Endocrinology: Thyroid and Parathyroid Flashcards
what is the second largest endocrine gland?
thyroid
location of thyroid
base of neck
below SCM
thyroid hormones derived from which AA?
tyrosine
thyroid hormone is under regulation by____? (2)
dietary idodine
HPA (tsh coming from AP)
what inhibits TSH release (4)
glucocorticoids somatostatin dopamine AND incr plasma levels of T3 and T4
- TRH binds to_______ in the _____
- causing ___ in intracellular [_____]
- which results in ____ and release of ___ into ___
- G protein coupled rec, AP
- INCR, CA2+
- exocytosis, TSH, systemic circulation
t4
tetraiodothyronine
t3
triiodothyronine
is the thryoid vascular?
yes very vascularized
follicular cells
involved with thyroid hormonesynthesis
which cells are involved with thyroid hormone synthesis
follicular cells
parafollicular cells or____
-produce?
c cells
-produce calcitonin
what does calcitonin do
metabolizes calcium
main funct of thyroid gland
to produce and store thyroid hormone
what fills the follicle?
-what is contained in it?
colloid
contains protein–thyroglobulin (tg)
role of thyroglobulin
synthesis and storage of thryoid hormone
TSH stimulates productino of___
T4
explain polarity of thyroid follicular cells?
each side or compartment of cell has specific functions pertaining to synthesis of T hormones
- –apical surface: faces follicular lumen–colloid storage
- –basolateral surface: faces interstitum–exposed to bloodstream
where does TSH bind to?
receptor sites on PLASMA MEM of follicular cells
what happens after TSH binds to rec in follicular cell? (4 steps)
- immed release of stored thyroid hormone
- incr in iodide uptake and oxidation
- incr in thyroid hormone synthesis
- incr of prostaglandin synthesis and secretion
where are t3 and t4 produced.. stored?
in thyroid gland
STORED: follicles–in the sacs with thyroglobulin
which is more potent.. t3 or t4
t3
in blood, which is normally in higher levels t3 or t4
t4 45X higher
what does the activity of t3 depend on
enzyme that converts t4–t3
*found outside thyroid
what is the enzyme responsible for converting t4–t3
type 1 Deiodinase
type 2 Deiodinase
type 3 ‘’
type 1 Deiodeinase is found where and what is its function
liver kidney and thyroid
functoin: generates T3 for circulation
type 2 deiodinase is found where and function
cells of brain, pituitary and brown fat tissue
Function: converts T4–T3
type 3 deiodinase is found where and function
placenta, brain and skin
leads to generation of rT3
what do we need when we want to convert t4–t3?
List the carrier proteins
carrier proteins
*they bind and transport T4/T3
- Thyroxine binding globulin
- albumin
- thyroid binding prealbumin
release of TSH is mostly inhibited by T3 or T4
*circulation or pituitary T3?
T3
**pituitary/hypothalamic T3 has greater effect
thyroglobulin is synthesized in?
follicular cell
Tg is secreted throuhg____? and into____?
apical membrane into follicular lumen–storaged in Colloid
what diseases can ciruclating thyroglobulin levels are elevated?
graves
thyroiditis
where is thyroxine binding globulin produced
in liver
Thyroid produces 90% _____ (T4 or T3?) and 10%_____
90%=T4
10%=T3
where is Iodine stored?
Follicles
when there is active secretion, what is the morphology of the follicular cell?
columnar
hypo or hyperthyroidism if we do not get in enough iodine from diet?
HYPOthyroidism—bc we cannot make T3 from T4
Role of thyroid hormones
- Neuronal and skel development
- Heat production and oxygen consumption at rest
- Stim bone turnover–increasing formation and reabsoprtion
- secretes calcitonin to lower serum Ca levels
- incr number of catecholamine receptors in heart
- incr RBC production
- alter metabolism of carbs, fats, and protein
the synthesis of thyroid hormones takes place____
in colloid space
the apical surface of the follicuar epithelium faces??
the colloid
NOT interstitial space
no access to bloodstream
main functions of thyroid hormones
breathing energy production HR cognitive function mood body wt muscle strength menstrual cycle body temp cholesterol levels growth and development intestinal flow digestion
which hormone is the indicator measured in a lood test to screen for hypothyroidism?
TSH
TSH LAB LEVELS:
- HIGH tsh indicates?
- LOW TSH inds?
- LOW thyroid hormones–hypothyroidism
2. HIGH thyroid hormones–hyperthyroidism
list some factors that increase conversion of T4 to T3
stress trauma low cal diet inflamamtion toxins infections liver/kidney issues
which enzyme is mostly resp for conversion of T4-T3 in hyperthyroid PTs?
Type 1 deiodinase
which enzyme is the main source of T3 in euthyrioid state
-imp source of_____?
Type 2 deiodinase
**imp source of intracellular T3
thyroid hormone affect on cardiovasc systm?
+inotropic
+chronotropic
incrs CO and blood volyme
decrs systemic vasc resistance
which is MC primary or secondary hypoT?
primary–95% cases
what can occur if hypotyroidism occurs in utero?
cretinism or mental retardation
pathophys behind primary hypothyroidism
-causes?
AUTOIMMUNE–Hashimoto
destruction of the thyroid parenchyma
can also be result from surgery or radioactive iodine tx
define secondary hypoth
- what is decrease
- causes
decrease TSH and decrease T4 T3
disorder of anterior pituitary or hypothal
lack of stimulation of the TSH receptor because of impaired TRH release
Hyperthyroidism hgiher in M or W?
women
MC cause of hyper T in adults?
diffuse toxic goiter or **Grave’s disease****
define graves disease
AUTOIMMUNE–excess thyroid hormone bc of TSH receptor stimulation by immunoglobulin G
-results in continuous stimulation of TSH-receptor by TSH-like antibodies–results in excess T4/T3 production
Graves disease MC in M or W?
