18.7 THYROID GLAND Flashcards
butterfly-shaped thyroid gland is located inferior to the?
larynx (voice box)
It is composed of right & left lateral lobes on each side of the trachea and are connected by what
an isthmus (narrow passage) anterior to the trachea
about 50% of thyroid glands have a small 3rd lobe called ?
pyramidal lobe (extends superiorly from the isthmus)
microscopic spherical sacs that make up most of the thyroid gland are called?
thyroid follicles
the wall of each follicle consists of cells called what?
follicular cells - extend to the lumen (internal space) of follicle
what surrounds each follicle
a basement membrane
when follicular cells are inactive their shape is?
low cuboidal to squamous
under the influence of TSH they become active in secretion and their shape becomes?
range from cuboidal to low columnar
which 2 hormones do the follicular cells produce? (THYROID HORMONES)
thyroxine (tetraiothyronine) T4 - 4 atoms iodine
triiodothyronine T3 - 3 forms of iodine
A few cells called what lie between follicles?
parafollicular cells or C cells
What hormone do the parafollicular cells or C cells produce ?
calcitonin which helps regulate calcium homeostasis
how do thyroid follicular cells trap iodine ions? What happens as a result of this?
By actively transporting them from the blood into the cytosol
Result - thyroid gland normally contains most of the iodine in the body
While follicular cells trap iodine, they also synthesize thyroglobulin (TGB) which is
a large glycoprotein produced in the rough ER, modified in golgi complex and packaged into secretory vesicles
some amino acids in TGB are tyrosines that will become donated. Negatively charged iodine ions cannot bind to tyrosine until they undergo what?
oxidation -> removal of electrons to iodine
as iodine atoms (I0) form after oxidation, they react with?
tyrosines that are part of thyroglobulin molecules
the thyroglobulin (TGB) with attached iodine atoms, a sticky material that accumulates and is stored n the lumen of the thyroid follicle is termed?
colloid
in the last step of synthesis of thyroid hrmone two T2 molecules join to form __? or one T1 and one T2 join to form __?
T4 T3
How do droplets of colloid reenter follicular cells ?
pinocytosis
after colloid reenters, they merge with?
lysosomes
how do T3 and T4 go into the PM into inserstial fluid into the blood
they diffuse because they are lipid-soluble
is T3 or T4 secreted in greater quantity ?
T4
is T3 or T4 more potent?
T3
AFTER t4 enters a body cell, what happens
it is converted to T3 by removal of one iodine
1 function of thyroid hormones is increasing the basal metabolic rate, what is this?
the rate of energy expenditure under standard or basal conditions (awake, at rest, fasting)
