> For the complete documentation index, see [llms.txt](https://thisispiggy.gitbook.io/my-wiki/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://thisispiggy.gitbook.io/my-wiki/01-step-1/endocrinology/01-thyroid.md).

# 01 Thyroid

## Parathyroid Embryology

### Pharyngeal pouch 3

[\_](https://github.com/thisispiggy/my-wiki/tree/601ff771dc2fac1318ae8b59435ac8485628fd81/01%20Step%201/Endocrinology/Pharyngeal%20pouch%203%20forms/README.md)Forms the **inferior parathyroid glands** (dorsal wing) and **thymus** (ventral wing)., ![](https://f001.backblazeb2.com/file/wikiFiles/qA8z7j5.jpg)

### Pharyngeal pouch 4

[\_](https://github.com/thisispiggy/my-wiki/tree/601ff771dc2fac1318ae8b59435ac8485628fd81/01%20Step%201/Endocrinology/Pharyngeal%20pouch%204%20forms/README.md)Forms the **superior parathyroid glands** (dorsal wing) and **ultimobranchial body** (ventral)., ![](https://f001.backblazeb2.com/file/wikiFiles/qA8z7j5.jpg)

[\_](https://github.com/thisispiggy/my-wiki/tree/601ff771dc2fac1318ae8b59435ac8485628fd81/01%20Step%201/Endocrinology/Migration%20of%20pharyngeal%20pouch%203%20and%204/README.md)Note that the parathyroid glands formed by pharyngeal pouch 3 migrate below the parathyroid glands of pharyngeal pouch 4..

![](https://f001.backblazeb2.com/file/wikiFiles/sQ9rM79.jpg)

[\_](https://github.com/thisispiggy/my-wiki/tree/601ff771dc2fac1318ae8b59435ac8485628fd81/01%20Step%201/Endocrinology/Parafollicular%20C%20cells%20of%20thyroid%20made%20from/README.md)**Neural crest cells** subsequently migrate into the ultimobranchial body to form **parafollicular C-cells of the thyroid gland**..

### Postbranchial body

[\_](https://github.com/thisispiggy/my-wiki/tree/601ff771dc2fac1318ae8b59435ac8485628fd81/01%20Step%201/Endocrinology/Postbranchial%20body%20aka/README.md)Aka ultimobranchial body.,

### Ectopic thymic and parathyroid tissues

[\_](https://github.com/thisispiggy/my-wiki/tree/601ff771dc2fac1318ae8b59435ac8485628fd81/01%20Step%201/Endocrinology/Ectopic%20thymic%20and%20parathyroid%20tissue%20locations/README.md) can be found in the **lateral regions of the neck** along its path of migration.,

![](https://f001.backblazeb2.com/file/wikiFiles/TVw457H.jpg)

## Thyroid Formation

[\_](https://github.com/thisispiggy/my-wiki/tree/601ff771dc2fac1318ae8b59435ac8485628fd81/01%20Step%201/Endocrinology/Thyroid%20diverticulum%20derived%20from/README.md)On day 24, the **primitive pharynx of the embryological foregut derives the thyroid diverticulum** which in turn forms the thyroid gland.\
Foregut, between copula and Tuberculum impar.. ![](https://f001.backblazeb2.com/file/wikiFiles/C0gMImx.jpg)

[\_](https://github.com/thisispiggy/my-wiki/tree/601ff771dc2fac1318ae8b59435ac8485628fd81/01%20Step%201/Endocrinology/How%20does%20thyroid%20diverticulum%20move%20to%20its%20adult%20position/README.md)The thyroid diverticulum migrates **caudally down the midline, ventral to the hyoid bone and laryngeal cartilages**, to its adult anatomic position..

![](https://f001.backblazeb2.com/file/wikiFiles/dOij8GI.jpg)

### Thyroglossal duct

[\_](https://github.com/thisispiggy/my-wiki/tree/601ff771dc2fac1318ae8b59435ac8485628fd81/01%20Step%201/Endocrinology/Thyroglossal%20duct%20is%20and%20can%20become/README.md)The thyroid remains connected to the tongue via this duct during thyroid development and migration, which later obliterates.

Typically regresses, but may form the adult **pyramidal lobe** of the thyroid.

