Med Phys: Thyroid Hormones And Calcium Balance Flashcards
1
Q
What does the thyroid gland consist of that secretes thyroid hormones?
A
Multiple follicles or acini.
2
Q
What do Parafollicular or C-cells in the thyroid gland secrete?
A
Calcitonin.
3
Q
What is the most abundant form of thyroid hormone?
A
T4 (thyroxine).
4
Q
What is the most active form of thyroid hormone?
A
Triiodothyronine (T3).
5
Q
What is essential for thyroid hormone synthesis?
A
Iodine.
6
Q
What does TRH from the hypothalamus stimulate the anterior pituitary gland to produce?
A
Thyroid stimulating hormone (TSH).
7
Q
Thyroid hormones limit their own secretion by inhibiting the release of what?
A
Both TRH and TSH.
8
Q
What type of mechanism is the inhibition of TRH and TSH?
A
Negative feedback mechanism.
9
Q
What two things are required for thyroid hormone synthesis and release into the bloodstream?
A
Tyrosine and Iodine.
10
Q
Describe the first step of thyroid hormone synthesis.
A
Thyroglobulin is synthesized and discharged into the follicle lumen.
11
Q
What happens in the second step of thyroid hormone synthesis?
A
Iodide is trapped, moving from plasma to thyroid gland cells.
12
Q
What occurs in the third step of thyroid hormone synthesis?
A
Iodide is oxidized to iodine by peroxidase.
13
Q
What is formed when iodine is attached to tyrosine in colloid?
A
DIT and MIT.
14
Q
What happens during the coupling step of thyroid hormone synthesis?
A
Iodinated tyrosines are linked together to form T3, T4, and RT3.
15
Q
What occurs in the sixth step of thyroid hormone synthesis?
A
Thyroglobulin colloid is endocytosed and combined with a lysosome.
16
Q
What happens in the final step of thyroid hormone synthesis?
A
T3 and T4 are cleaved and released into the bloodstream.
17
Q
What is the result of MIT + DIT?
A
T3 (triiodothyronine).
18
Q
What is the result of DIT + DIT?
A
Thyroxine (T4).
19
Q
Where does thyroid hormone act?
A
All cells.
20
Q
How does thyroid hormone impact basal metabolic rate?
A
Increases.
21
Q
How does thyroid hormone impact mitochondrial size, number, and activity?
A
Increases it.
22
Q
How does low thyroid hormone impact weight?
A
Causes gain of weight.
23
Q
How does excess thyroid hormone (hyperthyroidism) impact weight?
A
Causes loss of weight.
24
Q
How does thyroid hormone impact GIT absorption?
A
Enhances.
25
How does thyroid hormone impact glycolysis, gluconeogenesis, and glycogenolysis?
Promotes.
26
How does thyroid hormone impact fat metabolism?
Enhances.
27
How does thyroid hormone impact the oxidation of FFA?
Accelerates.
28
How does thyroid hormone impact amino acid uptake and protein synthesis?
Increases.
29
How does thyroid hormone impact skeletal muscles, bone, and teeth development?
Promotes development of all.
30
How does thyroid hormone impact the effect of growth hormone?
Potentiates the effect of growth hormone.
31
What impact can lack of thyroid hormone during early life cause?
Cretinism. Short stature and mental deficits.
32
How do T4 and T3 impact the function of Beta Adrenergic receptors?
Increase the function
33
What can treat many of the effects of T4/T3?
Beta blockers.
34
What effect does thyroid hormone have on the CNS?
Stimulatory.
35
How does thyroid hormone impact systolic blood pressure?
Increases the number and affinity of Beta Adrenergic receptors in the heart.
36
How does thyroid hormone impact diastolic blood pressure?
Causes a decrease due to increased metabolism which causes vasodilation.
37
How does hyperthyroidism impact metabolic rate and energy production?
Increased.
38
How does hyperthyroidism impact weight?
Causes weight loss.
39
Does hyperthyroidism cause diarrhea and vomiting?
Yes.
40
How does hyperthyroidism impact the cardiovascular system?
Causes palpitations.
41
What type of hypertension does hyperthyroidism cause?
Systolic hypertension (normal or low diastolic pressure).
42
How does hyperthyroidism impact CNS excitability?
Causes nervousness, irritability, and anxiety.
43
Does hyperthyroidism cause exophthalmos and/or goiter?
Yes.
44
What is exophthalmos?
Protrusion of the eyeballs, as seen in Graves disease.
45
What is a common cause of hyperthyroidism?
Graves' disease.
46
How are autoimmune antibodies involved in Graves' disease?
They bind to TSH receptor and cause increased thyroid hormone release.
47
How does hypothyroidism impact energy production?
Causes decreases in energy production.
48
How does hypothyroidism impact weight?
Causes weight gain.
49
How does hypothyroidism impact heart rate?
Causes bradycardia.
50
What intolerance does hypothyroidism cause?
Cold intolerance.
51
How does hypothyroidism impact CNS activity?
Decreased CNS activity.
52
How does hypothyroidism impact protein synthesis?
Decreases protein synthesis which can cause anemia, alopecia, and dry skin.
53
How does hypothyroidism impact plasma lipids and cholesterol?
Increases.
54
If hypothyroidism etiology is due to pituitary gland issue, how will TSH, T3, T4, and iodine levels be impacted?
Decreased TSH, low T3 and T4, normal iodine levels.
55
What can untreated hypothyroidism in a newborn cause?
Cretinism.
