Physiology of thyroid and parathyroid Flashcards
(115 cards)
1
Q
Thyroid hormones are synthesized and secreted by what?
A
Cuboidal epithelial cells
2
Q
Follicle has basolateral membrane facing the
A
blood
3
Q
Follicle has apical membrane facing the
A
lumen
4
Q
Where is thyroid hormone stored?
A
In colloid of the follicle
5
Q
What is the more potent thyroid hormone?
A
T3
6
Q
What is the thyroid hormone that is in higher abundance?
A
T4
7
Q
Thyroid secretion is primarily controlled by
A
thyroid stimulating hormone
8
Q
C cells release
A
calcitonin
9
Q
Most GI absorption of iodide occurs via
A
passive diffusion between cells of small intestine
10
Q
If pt is iodine deficient, this will inhibit the ability to make what?
A
T3/4
11
Q
Iodide pump will pump iodide into _________ and concentrates iodide into _______
A
follicular cells; thyroid gland
12
Q
Iodide must be pumped into the
A
follicular cell
13
Q
How does iodide get pumped into follicular cells?
A
By utilizing Na gradient and Na/K ATPase (Na/I symporter)
14
Q
Loss of TSH will _______ iodide pump
A
decrease
15
Q
What will inhibit Na/I symporter?
A
Thiocyanate (SCN) and perchlorate (ClO4)
16
Q
Cigarette smoke contains thicyanate so smokers can develop
A
hypothyroidism and get a thyroid
17
Q
What is thyroglobulin responsible for?
A
Carrying tyrosine residues
18
Q
Thyroglobulin is found inside
A
follicular cells
19
Q
Thyroglobulin is synthesized in ______ and released via ______
A
ER; Golgi
20
Q
Thyroglobulin will transport and store what?
A
T3/4
21
Q
What are peroxidases required for?
A
To incorporate iodine onto tyrosine residues
22
Q
Binding of iodine with thyroglobulin is called
A
organification of thyroglobulin
23
Q
What do you call high levels of iodide that can inhibit organification and synthesis of thyroid hormones?
A
Wolff-Chaikoff effect
24
Q
Tyrosine is first iodized to _______________ then to _______________
A
monoiodotyrosine (MIT) ; Diiodotyrosine (DIT)
25
WHere is thyroid hormone stored?
in colloid
26
What can the thyroid gland store?
Large amounts of thyroid hormone
27
The release of T3/4 occurs through _____________ of colloid
lysosomal digestion
28
Colloid enters the thyroid gland through ________ after bidning to _________
endocytosis; megalin
29
How is the megalin-TG complex carried across the cell?
By transcytosis (microtubules help in the transport)
30
MIT and DIT will undergo
de-iodination
31
What is pendrin?
An iodide-chloride antiporter located on apical membrane
32
Upon entering the blood, more than 99% of T3/4 binds to what?
Thyroxine binding globulin (TBG)
33
Where is TBG (thyroxine-binding globulin) made?
The liver
34
If pt has liver failure and cannot make TBG, what will happen?
Increase of free concentration of T3/4
35
During pregnancy or use of oral contraceptives with estrogen, what happens to TBG?
Inhibit degradation of TBG and could lessen amount of free T3/4 in circulation
36
T4 can become de-iodinated to form the more active T3 through
peripheral deiodinases (aka 5'-iodinase)
37
D2 deiodinase can be inhibited by
propylthiouracil (PTU)
38
If D1 activity increased, this can lead to
hyperthyroidism
39
If D1 activity decreases, this could lead to
hypothyroidism
40
Thyroid hormone has a very prolonged effect on
BMR
41
What are stimulatory factors for thyroid hormone?
- TSH
- Thyroid stimulating immunoglobulins
- Increased TBG levels
42
What are inhibitory factors for thyroid hormone?
- Iodide def
- Deiodinase def
- Excessive iodide intake
- Perchlorate, thiocyanate
- Propylthiouracil (PTU)
- Decreased TBG levels (liver dz)
43
What secretes thyroid releasing hormone?
Hypothalamus
44
Thyroid releasing hormone acts on what?
Thyrotrophs of the anterior pit to secrete TSh
45
T3/4 can negatively feedback onto anterior pituitary to inhibit release of what?
TSH
46
Free T3 will _______ TRH receptors on the anterior pituitary
down regulate
47
TSH activates adenylyl cyclase via _____ to increase cAMP in the follicular cells
G alpha s
48
Every step of thyroid hormone biosynthesis is essentially increased when ______ binds to its receptor
TSH
49
Thyroid hormone will increase O2 consumption in all tissues except brain, gonads and spleen by inducing synthesis and increasing activity of
Na/K ATPase
50
Thyroid hormone will _________ glucose absorption from GI tract
increase
51
Thyroid hormone can potentiate effects of
catecholamines, glucagon and GH
52
What does thyroid hromone do to cardiac output?
Increases it
53
Thyroid hormone will _______ beta,1-adrenergic receptors
up-regulation
54
Since thyroid hormone increases BMR and O2 consumption, this will
increase demand for O2 in tissues
55
Increased cardiac output from thyroid hormone due to
increase in beta,1-adrenergic receptors
56
What is given to patients with hyperthyroidism to block the cardiac effects, especially during thyroid storm?
Metoprolol
57
How does thyroid hormone affect bones?
