Endo Lec 4 Flashcards
thyroid gland (def.)
bi-lobed gland in front of trachea
thyroid gland made of ..
-follicles and parafollicular cells
thyroid gland follicles are made of
–follicular cells lining the surface and a cavity filled with colloid (gelatinous material)
resting vs. actively secreting follicle
actively secreting follicle increases in size
parafollicular cells secrete
calcitonin
thyroid follicles secrete
T3 & T4
list of thyroid hormones
- T3
- T4
- calcitonin
thyroid hormones synthesized from
tyrosine and I2
intermediates of thyroid hormones synthesis
- Monoiodotyrosine (MIT)
- Di-iodotyrosine (DIT)
active end products of thyroid hormones synthesis
- Tri-iodothyronine (T3)
- Tetra-iodothyronine or thyroxine (T4)
synthesis of thyroid hormones
- iodide is cotransported with Na+ into follicle cell and I- diffuses into colloid
- Iodide is oxidized and attached to tyrosines in thyroglobulin (TG)
- formation of T3 + T4 attached to TG
- endocytosis of TG containing T3,T4 molecules into follicle cell
- lysosomal enzymes release T3/T4 from TG
- T3/T4 secretion out of follicle cell
TG (thyroglobulin) is synthesized in ….and secreted to…
- follicle cell
- secreted to colloid
NIS stands for
sodium-iodide symporter (active transport)
Thyroid follicular cells (also called…)
thyroid epithelial cells or thyrocytes
thyroglobulin (TG)–def.
glycoprotein that contains tyrosine
iodination of tyrosine form..
iodotyrosines (MIT & DIT)
Tyr + 1 iodine =
MIT
Tyr + 2 iodine=
DIT
MIT stands for
-Monoiodotyrosine
DIT stands for
–Di-iodotyrosine
DIT + MIT=
tri-iodothyronine (T3)
DIT + DIT=
`tetra-iodothyronine/thyroxine (T4)
T3 stands for…(1 name)
tri-iodothyronine
T4 stands for.. (2 names)
- tetra-iodothyronine
- thyroxine
T4 storage __ T3 storage in colloid
> (greater)
T4 secretion __ T3 secretion in blood
> (greater)
during thyroid hormones synthesis, there is recycling of …
I- and amino acids
T3 & T4 are transported in blood mainly bound to…
thyroid binding protein (TBP)
T3 amount free in blood (%)
0.3%
T4 amount free in blood (%)
0.03%
which is more potent (T3/T4)?
T3 is 3-8x more potent than T4
which is prohormone/biologically active form (T3 & T4)?
prohormone: T4
biologically active form: T3
… is converted to … in
- T4
- T3
- peripheral cells and liver
which is produced more %(T4 OR T3)
T4 (90%) vs T3 (10%)
T3 binds to ..
nuclear receptors
control of thyroid hormone secretion
↑ TRH secrection
↑ TSH secerection
↑ T3/T4 secrection
↑ T3/T4 (feedback)
(-) TSH secretion
(-) TRH secretion
↑ T3/T4 (feedback)
(-) TSH secretion
(-) TRH secretion
physiological actions of T3/T4
- act on most tissues (change in transcription and translation process)
- increase metabolism
- required for growth and development
7 metabolic effects of T3
- Catabolism/anabolism ↑
- ↑ BMR (basal metabolic rate), ↑O2 consumption ↑heat
- ↑ carbohydrate absorption/use
- ↑ protein breakdown (muscle)
- ↑ fat breakdown
- ↑ cholesterol metabolism
- ↑ serum cholesterol (LDL)
5 growth + development effects of T3
- Act as “tissue growth factors”
- Small amounts stimulate protein synthesis
- Increase GH/IGF-1 production
- Essential for CNS maturation during fetal
stage - Maternal hypothyroidism results in poor
fetal CNS development and mental
developmental disability
3 permissive effects of T3
- Cardiovascular system (beta adrenergic
receptors): increased HR and contractility,
increased blood pressure - Potentiation of Sympathetic Nervous System
(beta-2 adrenergic receptors) - Reproductive system: necessary for normal
function and fertility
graves’ disease def. + problem
- is the over activity of gland
- autoimmune disorder
- antibody to TSH receptor stimulates thyroid hormone production
graves’ disease associated with
- increased BMR (basal metabolic rate)
- exophthalmos (bulging or protruding eyeballs)
- goitre
hashimoto’s thyroiditis def. + problem
- is the underactivity of gland
- autoimmune disorder
- TPO (thyroid peroxidase) antibody destroy thyroid gland to block hormone synthesis
hashimoto’s thyroiditis is the most common
autoimmune cause of hypothyroidism
hashimoto’s thyroiditis associated with
- myxedema (adult-onset) = severely advanced hypothyroidism, swollen puffy skin
- goitre
- cretinism (in children only)= underactive thyroid function at birth
11 hypothyroidism symptoms
- Lethargy
- Weight gain
- Cold intolerance
- Constipation
- Nausea / low appetite
- Menorrhagia (heavy periods)
- edema
- Shortness of breath
- “myxedema madness”
- Dry skin
- Brittle hair and nails
goitre can happen for both … cases
hypothyroid and hyperthyroid
goitre formation (hyperthyroidism)
thyroid gland enlarges ↑ T3/T4 strong negative feedback ↓ TSH ↓ TRH
goitre formation (hypothyroidism)
↓ T3/T4 (+) ↑TRH, ↑TSH thyroid gland enlarges no iodine T3/T4 remain low
TSH measurement is the ….. for thyroid function
best single screening test
Changes in TSH occur often before measurable changes
in T4 or T3 are present
TSH reflects the true state
of Free T4, Free T3
Iodine deficiency in the diet is the most common cause of
– Hypothyroidism
– Goitre
– Developmental/intellectual disability
– Preventable brain damage
µg iodine/day only needed?
150 µg iodine/day