56
What can occur if cretinism is left untreated?
Mental delay can develop.
57
How should congenital hypothyroidism be treated?
Thyroid hormones.
58
What does calcium cause in the blood?
Coagulation.
59
How does calcium impact muscle contraction?
Causes muscle contraction.
60
How does vitamin D affect calcium?
Increases calcium reabsorption from the intestine.
61
What does parathyroid hormone do with the calcium from bones?
Mobilizes it
62
What is the function of calcitonin?
Lowers blood calcium levels.
63
How does calcitonin lower blood calcium levels?
1. Inhibits osteoclasts reducing bone resorption.
2. Stimulates osteoblasts to deposit calcium into bone.
64
What does calcitonin inhibit to reduce bone resorption?
Osteoclasts.
65
What does calcitonin stimulate to deposit calcium into bone?
Osteoblasts.
66
What is PTH a major hormone that regulates?
Serum calcium.
67
What happens to PTH secretion when serum Ca2+ decreases?
Increases.
68
What actions of PTH produce an increase in serum Ca2+?
Increase in serum Ca2+ and decrease in serum phosphate.
69
What does PTH cause the bones to release into the blood when blood calcium is low?
Calcium.
70
How does parathyroid hormone impact renal phosphate reabsorption?
Inhibits renal phosphate absorption.
71
What does PTH do to phosphate excretion?
Increases.
72
What is phosphaturia?
Excess of phosphates excreted in urine.
73
What does PTH do to renal calcium reabsorption?
Increases.
74
How does PTH lead to increased intestinal Ca2+ absorption?
PTH stimulates the activity of 1-alpha hydroxylase in kidneys and increases formation of 1,25 DHCC.
75
What causes primary hyperparathyroidism and what does it result in?
Caused by parathyroid adenoma and results in increased PTH secretion.
76
What does hyperparathyroidism cause to serum Ca2+?
Increased (hypercalcemia).
77
What does hyperparathyroidism cause to serum phosphate?
Decreased (hypophosphatemia).
78
What does hyperparathyroidism cause to urinary phosphate excretion?
Increased (hyperphosphaturia).
79
What does hyperparathyroidism cause to bone resorption?
Increased.
80
How does hypoparathyroidism impact calcium levels in the blood?
Causes less calcium in the blood (hypocalcemia).
81
Why does hypoparathyroidism cause tetany?
Decreased blood serum Ca++ decreases threshold for nerve signals.
82
What are two signs of hypocalcemia?
Carpopedal spasm and Chvostek's sign.
83
How does hypoparathyroidism impact phosphate?
Causes increased phosphate in the blood (hyperphosphatemia) and decreased phosphate in urine (hypophosphaturia).
84
How can hypoparathyroidism be treated?
High doses of vitamin D and calcium intake.
85
What is the active form of vitamin D?
1,25-dihydroxycholecalciferol (1,25 DHCC).
86
What catalyzes the production of 1,25 DHCC in the kidney?
1-alpha-hydroxylase, which increases its activity in response to decreased serum Ca2+.
87
What does 1,25 DHCC cause in terms of bone resorption?
Increases bone resorption, providing Ca2+ and PO4 for mineralization of new bone.
88
How does 1,25 DHCC impact renal absorption of calcium and PO4?
Increases renal absorption of both.
89
How does 1,25 DHCC impact intestinal calcium and PO4 absorption?
Causes increased absorption.
90
How does PTH impact renal absorption of calcium and PO4?
PTH causes absorption of Ca2+ but excretion of PO4.
91
What can cause a vitamin D deficiency?
- Diet
- Lack of sun
- Renal and liver diseases.
92
What does vitamin D deficiency lead to in children?
Rickets.
93
What does vitamin D deficiency lead to in adults?
Osteomalacia.
94
How does a vitamin D deficiency impact calcium levels?
Leads to decreased calcium levels.
95
What does calcitonin have the opposite function of?
PTH.
96
What stimulates calcitonin secretion?
Increased serum Ca++.
97
What does calcitonin lower in the blood?
Circulating Ca2+ and PO4 levels.
98
How does calcitonin inhibit bone resorption?
By inhibiting osteoclastic activity.
99
Why are calcitonin levels increased in pregnancy?
Protects the mother from excessive Ca2+ loss from bones during pregnancy.
100
How does calcitonin impact skeletal development?
Helps in skeletal development.
101
What is Paget's disease?
A disease characterized by extensive breakdown of bone tissue.
102
Why is calcitonin used to treat Paget's disease?
Calcitonin can inhibit the overactive osteoclastic activity in Paget's disease.
103
What is the stimulus for the release of calcitonin?
Elevated blood calcium levels.
104
What is the function of calcitonin in regard to bones?
Stimulates Ca2+ deposition into bones (osteoblastic)
105
How does calcitonin impact Ca2+ in intestines?
Reduces Ca2+ uptake
106
What is the function of calcitonin in relation to the kidneys?
Reduces Ca2+ uptake
107
What is the stimulus for the release of parathyroid hormone (PTH)?
Decreased blood calcium levels.
108
What is the function of PTH in relation to the bones?
Stimulates Ca2+ to be taken up from bones (osterclastic activity)
109
What is the function of PTH in the intestines?
Increase Ca2+ uptake
110
What is the function of PTH in kidneys?
Increases Ca2+ uptake in kidneys
111
What do osteoclasts do?
Break down bone.
112
What do osteoblasts do?
Build bone.
113
What is bone resorption?
Process of breaking down bone tissue.
