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ENDO > ENDO Week 5 > Flashcards

ENDO Week 5 Flashcards

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1
Q

what is the structure, primary and secondary role of the thyroid gland

A

bilobed endocrine gland in the neck

primary role is secretion of thyroid hormones

secondary role is secretion of calcitonin

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2
Q

where is the thyroid gland located

A

Below the larynx, anterior, wrapping around the trachea

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3
Q

what is the thyroid gland made up of

A

numerous spherical follicles, lined by a simple cuboidal, secretory epithelial cells, filled with colloid

increased colloid, cells are flat = inactive
decreased colloid, cells cuboidal or columnar = active

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4
Q

the thyroid gland is highly vascularized true or false

A

true

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5
Q

what cells are found around the follicles

A

Clear cells
C cells/parafollicular cells

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6
Q

where does the thyroid develop from

A

evagination from the floor of the embryonic pharynx

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7
Q

what connects the two lobes

A

isthmus

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8
Q

what is colloid and what does it consist of

A

protein rich fluid, consists of glycoprotein and thyroglobulin

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9
Q

what does the thyroid gland secrete

A

2 major iodine containing hormones (Amine hormones)

T3 and T4

and calcitonin (by C cells)

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10
Q

what does T3 and T4 stand for

A
  • Thyroxine (tetraiodothyronine/T4)
  • Triiodothyronine (T3)
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11
Q

what are T3 and T4 derived from and what is their action

A

-Derived from modification of an amino acid (tyrosine)

-Act on most cells of the body to promote carbohydrate, protein and lipid metabolism

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12
Q

what is the 1st step of thyroid hormone biosynthesis (hint: thyroglobulin)

A

Thyroglobulin (a glycoprotein) is synthesized in the follicular cells and secreted into colloid by exocytosis

Packaged in secretory vesicles into follicular lumen

Numerous tyrosine amino acids are attached to each thyroglobulin molecule

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13
Q

what happens during iodide trapping

A

also known as iodide pump or sodium iodide cotransporter

(secondary) actively pumps iodide (I-) into follicular cells

Symporter: transports two Na+ ions and I- ion into the cell

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14
Q

what occurs after iodide is pumped into the cell

A

Pendrin (an anti porter), located on the apical surface of the parafollicular cell, moves iodide from thyroid follicular cells into the follicular lumen (colloid) for oxidation to take place

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15
Q

what is oxidation

A

Reaction is catalyzed by peroxidase (TPO) in the follicular cell membrane

Peroxidase makes I- to I2
* I2 is the reactive form

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16
Q

what is the next step after oxidation

A

organification of I2

Oxidized iodine (I2) binds tyrosine amino acids on thyroglobulin molecules to form MIT and DIT

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17
Q

what does MIT and DIT stand for

A

monoiodotyrosine

diiodotyrosine

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18
Q

what occurs after organification of I2

A

the coupling of MIT and DIT

1 MIT and 1 DIT forms
T3

2 DIT forms T4

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19
Q

where does this iodinated thyroglobulin go after?

A

stored in the follicle lumen until gland is stimulated to
secrete

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20
Q

is thyroglobulin released into blood

A

no

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21
Q

what gets released into blood

A

T3, T4 and small amount rt3 (inactive)

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22
Q

why are the iodinated tyrosines (MIT and DIT) then deiodinated

A

to recover iodine and bound tyrosines and then recycle

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23
Q

are thyroid hormones lipophilic or lipophobic

A

lipophillic, diffuse easily across membranes

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24
Q

where are hormones stored after formation

A

stored in follicles (enough for 2-3 months)

