it formed
Hydrogen peroxidase
DUOX1 and DUOX2
What travels into the thyroid follicular cell via NIS
2 sodiums and an iodide
What is NIS
Sodium iodide sympoter
What transports iodide from the thyroid follicular cell to the colloid
pendrin PDS
What is the role of ER and golgi body in the thyroid follicular cell
Gives thyroglobulin
What is used to recycle iodide
Iodotyrosine dehalogenase 1
What % of the thyroid hormones produced are T4
80-90%
What is the role of cAMP in controlling thyroid follicular cells
Regulates NIS and moves it to the membrane
Upregulates di-iodinase 2 production which converts T4-T3
Upregulates thyroglobulin
Upregulates oxidising agents
Upregulates digestion of thryoglobulin
What molecule must be removed to convert T4 to T3
Iodide
What family of enzymes removes iodides from T4
Deiodinases
Which specific deiodinases convert T4 into T3
D1 and D2
What does D3 do
Converts T4 into the inactive reverse T3
Where is D1 most expressed
Liver, kidney and muscle
Where is D2 most expressed
Brain and pituitary
In what condition is D2 upregulated and why
Hypothyroidism
T4 levels will fall, but D2 is upregulated so that the T4 that is produced in all converted into T3
How is thyroid function regulated
- Inverse relationship between iodine levels in the thyroid and rate of hormone formation
What is released from the hypothalamus to stimualte pituitary to secrete TSH
TRH
How are T4 and T3 transported through the body
Via thyroid binding globulin
What kind of receptor is the thyroid hormone receptor
Nucleus receptor
Describe the structure of the thyroid hormone receptor
- 2 TRs stuck together with a corepressor stuck to it
What happens when T3 binds to one of the receptor units
Corepressor leaves
Dimer breaks up
Attracts co-activator
This activates transcription
In general, what is effect of thyroid hormones on the body
Increases basal metabolic rate
Define hyperthyroidism
Over active thyroid
Define thyrotoxicosis
State of having too much thyroid hormone
What are the effects on the cardiovascular system when the person has hyperthyroidism
Increased metabolic rate, so produces heat
To get rid of heat, more blood goes to the skin
HR and CO increased
Prone to AF
What metabolic changes can be expected in somebody with hyperthyroidism
- Increased appetite
- Heat intolerance
- Protein and lipid degradation
- Weight loss and myopathy
- Accelerated insulin turnover
- Hyperglycaemia
Why is T1D and hyperthyroidism linked
Both autoimmune
What is the effect of hyperthyroidism on the nervous system
Anxious, cross
Increases threshold of seizures
Why does Graves disease lead to
Autoimmune process affecting thyroid gland affects the eyes and causes cytokine release at back of the eyes
Name 2 signs of hyperthyroidism that can be seen on the skin
Plummer nails
Pretibial myxoedema
What is the effect of hyperthyroidism on the GI tract
Weight loss
Increased motility
Increased appetite
Transaminitis
What is transaminitis
Damage to liver leading to elevated liver enzymes
What is the effect of hyperthyroidism on bones
Accelerated osteoclast activity
Hypercalcaemia
Osteroporosis
What are the effects of hyperthyroidism on haematological system
Pernicious anaemia
B12 deficiency
What are the effect of hyperthyroidism on the reproductive system
Oligomenorrhoea
Gynecomastia
Erective dysfunction
What is glynecomastia
Breakdown of testosterone
Define Grave’s disease
Autoimmune condition leading to invasion of thyroid gland by B and T cells
How do the antibodies against TSH receptor act during Graves disease
Act in same way as TSH so stimulate an overexpression in normal function of the thyroid
What proteins do antibodies target in Graves disease
TSH receptor
Thyroid peroxidase
Thyroglobulin
Name 4 risk factors for Grave’s disease
- HLA status
- Infection
- Stress
- Female sex
Why do pregnant women often have thyrotoxicosis
Hcg acts on the TSH receptor- transcient thyrotoxicosis
What are the key hormone level differences in hyperthyroidism
Elevated T4 and T3
Suppressed TSH
What thionamide drugs are most commonly used to manage hyperthyroidism
Propylthiouracil
Carbimazole
What changes to the skin happen in hypothyroidism
- Put on weight
- Skin dries out
- Hair dries
- Lose outer third of eyebrow
What cardiovascular changes in a person with hypothyroidism
Sinus bradycardia
J waves of hypothermia
Is there more or less LDL cholesterol in hypothyroidism
More
What changes occur in the GI tract in people with hypothyroidism
Reduced appetite
Constipation
Are reflexes slow or hyper in hypothyroidism
Slow
What changes occur in the renal system in hypothyroidism
Reduced GFR
Mild hyponatraemia
What haematological changes occur in hypothyroidism
Normochromic normocytic anaemia
Is GLUT4 stimulated decreased or increased in hypothyroidism
Decreased
What endocrine changes occur in hypothyroidism
Delayed puberty, reduced libido, erectile dysfunction
What characterises Hashimotos disease
Antibodies against thyroid oxidase
What is endemic goitre
Not making enough thyroid hormone so the pituitary releases more TSH stimulating it to grow