**Foramen cecum** indicates the **former site of the duct**., ![](https://f001.backblazeb2.com/file/wikiFiles/DFJ7vWV.jpg)

A thyroglossal duct cyst/sinus occurs when part of the **thyroglossal duct fails to obliterate correctly, subsequently forming a cyst or sinus.**

![](https://f001.backblazeb2.com/file/wikiFiles/UvO1Ml6.jpg)

[\_](https://github.com/thisispiggy/my-wiki/tree/601ff771dc2fac1318ae8b59435ac8485628fd81/01%20Step%201/Endocrinology/Thyroglossal%20duct%20cyst%20location/README.md)Is commonly located **ventral to the hyoid bone and laryngeal cartilage**.,

![](https://f001.backblazeb2.com/file/wikiFiles/J3clOOi.jpg)

[\_](https://github.com/thisispiggy/my-wiki/tree/601ff771dc2fac1318ae8b59435ac8485628fd81/01%20Step%201/Endocrinology/Thyroglossal%20duct%20cyst%20symptoms/README.md)Symptoms:

![](https://f001.backblazeb2.com/file/wikiFiles/n1FTTnk.jpg)

In front of hyoid bone (right):

![](https://f001.backblazeb2.com/file/wikiFiles/7V9KcU9.jpg)

Moves because still connection with mouth/tongue..

### Ectopic thyroid tissues:

[\_](https://github.com/thisispiggy/my-wiki/tree/601ff771dc2fac1318ae8b59435ac8485628fd81/01%20Step%201/Endocrinology/Ectopic%20thyroid%20tissue%20location.%20When%20and%20why%20do%20they%20grow%20larger.)

* Puberty/pregnancy: more demand for thyroid hormone, leads to stimulation and growth of thyroid tissue
* Hypothyroidism stimulates more production of ectopic tissue.,

  ![](https://f001.backblazeb2.com/file/wikiFiles/5RNRU9l.jpg) 

[\_](https://github.com/thisispiggy/my-wiki/tree/601ff771dc2fac1318ae8b59435ac8485628fd81/01%20Step%201/Endocrinology/Thyroglossal%20duct%20cyst%20at%20tongue%20aka/README.md)A **lingual cyst** occurs when a **thyroglossal duct cyst is located at the base of the tongue**..

## Thyroid and parathyroid anatomy

[\_](https://github.com/thisispiggy/my-wiki/tree/601ff771dc2fac1318ae8b59435ac8485628fd81/01%20Step%201/Endocrinology/Thyroid%20anatomy/README.md)The **thyroid gland** consists of 2 lobes located anterolaterally, which span the area between the oblique line of the thyroid cartilage and the 5th tracheal ring..

![](https://f001.backblazeb2.com/file/wikiFiles/XBcdYZg.jpg) ![](https://f001.backblazeb2.com/file/wikiFiles/Zetcgfw.jpg) ![](https://f001.backblazeb2.com/file/wikiFiles/Xyztuu5.jpg)

### isthmus

[\_](https://github.com/thisispiggy/my-wiki/tree/601ff771dc2fac1318ae8b59435ac8485628fd81/01%20Step%201/Endocrinology/Isthmus%20is/README.md)Thin band of tissues between 2 lobes., ![](https://f001.backblazeb2.com/file/wikiFiles/Y4enSqj.jpg)

### Pyramidal lobe

[\_](https://github.com/thisispiggy/my-wiki/tree/601ff771dc2fac1318ae8b59435ac8485628fd81/01%20Step%201/Endocrinology/Pyramidal%20lobe%20is/README.md)Lobe above isthumas. Remnant of thyroglossal duct., ![](https://f001.backblazeb2.com/file/wikiFiles/Y4enSqj.jpg)

### Blood supply

[\_](https://github.com/thisispiggy/my-wiki/tree/601ff771dc2fac1318ae8b59435ac8485628fd81/01%20Step%201/Endocrinology/Thyroid%20blood%20supply/README.md)The thyroid receives arterial supply from the **superior (via external carotid)** and **inferior thyroid (via thyrocervical trunk of subclavian) arteries**.. ![](https://f001.backblazeb2.com/file/wikiFiles/Zetcgfw.jpg)

### Vein drainage

[\_](https://github.com/thisispiggy/my-wiki/tree/601ff771dc2fac1318ae8b59435ac8485628fd81/01%20Step%201/Endocrinology/Thyroid%20drained%20by/README.md)Three separate veins provide drainage of the thyroid gland:

* **Superior thyroid vein** — Drains to internal jugular vein
* **Middle thyroid vein** — Drains to internal jugular vein
* **Inferior thyroid vein** — Drains to the brachiocephalic vein..

