Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

RDS Test 4 > B8.058 Prework 1: Thyroid Gland > Flashcards

B8.058 Prework 1: Thyroid Gland Flashcards

1
Q

describe the H-P-T axis

A 
hypothalamus > TRH
anterior pituitary (thyrotropes) > TSH
thyroid gland (thyrocytes) > thyroid hormones
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

importance of iodide

A

necessary for synthesis of thyroid hormones
minimum - 75 ug/day
recommended - 150 ug/day

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

where is iodide stored in the body

A

thyroid (8000 ug)

hormone pool, in circulation within T3 and T4 (600 ug)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

primary steps in thyroid hormone synthesis and secretion

A
  1. stimulated by TSH
  2. uptake of iodide
  3. thyroglobulin: iodination, organification, and coupling
  4. secretion
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

composition of thyroid tissue

A

numerous follicles

  • lined by thyrocytes (functional cells that make hormone)
  • filled with colloid containing thyroglobulin
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

description and regulation of iodide uptake

A 
active process:
-achieved via Na/I symporter
-requires energy
regulation:
-internal autoregulatory mechanisms
-TSH drives iodide from blood into lumen of thyroid follicle
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

where is TPO found

A

membrane bound in lumen of follicle

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

TPO requirements for function

A

Tg (substrate)
iodide
H2O2 (NADPH oxidase)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

what is thyroglobulin (Tg)

A

660 kD homodimer
regulated by TSH
contains 120-140 tyrosine residues
iodinated by TPO

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

function of TPO

A

responsible for iodination/organification and coupling of Tyr in Tg molecules

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

result of TPO

A

20-30 Tyr become iodinated
20-25% (6-8) of the MIT/DIT become coupled
stored in this form

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

secretion of thyroid hormone

A

stimulated by TSH

  1. pinocytosis
  2. lysosome fusion
  3. hydrolysis
  4. secretion
  5. deiodination
    * *hormone is cleaved out of the Tg before moving into circulation
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

thyroid hormone in circulation

A

exist both in free and bound form
70-75% is bound to thyroid binding globulin (TBG)
<1% is free, but this amt is biologically important

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

describe TBG

A

made in the liver
high affinity for T4/T3
70-75% of T4/T3 is bound to TBG

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

increased expression of TBG

A

pregnancy
newborns
oral contraceptives (due to E)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

decreased expression of TBG

A 
androgens (anabolic steroids)
large doses of glucocorticoids
chronic liver disease
severe systemic illness
active acromegaly
kidney disease with proteinuria
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

other thyroid binding proteins in circulation (not TBG)

A 
transthyretin/thyroxine binding pre-albumin (TBPA)
-10% of T4
albumin
-low affinity
-15% of T4/T3
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

T4 half life

A

8 d

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

T3 half life

A

1-3 d

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

conversion of T4

A

40% of secreted T4 is converted to T3 in the periphery (majority of what is secreted is T4)
30% of secreted T4 is converted to rT3 in the periphery

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

5’ Deiodinase

A

converts T4 to T3
type 1: thyroid, kidney, liver
type 2: pituitary, brain, brown adipos

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

5 Deiodinase

A

converts T3 to T2
converts T4 to rT3
inactivates hormone at target tissues
found in kidney, liver, skin, and placents

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

mechanism of propylthiouracil

A

inhibits type 1 5’ Deiodinase and TPO

used in hyperthyroidism to maintain T4 state (less potent)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

potency of thyroid hormones

A

T3 > T4 (10x)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

negative feedback of T4/T3 on HPT axis

A
  1. hypothalamus
    - decreased TRH
  2. pituitary
    - predominant mechanism
    - T4 conversion to T3 by type 2 5’DI
    - decreases response to TRH by decreasing TRH-R expression
    - decreases synthesis and secretion of TSH
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
26
Q

why does a goiter form

A

iodide deficiency
leads to low thyroid hormone synthesis/secretion
increased activity in gland to attempt to stimulate production > larger gland

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
27
Q

thyroid hormone receptors

A

nuclear; alter gene expression (slow)

  • at least 6 types
  • number is regulated (decreased by fasting)
  • bind T3 with higher affinity than T4
  • expressed in most tissues/cells
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
28
Q

primary roles of thyroid hormone

A 
regulate protein metabolism
regulate glucose metabolism
regulate lipid metabolism
regulate basal metabolic rate (BMR)
important during CNS fetal development
29
Q

TH and protein metabolism

A

growth permissive effects

  • stimulates GH expression (and IGF)
  • stimulates metabolic proteins and enzymes (mitochondria)
  • promotes calcification within cartilage
30
Q

effect of EXCESS TH on protein metabolism

A

protein catabolism

31
Q

TH and glucose metabolism

A

potentiated actions of insulin

-stimulates glycogen synthesis and glucose utilization

32
Q

effect of EXCESS TH on glucose metabolism

A

reverse of normal effect

  • increases glycogenolysis
  • altered glucose utilization
  • enhances actions of epinephrine via induction of B-AR expression
33
Q

TH and lipid metabolism

A

stimulates cholesterol synthesis and also its conversion to bile (decreases cholesterol levels)

