Thyroid Metabolic Hormones Flashcards
thyroid gland 2 main hormones
T4 93%
T3 7%
also produces calcitonine
calcitonine
minor role in maintaining Ca2+ and phosphate
chronic lack of TH
decrease BMR to 40-50% below normal
will feel cold and gain weight possibly
chronic excess TH
increase BMR to 60-100% above normal
feel hot and lose bw possibly
iodine
chemical element
turn into ion iodide
have to consume iodiDe
only thyroid gland needs iodide in the body
iodide pump
actively transport the iodides from the blood into the thyroid gland
iodide trapping
iodide trapping
not very effective
20% of iodide in blood is taken by thyroid gland
rest is excreted by kidney
colloid
in follicles of the thyroid gland
mainly composed of glycoprotein called thyroglobulin
thyroglobulin
contains TH and secretes into follicular colloid to be stored
prehormone
contains 70 tyrosine amino acids
reservoir of TH hormones
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
what happens to thyroglobulin once TH is synthesized
TH remains attached to it
how is T3 and T4 released from thyroid gland
proteinases digest thyroglobulin and releases the hormones
diffuse from the thyroid cells into the blood
what can cause iodide deficency
lack of deiodinase enzyme because can’t recycle iodide
how does T3 and T4 get transported to the tissues
combine with several plasma binding proteins :
thyroxine-binding globullin (mainly
Thyroxine-binding prealbumin
albumin
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
general effect of TH
cause nuclear transcription of genes for synthesizing large number of substances
what 4 substances are synthesized by TH
enzymes
structural proteins
transport proteins
other
what hormones binds the most to receptors
T3 (more than 90%)
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
