Thyroid Gland Lopez Lecture Flashcards
Factors increasing T4 –> T3 conversion
obesity, cold, hyperthyroid
factors decreasing T4 –> T3 conversion
pregnancy fasting beta-blockers hepatic/renal failure aging hypothyroid
Enzymes converting T4 –> T3 into its active form
deiodinases type 1 and type 2
outer ring iodination
Enzymes converting T4—> T3 into its inactive form
deiodinase type 3
inner ring iodination
TSH Abs do what?
stimulate TH synthesis
TH stimulatory factors
increased TBG levels such as during pregnancy
What proteins are synthesized under the influence of thyroid hormones?
Na-K ATPase beta1 adrenergic receptor lysosomal enzymes proteolytic enzymes structural proteins
Na-k ATPase
in most tissues it is stimulated by thyroid hormone
proteins in cardiac muscle stimulated by TH
beta1 adrenergic receptors, Ca-ATPase
what factors inhibit TH synthesis?
PTU thiocyanate percholate Wolff-Chakioff effect liver disease
what is the first step of TH in acting on target tissues?
T4 has to be deiodinated by 5’ iodinase to T3
What actions does TH have on the body?
it acts on virtually all tissues of the body
creates heat, protein synthesis, increases basal metabolic rate, and oxygen consumption. acts synergistically with GH and somatomedins.
What agens prevent the conversion of T4 to T3?
hepatic failure, renal failure, beta adrengeric blocking agents, and pregnancy, fasting, stress
Obesity
increases T4—> T3 conversion
How does TH work inside the cell?
somehow it gets into the cell and binds to a nuclear receptor. it translocates to nucleus and stimulates nuclear transcription by binding to thyroid regulatory element on DNA
TH effects on growth
bone maturation and growth formation
TH on CNS
maturation of CNS
TH on BMR
increases synthesis of Na-K ATPases, O2 consumption, heat production, BMR
TH on metabolism
increase in glucose absorption, glycogenolysis, gluconeogenesis, lipolysis, protein synthesis and degradation (net catabolic)
TH and cardiovascular
increases cardiac output
What accounts for TH’s stimulation of metabolism?
the synthesis of Na-K ATPases: leads to O2 consumption and heat production
how does BMR increase under influence of TH?
new Na-K ATPases: a single does of T4 (thyroxine) can increase BMR a few hours after injection, and long lasting (6 hrs)
What effect does hypothyroidism have on BMR?
decreases it
what effect does hyperthyroidism have on BMR?
increases it
TH effect on lipid metabolism
stimulates FA metabolism—> increases FA plasma levels, FA intake into the liver, beta oxidation of the FAs
TH have what kind of proportional relationship to cholesterol and glycerol?
inverse
what will blood cholesterol look like in patients with hypothyroidism?
it will be increased
Vit. A and TH
TH is required for conversion of carotene to vitamin A
hypothyroidism can suffer blindness/yellowing of skin
carbohydrate metabolism
TH increases gluconeogenesis, glycogenolysis to generate glucose
enhancement of insulin dependent entry of glucose into cells
Cardiovascular effects
DIRECT (7)
increases proteins in muscles
1) myosin heavy chain alpha/beta ratio
2) Na-K ATPase
3) G protein stim/inhibitory ratio
4) Sarcoplasmic Ca-ATPase
5) increases ventricular contractility and function
6) decreases peripheral vascular resistance
7) beta adrenergic signaling
Cardiovascular effects
Indirect (4)
increased heat production
decreased peripheral resistance
decreased diastolic pressure
increase in reflex adrenergic stimulation
“ultimate” outcomes on the cardiovascular system due to TH
increase in cardiac rate and output
increase in blood volume (direct and indirect)
Type 1 deiodinase
found mostly in the peripheral tissues
Type 2 deiodinase
found mostly in the brain
Pendrin
the transporter for iodide across the apical surface of the follicular cell
iodide, NOT iodine
what are the “two” main players in the lumen of the follicle?
iodine (I2) and thyroglobulin with tyrosine moities
intrathyroidal deiodinase = function?
breaks down the Thyroglobulin-MIT-DIT —> TG, tyrosine, MIT, DIT
how much iodide will be taken up in the first 6 hours after injection?
what % indicates hyperthyroidism? hypothyroidism?
25%
60%
10% roughly
transthyretin
responsible for getting T4 to brain, kind of like thyroid binding globulin
what test can measure TBG?
T3 resin uptake test
the T3 resin test will indicate what general character of T3 during hepatic failure?
increased T3-bound resin, because there is a DECREASE in liver produced TBG
T3 resin levels will increase during
hepatic failure when TBG is decreased or when T3 levels are increased in the blood already
T3 resin uptake will decrease when
TBG is increased or endogenous
T3 is decreased
Thyroid hormones stimulate the
synthesis of cardiac beta-1 adrenergic receptors
used by norepinephrine
what branch of the nervous system is highly functioning when TH is high in the body, and why
sympathetic nervous system because beta adrenergic receptors are being produced in quantity. so when TH is high, there are more beta-adrenergic receptors on the heart for example
bone formation is stimulated synergistically with
TH and GH and somatomedins
deficient TH during perinatal years
leads to abnormal development of synapses
decreased dendritic branching and myelination
neutral changes induced by thyroid hormone deficiency cause cretinism
TH deficiency in children during the ____ period causes
perinatal = “of or relating to the time, usually a number of weeks, immediately before and after birth.”
decreased dendritic branching and myelination
abnormal development of synapses
Metabolism: hypo/hyper
hyper: heat intolerance, weight loss, increased BMR
hypo: cold intolerance, weight gain, decreased BMR
Skin: hypo/hyper
hyper: excess sweating
hypo: dry skin, myexidema
Bone: hypo/hyper
hyper: osteoporosis
hypo: stunted growth
CV system: hypo/hyper
hyper: tachycardia, atrial fibrillation, palpitations, high-output heart failure
hypo: bradycardia, decreased contractility, decreased cardiac output
CNS: hypo/hyper
hyper: agitation, anxiety, difficulty concentrating, hyperreflexia
hypo: cretinism (congenital) in kids, listlessness/slowed movement/somnolence/impaired memory/decreased mental capacity
INTESTINE: hypo/hyper
hyper: diarrhea
hypo: constipation
