BSI 2 Lecture 49: Endocrine 3 Flashcards

1
Q

What major hormones does the thyroid gland secrete?

A

T3, T4, and Calcitonin

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2
Q

What cells in the thyroid secrete triiodothyronine and thyroxine?

A

Follicular cells

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3
Q

What cells in the thyroid secrete Calcitonin?

A

Parafollicular cells (C cells)

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4
Q

What are the thyroid hormones T3 and T4 responsible for?

A

Basal metabolic rate

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5
Q

What controls secretion of thyroid hormones?

A

Thyroid releasing hormone and somatostatin secreted by the hypothalamus and then thyroid stimulating hormone secreted by the anterior pituitary

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6
Q

What does TSH do to the follicular cells in the thyroid?

A

It increases proteolysis of thyroglobulin, it increases activity of the iodide pump, increases iodination of thyroglobulin, and increases number, size, and activity of thyroid follicular cells

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7
Q

What is the thyroid gland composed of?

A

Cuboidal epithelial cells formed into round follicles which contain a colloid composed of the T3 and T4 hormones with scattered C cells

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8
Q

Describe the process of synthesizing T3 and T4

A

1) Thyroglobulin gets synthesized in the follicle cell and is transported to the lumen
2) Sodium and Iodide are co-transported into the follicle cell where iodide is moved into the lumen
3) Iodide can attach to either one place (MIT) or two places (DIT) on the thyroglobulin.
4) DIT + MIT = T3 and DIT + DIT = T4
5) The thyroglobulin and T3/T4 complex leaves the lumen by endocytosis into the follicle cell
6) Lysosomal enzymes split and release T3 and T4
7) Amino acid residues are reused to make thyroglobulin

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9
Q

What percentage of the secretions of the thyroid gland is T4?

A

~93%

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10
Q

What happens to most of the T4 in tissues?

A

It is converted to T3

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11
Q

Which one is stronger, T3 or T4?

A

T3

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12
Q

Which one has a shorter half life, T3 or T4?

A

T3

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13
Q

How much iodinated thyroglobulin can the thyroid store?

A

About a 2-3 month supply

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14
Q

How are the thyroid hormones transported?

A

Bound to plasma proteins (Thyroxine-binding globulin)

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15
Q

What does the parathyroid release?

A

PTH

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16
Q

What does parathyroid hormone do?

A

Affects GI absorption, renal excretion, and exchange with bone itself

17
Q

What two cell types are found in parathyroid glands?

A

Chief cells and oxyphil cells

18
Q

What does PTH do to calcium and phosphate levels?

A

It increases calcium levels by increasing reabsorption and decreases phosphate levels by excreting it faster than the bone can reabsorb

19
Q

How does PTH increase GI absorption?

A

It increases the formation of 1, 25-dihydroxycholecalciferol by the kidneys from vitamin D

20
Q

What is the stimulus for PTH secretion?

A

Low levels of calcium