Thyroid Metabolic Hormones Flashcards by Mia Hebert

thyroid gland 2 main hormones

T4 93%
T3 7%
also produces calcitonine

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calcitonine

minor role in maintaining Ca2+ and phosphate

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chronic lack of TH

decrease BMR to 40-50% below normal
will feel cold and gain weight possibly

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chronic excess TH

increase BMR to 60-100% above normal
feel hot and lose bw possibly

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iodine

chemical element
turn into ion iodide
have to consume iodiDe
only thyroid gland needs iodide in the body

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iodide pump

actively transport the iodides from the blood into the thyroid gland
iodide trapping

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iodide trapping

not very effective
20% of iodide in blood is taken by thyroid gland
rest is excreted by kidney

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colloid

in follicles of the thyroid gland
mainly composed of glycoprotein called thyroglobulin

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thyroglobulin

contains TH and secretes into follicular colloid to be stored
prehormone
contains 70 tyrosine amino acids
reservoir of TH hormones

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formation of TH

peroxidase is needed to add 3-4 iodide molecules to 2 tyrosines

TH stored in body for 2-3 months so takes time to observe effects of deficiency

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what happens to thyroglobulin once TH is synthesized

TH remains attached to it

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how is T3 and T4 released from thyroid gland

proteinases digest thyroglobulin and releases the hormones
diffuse from the thyroid cells into the blood

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what can cause iodide deficency

lack of deiodinase enzyme because can’t recycle iodide

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how does T3 and T4 get transported to the tissues

combine with several plasma binding proteins :
thyroxine-binding globullin (mainly
Thyroxine-binding prealbumin
albumin

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what is the rate of release of T3 and T4 to the tissues

T3: one day
T4: 6 days because plasma binding protein has higher affinity for T4

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general effect of TH

cause nuclear transcription of genes for synthesizing large number of substances

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what 4 substances are synthesized by TH

enzymes
structural proteins
transport proteins
other

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what hormones binds the most to receptors

T3 (more than 90%)

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once TH is attached to receptor, attach to DNA…

receptors activate and initiate transcription process
messenger RNA formed
new proteins formed by RNA translation on cytoplasmic ribosomes

effects of TH on mitochondria

increase number of mitochondria
increase total membrane surface (size) of mitochondria
increase formation rate of ATP

effects of TH on carbohydrate metabolism

increase metabolic enzymes
increase absorption rte of glucose from GI tract
increase uptake rate of glucose by cells
enhances glycolysis
enhances gluconeogenesis
increase insulin secretion, and uptake by tissues
decreases glycogen stores in the liver and skeletal m. glycogennolysis, more glucose enters circulation

effects of TH of fat metabolism

increase fat catabolism, lipolysis in adipose tissue
increase FFA concentration in plasma
accelerate oxidation of FFA by cells
decrease cholesterol, phospholipids and tryglycerides
increase fat anabolism in the liver

lack of TH, hypothyroidism

excessive fat deposition in liver
can cause arteriosclerosis due to accumulation of cholesterol

effects of TH of protein metabolism

increase protein synthesis

effects of hyprethyroidism on protein

increase proteolysis weaken m. overtime

effects of TH on vitamin metabolism

increase quantity of enzymes and need for vitamins can cause relative vitamin deficiency unless increase intake

effects of TH on the body (3)

increase transport rate of Na and K ions increase heat production cell membranes become leaky to Na ions

effects of TH on growth

lack causes retarded growth rate in children excessive causes rapid skeletal growth

effects of TH onCV system

increase BF and CO because of rapid utilization of oxygen increase HR increase strength of heart beat increase slightly BV because of vasodilation increase arterial pressure

effects of TH on respiration

increase rate and depth bc increased rate of metabolism and use for oxygen

effects of TH on GI tract

increase secretion rate of digestive juices and motility of GI tract Excess causes diarrhea Lack causes constipation

effects of TH on CNS

increase brain activity excess causes anxiety, extreme worry and paranoia

effects of TH on muscle function

muscle becomes weakened with excess TH because of excessive protein catabolism lack causes muscles to become sluggish and slow relaxation after a contraction excess causes muscle tremor because of increased reactivity of neural synapses in the are of the spinal cord that controls muscle tone

summary of metabolic effects of TH

regulation of TH secretions

hypothalamic hormone called TRH secreted by nerve endings in the median eminence of the hypothalamus

mechanism controlling TH secretions

TRH transported to ant pituitary through hypothalamic-hypophysial portal vessel TRH binds with receptor on pit cell membrane activates second messenger cells in ant. pit. produce and release TSH TSH binds with receptor on basal membrane surface of thyroid cell

TSH causes increased release of TH because of

proteolysis of thyroglobulin activity of iodide pump iodination of tyrosine for forming TH size and number of thyroid cells

control secretion of TSH by negative direct feedback

concentration level of TH feedback to ant. pit.

control secretion of TSH by negative indirect feedback (5)

increased TH increased metabolic function increased heat increased body temp affects hypothalamus

feedback diagram

hyperthyroidism

thyroid gland increase 2 to 3 times normal size increase number and size of cells increased secretion rate goiter

hyperthyroidism causes

autoimmunity antibodies bind to TSH receptors thyroid adenoma

symptoms and consequences of hyperthyroidism

high state of excitability intolerance to heat increased sweating mild to extreme weight loss different degrees of diarrhea muscle weakness nervousness protrusion of eyeballs extreme fatigue inability to sleep tremor of hands other psychiatric disorders

hypothyroidism cause

autoimmunity destroys gland thyroid inflammation: secretion of TH stops or diminished lack of iodine: prevents production of TH

genetic abnormality affecting TH production

deficient iodide-trapping mechanism

symptoms and consequences of hypothyroidism

fatigue extreme somnolence extreme muscular sluggishness slow HR decreased BV and CO increased weight constipation mental slugishness scaling of skin edematous appearance increase of blood cholesterol

comparison of hyper and hypo