  ![](https://f001.backblazeb2.com/file/wikiFiles/NbiWZwz.jpg) 

[\_](https://github.com/thisispiggy/my-wiki/tree/601ff771dc2fac1318ae8b59435ac8485628fd81/01%20Step%201/Endocrinology/Thyroid%20consists%20of/README.md)The functional anatomy of the thyroid gland consists of:

* **Follicles**
* **Colloid**
* **Parafollicular cells**..

  ![](https://f001.backblazeb2.com/file/wikiFiles/rxUUupK.jpg) 

  ![](https://f001.backblazeb2.com/file/wikiFiles/9iCIu6l.jpg) 

Thyroid follicles are formed by single layer of epithelial cells known as **follicular cells** which **synthesize, store and secrete thyroid hormone.**

### Colloid

[\_](https://github.com/thisispiggy/my-wiki/tree/601ff771dc2fac1318ae8b59435ac8485628fd81/01%20Step%201/Endocrinology/Colloid%20stores/README.md)Found within the lumen of each thyroid follicle. In this compartment, thyroid hormone is stored as a component of thyroglobulin.,

### Parafollicular cells

[\_](https://github.com/thisispiggy/my-wiki/tree/601ff771dc2fac1318ae8b59435ac8485628fd81/01%20Step%201/Endocrinology/Parafollicular%20cells,%20C%20cells,%20function/README.md)Synthesize and secrete the hormone calcitonin.,

![](https://f001.backblazeb2.com/file/wikiFiles/K2q1JqN.jpg)

### Follicular vs parafollicular

[\_](https://github.com/thisispiggy/my-wiki/tree/601ff771dc2fac1318ae8b59435ac8485628fd81/01%20Step%201/Endocrinology/Differences%20between%20follicular%20and%20parafollicular%20cells%20of%20thyroid/README.md)The follicular cells of the thyroid gland are derived from **endoderm.** Parafollicular C cells are derived from **neural crest cells**..

### Parathyroid

[\_](https://github.com/thisispiggy/my-wiki/tree/601ff771dc2fac1318ae8b59435ac8485628fd81/01%20Step%201/Endocrinology/Parathyroid%20glands%20are/README.md)These are 4 small circular glands found on the posterior surface of the thyroid gland. *Clinical Correlate*: Thyroid surgery is a common cause of removal or damage to the parathyroid glands.. ![](https://f001.backblazeb2.com/file/wikiFiles/jlQ1REo.jpg)

## Thyroid physiology

### Thyroid hormones

[\_](https://github.com/thisispiggy/my-wiki/tree/601ff771dc2fac1318ae8b59435ac8485628fd81/01%20Step%201/Endocrinology/Thyroid%20hormone%20contains%20element/README.md)Contain element **Iodine**, found in table salt..

[\_](https://github.com/thisispiggy/my-wiki/tree/601ff771dc2fac1318ae8b59435ac8485628fd81/01%20Step%201/Endocrinology/Iodine,%20to%20be%20made%20to%20thyroid%20hormones,%20needs%20to%20be:/README.md)In order to be incorporated into thyroid hormones, iodine needs to be

![](https://f001.backblazeb2.com/file/wikiFiles/vn8lmbX.jpg)..

[\_](https://github.com/thisispiggy/my-wiki/tree/601ff771dc2fac1318ae8b59435ac8485628fd81/01%20Step%201/Endocrinology/Three%20types%20of%20thyroid%20hormones/README.md)There are three types of thyroid hormone:

* **Thyroxine** (T4)
* **Triiodothyronine** (T3)
* **Reverse triiodothyronine** (rT3)..

