thyroid hormone Flashcards
1
Q
what are the hormones released by the thyroid gland?
A
Tri iodothyronine (T3)
Tetra iodothyronine (T4)
Calcitonin –> decreases the calcium level
2
Q
what is the function of parathyroid gland?
A
release parathyroid hormone —> increase calcium level in the blood and phosphorus hemostasis
3
Q
what type of hormone thyroid hormone?
A
amino acid derived hormones
derived from tyrosine
catacheloamines are also tyrosine derived
4
Q
what are the components required to make thyroid hormone?
A
2 tyrosine residues
iodine
5
Q
where are the tyrosine residue trapped in?
A
protein called thyroglobulin
6
Q
what form is the iodine trapped as?
A
iodide
7
Q
what determines the activity of the thyroid hormone?
A
position of the iodine
8
Q
where is the iodine positioned in T3?
A
T3 is the most active one
its positioned in 3,5,3
9
Q
what is the iodine position in reverse T3?
A
reverse T3 is inactive form of T3
the position of iodine is 3,3,5
10
Q
how is T4 converted into T3?
A
deiodination via 5-iodinase
11
Q
what is the precursor for T4 and T3?
A
thyroglobulin
12
Q
what processes happen to the thyroglobulin ?
A
it gets iodinated
and glycosylated
13
Q
what is thyroglobulin rich in?
A
rich in tyrosine residues
14
Q
what happens to the tyrosine residues in the thyroglobulin ?
A
it is the binding site for iodine —> gets iodined
15
Q
what are the inactive precursors of thyroglobulin ?
A
mono iodotyrosine ( MIT ) –> one iodine
di ido tyrosine ( DIT ) –> 2 iodines
70% of the iodine is present like this
16
Q
what about the other 30% of iodine?
A
present in T4 and T3 form
17
Q
where is most of the body iodine found?
A
thyroglobulin
18
Q
what prevents iodine from escaping ?
A
iodination –> once its bound to tyrosine it is trapped
19
Q
from what does T4 result from?
A
coupling of 2 di iodo tyrosine
2 + 2 = 4
20
Q
from what does T3 result from?
A
coupling of 1 mono iodo tyrosine + 1 di iodo tyrosine
1 + 2 = 3
21
Q
How does the coupling happen ?
A
oxidation reaction
22
Q
what enzyme is responsible for the oxidation?
A
thyroperoxidase ( TPO )
23
Q
what happens to the hormone once its released?
A
remain integral of thyroglobulin until it is degraded n released when it is degraded
24
Q
where does the synthesis of thyroid hormone occur?
A
luminal portion of the follicular cells and it moves to the basal
25
describe the process of thyroid hormone synthesis ?
Ribosomes of RER will synthesize the thyroglobulin
thyroglobulin will be transported to golgi apparatus --> in golgi apparatus will be glycosylated
vesicle will take the thyroglobulin and will undergo exocytosis to enter the colloid
Iodine uptake happens and enter the blood into the follicular cell , iodine enter in the form of iodide
2 iodide joins together to form iodine ( I2)
MIT and DIT are formed by attaching iodine to the tyrosine
T3 form by coupling for MIT + DIT
T4 form by co
coupling of DIT + DIT
endocytosis of T3 AND T4 to be stored and released when degradation of thyroglobulin
26
why is golgi apparatus important for glycosylation ?
required for targeting signalling and formation formation of 3D structure
27
what is the function of peptidases and proteases?
hydrolyses the thyroglobulin into its constituents amino acids which are then discharged into extracellular spaces
28
what happens to the T3 and T4 after libration from thyroglobulin ?
it is deionidated by deionidase
the resulting tyrosine and iodide are returned to further utilization
29
what does the serum level of thyroglobulin indicates?
it is used to detect endogenous thyroid secretion
for example when patients are using T4 oral replacement
30
what method is used to transport iodine from bloodstream to inside the cell ?
since iodine concentration is higher inside the cell than the capillary since the iodine is stored in the thyroid
it requires active transport and energy
31
what is primarily active transport?
utilization of energy from ATP to move substances against their concentration gradient
example : Sodium potassium pump
moves 3 sodium out ( theres more NA out than inside )
moves 2 to potassium in (theres more K inside than out )
32
what is secondary active transport ?
transporter that uses energy from existing gradient created by primary active transport ( NA/K pump ) to move another substances against it is gradient
example Sodium iodine symport --> uses Sodium flow inside the cell to bring Iodine in along with it
33
what concentration gradient is created by the NA/K pump?
it will make NA outside more than inside so NA will passively move in to the cell because it is moves with the gradient
make K more inside the cell than outside making K leaves passively with the concentration
34
what is the difference between symport and antiport ?
symport -----> move the 2 substances in the same direction
antiport ---> move the 2 substances in opposite direction
35
what is the function of Sodium iodide symport ?
when Na moves with its concentration gradient it takes an iodide ( which is moving against its conc gradient ) with it
requires energy and concentration gradient difference but this energy /concentration difference is from the primary NA/K pump
36
what stimulates the NA/I symporter?
it is activated by TSH via G protein coupled mechanism --> increases CAMP ---> activates the symporter
37
what are the general functions of thyroid hormone?
necessary for normal growth
differentiation
sex and mental development
Regulate the speed of metabolism
38
what is the massive iodine concentration inside the cell can be used for in regard of investigations?
