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CC 2 LAB > THYROID GLAND > Flashcards

THYROID GLAND Flashcards

1
Q

Location and morphology of thyroid gland

A

The thyroid gland is a butterfly-shaped endocrine organ located in the lower neck, in front of the trachea, just below the larynx.

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2
Q

Function of the thyroid gland

A

It plays a crucial role in regulating metabolism through the secretion of thyroid hormones (T3 and T4) and calcitonin.

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3
Q

• Ring-shaped structure

A

Follicle / Follicular cells

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4
Q

• Basic Unit: Spherical structures filled with colloid (a gel-like substance).

• Lined by follicular cells (simple cuboidal or columnar epithelium).

A

Thyroid Follicles

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5
Q

Thyroid Follicles FUNCTION

A

Synthesize and secrete thyroid hormones (T3 and T4).

Colloid contains thyroglobulin, a precursor to these hormones.

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6
Q

• Colloid (aka.____ or _____)
- hormones
- thyroglobulin
- glycoproteins

A

Cavity or Lumen

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7
Q

Colloid

• It stores_____, a precursor protein needed to make thyroid hormones.

• The colloid appears_____ under the microscope when stained (e.g., with H&E stain).

A

thyroglobulin

pink

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8
Q

Colloid

• It stores_____, a precursor protein needed to make thyroid hormones.

• The colloid appears_____ under the microscope when stained (e.g., with H&E stain).

A

thyroglobulin

pink

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9
Q

Thyroglobulin

• Thyroglobulin is a large glycoprotein synthesized by_____ cells.

• It is stored in the____ and serves as a template for making_____

• _____is added to thyroglobulin in the colloid to produce these hormones.

A

follicular

colloid; T3 and T4.

Iodine

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10
Q

Colloid (aka. Cavity)

Synthesizes (3)

A
  • hormones
  • thyroglobulin
  • glycoproteins
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11
Q

Follicle
• cavity surrounded by simple cuboidal epithelium called…

A

Follicular Cells

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12
Q

Follicular Cells
•_______ near the capillary blood supply
•_______
- adjacent to the colloid
- synthesis and storage of thyroid hormones
- iodination, exocytosis, and the initial phase of hormone secretion occur

A

Bases

Apices

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13
Q

Parafollicular Cells
• aka

A

C cells

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14
Q

Parafollicular cells produces what?

A

Calcitonin

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15
Q

Role of Calcitonin

• Target:
• Purpose:

A

Bones, kidneys, and intestines.

To lower blood calcium levels when they are too high.

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16
Q

Roles of calcitonin

• : Prevents osteoclasts (bone cells that break down bone tissue) from releasing calcium into the bloodstream.

• : Increases calcium excretion in the kidneys.

A

Inhibits Bone Resorption

Promotes Calcium Excretion

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17
Q

Thyroid Hormone
Synthesis
•_____
- major component of thyroid hormone

A

iodine

18
Q

Sources of Iodine

A

• dietary intake
• deiodination of organic iodine-containing moieties within the gland

19
Q

glycoprotein synthesized by the rough endoplasmic reticulum in the basal and perinuclear regions of the follicular cell

A

TGB or Tg

20
Q

• Thyroglobulin (TGB or Tg)
- modified by the______, packaged into_____

• vesicles undergo_____, releasing Tg into the lumen

A

Golgi complex

vesicles

exocytosis

21
Q

Thyroid Hormone Synthesis

1-7

A
  1. Uptake of lodide
  2. Oxidation of lodide
  3. lodination of the tyrosyl residues on Tg
  4. Coupling
  5. Proteolysis of Tg
  6. Deionidation of iodotyrosines
  7. Deionidation of T, to T3
22
Q
  1. Uptake of Iodide

• What happens: Iodide ions (I⁻) are actively transported into the_____ from the blood via a protein called the_______.

• Why: Iodide is the raw material needed to make thyroid hormones.

A

follicular cells

sodium-iodide symporter (NIS)

23
Q
  1. Oxidation of Iodide

• What happens: Iodide ions (I⁻) are oxidized into iodine (I₂) by the enzyme _________in the______

• Why: Iodine is the active form needed for hormone synthesis.