![](https://f001.backblazeb2.com/file/wikiFiles/iJkDPBe.jpg)

### T4 vs. T3

[\_](https://github.com/thisispiggy/my-wiki/tree/601ff771dc2fac1318ae8b59435ac8485628fd81/01%20Step%201/Endocrinology/T4%20and%20T3%20differences/README.md)

* T4 makes up the majority of thyroid hormone produced. It has a longer half life than T3.
* T3 is less abundant but more potent than T4.
* Reverse T3 (rT3) is found in the blood and has **no biologic activity**..

### 5-deiodinase

[\_](https://github.com/thisispiggy/my-wiki/tree/601ff771dc2fac1318ae8b59435ac8485628fd81/01%20Step%201/Endocrinology/5-deiodinase%20function%20and%20where%20does%20it%20work/README.md)Deiodinate T4 to T3 in peripheral tissues., ![](https://f001.backblazeb2.com/file/wikiFiles/4YzCP46.jpg)

\[\_]\(5'-deiodinase inhibited by)Inhibited by

* propylthiouracil
* propanolol
* amiodarone.,

![](https://f001.backblazeb2.com/file/wikiFiles/VSM7dh0.jpg) propanolol: for thyrotoxin. Catecholamine can result in hyperthyroidism

Also amiodarone: ![](https://f001.backblazeb2.com/file/wikiFiles/cCEenLZ.jpg)

### Thyroglobulin

[\_](https://github.com/thisispiggy/my-wiki/tree/601ff771dc2fac1318ae8b59435ac8485628fd81/01%20Step%201/Endocrinology/Thyroglobulin%20is,%20function,%20made%20where/README.md)

* **large, tyrosine-rich glycoprotein** 
* Synthesizes T3/T4
* **resides in the colloid.**
* Made by follicular cells.,

  ![](https://f001.backblazeb2.com/file/wikiFiles/hoJU9Fo.jpg) 

### Thyroid Hormone Synthesis

[\_](https://github.com/thisispiggy/my-wiki/tree/601ff771dc2fac1318ae8b59435ac8485628fd81/01%20Step%201/Endocrinology/Thyroid%20hormone%20synthesis%20overview/README.md)Overview steps of thyroid hormone synthesis:

1. Iodide transport into follicular cells
2. Iodide oxidized to I2
3. Tyrosine added to I2, becoming DIT/MIT
4. DIT/MIT coupling
5. Proteolysis releases thyroid hormones..

![](https://f001.backblazeb2.com/file/wikiFiles/kbPuUdQ.jpg) ![](https://f001.backblazeb2.com/file/wikiFiles/j20w5R0.jpg)

[\_](https://github.com/thisispiggy/my-wiki/tree/601ff771dc2fac1318ae8b59435ac8485628fd81/01%20Step%201/Endocrinology/How%20is%20iodine%20transported%20into%20follicular%20cell/README.md)Iodide (I-) is transported into the follicular cell via the **Na-I cotransporter** and then into the lumen of the follicle.. ![](https://f001.backblazeb2.com/file/wikiFiles/pDx0Gz0.jpg)

### Thyroid peroxidase

[\_](https://github.com/thisispiggy/my-wiki/tree/601ff771dc2fac1318ae8b59435ac8485628fd81/01%20Step%201/Endocrinology/Thyroid%20peroxidase,%20where%20and%20functions/README.md)

* Found on the luminal surface of the follicular cell, **oxidizes** I- to I2 (iodine).
* Conjugates I2 to tyrosine residues on thyroglobulin to form monoiodotyrosine (MIT) and diiodotyrosine (DIT) residues. This reaction is called **organification**.  

  MIT: 1 iodine  

  DIT: 2 iodine
* **Couples MIT and DIT**.,  

![](https://f001.backblazeb2.com/file/wikiFiles/4TsTDAD.jpg) ![](https://f001.backblazeb2.com/file/wikiFiles/aJUfEY4.jpg)

\[\_]\(What's T4 and T3 coupled from)

* DIT + DIT = T4
* MIT + DIT = T3..