radioactive isotopes in case of thyroid disease
39
where is the receptor for thyroid hormone present?
it is intracellular --> intranuclear receptor
40
how does Thyroid hormone produces its effects?
it binds to the nuclear receptor which is attached to the DNA
once T3 binds to the receptor it dimerizes it with another T3 receptor to form HOMODIMER or with other receptors to FORM HETERODIMER
This will increase the gene transcriptional factors and promoter regions ----> Triggering the production of mRNA
41
what receptors dimerizes with the T3 receptor to form HETRO DIMER?
retinoic acid receptor
42
what is the action of thyroid hormone on metabolic rate ?
in most tissues = increases metabolic rate
brain, spleen, testis
43
how does thyroid hormone increases metabolic activity?
1- Increases the number and size of mitochondria
2- Stimulates the synthesis of enzymes in respiratory chain
44
how does it stimulates the resting metabolic rate?
increasing NA/K atapse activity
increases to 100% in excess hormone
decrease by 50% in deficiency
45
what is the effect of thyroid hormone on energy?
- increase synthesis of cytochrome c oxidase ( COMPLEX 4 )
increases oxidative phosphorylation
increases synthesis of ATP
it also increases consumption of ATP
46
what is the effect of thyroid on protein metabolism?
in first increases the synthesis of protein and nucleic acid ( in low conc )
afterwards it will activates degradation of protein ( in high conc )
47
what is the effect of lipid metabolism?
lipolysis
oxidation of fats
48
what is the effect of it in carbonhydrate metabolism ?
accelerate the absorption of carbonhydrates in the intestine
Activate glycogenlysis ( glycogen break down )
increases glucose lvl in the blood
49
what do you investigate in in cases of suspected thyroid problems?
thyroid stimulating hormone ( TSH )
total Thyroxine and T3
free T4 and T3
50
what is more reliable total T4 and T3 or free T3 AND T4?
total includes the bound and inbound T3 and T4 so it is less reliable
Free is this means that the T3 and T4 are available ( unbound ) to bind to the receptor --> more reliable
51
what is the effect of thyroid hormone on TSH?
it is negative feedback so
high amount of Thyroid = low amount of TSH
low amount of thyroid = high amount of TSH
52
what happens in primary hyperthyroidism?
in primary this means the issue is in the gland itself it is secreting thyroid hormone without stimulus from the pituitary
53
what are the levels of thyroid hormone and TSH in primary hyperthyroidism?
high amount of thyroid hormone
low amount of TSH due to the inhibition effect
54
what is secondary hyperthyroidism?
hyperthyroidism due to excessive stimulation from the pituitary gland due to problems in the in the pituitary gland not in the thyroid
55
what are the levels of thyroid hormone and TSH in secondary hyperthyroidism?
High amount of thyroid hormone
high amount of TSH cuz it is the stimulant for Thyroid
56
what are the symptoms of hyperthyroidism?
rapid heartbeat
weight loss
heat intolerance
anxiety
exophtalamus ( due to accumulation of mucus and stuff behind the eye and degradation of the muscles )
57
what is primary hypothyroidism?
low levels of thyroid hormone due to a problem in the gland ITSELF not the pituitary
58
what are the levels of thyroid and TSH in primary hypothyroidism?
low level of thyroid
high lvl of TSH to try and stimulate the thyroid to produce even though it cant
more common than 2nd hypothyroidism
59
what is secondary hypothyroidism ?
hypothyroidism due to less stimulation from pituitary but no problems in the thyroid gland itself
60
what are the levels of thyroid hormone and TSH in secondary hypothyroidism ?
low lvl of thyroid hormone cuz no TSH to stimulate it
low level of TSH
61
what are the signs and symptoms of hypothyroidism?
slow metabolism
tired
weight gain
cold intolerance
62
what are examples of disease that causes primary hypothyroidism?
destruction of the thyroid gland due to autoimmune --> hashimoto disease
radioiodine or surgical treatment of hyperthyroidism
63
goiter can be associated with what?
hyperthyroidism or hypothyroidism
64
what is the main causes of goitre?
high TSH
For example in iodine deficiency , this will lead to primary hypothyroidism because theres no iodine for the gland to use to make thyroid so this will lead to low levels of thyroid and the pituitary will sense this and try to stimulate the gland by secreting TSH
65
what secretes calcitonin?
Parafollicular cells
aka C cells
66
what is the function of calcitonin?
it will reduce the levels of calcium in the blood by various methods
ca secretion in urine
promotes ca deposition
inhibit ca absorption from intesstine
67
how is PTH synthesized?
in RER as large precursor called prePTH
then it will get modified later and cleaved
68
what is the half life of parathyroid hormone ?
5-10 minutes in the blood before being rapidly metabolized by the liver and the kidneys
69
what cells produce PTH?
chief cells
70
what is the function of PTH?
increases the calcium levels by various methods
including increase ca absorption and re absorption
bone degradation for calcium
increase vitamin D level
71
what is the signaling method for the PTH receptor ?
the receptor is PTHR1 and it is G protein coupled receptor
G protien --> adenylyl cyclase --> CAMP --> protein kinase a ( PKA )
72
where is the PTHR1 receptor expressed?
bone and kidney cells primarily