A

thyroid peroxidase (TPO)

follicular lumen (the colloid).

24
Q
  1. Iodination of Tyrosyl Residues on Thyroglobulin (Tg)

• What happens: The enzyme TPO attaches iodine to specific tyrosine residues on thyroglobulin (Tg), a glycoprotein produced by follicular cells.

• Why: This step forms______ and _______ the building blocks of T3 and T4.

A

monoiodotyrosine (MIT) and diiodotyrosine (DIT),

25
Q
  1. Coupling

• What happens: Two iodinated tyrosines (MIT and/or DIT) are coupled together by TPO to form:

•	Why: T3 and T4 are the active thyroid hormones.
A

• T3 (triiodothyronine): MIT + DIT

• T4 (thyroxine): DIT + DIT

26
Q
  1. Proteolysis of Thyroglobulin

• What happens: Thyroglobulin, now containing T3 and T4, is endocytosed back into the follicular cells._______ break it down to release T3 and T4 into the bloodstream.

• Why: This step liberates the hormones for secretion.

A

Lysosomal enzymes

27
Q
  1. Deiodination of Iodotyrosines

• What happens: Any leftover MIT and DIT that weren’t used are deiodinated by the enzyme_________, recycling iodine and tyrosine for future hormone synthesis.

• Why: To conserve iodine and prevent waste

A

iodotyrosine deiodinase

28
Q
  1. Conversion of T4 to T3

• What happens: In peripheral tissues (like the liver and kidneys), T4 is converted to the more active T3 by the enzyme________.

• Why: T3 is the main active form of thyroid hormone, regulating metabolism at the cellular level.

A

iodothyronine deiodinase

29
Q

Uptake of iodide
– inorganic iodide transported to follicular cell by_____ located in the basolateral membrane

A

NIS

Sodium Iodide Symporters

30
Q

■ NIS activity modulated by_____
■ uptake also influenced by serum iodide levels

A

TSH - Thyroid Stimulating Hormone

31
Q
  1. Oxidation of iodide
    – Iodide then diffuses across the apical surface of the follicular cell to the lumen of the follicle via…
A

pendrin cotransporter

32
Q
  1. Oxidation of iodide
    – In the apical membrane, iodide is
    oxidized to active iodine (I2) by_____

This reaction is catalyzed by the heme-containing enzyme_____

A

hydrogen peroxidase

thyroid peroxidase (TPO)

33
Q

Iodide -> iodine

A

Hydrogen peroxidase

34
Q
  1. Iodination of tyrosyl residues on Tg

– iodine is immediately incorporated into the tyrosine residues of the
large glycoprotein_______
molecules

A

thyroglobulin

35
Q
  1. Coupling

– Iodinated thyroglobulin in the colloid of the follicle undergoes coupling of iodinated tyrosine molecules
– The reaction is catalyzed by_____

A

TPO

36
Q

The Products of Coupling

■ The coupling of two tyrosine residues each iodinated at two positions (diiodotyrosine, T2 or DIT) produces___________
■ The combination of DIT with monoiodotyrosine (MIT or T1) produces
__________

A

tetra-iodothyronine or thyroxine (T4)

triiodothyronine (T3)

37
Q

Storage and Release of T4 and T3

■ Thyroid hormones are stored in this state and released when the thyroglobulin molecule is taken up by a process of _______into the follicular cells via_____

A

pinocytosis (cell drinking)

megalin

38
Q

Storage and Release of T4 and T3
■ This process is stimulated
by____ and the thyroglobulin
ends up in lysosomes

A

TSH

39
Q
  1. Proteolysis of Tg

– Within______, hydrolysis of the
thyroglobulin molecules occurs and
results in the release of T4 and T3
– Both T4 and T3 are released into
circulation

A

lysosomes

40
Q
  1. Deiodination of______ within the thyroid gland and reuse of liberated iodide
A

iodotyrosines

41
Q
  1. Deiodination of T4 to T3
    – about half of all T4 is monodeiodinated in the_____position to form T3
    – 40% is deiodinated at the inner ring,
    forming___
A

5’

rT3 - Reverse triiodothyronine

CC 2 LAB (35 decks)

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