![](https://f001.backblazeb2.com/file/wikiFiles/TDS8fup.jpg) ![](https://f001.backblazeb2.com/file/wikiFiles/GHIjk6v.jpg)

[\_](https://github.com/thisispiggy/my-wiki/tree/601ff771dc2fac1318ae8b59435ac8485628fd81/01%20Step%201/Endocrinology/Iodinated%20thyroglobulin%20stored%20and%20released%20how?/README.md)Iodinated thyroglobulin is **stored in colloid within the follicular lumen**. Upon stimulation by TSH, follicular cells endocytose thyroglobulin and lysosomal enzymes digest thyroglobulin, secreting T3 and T4 into the circulation.. ![](https://f001.backblazeb2.com/file/wikiFiles/kbPuUdQ.jpg)

[\_](https://github.com/thisispiggy/my-wiki/tree/601ff771dc2fac1318ae8b59435ac8485628fd81/01%20Step%201/Endocrinology/Residual%20MIT/DIT%20fate/README.md)Residual MIT and DIT are deiodinated by **thyroid deiodinase**. The I2 that is generated is recycled to synthesize more thyroid hormone..

[\_](https://github.com/thisispiggy/my-wiki/tree/601ff771dc2fac1318ae8b59435ac8485628fd81/01%20Step%201/Endocrinology/Na-I%20transporter%20inhibited%20by/README.md)The Na-I transporter is competitively inhibited by anions including:

* **Thiocyanate** \[SCN]−
* **Perchlorate**
* **Pertechnetate**.,

These anions inhibit the uptake of I- into follicular cells, thereby interfering with the synthesis of thyroid hormone.

![](https://f001.backblazeb2.com/file/wikiFiles/pDx0Gz0.jpg)

### Thyroid peroxidase

[\_](https://github.com/thisispiggy/my-wiki/tree/601ff771dc2fac1318ae8b59435ac8485628fd81/01%20Step%201/Endocrinology/Thyroid%20peroxidase%20inhibited%20by/README.md)Inhibited by **propylthiouracil** and **methimazole**.,

![](https://f001.backblazeb2.com/file/wikiFiles/VSM7dh0.jpg)

### Wolff-Chaikoff effect.

[\_](https://github.com/thisispiggy/my-wiki/tree/601ff771dc2fac1318ae8b59435ac8485628fd81/01%20Step%201/Endocrinology/Wolff-Chaikoff%20effect%20is/README.md)High levels of iodine inhibit thyroid hormone synthesis by blocking the organification step. Less synthesis of MIT/DIT.,

### Amiodarone

[\_](https://github.com/thisispiggy/my-wiki/tree/601ff771dc2fac1318ae8b59435ac8485628fd81/01%20Step%201/Endocrinology/Amiodarone%20effect%20on%20iodine/README.md)

![](https://f001.backblazeb2.com/file/wikiFiles/B2Tic5C.jpg) ![](https://f001.backblazeb2.com/file/wikiFiles/cCEenLZ.jpg) Competes with T4\
Check TSH level in patients before start amiodarone..

### Radioactive Iodine

[\_](https://github.com/thisispiggy/my-wiki/tree/601ff771dc2fac1318ae8b59435ac8485628fd81/01%20Step%201/Endocrinology/Radioactive%20iodine%20characteristics%20and%20uses/README.md)

![](https://f001.backblazeb2.com/file/wikiFiles/Gbjujnb.jpg)..

### Thyroxine-Binding Globulin, aka TBG

[\_](https://github.com/thisispiggy/my-wiki/tree/601ff771dc2fac1318ae8b59435ac8485628fd81/01%20Step%201/Endocrinology/T3/T4%20transported%20by/README.md)Three proteins are involved in the transport of T3 and T4 in the blood:

* **Thyroxine-binding globulin** (TBG) has the highest affinity for T3 and T4, and binds the majority of T3 and T4 in peripheral blood.  However, it has the lowest plasma concentration of the three proteins.
* **Albumin** carries T3 and T4, and has the highest plasma concentration.
* **Transthyretin** (aka pre-albumin) transports T4 only..

[\_](https://github.com/thisispiggy/my-wiki/tree/601ff771dc2fac1318ae8b59435ac8485628fd81/01%20Step%201/Endocrinology/Bound%20T3/T4%20active%20or%20inactive/README.md)Only free T3 or T4 is active, whereas TBG-bound T3 or T4 is inactive. However,

![](https://f001.backblazeb2.com/file/wikiFiles/ioKs6i0.jpg)

TBG acts as pool of T4 to be released..

