HYPOTHYROIDISM Flashcards
what is the largest endocrine gland?
thyroid
where is thyroid located?
below larynx and wraps around the anterior and lateral sides of the trachea
what does the thyroid consist of?
2 large lobes connected by narrow anterior isthmus
what secretes t3 and t4?
thyroid follicles
what do the thyroid follicles consist of?
it is filled with colloid and lined by follicular cells
where are parafollicular thyroid cells (C cells) located?
between the follicular cells
what do parafollicular cells secrete?
calcitonin which lowers blood calcium levels
what does the hypothalamus release when there are low levels of t3/t4 and low metabolic rate or decreased body temp?
TRH
what does pituitary gland release after hypothalamus’s release?
TSH (thyrotropin stimulating hormone)
when the thyroid releases t3 and t4 what happens in a person who has low levels, low metabolic rate and so on?or decreased body temperature?
increases t3 and t4
increases metabolic rate
increases temperature
when are thyroid hormones produced?
when thyroid gland is stimulated by TSH from the anterior pituitary
80% t4 and 20% t3
what is the primary active thyroid hormone?
T3
200-300X MORE ACTIVE THAN T4!
what does t4 wait to do?
it circulates through body and waits to be converted on demand by your cells into the active t3 hormone
where are stored thyroid hormones in the follicular lumen bound to?
a protein called TG (thyroglobulin)
can bound hormones diffuse into cells?
no
what can unbound hormones bind to?
and what do they do
they can bind to thyroid receptors and exert effects on metabolic rate and temperature regulation
what are reasons for the inhibition of the conversion of t4 to t3?
aging, fasting/calorie restriction, any type of inflammation, lack of sleep, stress, acute and chronic conditions (Kidney and liver), IBD (intestinal probs), obesity, alcohol
what meds are responsible for the inhibition of the conversion of t4 to t3?
amiodarone, propranolol, propylthiouracil
how do the thyroid hormones increase metabolism?
- increases transcription of cell membrane Na+/K+ ATPase-> oxygen consumption
- enhances fatty acid oxidation and heat generation
- gluconeogenesis, glycolysis, lipolysis
how do the thyroid hormones aid in growth and development?
- protein synthesis
- regulates cholesterol and triglyceride metabolism
- affects brain, reproductive system, and bone development and growth
how do the thyroid hormones have interrelated actions with catecholamines?
- thyroid hormones enhance responsiveness to catecholamines (“fight or flight response”)
- increase expression of catecholamine receptors
what are the 3 catecholamines?
…
what is one additional function of thyroid hormone that is huge and hasnt been mentioned yet?
regulating pituitary hormone synthesis (feedback loop)
whats the definitions of hypothyroidism?
failure of thyroid gland to produce sufficient thyroid hormones to meet metabolic demands
common clinical disorder
whats the epidemiology of hypothyroidism?
1 in 300 people
85% are women
5% people over 60 y/o affected
what is included in primary hypothyroidism?
this is primary gland failure
includes congenital abnormalities, autoimmune destruction (hashimotos), iodine deficiency, and infiltrative diseases
what is included in iatrogenic hypothyroidism?
thyroid surgery,radioiodine therapy, and neck irradiation
what meds are involved in medication- induced hypothyroidism?
amiodarone, lithium, propylthiouracil, methimazole
are iatrogenic and med- induced hypothyroidism primary or secondary?
primary
what is the definition of secondary hypothyroidism?
insufficient thyroid gland stimulation by pituitary gland (2ndary or central hypothyroidism) or hypothalamus (tertiary hypothyroidism)
what are some important hypothyroidism symptoms?
intolerance to cold
constipation
dry skin
fatigue
weight gain
menstrual irregularities/ infertility
hair thinning/loss
what are some signs of hypothyroidism?
bradycardia
thin or brittle hair
macroglossia
periorbital/peripheral edema
goiter
lateral eyebrow thinning
delayed DTRs
what are the 6 p’s of congenital hypothyroidism?
pale
puffy face
protuberant tongue
poor brain development
pot-bellied
protruding umbilicus
who should be screened for hypothyroidism??
all patients with symptoms of hypothyroidism
can asymptomatic patients w/ risk factors for hypothyroidism be screened?
yes
what are the risk factors for hypothyroidism?
- hx autoimmune dz
- hx of head or neck irradiation
- previous radioactive iodine therapy
- goiter presence
- fmhx of thyroid disease
- treatment with drugs known to influence thyroid function
what are the screening guidelines according to the ATA?
measure thyroid fxn in all adults starting at 35 y/o and every 5 years thereafter; more fq screening appropriate for high-risk or symptomatic patients
what is the subclinical diagnostic testing for primary hypothyroidism?
elevated TSH
normal T3/T4
what is the overt diagnostic testing for primary hypothyroidism?
elevated TSH
low T4/ low-normal T3
what is an important diagnostic test for primary hypothyroidism regardless of thyroid hormone levels?
antibody testing!
what antibodies does the antibody test for primary hypothyroidism include?
thyroid peroxidase, and thyroglobulin
(TPO and TBGs)
what is the purpose of the antibody test for primary hypothyroidism?
helps in subclinical hypothyroidism or goiter and if there is active thyroiditis
what does presence of antibodies mean in antibody test for primary hypothyroidism?
presence of antibodies means autoimmune hypothyroidism (hashimoto thyroiditis)
what is the diagnostic test results in secondary hypothyroidism?
decreased TSH
decreased T3/T4
what is the treatment for hypothyroidism?
levothyroxine- t4
1.6 mcg/kg PO daily
taken in the morning, 30 min before eating or bedtime
what is the goal TSH level of someone receiving treatment?
1-2
when should TSH be checked during treatment?
every 4-6 weeks and titrate dose appropriately
what should not be taken within 4 hours of taking levothyroxine?
calcium and iron supplements
should you maintain brand name or generic products or can you switch back and forth?
do not switch back and forth
what is the most common cause of persistently elevated TSH levels?
poor adherence to therapy
what treatment is given in a patient with persistent symptoms despite TSH level in the lower normal range?
combination t3/t4 therapy may be used in select patients
armour thyroid
levothyroxine plus liothyroxine (cytomel)
what is a rare but life threatening condition related to hypothyroidism?
myxedema coma
most severe manifestation of hypothyroidism
when does myxedema coma occur?
when the bodys compensatory responses to hypothyroidism are overwhelmed by a precipitating factor such as failure to reinstate thyroid replacement therapy, infxn, hypoglycemia, meds
what is a clinical presentation of myxedema coma
specifically seen in the face?
generalized puffiness, macroglossia, ptosis, periorbital edema
what is a clinical presentation of myxedema coma
specifically seen in the lower extremities?
non-pitting edema
what is a clinical presentation of myxedema coma
specifically seen neuro wise?
deterioration of mental status- confusion, psychosis, rarely coma
what is a clinical presentation of myxedema coma
specifically temperature wise?
hypothermia <35.5 deg (95.9 degF)
what is entailed in ICD admission for someone with myxedema coma?
ventilatory, electrolyte, and hemodynamic support, thyroid replacement
