Exam 1: Thyroid Flashcards
Thyroid gland location
Below larynx on each side of trachea
2 hormones that thyroid gland secretes
T4 (93%)
T3 (7%)
T4 AKA
Thyroxine
T3 AKA
Triiodothyronine
Almost all T4 eventually converted to
T3 (in tissues)
Which thyroid hormone is more potent
T3 (4x)
Thyroid secretes ____ which decreases blooc Ca2+
Calcitonin
Calcitonin opposes action of
PTH and vitamin D
Colloid
Secretory substance containing thyroglobulin
Thyroglobulin is precursor for
T3 and T4
____ required for formation of T3 and T4
Iodine
How much iodine must be ingested per week for normal amounts of hormone
1mg
Found in table salt
____ of absorbed iodide taken up by thyroid, the rest is ___
1/5
Excreted by kidneys
Thyroid composed of large # of ____ filled w/ colloid
Follicles
Transport of iodides from blood into follicle requires
Sodium iodide symporter
Sodium iodide symporter cotransports
1 iodide w/ 2 sodiums
Sodium iodide symporter coupled to
Na/K pump
Sodium iodide symporter stimulated by
TSH
Before adding iodine to thyroglobulin it combines w/
Thyroid peroxidase
Precursor of all thyroid hormones
Thyroglobulin
Thyroglobulin is made up of
70-130 tyrosine residues
20% iodinated
1st essential step in formation of thyroid hormones
Oxidation of iodide
Requires oxidase and H2O2
Thyroid gland can store ____ worth of hormone
2-3 months
Organification of thyroglobulin
Combining w/ iodide
Tyrosine + 1 iodide
Monoiodotyrosine (MIT)
MIT + iodide
Diiodotyrosine (DIT)
DIT + iodide
T3
T3 + iodide
T4
____ stimulates thyroglobulin uptake
TSH
____ stimulates release of DIT, MIT, T3, T4 out of cell
TSH
Biosynthesis depends on products of 3 genes
Sodium iodide symporter
Thyroglobulin
Thyroid peroxidase
Prior to release thyroid hormones are
Cleaved from thyroglobulin
> 99% of T3/4 are bound to
Plasma proteins
Binding to plasma proteins provides
Controlled slow release
TSH secretion is inhibited by
High T4 levels
Sensitivity of pituitary to TRH depends upon
Intrapituitary T3 levels
When T4 serum levels drop what happens to intrapituitary T3
Also goes down
TSH controlled by
Hypothalamic thyrotropin-releasing hormone (TRH)
TRH is a
Phospholipase C 2nd messenger
TRH release stimulated by exposure to
Cold
TSH receptors present on surface of
Thyroid follicular cells
Works w/ cAMP
TSH increases:
- Proteolysis of thyroglobulin
- Iodide pump
- Iodination of tyrosine
- Size, activity, # of thyroid cells
Plasma proteins used to transport thyroid hormones
Thyroxine-binding globulin
Transthyretin (thyroxine-binding prealbumin)
Thyroxine-binding globulin (TBG)
Highest affinity for T3/4
77% T4 bound to TBG
TTR has lower affinity for ___ and quantity in blood is ___
T4
Higher
TTR does not effectively bind
T3
Serum T4 is ____ bound and ____ free
- 96% bound
0. 04% free
Serum T3 is ____ bound and ____ free
- 6% bound
0. 4% free
Main action of thyroid hormones
Increase transcription of lots of genes
Thyroid hormone effect on cellular metabolic activity
Inc # and activity of mito
Inc transport of ions (Na/K pump)
Thyroid hormone effect on growth
Promotes growth
Hyperthyroid children grow ____ but duration may be _____
Faster; shortened (epiphyseal closure earlier)
Thyroid hormones promote growth of ____ especially during _____
Brain; fetal neonatal period
Thyroid hormones decrease concentrations of plasma contents:
Cholesterol
Phospholipids
Triglycerides
T3/4 ___ rate of cholesterol secretion into bile and ____ fecal loss
Increase; increase
**increase LDL receptors to promote rapid removal
Thyroid hormone ____ body weight
Decreases
CV effects of thyroid hormone
Inc blood flow Inc CO - inc HR and strength Inc systolic BP Dec diastolic BP
Thyroid hormone on CNS
Inc rapidity of thought (cerebration)
Thyroid hormone on skeletal muscle
Enhances contraction
Excessive T3/4 ____ muscle contraction
Weakens
Bc of excessive protein catabolism
Hypothyroidism causes muscles to be ___
Sluggish and contract slowly
Characteristic sign of hyperthyroidism is
Fine muscle tremor
Hypothyroidism in M/F causes
Loss of libido
Excesses of thyroid hormone in men can cause
Impotence
Hypo women usually have __ or __
Menorrhagia or polymenorrhea
Hyper women can have ____ and ____
Oligomenorrhea and amenorrhea
Deficiency in thyroid hormone in children can cause
Stunted growth
Thyroid hormones control
Basal metabolic rate
Inc in secretion of thyroid hormones exaggerates responses of
Ne/epi in SNS
Inc in metabolic rate and body heat suppress TSH release via
Inhibition of TRH
Cause acute dec in TSH secretion
Both hypo and hyperthyroidism ____ serum cholesterol
Decrease
Goiter
Enlargement of thyroid gland
Possible to have a goiter and be:
Hypothyroid
Euthyroid
Hyperthyroid
Example of euthyroid goiter
Dietary iodine deficiency
Dietary iodine deficiency
T3/4 dec — TSH inc, stimulates growth of thyroid
Example of hyperthyroid goiter
Graves disease
Thyroid adenoma
Graves’ disease
Thyroid stim by abnormal immunoglobulins against TSH receptor
Endemic cretinism
Iodine deficiency in utero
Cretinism
Forms of hypothyroid beginning at/before birth
Cretinism characterized by
Failure of body growth and intellectual development disorder
In cretinism, skeletal growth ______ than soft tissue growth
More inhibited
Hashimoto’s disease
Autoimmune disorder
Destoyr thyroid
Preceded by thyroiditis
MC cause of hypothyroidism in US
Chronic lymphocytic thyroidtis (AKA Hashimoto)
Reverse T3
3,3’,5’-triiodothyronine (inactive)
Myxedema
Generalized nonpitting edema
Seen w/ hypothyroid