34
Q

effect of EXCESS TH on lipid metabolism

A

increases lipolytic actions of other hormones

results in increased fat metabolism

35
Q

effect of LOW TH on lipid metabolism

A

can lead to hypercholesterolemia

-regulates hepatic LDL-R

36
Q

TH and basal metabolic rate (BMR)

A

regulates oxidative phosphorylation (Na+/K+ATPase)

  • transcription and activity
  • altered oxygen consumption and heat production
37
Q

effect of LOW TH on BMR

A

can lead to a 50% decrease

38
Q

effect of EXCESS TH on BMR

A

can increase BMR 80%

39
Q

effect of TH on bone

A

stimulates linear growth and development and bone maturation (via GH)

40
Q

effect of TH on skin & hair

A

required for normal follicle development and epidermis renewal

41
Q

effect of TH on GI tract

A

can increase GI motility

42
Q

effect of TH on the heart

A

regulates sensitivity of B1 receptors
increased CO by increasing HR and SV
excess TH will cause vasodilation

43
Q

effect of TH on brain development

A

promotes dendritic branching
promotes proliferation of axons
promotes formation of synpases
regulates myelinization within the cortex

44
Q

symptoms of hypothyroidism

A 
weight gain
cold intolerance
decreased perspiration
constipation
bradycardia
fatigue
muscle stiffness
depression
dry skin and hair
menstrual disturbances
45
Q

symptoms of hyperthyroidism

A 
weight loss
heat intolerance
increased sweating
frequent BMs
tachycardia and palpitations
fatigue
muscle weakness and hypotrophy
increased excitability and nervousness
moist skin and hair
menstrual disturbances
46
Q

assessment of thyroid hormone levels

A

TSH assay
total T4 or T3 assays
free T4
rT3 assay

47
Q

other assessments of thyroid function

A 
anti-thyroid Abs
-TPO
-thyroglobulin
-TSI
TBG assay (carrying capacity)
RAIU and thyroid scans
fine needle aspiration cytology
48
Q

TRH test process

A

assess the responsiveness of pituitary thyrotropes to exogenous administration of TRH
outcomes:
1. excess TH > reduced response due to downregulation of the TSH receptor by TH
2. deficient TH > increased response due to upregulation of the TSH receptor from reduced TH negative feedback

49
Q

characterize thyroid disorders in general

A

very common

women are affected more often than men (10:1)

50
Q

causes of hypothyroidism

A 
iodide deficiency
congenital/cretinism
non-thyroidal illness
thyroiditis
endemic goiter
sporadic goiter
51
Q

congenital hypothyroidism

A

deficiency in utero

mental and growth retardation (can be treated)

52
Q

non-thyroidal illness (euthyroid sick syndrome)

A

shift in conversion of T4 from T3 to rT3 (inactive)

53
Q

types of thyroiditis

A
  1. subacute - granulomatous (deQuervain)
  2. Reidel
  3. Hashimoto
54
Q

subacute, granulomatous (deQuervain) thyroiditis

A

viral infection, URI

typically resolve over time

55
Q

reidel thyroiditis

A

rare

fibrosis, calcification of gland

56
Q

hashimoto thyroiditis

A

autoimmune disease that attacks/ destroys the thyroid gland

autoreactive T cells and Abs to thyroid antigens (TPO or Tg)

57
Q

sporadic goiter

A

due to mutations in Tg or TPO

58
Q

treatment of hypothyroidism

A 
exogenous T4 (levothyroxine)
-better than  T3 because it has a longer half life and is less potent so there's not as much of a risk of overdose
59
Q

etiologies of hyperthyroidism

A

Graves disease
adenomas of the thyroid gland
pituitary adenomas
thyrotoxicosis

60
Q

what is Graves disease

A

autoimmune disease
thyroid stimulating immunoglobulins (TSI) directed against the TSH-R, inducing function
no negative feedback on TSH production

61
Q

epidemiology of Graves

A

5:1 , F:M
60-80% of hyperthyroidism
most prevalent autoimmune disorder in the US

62
Q

predisposing factors for Graves

A

sex (female)
stress
smoking

63
Q

symptoms of graves

A 
nervousness
fatigue
rapid heartbeat or palpitations
weight loss
50% get ophthalmopathy (exophthalmos)
64
Q

treatment of hyperthyroidism

A 
radioactive iodine to destroy gland
thyroidectomy (avoid parathyroid glands)
antithyroid drugs
-PTU
-carbimazole/ methimazole
65
Q

carbimazole/ methimazole mechanisms

A

TPO inhibition

66
Q

hot thyroid nodules

A

functional - take up radiotracer
secrete thyroid hormone
-hyperthyroidism
ablate w radiotracer

67
Q

cold thyroid nodules

A

nonfunctional- do not take up radiotracer
non-secretory
increased association with malignancy
-FNA cytology > surgery

68
Q

primary hypothyroidism findings

A

T4 low

TSH high

69
Q

secondary hypothyroidism findings

A

T4 low

TSH normal or low

RDS Test 4 (17 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2025 Bold Learning Solutions. Terms and Conditions