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Histo III > The Endocrine System: Thyroid and Parathyroid > Flashcards

The Endocrine System: Thyroid and Parathyroid Flashcards

1
Q

Thyroid: Metabolic regulator

Thyroid Gland Anatomy

A

Two lobes connected by isthmus

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2
Q

The thyroid is important for…

A

metabolism

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3
Q

Thyroid: Metabolic regulator

Thyroid Gland Organization

A

Outer capsule
Dense CT
Parathyroid glands
Lobules separated by CT Septa
Follicles - parenchyma

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4
Q

Thyroid: Metabolic regulator

Describe the follicles of the thyroid gland.

A

Lined with simple epithelium
Filled with colloid

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5
Q

Thyroid: Metabolic regulator

What is the structural difference between active vs. inactive thyroid follicles?

A

Inactive: squamous
Active: cuboidal to columnar

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6
Q

Thyroid: Metabolic regulator

What is colloid?

A

Thyroglobulin - the storage form of thyroid hormone
Large glycoprotein with no hormone activity
140 tyrosine residues used to make thyroid hormones

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7
Q

Thyroid: Metabolic regulator

Thyroid Stimulating Hormone (TSH)

A

Produced by pituitary in response to TRH from hypothalamus
Induces all phases of thyroid hormone production

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8
Q

Thyroid: Thyroid Hormone Production

Where is Thyroglobulin produced? What happens to it after production?

A

Produced in RER
Glycosylated
Exocytoses into the follicular lumen

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9
Q

Thyroid: Thyroid Hormone Production

Iodide from blood

A

Transported by symporter
Oxidized after released into lumen

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10
Q

Thyroid: Thyroid Hormone Production

Iodination of Thyroglobulin

A
  • Anion transporter, Pendrin, transports iodide to lumen
  • At apical surface, iodide is oxidized to iodine by thyroid peroxidase
  • In follicle lumen, tyrosine residues of thyroglobulin are iodinated by covalent binding of 1-2 iodine molecules
  • Iodinated tyrosines are conjugated to produce mature hormones
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11
Q

Thyroid: Thyroid Hormone Production

Release of T3 and T4

A
  • Iodinated thyroglobulin is absorbed into follicular cells through endocytosis
  • Vesicles fuse with lysosomes, and are then transported to basal region
  • T3 and T4 are freed from thyroglobulin and released from basal surface into capillaries
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12
Q

Thyroid: Thyroid Hormones

What hormones are produced in the thyroid?

A

T3 and T4
Calcitonin

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13
Q

Thyroid: Thyroid Hormones

What is the function of T3 and T4?

A

they act on nuclear receptors
Important for growth, cell differentiation, basal metabolic rate, and oxygen consumption

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14
Q

Thyroid: Thyroid Hormones

What do T3 and T4 affect the metabolism of?

A

Carbohydrates
Lipids
Proteins

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15
Q

Thyroid: Thyroid Hormones

Calcitonin opposes…

A

PTH action

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16
Q

Thyroid: Thyroid Hormones

What happens to T3 and T4 after release from the thyroid?

A

T3 and T4 release → target organs: ↑Growth, development, metabolism, body heat production
T3 and T4 release → T4 → Liver and Kidney → T4 converted to T3
T3 and T4 release → T3 crosses BBB → T3 inhibits hypothalamus
T3 and T4 release → feedback → inhibits TSH from pituitary to reduce T3 and T4

17
Q

Thyroid

Where are Parafollicular Cells found? What do they contain?

C Cells

A

Found between follicular cells and basement membrane
Contain granules of calcitonin (release calcitonin)

18
Q

Thyroid

What is the function of calcitonin?

A

Inhibits osteoclast activity

19
Q

What induces the release of calcitonin?

A

High blood calcium

20
Q

Parathyroid

Parathyroid Anatomy

A

Found in the posterior capsule of the thyroid
Variation in location: embryonic migration differences

21
Q

Parathyroid

Parathyroid Organization

A

Chief cells (hormone producing - PTH) - smaller and darker staining
Oxyphil cells - large eosinophilic cells
Reticular fibers support chief cells

22
Q

Parathyroid

How is PTH Release regulated?

A

Chief cells have a calcium receptor that detects blood calcium levels
When calcium binds, inhibits PTH Release
If calcium levels are low, PTH release proceeds

23
Q

Parathyroid

What is the default state of chief cells?

A

Default state is to release PTH; if Calcium levels are high enough, it inhibits PTH release

24
Q

Parathyroid

Parathyroid cells release…

A

PTH

25
Q

Parathyroid

Parafollicular cells release…

A

Calcitonin

26
Q

Parathyroid

What is the difference between PTH and Calcitonin?

A

PTH → ↑ blood calcium in response to ↓ calcium
Calcitonin → ↓osteoclast activity in response to ↑ blood calcium → ↓ blood calcium

27
Q

Parathyroid

What are the three mechanims to increase blood calcium?

A
  1. Degredation of bone by osteoclasts
  2. ↑ calcium absorption in kidneys
  3. ↑ calcium absorption in GI Tract
28
Q

Parathyroid

What is parathyroid hormone (PTH)?

A

Polypeptide regulator of blood calcium

29
Q

Parathyroid

What is the function of PTH in bones?

A

Targets osteoblasts to produce osteoclast stimulating factor
Osteoclasts absorb bone tissue, releasing calcium and phosphate

30
Q

Parathyroid

What is the function of PTH in the kidneys?

A

Reduces phosphate levels by reducing phosphate absorption in renal tubules - and increases calcium absorption
Stimulates vitamin D synthesis, increasing GI calcium absorption

31
Q

Parathyroid

What is the cell types found in the Parathyroid?

A

Oxyphil cells
Chief cells

Histo III (8 decks)

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