WOMEN
*third to fourth decades of life
TSH secreting pituitary adenomas
increased thyroid hormone release in response to elevated TSH levels from TSH-secreting adenoma on AP
- small percent of all pituitary adenomas
- results=increase TSH levels
why is TSH low in primary hypert?
beacuse the thyroid gland is secreting T4/T3 without being told to do so… aka:
- increase neg feedback to AP
- ending in decrease levels of TSH and HIGH t4/t3 because issue is the thyroid gland and not AP
Why is TSH high in secondary hyperthyroidism?
because the increase in T4/T3 levels is due to AP issue aka over-secreting of TSH…. the negative feedback is not working on the AP since the AP gland is the issue
what is the hormone in determining primary and secondary hyper/hypo thyroidism?
TSH
why is TSH high in primary hypothyroidism?
since thyroid gland is root cause of decrease levels of t3/t4…… this decreases negative feedback to AP….telling AP to release MORE tsh.. but thyroid gland is not listening
Why is TSH low in secondary hypothyroidism?
now AP gland is the issue:
-AP is not secreting enough TSH— therefore the thyroid is not going to secrete enough T3/T4
list causes for hyperthyrodism
toxic nodules Grave's disease Pituitary tumor Amiodarone toxicity Struma Ovarii--ovarian tumor that secretes thyroid horm
what is a toxic nodule
thyroid nodule that become independent of the pituitary and secretes excess thyroid hormone
what is graves disease
patho *
autoimmune *** primary hyperthyroidism
body produces antibodies AGAINST (autoantibodies)–they bind to TSH receptors on thyroid and act like TSH–stimulating release of T3/T4
MC cause of hyperT?
Grave’s disease
where are the largest calcium storage
bones
list the three hormones that regulate [ca]
parathyroid hormone (PTH)
calcitonin
Vit D
Calcium:____?
Iodine:_____?
Ca—>parathyroid
Iodine—?thyroid
PTH and Vit D effects on blood calcium levels
they increase it
calcitonin’s effect on blood Ca levels
decreases it
where is calcitonin secreted
follicular cells of thyroid
when is PTH released?
when blood calcium levels are LOW
is PTH secretion regulated by ant pit?
NO
what regulates secretion of PTH?
serum [ca]
three ways PTH increases blood [ca]?
- stimulates osteoclasts to b/d bone
- increase reabsorption of CA in kidneys
- incr conversion of inactive Vit D–>active vit D–>increases [ca] in GI tract
what is normal CA range?
8.9–>10.1 mg/dL
Other than increase [ca], what else does PTH do?
decreases phosphate
- tells kidney to decr phosphate reabsoprtion
- this prevents hyperphosphatemia beacuse PTH tells bones to breakdown–releases CA annnnnnnnd Phosphate—-
what do bones release when they break down
CA
Phosphate
PTH causes serum [ ] of:
Ca to ____
Phosphate to____
increase [ca]
decrease [phos]
role is vit d in body (3)
*what is vit D’s affect on blood [ ] of ca and phos?
- increases absorption of ca and phosphate from GUT
- increases bone resorption–so Ca and phos can be released into blood
- increases phosphate reabsorption in kidneys
INCREASES blood [ca] and [phos]
both vit d and PTH ___ calcium
increase
calcitonin is made in what cell
parafollicular cells of THYROID
Ca2+ is imp for?
muscle contractility
vit d is converted to active vit d where?
liver
PTH and relationship to bones
PTH increases osteoclastic activity–tells bones to break down the Ca + phosphate (mainly CA)
PTH and relationship to kidneys
tells renal tubular cells to incr reabsorbe CA and decrease reabsoprtion of phosphate—so phopshate is excreted in urine
intestinal absoprtion of calcium increases via?
vit D
agonist hormone to vit d and PTH
Calcitonin
role of Vit D
- increases absorption of CA and phosphate from gut
- increases bone resorption to help release CA into circulation
role of calcitonin
decrs blood CA by using CA to build bone—decreasing renal reabsoprtion of calcium
excess of PTH and or VIt D can cause?
hypercalcemia
too little PTH and or vit d can cause?
hypocalcemia
too much calcitonin or too little calcitonin can cause?
not much in terms of hypo or hypercalcemia — role in this case is more minor compared to PTH and Vit D
bone breakdown and decreased renal excretion of CA can lead to?
hypercalcemia
bone sequestration of calcium and renal failure can lead to?
hypocalcemia
MC pathology for cause of hyperparathyroidism?
parathyroid adenoma in one gland or more
PTH inhibits reabsorption of?
phosphate and HCO3
**then phosphate is excreted in urine
intestinal absoprtion of ____ is ____ via actions of vit D
calcium
increasd
how does calcitonin decease [ca]
uses calcium to build bone–decreasing renal absorption of calcium
99% of CA is found?
in bone
where is most of the CA? ECF or ICF?
ECF
nornal CA levels?
8.5-10 mg/dk
what is required for intestinal ca absoprbs?
vit d
ca2+ is important for what?
blood clotting
bone
normal celluar and neruomuscular function
three hormoes that regulate CA
vit d (calcitriol) and PTH—>stimulate ca reabsoption into body
-increases blood CA levels
-
calcitonin–> decreases CA blood levels
PTH affect on phosphate
inhibits reabsoprtion
***so phosphate is usually in opp direction of PTH in PRIMARY parathyroid issues