[\_](https://github.com/thisispiggy/my-wiki/tree/601ff771dc2fac1318ae8b59435ac8485628fd81/01%20Step%201/Endocrinology/TBG%20increased%20and%20decreased%20by/README.md)Conditions where TBG is increased (e.g. pregnancy) or decreased (e.g. liver failure) can affect total T3 or T4 levels. Increased estrogen during **pregnancy** causes increased TBG, which results in increased total T3 and T4 levels. However, the free T3 and free T4 levels are actually normal (therefore, pregnancy is not a hyperthyroid state)..

![](https://f001.backblazeb2.com/file/wikiFiles/U6cJyJ8.jpg)

![](https://f001.backblazeb2.com/file/wikiFiles/Fe5iN2R.jpg)

### Thyroid Hormone Receptors

[\_](https://github.com/thisispiggy/my-wiki/tree/601ff771dc2fac1318ae8b59435ac8485628fd81/01%20Step%201/Endocrinology/Thyroid%20Hormone%20Receptors/README.md) these are..

![](https://f001.backblazeb2.com/file/wikiFiles/OhoiI1U.jpg)

### Thyroid Hormone functions

[\_](https://github.com/thisispiggy/my-wiki/tree/601ff771dc2fac1318ae8b59435ac8485628fd81/01%20Step%201/Endocrinology/Thyroid%20hormone%20functions/README.md) It mediates:

* **Metabolism** and growth
* **Glucose, lipid metabolism**
* **Cardiac** function
* **Bone** growth
* **CNS** and **ANS activity**
* **Temperature regulation**.,

### Thyroid Hormones Metabolic Effect

[\_](https://github.com/thisispiggy/my-wiki/tree/601ff771dc2fac1318ae8b59435ac8485628fd81/01%20Step%201/Endocrinology/Thyroid%20hormone%20metabolic%20effect/README.md)Increases basal metabolic rate and oxygen consumption via multiple mechanisms, including:

* Increasing glycogenolysis and gluconeogenesis
* Increasing lipolysis
* increases LDL receptor in liver > **decrease serum LDL**
* increase cholesterol secretion in bile
* decrease cholesterol/TG concentration
* increases basal metabolic rate (amount of energy used if slept all day)
* Increasing and upregulating Na/K ATPase activity (more ATP needed, higher RR/temp)..

[\_](https://github.com/thisispiggy/my-wiki/tree/601ff771dc2fac1318ae8b59435ac8485628fd81/01%20Step%201/Endocrinology/Hyper%20vs%20hypothyroid%20patient%20symptoms/README.md)

* hyperthyroid patient: hyperglycemia, weight loss, tachycardia, tachypnea
* hypothyroid patient: high cholesterol..

### Thyroid Hormones and Bone

[\_](https://github.com/thisispiggy/my-wiki/tree/601ff771dc2fac1318ae8b59435ac8485628fd81/01%20Step%201/Endocrinology/Thyroid%20hormone%20and%20bone%20growth/README.md)Affects growth and maturation by **promoting bone growth/turnover**, and **acting synergistically with growth hormone and insulin-like growth factor-1** (IGF-1).,

### Thyroid Hormones and CNS

[\_](https://github.com/thisispiggy/my-wiki/tree/601ff771dc2fac1318ae8b59435ac8485628fd81/01%20Step%201/Endocrinology/Thyroid%20hormone%20and%20CNS/README.md)Is important in perinatal maturation of the central nervous system (CNS).,

A hypothyroid neonate is at an increased risk for mental retardation.

### Thyroid Hormones and Cardiac Effect

[\_](https://github.com/thisispiggy/my-wiki/tree/601ff771dc2fac1318ae8b59435ac8485628fd81/01%20Step%201/Endocrinology/Thyroid%20hormone%20and%20cardiac%20effect/README.md)Affects the autonomic nervous system (ANS) by **increasing sympathetic activity (β-adrenergic tone)**., For example, thyroid hormone leads to the up-regulation of β1-adrenergic receptors in the heart.

