Thyroid anatomy and physiology Flashcards
when does the thyroid gland form in foetus
4 weeks
formation of thyroid gland
Starts off at base of tongue starts descending downwards, goes infront of larynx, migrates all way down to final position- Infront of tracheal rings
Splits into right and left lobe, joined by an isthmus
what does the thyroid gland split into and what is it connected by
right and left lobe connected by isthmus
how may you clinically see a cyst
if you ask patient to move tongue outwards
what do the parathyroid glands secrete
parathyroid
how many parathyroid glands are there
4
thyroid gland and trachea
encricled around it
4 glands at bakc
what hromones does the hyroid produce
thyroxine, calcitonin, t4, t3
uniqueness of thyroid gland
Largest endocrine gland, only lobe that you can palpate, only one that requires substances from environment
what substance from the environment does the thyroidg land need
iodine
basic functional unit of thyroid
follicle
follicular cells
parafollicular cells
which type of cells are follicular cells
cuboidal
where is t3 and t4 produced
follicular cells
where is calcitonin produced
parafollicular cells
negative feedback system
hypothalamus produces TRH - stimulates pituitary to produce thyroid stimulating hormone which stimulates the thyroid gland to produce t3 and t4
what is t4 converted into
active t3
what happens if have appropriate number of thyroid hormones
negative feedback system back to hypothalamus to switch it off so too much isnt produced
what happen sif have too little t3 and 4
increased up regulate hypothalamus and pituitary
where is thyroglobulin produced
in colloid
thyroid hormone synthesis process
Uptake and conc of iodide into follicular cells
Iodide oxidated to iodine
Gets transported into colloid - iodination of thyroigoloubulin
Formation of those two products
Iodine attaches to tyrosine residues to form either mono iodotyrosine unit - one single iodine
Or if two iodines that are attached to thyroglobulin then di-iodotyrosine unit
Mit and dit then have three iodine resisudes in total - t3
If get two di attaching then you get dit and dit- 4 iodine residues- thyroxine
what is most thyroid stored as
t4 - thyroxine
which is more potent t3 or t4
t3
where can t4 be converted to t3
in liver and kidney
is t4 biologically active
no, nly t3 is
how are t3 and t4 transported
Bound to serum proteins:
thyroxine binding globulin - 70%,
thyroxine binding pre albumin 20%
Albumin 5%
can bound hormones enter the cell and regulate it
no only unbound can, so t3 is less tightly bound
what is metabolic state linked to
T3
effects of thyroid hormone
- Increases metabolic rate by increasing number and size of mitochondria
○ Increase oxygen use and rates of atp hydrolysis
○ Increase synthesis of resp chain enzymes- Can effect all cells
- Increase thermogenesis - feel heat more if overacive thyroid
- Incrrease glucose uptake so can sustain metabolism
- wOrks on liver to increase glycogenolysis ; breakdown of glycogn
- Increases lipolysis- fat breakdown
- Can work on lungsa nd heart- increases breathing rate and heart rate
Everything is upregulated
what to treat over active thyroid with
beta blocker
symptoms associated with hyperthyroidism
Palpitations, tremors, sweats , shakes
everything is fast , hair loss, weight loss, bowels speeding up- diarrhoea - warm palms, anxiety
Increases body responsiveness to adrenaline and sympathetic NS neurotransmitter, noradrenaline by increasing number of receptors
how are t3 and t4 degraded
by diodinases - d1,d2,d3
what is t4 degraded by and to
by d1 into t3
what else can t4 be broken down to besides t3
inactive reverse t3 via d3
where is d1 found
liver and kidney
where is d2 found
heart and skeletal muscle, cns , fat, thyroid and pituitary
where is d3 found
foetal tissue and placenta
hypothyroidism clinical features
everything slow , weight gain, slower, sluggish, bradycardia , constipation as bowels have slowes, metabolism slowed, low mood, forgetfulness
secondary thyroid issue
things that feed into the issue hypothalamus/ pituitary etc
primary issue
failure of the gland
what might a lack of iodine cause
hypothyroidism
what is a mix oedema crisis
hypothyroid crisis
disease of over active thyroid
graves disease
- Autoimmune condition results from own body producing tsh receptor antibodies - they are stimulating antibodies- stimulate thyroid gland to overproduce t4 and t3
Problems with eyes- thyroid eye disease , mild = redness dry eyes, extreme= bulgy eyes
what is a goitre
enlarged thyroid gland