- Promote bone formation
- Promote ossification and fusion of bone plates and maturation
58
Thyroid hormone is essential for _________ of CNS
normal maturation
59
Thyroid hormone will cross lipid cell membranes and bind to its ____________ to cause a number of cellular events
nuclear receptor
60
Hypothyroid will have lower BMR, which can lead to
weight gain, cold sensitivity, lethargy and hypoventilation
61
Hyperthyroid will increase BMR which can lead to
weight loss, increased heat production and intolerance, dyspnea (shortness of breath) and restlesness
62
Myxedema is the result of
chronic hypothyroidism
63
What is the most common cause of hypothyroidism?
Auto-immune destruction of the thyroid gland (thyroiditis)
64
In Myxedema, if the defect is in the thyroid gland, then what will TSH levels be?
Increased
65
In Myxedema patients, if the defect is the inability to release TRH or TSH, then what will TSH levels be?
decreased
66
Excessive production of thyroid hormone can lead to what autoimmune disease?
Grave's disease
67
What are ways that excessive thyroid hormone can be produced?
- Tumor within hypothalamus (increases TRH)
- Increase prod of TH due to neoplasm in thyroid gland
- Auto-antibodies that bind to TSH receptor and induce hypersecretiin of TH
- TOo musch TH given to a patient
68
In case of excessive thyroid hormone, it will negatively feedback to inhibit what? (Unless issue is hypothalamus)
TSH
69
If issue with excessive thyroid hormone is in hypothalamus, then what will levels of TSH be?
Increased
70
Excess TH or TSIs can have ______ effects on thyroid gland and cause it to become enlarged
trophic
71
Iodine def will result in the inability to make thyroid hormone and _____ levels will increae due to loss of negative feedback
TSH
72
What are situations that would not cause a goiter?
- Exogenous T3/4 administration
- TSH deficiency
73
What cells are responsible for synthesizing and secreting PTH?
Chief cells
74
What regulates PTH secretion from parathyroid gland?
Ionized, extracellular calcium
75
What does intracellular calcium do to PTH?
Decreases it
76
DAG activates
protein kinase C
77
IP3 causes release of
intracellular calcium
78
When ionized calcium binds to CaSR then _______ gets activated and phospholipase C converts PIP2 to IP3 and DAG
G alpha q
79
When calcium does not bind to CaSR, then intracellular Ca _______ and PTH will be secreted
decreases
80
Chronic hypocalcemia can cause
secondary hyperparathyroidism
81
Chronic hypocalcemia can occur due to
chronic kidney disease (cant make Vit D3), or Vit D3 deficiency from diet
82
Chronic hypercalcemia will cause for decreased synthesis and storage of
PTH
83
84
Hypermagnesemia will inhibit
PTH secretion
85
Severe, chronic hypomagnesemia will do what?
Inhibit PTH secretion
86
Excess Vit D3 will do what to PTH synthesis and secretion?
Inhibit
87
Decreased plasma Ca will increase PTH secretion, and have what effects on the kidney?
- Decrease phosphate reabsorption in proximal tube
- Increased Ca reabsorption in distal tube
- Increase urinary cAMP
88
Decreased plasma Ca will increase PTH secretion, and have what effects on the bones?
Increased bone resorption
89
Decreased plasma Ca will increase PTH secretion, and have what effects on the intestine?
Increased Ca absorption
90
PTH receptor sensitivity is higher on _______ than ________
osteoblasts; osteoclasts
91
In the case of chronic release of PTH, this will stimulate the osteoblast to increase the release of _________
cytokines
92
Phosphate release will stimulate the production of __________ from osteoblasts and osteocytes
Fibroblast growth factor 23 (FGF23)
93
In order to get free ionized Ca from bone resorption, we must
excrete phosphate
94
PTH will inhibit phosphate reaborption at the
proximal tubule
95
Thiazides can promote calcium reabsoprtion by blocking
Na/Cl transporter and cause loweing of intracellular Na
96
What does calcitriol do?
Increase Ca absorption from the SI
97
Low Ca, Low PTH
primary hypoparathyroidism
98
High PTH, low Ca
Secondary hyperparathyroidism
99
High PTH, High Ca
Primary hyperparathyroidism
100
Low PTH, High Ca
PTH independent Hypercalcemia
101
Primary hyperparathyroidism is most commonly assoc with
parathyroid adenomas to secrete increased PTH
102
Who has "Stones, Bones and Groans"
Primary hyperparathyroidism
103
Treatment for secondary hyperparathyroidism
Vit D3 replacement and phosphate binders
104
Treatment of hypoparathyroidism
Ca supplement and Vit D3 analog
105
What si pseudohypoparathyroidsim?
Inherited autosomal dominant disorder where the action of PTH on bone and kidney is defective
106
Treatment of pseudohypoparathyroidsim
Ca supplement and Vit D3 analog
107
Treatment of humoral hypercalcemia of malignancy?
Remove the PHT-rp secreting tumor.
But before, need to be on loop diuretic (furosemide) and inhibitor of bone resorption (etidronate)
108
What is Familial hypocalciuric hypercalcemia?
Autosomal dominant disorder where Ca sensing receptors are mutates and parathyroid gland are thick?
109
Net effect from familial hypocalciuric hypercalemia
Increased plasma Ca and decreased plasma phosphate
110
What is treatment of familial hypocalciuric hypercalemia?
Loop diuretic and bone resorption inhibitor
111
What synthesizes and secretes calcitonin?
Parafollicular cells
112
Calcitonin inhibis
Osteoclastic bone resorption
113
Vit D3 will promote
bone mineralization
114
Bone resorption is stimulated by
high and chronic PTH and Vit D3
115
Bone resorption is inhibited by
calcitonin
