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6.Endocrine System > Endo Physiology > Flashcards

Endo Physiology Flashcards

1
Q

Describe the basic structure and location of thyroid gland

A

It has two lobes, right and left, the lobes are connected by an isthmus. Sometimes there is a third lobe above the isthmus called the pyramidal lobe.

It is located overlying the trachea and just below the thyroid and cricoid cartilage

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2
Q

Describe the blood supply of thyroid

A
  1. Superior thyroid artery that comes from External carotid artery ( 1st branch)
  2. Inferior thyroid artery that comes from thyrocervical trunk which branches from subclavian artery
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3
Q

The pyramidal lobe of the thyroid is a persistent remnant of the__

A

Thyroglossal duct

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4
Q

Explain the embryology of thyroid gland

A

The thyroid gland starts development at the midline floor of the pharyngeal arches.
Here at a point called the foramen cecum near the base of the tongue, the endodermal epithelial cells proliferate and form the thyroid diverticulum
The thyroid diverticulum then descends down towards the trachea while maintaining connection to the tongue through the thyroglossal duct which later degenerates
It overlies the trachea, at this point, the ultimobranchial body derived from the 4th pharyngeal pouch containing neural crest cells fuses with with the thyroid diverticulum to form C-cells.

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5
Q

Name the two remnants of thyroglossal duct in child/adult

A
  1. Foramen cecum in tongue
  2. Pyramidal lobe of thyroid
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6
Q

Thyroglossal duct cyst

A

Is a persistent remnant of thyroglossal duct found in anterior midline of neck, usually painless. It moves with swallowing/protrusion of tongue

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7
Q

Ectopic thyroid common location

A

Base of tongue

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8
Q

Common presentation of ectopic thyroid

A

Mass at the base of tongue at puberty or pregnancy

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9
Q

Removal of ectopic thyroid may lead to ?

A

Hypothyroidism if it is the only thyroid tissue available

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10
Q

In some cases the ectopic thyroid causing hypothyroidism stimulates increase TSH which causes it to decrease in size; true/false

A

False, it will increase in size

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11
Q

T3,T4 long form and amino acid amd element involved in formation

A

T3- Triiodothyronine
T4- Thyroxine

Tyrosine and Iodine

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12
Q

Explain Thyroid hormone synthesis

A

It occurs in the following steps:

  1. Iodide uptake by follicular cells
    The plasma Iodide is taken up by follicular cells through NaI Sympoter ( NIS)
  2. Oxidation of Iodide to Iodine
    In the follicular cells, the Iodide is the oxidized to form I2 by enzyme thyroid peroxidase ( TPO) then transported to the lumen( colloid)
  3. Organification
    In the colloid, Thyroid peroxidase incorporates Iodine into tyrosine residue on thyroglobulin molecule forming MIT/ DIT
  4. Coupling
    Thyroid peroxidase couples MIT/ DIT ( monoiodotyrosine/ diiodotyrosine) to T3/T4
  5. Proteolysis and secretion
    Then thyroglobulin with T4/T3 molecules is endocytosed back into the follicular cells, here the thyroglobulin is cleaved and T3/T4 are released into the plasma
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13
Q

Which ions inhihit the NIS

A

Perchlorate
Pertechnetate

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14
Q

TPO functions

A
  1. Oxidation of iodide to iodine
  2. Organification of iodine to tyrosine residues on thyroglobulin
  3. Coupling of MIT/DIT to form T3/T4
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15
Q

In autoimmune thyroid diseases which antibodies are common?

A

TPO antibodies

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16
Q

Which thyroid hormone is produced in abundance? By what percentage?

A

T4- thyroxine, 90% of thyroid hormone is T4

17
Q

T3 is more potent than T4; true/false?

A

True

18
Q

The enzyme that converts T4 to T3 in peripheral tissues is called?

A

5’-deiodinase

19
Q

Medication used in hyperthyroidism and mechanism

A
  1. Propylthiouracil ( PTU) ; inhibits TPO and 5’- deiodinase enzymes
  2. Methimazole; inhibits TPU
  3. Propranolol; weak inhibitor of 5’-deiodinase
20
Q

Propylthiouracil ( PTU) and Methimazole belong to a group of drugs called

A

Thionamides

21
Q

The perfect drug in thyrotoxicosis

A

Propranolol

22
Q

Wolff- Chaikoff effect

A

It is the body’s regulatory mechanism to prevent us from hyperthyroidism in case of too much exposure to iodine by switching off TPO enzyme

23
Q

How does Amiodarone affect the body in relation to thyroid hormones

A

Amiodarone may cause hypothyroidism, through wolff chaikoff effect because it contains Iodine
Also competes with T4 for 5’-deiodinase therefore decreasing T3 levels
This may trigger increase in TSH levels

24
Q

Thyroid hormones are bound to which proteins in the plasma?

A
  1. Thyroxine Binding Globulin ( TBG)
  2. Transthyretin
  3. Albumin
25
Q

What are the effects of Estrogen on thyroid hormones?

A

Estrogen increases the levels of TBG, therefore TBG binds more T4, therefore less free T4 in the plasma, the body detects this and stimulated increase in TSH, TSH then stimulates the thyroid to release more T4 which will return plasma T4 to normal levels and TSH will go back to normal but Total T4 will increase.

26
Q

What is liver failure effect on Thyroid hormones

A

Tbg is produced in liver so incase of liver failure tbg decreases this will decrease amount of T4 bound therefore increasing free T4 in the plasma. This results in decreased TSH which will decrease production of T4 causing decrease in total T4

27
Q

Effects of liver failure on Thyroid hormones

A

Opposite of esteogen

28
Q

Effects of liver failure on Thyroid hormones

A

Opposite of esteogen

29
Q

Thyroid hormones exert it’s effect through __ receptors

A

Nuclear

30
Q

Mention the 7 functions of thyroid hormone

A
  1. Brain maturation; related to cretinism in hypothyroidism
  2. Increased Basal metabolic rate; through Na/K ATPases increasing RR, Oxy consumption and high temp; related to weight loss in hyperthyroidism
  3. Increasing Beta receptors; increased CO,HR,SV & contractility; related to Tachycardia in hyperthyroidism
  4. Elevated Blood sugar ; related to hyperglycemia in hyperthyroidism
  5. Increase Breakdown of lipids ; related to increased cholesterol in hypothyroidism
  6. Bone growth ; related to cretinism
  7. Surfactant synthesis in Babies
31
Q

Regulation of thyroid hormones

A

+TRH- + TSH-+ follicular cells - T3/T4

In case of increased T3/T4 there will be negative feedback on birth TRH and TSH

6.Endocrine System (2 decks)

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