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25
how is TH released after being stimulated
iodinated thyroglobulin is taken back into the follicular cells by endocytosis and are digested by lysosomal enzymes to release T4 and T3 into the surrounding capillaries
26
what is thyroid deiodinase enzyme action
to deiodinate leftover MIT and DIT
27
what percent of released TH is T3 or T4
93% is thyroxine (T4) 7% is T3
28
are TH bound or unbound
99% of TH is bound with plasma proteins
29
what are the plasma proteins that TH are bound to
-Thyroxine-binding globulin (TBG; 70% of hormone bound) *Binds to t4 the most -Less binding thyroxine-binding prealbumin (Transthyretin) -Albumin
30
what percent of TH is active (in its free form)
approx 1%
31
what is the onset and duration of action for TH
slow onset long duration of action
32
what affect does liver failure have on TH
Liver failure could lead to less protein to bind to
33
where are the receptors located for TH
nucleus
34
how do T3 and T4 differ
T3 is the most active (rapid acting) as it has a more affinity to receptors and less affinity to plasma proteins 90% of hormone synthesized is T4 however it has more affinity to plasma proteins and less affinity to receptors
35
what are RT3
inactive hormone formed during thyroid hormone synthesis
36
which hormone is considered a pro hormone
T4 is considered a prohormone for T3
37
why is TH needed for growth and CNS
required to achieve adult stature required for CNS maturation TH deficiency causes irreversible mental retardation
38
describe the regulation of thyroid secretion and thyroid stimulating immunoglobulin
Hypothalamus secretes TRH which stimulates the anterior pituitary to secrete TSH via cAMP pathway Thyroid stimulating immunoglobulin: antibodies to TSH receptors, binds to TSH receptors and stimulate the gland to increase T3 and T4***
39
what does chronic TSH elevation cause
hypertrophy of the gland
40
what would primary, secondary and tertiary conditions of TH equates to which structures
primary = thyroid gland secondary = ap tertiary = hypothalamus
41
what structures are the cause of raised/lowered TSH
ap or hypothalamus
42
what is hyperthyroidism
Exostimulation for TSH by thyroid stimulating antibodies/immunoglobulins = graves disease
43
what kind of disorder is graves disease
60-80% of hyperthyroidism is graves disease autoimmune hyperthyroidism
44
what causes graves disease
Thyroid stimulating immunoglobulins (TSI) stimulate the TSH receptor*** Stimulates TPO and thyroglobulin release = graves disease
45
what are some signs and symptoms of hyperthyroidism
hair loss exopthalmos tachycardia tremor goitre diarrhea increased appetite sweating weight loss
46
what can cause primary and secondary hyperthyroidism
primary: Graves disease, Activating the TSH receptor through thyroid stimulating antibodies secondary: TSH secreting pituitary adenoma
47
what disease is commonly related to hypothyroidism
Most common cause is Hashimoto thyroiditis: destruction of thyroid tissue
48
what is hashimotos thyroiditis disease mechanism of action
antibodies act against thyroid peroxidase and thyroglobulin → destruction of thyroid tissue *** Inhibiting TPO and thyroglobulin release = hashimoto
49
how does hypothyroidism present in adults vs kids
myoexdema in adults and cretinism in kids (because decrease cns development, decrease GH)
50
what is the difference between primary and secondary hypothyroidism
primary = T3 and T4 is low secondary = TSH is low**
51
what are symptoms of hypothyroidism
coarse, thin hair myxoedemic (non pitting edema, because of mucopolysaccharide accumulation) bradycardia cold skin/intolerance to cold weight gain goitre constipation slow reflexes
52
what is goitre and what is it caused by
visible enlargement of the thyroid gland and it is caused by decreased dietary iodine or hyper/hypothyroidism
53
why does hyperthyroidism cause tachycardia
TH and catecholamines have a permissive effect where TH increases epi and norepi receptors causing increased heart rate***
54
what is cretinism caused by and what does it lead to
congenital hypothyroidism impaired development of the brain and skeleton dwarfism
55
what is the effect of hyperthyroidism and hypothyroidism on protein metabolism
Low thyroid hormone = increase protein synthesis High thyroid hormone = increase protein degradation
56
what is the effect of TH in carbohydrate normal function
increases all processes of carbohydrate including glucose absorption, glycogenolyis, gluconeogenesis
57
what is the TH action on heart normal hyperthyroidism hypothyroidism
normal: increase heart rate, increase contractibility, increase cardiac output due to increase (Na+/K+ ATPase) hyperthyroidism: tachycardia hypothyroidism: bradycardia
58
what is the TH action on liver normal hyperthyroidism hypothyroidism
normal: increase gluconeogenisis, cholesterol catabolism, drug metabolism due to increase enzyme synthesis hyperthyroidism: decrease serum cholesterol hypothyroidism: increase serum cholesterol
59
what is the TH action on skeletal muscle normal hyperthyroidism hypothyroidism
normal: maintains protein turnover, energy metabolism due to increase mitochondrial activity hyperthyroidism: muscle weakness and wasting hypothyroidism: stiffness, cramps
60
what is the TH action on brain normal hyperthyroidism hypothyroidism
normal: critical for infants for neurodevelopment, maintains cognition hyperthyroidism: anxiety, insomnia hypothyroidism: slow cognition, lethargy
61
what is the TH action on bone normal hyperthyroidism hypothyroidism
normal: stimulates bone turnover hyperthyroidism: osteoperosis hypothyroidism: delayed bone age in children, growth retardation
62
what is the TH action on adipose tissue normal hyperthyroidism hypothyroidism
normal: increase in lipolysis hyperthyroidism: weight loss hypothyroidism: weight gain
63
what is the TH action on skin normal hyperthyroidism hypothyroidism
normal: maintains epidermal turnover and sweat gland activity hyperthyroidism: warm, moist skin hypothyroidism: dry, cool skin
64
what is the TH action on GI tract normal hyperthyroidism hypothyroidism
normal: increased motility hyperthyroidism: diarrhea hypothyroidism: constipation
65
what is the TH action on BMR normal hyperthyroidism hypothyroidism
normal: increase oxygen consumption, heat production hyperthyroidism: heat intolerance, sweating hypothyroidism: cold intolerance, decreased body temperature
66
why is goitre caused by hyperthyroidism
graves disease --> increase TSH antibodies --> increase gland stimulation --> TSH like action --> goitre
67
why is goitre caused by hypothyroidism
decrease T3 and T4 --> increases TSH --> stimulation of gland growth --> goitre

ENDO (8 decks)

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