thyroid Flashcards
making thyroid hormones
tyrosine becomes iodinated and then 2 of these are conjugation to make T3 or T4
where are the parathyroid glands location
4 on posterior surface in 4 corners of thyroid
colloid
glycoprotein, surrounded by connective tissue
what does T3 do?
responsible for most thyroid activity - half life of 1 day
what does T4 do?
largely converted to T3 intracellularly - half life of 7 days
thyroid hormones in blood are bound to?
albumin
thyroxine binding globulin
transthyretin
most of T3 and T4 are bound and so these have to broken down to be measured
affect on nucleus
activates nuclear receptors to activate DNA trasncription
normally occupied by inhibitory repressors which are displaced by T3 to start activation
Affect on mitochondira
direct action to increase oxidative phosphorylation
stimulates mitochondrial DNA transcription
possible causes of hypothyroidism
hypothalamic damage - less TRH from surgery
anterior pituitary damage - less TSH from surgery
thyroid damage - exposure to radioactive iodine, drugs or surgery
autoimmune - hashimoto’s disease
congenital - genetic/ developmental/ iodine deficiency
iodine deficiency - adult/ congenital
symptoms of underactive thyroid
slow metabolic rate tiredness cold intolerance weight gain bradycardia hypotension slow reflexes and speech dry skin thinning hair mucopolysaccharide deposits - around eyes
hashimoto’s disease
normal immune tolerance fails
autoreactive CD4+ T cells recruit B cells and CD8 + T cells to the thyroid
Anti-thyroid peroxidase
macroglossia
large tongue
congenital hypothyroidism
coarse features macroglossia floppy/ poor feeding mental retardation short stature failure to treat causes permanent developmental impairment - cretinism
causes of hyperthyroidism
TSH secreting tumour
autoimmune - graves
adenoma - tumour that secretes hormones
over treatment
hyperthyroidism
increase protein synthesis and muscle bulk
increased metabolism
increased heat production
increased oxygen consumption
symptoms of hyperthyroidism
weight loss heat tolerance tremor tachycardia arrhythmias muscle weakness diarrhoea goitre - highly vascularised eye sides - exophthalmus
exophthalmos
inflammatory process behind eyes
can threaten vision
graves disease
normal immune balance disrupted
anti-TSH receptors Antibodies generated that mimic TSH and stimulate receptor after binding
increases T£ and T4 synthesis
stage 1 of making T3 and 4
Na+/ I- symporter traps iodine ions in the cell at a higher concentration than outside
Stage 2 of making T3 and 4
iodination needs iodine not iodide and so Thyroid peroxidase oxidises iodide to free iodine using peroxide
stage 3 of making T3 and 4
thyro-globulin is the storage vehicle for T3 and 4 in follicles
stage 4 of making T3 and 4
iodination, tyrosine conjugation
transportation
thryo-globulin transports them in and out of colloid by exo and endocytosis
stage 5 of making T3 and 4
cleavage - loss of protein and T3 and 4 can be released
what does TSH stimulate
Na/I- symporter
thyroglobulin synthesis and exocytosis into colloid
affect on cell membrane
cell surface GPCR receptor which indirectly stimulates nuclear DNA transcription
thyroid hormone affect on organs
affects brain, liver, kidneys, muscle and fat
what else do the thyroid hormones do?
increase basal metabolic rate - generates heat and uses O2
- increases force and rate of contraction of heart
- increase sympathetic NS
- increases protein synthesis and growth
- increases cerebral activity
- increases action of GH
what are the types of thyroid cancer?
papillary - slow growing and linked to radiation
follicular
medullary - parafollicular C cells
anaplastic - undifferentiated
presentation of thyroid cancer
painless neck lump
lack of hormone secretion
