thyroid Flashcards
explain secretion and synthesis of thyroid hormone
in notes
T3 & T4 leave the thyroid gland by
T3 & T4 leave the thyroid gland by diffusion.
T3 and T4 are transported into blood by
by three transport proteins, Thyroxine binding globulin (TBG), transthyretin and albumin.
which is biologically active T3 OR T4?
T3
but T4 has negative feedback inhibition and can be converted to T3
There is a lot of biologically Active hormones in the blood T/F
false 99.7 percent is bond to TBG
Both T3 & T4 enter their target cells
Both T3 & T4 enter their target cells by diffusion.
how is T4 activated to T3
Deiodination (D1 AND 2) of outer ring = active T3
D3: inner ring- inactive T3
If too much thyroid activity is present what will happen
If too much thyroid activity is present T4 is converted to the inactive metabolite rT3 to reduce activity.
Function of thyroid hormones
The major activity of thyroid is to raise the Basal Metabolic Rate.
Increase CATABOLISM and anabolism
raising basal metabolic rate will ?
limit the effect of all other hormones on their respective target systems.
Increasing basal metabolic rate will increase temperature
by in creasing the UCP which is involved in brown fat and shivering . impact mito. by allowing it to release more heat .
mRNA also stimulates more mitochondria to be released
Indirect effect of Thyroid hormone in cardiovasc.
increase in heat and CO2 in tissue will cause a decrease in peripheral vascular Resistance –> decease in disatolic bp –> increase in adrenergic stimulation
Direct effect of thyroid hormone on cardiovas.
increase cardiac muscle, increase ventricular contraction, and decrease in peripheral vascular resistancce .
TR Alpha 1
TR beta 1
TR beta 2
TRα1is strongly expressed in cardiac and skeletal muscle.
TRβ1is expressed mainly in brain, liver, and kidney.
TRβ2is expressed in the pituitary hypothalamus.
which transporters transport T3 and T4 into cell
Monocarboxylate transporters (MCT8 and MCT10) transport T4 and T3
4 ways thyroid hormones are regulated
Thyroid hormone feedback regulation of gland activity via suppression of TRH and TSH secretion.
Autoregulation of thyroid gland activity via the Wolf-Chaikoff Effect.
Energy intake and adipose tissue stores regulate thyroid gland activity via leptin and CNS regulation of TRH secretion.
Environmental factors regulate via CNS regulation of TRH secretion
what nucleus does the leptin activate
PV and acurate
A high uptake of iodine by the thyroid will indicate
hyperthyroidism
hypothyroidism
effects on skin m cardiov., and respiratory
Skin and other tissues
Increased hyaluronic acid accumulation in connective tissue leading to puffy appearance (myxedema); increased dryness
Cardiovascular
Decreased cardiac output and increased peripheral resistance at rest; decreased blood volume
Respiratory
Maximum breathing capacity and diffusing capacity are reduced
hypothyroidism
effects on GI and CNS/PNS
Gastrointestinal
Reduced food intake and reduced system peristaltic activity (contributes to constipation)
Central and peripheral nervous system
Reduced development, myelination, and vascularity of fetuses and infants (cretinism)
Reduced blood flow and reduced intellectual functions
HYPOTHYROIDISM
Muscular and skeletal and renal effects
Muscular
Slow movement due to delayed muscle contraction and relaxation
Skeletal Impaired growth (greatest effect on limbs)
Renal, Water & Electrolytes
Reduced renal function & blood flow; delayed water excretion
Increased water retention
Hypothyroidism
RBCs and Reproductive
Hematopoietic
Reduced red blood cell mass
Reproductive
Reduced sexual maturation and delayed puberty in children
Reduced libido and ovulation in women; Reduced libido, impotence and oligospermia in men
hyperthyroidism
effects on skin eyes., and respiratory
Skin has a warm moist feel; Increased diffuse pigmentation; nails may be soft and friable; hair may be fine and friable
Eyes
Retraction of upper eyelid giving “stare” or “fish eyes” appearance
Cardiovascular
Increased cardiac output and decreased peripheral at rest; increased force of contraction (induced by increased metabolism)
hyperthyroidism
respiratory, GI, Nervous system
Respiratory
Vital capacity may be reduced and dyspnea is common
Gastrointestinal
Increased food intake but weight loss; Increased peristalsis
Nervous system
Nervousness, emotional lability and hyperkinesia (overall effect is similar to those associated with sympathetic nervous system activation)
hyperthyroidism
muscular, skletal, renal
Muscular
Weakness and fatigability
Skeletal
Demineralization of bone; increased excretion of Ca+ and PO4-
Renal, Water & Electrolytes
Increased blood flow and mild polyuria
hyperthyroidism
RBC, reproductive,
Hematopoietic
Increased red blood cell mass
Reproductive
Delayed sexual maturation in children
Abnormal menstrual cycles in women; Increased conversion of androgens to estrogens may lead to gynecomastia and erectile dysfunction in men