Hyperthyroid patient: tachycardia

[\_](https://github.com/thisispiggy/my-wiki/tree/601ff771dc2fac1318ae8b59435ac8485628fd81/01%20Step%201/Endocrinology/Thyroid%20hormone%20and%20temperature/README.md)Affects temperature regulation by **increasing thermogenesis** by increase more Na/K ATP pump.,

\[\_]\(4 B's of thyroid function)To recall major thyroid hormone functions, remember the **4 B's:**

* **B**MR (increase)
* **B**one growth
* **B**rain maturation
* **B**eta-adrenergic..

### Pregnancy and thyroid hormones

[\_](https://github.com/thisispiggy/my-wiki/tree/601ff771dc2fac1318ae8b59435ac8485628fd81/01%20Step%201/Endocrinology/How%20does%20pregnancy%20affect%20thyroid%20hormones%20levels/README.md) ![](https://f001.backblazeb2.com/file/wikiFiles/P27oanQ.jpg)..

### TRH

[\_](https://github.com/thisispiggy/my-wiki/tree/601ff771dc2fac1318ae8b59435ac8485628fd81/01%20Step%201/Endocrinology/TRH%20from,%20function/README.md)**Thyrotropin releasing hormone** (TRH) from the hypothalamus stimulates the secretion of thyroid stimulating hormone (TSH) by the anterior pituitary..

[\_](https://github.com/thisispiggy/my-wiki/tree/601ff771dc2fac1318ae8b59435ac8485628fd81/01%20Step%201/Endocrinology/TSH%20from,%20function,%20MOA/README.md)TSH from anterior pituitary stimulates increased synthesis and secretion of thyroid hormones, by binding follicular cell receptors and increasing intracellular levels of cAMP (**adenylate cyclase-cAMP mechanism**).. ![](https://f001.backblazeb2.com/file/wikiFiles/liJBqKd.jpg)

[\_](https://github.com/thisispiggy/my-wiki/tree/601ff771dc2fac1318ae8b59435ac8485628fd81/01%20Step%201/Endocrinology/TRH/TSH%20regulated%20how/README.md)T3 and T4 down-regulate TRH receptors in the anterior pituitary leading to an inhibition of TSH secretion. This is an example of negative feedback.. ![](https://f001.backblazeb2.com/file/wikiFiles/JAq7m2v.jpg) T3/T4 levels sensed by hypothalamus

### Thyroid-stimulating immunoglobulins, TSI

[\_](https://github.com/thisispiggy/my-wiki/tree/601ff771dc2fac1318ae8b59435ac8485628fd81/01%20Step%201/Endocrinology/Thyroid-stimulating%20immunoglobulins%20is,%20function,%20and%20association/README.md)**Auto-antibodies (IgG) against TSH receptors**. Binding to TSH receptors on follicular cells stimulates T3/T4 release., Patients with Graves disease exhibit high concentrations of TSI.

[\_](https://github.com/thisispiggy/my-wiki/tree/601ff771dc2fac1318ae8b59435ac8485628fd81/01%20Step%201/Endocrinology/normal%20thyroid%20hormone%20values/README.md) ![](https://f001.backblazeb2.com/file/wikiFiles/lcnzzWR.jpg)..

### Calcitonin

[\_](https://github.com/thisispiggy/my-wiki/tree/601ff771dc2fac1318ae8b59435ac8485628fd81/01%20Step%201/Endocrinology/Calcitonin%20produced%20by,%20and%20function/README.md)Produced by the parafollicular cells (C cells), serves to lower **blood calcium levels**. It does this by several mechanisms including:

* **Increasing osteoblastic activity in bone**
* **Decreasing osteoclastic activity in bone**
* Inhibiting intestinal absorption
* Inhibiting renal tubular reabsorption (promoting excretion in urine)

Minor role in human calcium handling, but used in pharmacologic therapy for hypercalcemia.,

[\_](https://github.com/thisispiggy/my-wiki/tree/601ff771dc2fac1318ae8b59435ac8485628fd81/01%20Step%201/Endocrinology/Calcitonin%20increased%20by/README.md)The stimulus for calcitonin secretion is **increased serum calcium concentration**..

[\_](https://github.com/thisispiggy/my-wiki/tree/601ff771dc2fac1318ae8b59435ac8485628fd81/01%20Step%201/Endocrinology/Calcitonin%20opposes%20what%20other%20hormone/README.md)Calcitonin opposes the actions of **parathyroid hormone** and is not important in normal Ca2+ homeostasis..