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NeuroEndocrine 3 > THyroid Gland > Flashcards

THyroid Gland Flashcards

1
Q

What does the thyroid produce and secrete via what cells

A

produces the prohormone Tetraiodothyronine (T4) and the active hormone Triiodothyronine

they are synthesized by the Follicular epithelial cells

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2
Q

WHat doe the C cells secret

A

Parafollicular cells that secret calcitonin

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3
Q

what is the name of the follicular lumen and what is stored in them

A

Colloid

this is where the newly synthesized hormones attach to the thyroglobulin

Iodine is also stored here as iodinated thyroglobulin

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4
Q

what makes up T4 structurally

A

2 diiodotyrosine (DIT)

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5
Q

what makes up T3 structurally

A 
1 monoiodotyrosine (MIT)
1 diiodotyrosine (DIT)
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6
Q

how much more T4 is produced then T3

A

10 times because T4 is the major secretory part

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7
Q

how is T3 produced in the periphery

A

T3 is produced by deiodinase via T4 or thyroxine

80 to 90 percent of T3 is produced in the periphery

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8
Q

What are some clinical states in which there is reduction in the conversion of T4 to T3

A

Fasting
Medical and surgical stress
Catabolic disease

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9
Q

What is the process of the synthesis of Thyroid hormones

A

Iodide enters the Follicular epithelial cell via the NIS from the bloodstream

THyroglobulin produced by the ER goes into the lumen there Iodine binds to the TG via peroxidase

this goes until T4, T3, MIT, and DIT are bound to the TG and stored in the Colloid

then when needed the cell pinocytosis the TG containing all the items

then proteases cleave off T3 and T4 to go and circulate

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10
Q

What does a deficiency in Deiodinase mimic

A

Dietary insufficiency of I- (iodide)

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11
Q

What T3 or T4 is favored if there is a restriction in Iodide

A

T3 is favored when the availabillity of Iodide is restricted

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12
Q

what happens if their is a mutation in Pendrin

A

Pendrin is a chloride/iodide pump into the colloid

if mutated can lead to affects in the cochlea leading to sensorineural hearing loss

this is called Pendred syndrome also usually have hypothyroidism and goiter

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13
Q

What can PTU be used for

A

To treat hyperthyroidism by blocking Peroxidase

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14
Q

what is the Wolff-Chaikoff effect

A

when there are high levels of Iodide it will inhibit the peroxidase and the process of organification and block the synthesis of Thyroid hormones

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15
Q

How can the activity of thyroid gland be assesed

A

via radioactive iodine uptake

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16
Q

During radioactive Iodide assesment, how does an individual with graves disease present

A

Have a extreme stimulation and uptake of the Iodide followed by a high turnover of the Iodide

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17
Q

How do thyroid hormones circulate the bloodstream

A

99 percennt are bound to a plasma protein ( THyroxine binding globulin, if not by that will get picked up by TTR or albumin

one percent is free

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18
Q

What is the half life of circulating T4 and T3

A

T4 half life is 6 days

T3 half life is 1 day

19
Q

WHat is the purpose of the T3 Resin uptake test

A

Determines how much T3, TBG and T4 are circulating in the blood

the resin will bind unbound labeled T3 that did not bind to the unbound TBG

from there you can determine the amount of TBG, T4 and T3 resin bound levels

20
Q

WHat are the levels of T4 and T3 resin uptake in: Hyperthyroidism

A

high T4

High T3 resin uptake

21
Q

WHat are the levels of T4 and T3 resin uptake in: Hypothyroidism

A

Decrease T4

Decrease T3 resin uptake

22
Q

WHat are the levels of T4 and T3 resin uptake in: high TBG

A

high T4

low T3 resin uptake

23
Q

WHat are the levels of T4 and T3 resin uptake in: LOw TBG

A

low T4

high T3 resin uptake

24
Q

WHat are the levels of T4 and T3 resin uptake in: Hepatic failure and how does that affect the synthesis and secretion of thyroid hormones

A

low TBG
High T3 resin uptake

therefore high levels of free T3 and T4 and serve as negative feedback that inhibits the synthesis of T3 and T4

25
Q

WHat are the levels of T4 and T3 resin uptake in PRegnancy and how does that affect the synthesis and secretion to thyroid hormones

