Thyroid and Parathyroid Flashcards
two cell types of the thyroid
- follicular cells
- Parafollicular cells, or C
cells
what type of hormones are thyroid hormones
monoamines but act like steroid
thyroid hormones are derived from
tyrosine
What causes thyroid hormones to act like steroids?
Iodine
synthesized by follicular cells and stored in the colloid
thyroglobulin (this is the first step of thyroid hormone synthesis)
a large glycoprotein containing many
tyrosine molecules
thyroglobulin
active transport
of iodine from blood via sodium-iodide symport (NIS) pump (needed to go against the iodine gradient - more iodine in follicular cells than in blood)
Iodine Trapping (2nd step of thyroid hormone synthesis)
iodine binds to thyroglobulin and gets
attached to tyrosine by thyroid peroxidase
Iodination of tyrosine (3rd step of thyroid hormone synthesis)
T1 and T2 are coupled to make T3 and T4
coupling reaction (4th step of thyroid hormone synthesis)
adds the iodine to tyrosine to make T3 and T4
thyroid peroxidase
thyroglobulin is digested, freeing T3 and T4
lysosome digestion
the biologically active thyroid hormone
T3
the most secreted thyroid hormone
T4
enzymes remove iodine to convert T4 to T3
plays a major role in regulating intracellular T3 levels in a tissue-specific manner
deiodinase
the primary trigger of thyroid hormone release
cold exposure
The primary carrier protein for thyroid hormones
Thyroxine-binding globulin (TBG)
How are steroid and thyroid hormone signaling different?
- Thyroid hormones
can’t diffuse across
cell membranes - Receptors aren’t regulated by heat shock proteins (HSP); receptor is already bound to
hormone response element (HRE) - Thyroid hormones
form heterodimers
decreased tolerance to cold is linked with
hypothyroidism
excessive heat production and sweating are seen in
hyperthyroidism
autoimmune disorder; your antibodies attack cells in thyroid (if
untreated leads to myxedema & coma)
Hashimoto’s disease
immune disorder in which
your body makes an antibody
that mimics TSH
Graves disease
was a common
cause of goiters (thyroid enlarges as it
tries to capture all the iodine it can)
Dietary iodine deficiency
congenital (condition at birth), often due to low
maternal thyroid hormone or dietary deficiency
- impaired growth
- slow movement
- poor thermoregulation
- intellectual disabilities
Cretinism
3 calciotropic hormones that regulate calcium balance
- parathyroid hormone (PTH)- primary regulator. produced in parathyroid gland
- Vitamin D- absorbs calcium from the intestines
- Calcitonin- produced in thyroid gland
principal cell type
arranged in clusters; produces hormone
chief cells
Main hormone of the parathyroid
parathyroid hormone
parathyroid hormone affect on calcium
Increases calcium concentration by acting on bone, kidney, and
intestine
- Increases osteoclast activity (release of calcium stored
in bone) - Decreases osteoblast activity
cause formation of bone and stores calcium
osteoblasts
resorb, or break down, bone and releases calcium
osteoclasts
stimulates PTH secretion.
Low concentrations of calcium
inhibits PTH secretion
High concentrations of calcium
result of hypoparathyroidism
tetany and seizures
result of hyperparathyroidism
kidney stones and osteoporosis
Protects Against Excessive
Bone Resorption
calcitonin
stimulates calcitonin secretion
High concentrations of calcium
what does calcitonin do
- acts to lower blood calcium
- inhibits osteoclasts