A

High TBG
low T3 resin uptake

low levels of free T3 and T4 since all our bound

therefore increase in production and secretion of T3 and T4

even with high levels of T3 and T4, the person is said to be clinically euthyroid because they are all bound

26
Q

What is the role of TSH and how is it regulated

A

used for the growth of the thyroid gland (tropic effect) and secretion of thyroid hormones

secreted by the anterior pituitary gland

regulated by TRH via the hypothalamus
and by the amount of free T3

this occurs at a steady rate

27
Q

What are the stimulatory factors of thyroid hormone secretion

A

TSH
Thyroid stimulating immunoglobulins
increased TBG levels (pregnancy)

28
Q

What are the inhibitory factors of the thyroid hormone secretion

A

I- deficiency
Deiodinase deficiency
Excessive I- intake (Wolff-Caikoff effect)

Perchlorate and Thiocynate (inhibit na and I cotransporter)

Propylthiouracil (PTU) inhibits peroxidase

Decreased TBG levels liver disease

29
Q

What is the purpose of the thyroid hormone

A

helps synthesize a vast araray of proteins
including Metabolic enzymes in liver and adipose tissue
Na/KK ATPase synthesis
and B adrenergic receptors and myosin in the heart

Matures the CNS

Does growth promoting bone formation

30
Q

WHat does thyroid hormones do to metabolic rate

A

Increase Basal metabolic rate by producing Na+/K+ ATPase

leads to o2 consumption and heat production

31
Q

How does thyroid hormones affect lipid metabolism

A

stimulate fat mobilization and increases FA in the plaasma

enhances FA oxidtion

decreases blood cholesterol and triglycerides

helps convert carotene to vitamin A

32
Q

How does thyroid hormones affect carbohydrate metabolism

A

increases Gluconeogenesis and glycogenolysis to generate glucose

enhances insulin dependent entry of glucose into the cell

33
Q

How does T3 affect Cardiac aoutput

A

Increases cardiac output by incrreasing preload via renin-angiotensin-aldosterone
decreases afterload
increases cardiac chronotropy and inotropy

34
Q

How does the thyroid hormone affect the cardiomyocyte

A

increases production of B1 receptors making the cell more sensitive to stimulation via the sympathetic nervous system

35
Q

Symptoms of Hyperthyroidism

A 
Increased BMR
Weight loss
heat intolerance
osteoporosis
agitation
anxeity
sweting
tachycardia
atrial fibrillation
diarrhea
high output heart failure
36
Q

Primary Hyperthyroidism

A

Graves disease
decrease in TSH
but there is TSH immnoglobulins that are stimulating TSH receptors without the presence of TSH these are called (TSI)

Major clinical signs: Exophthalamos due to the anti TSH receptor antibodies

elevated levels of T4 and T3

presence of circulating TSI

has goiter

37
Q

Secondary Hyperthyroidism

A

TSH secreting pituitary

similar issues as primary except Exophthalamos

38
Q

Hypothyroidism symptoms

A 
cold intolerance
weight gain
decrease in BMR
stunted growth
cretinism
dry skin
bradycardia
decress cardiac output heart failure
constipation
39
Q

Causes and treatments of hypothyroidism

A 
gland destruction: Hashimotos thyroiditis
inhibition of thyroid hormone synthesis
agenesis
hypothalamic disease
pituitary disease (Seehans syndrome)

Replacement doses of T4

  • higher doses required for adults since metabolism of T4 decreases with age
  • in women that have gone through menopause overprescribing T4 can lead to development of osteoporosis
40
Q

Hashimotos THyroiditis

A

Thyroid hormone synthesis is impaired by thyroglobulin or TPO antibodies leading to decreation of T3 and T4 secretion

TSH levels are high
-Goiter (tropic effect)

41
Q

Congenital Hypothyroidism

A

Iodide deficiency

impaired development of thyroid gland

deficit in thyroid hormones

Untreated leads to respiratory problems
cretinism
protruding tongue
mental retardation
jaundice
Dry skin
growth issues
42
Q

Seehan Syndrome

A

Postpartum hypopituitarism due to necrosis of the pituitary gland

difficulties lactating

other endocrine issues may be present

Amenorrhea is present (absence of menstration)

43
Q

Goiter

A

can develop from imbalances of the HPT axes

can be found in graves disease
Hyperthyroidism

and Primary hypothyroidism
-lack of Iodine in the diet

NeuroEndocrine 3 (17 decks)

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