Lecture 6-HLSC3P09 Thyroid Hormones

Thyroid Gland

An endocrine gland located over the trachea, composed of two large lateral lobes and responsible for producing thyroid hormones.

What are the large lateral lobes in the trachea connected by?

Isthmus

Thyroid Follicles

Spherical structures in the thyroid gland, consisting of follicular epithelial cells surrounding a lumen filled with colloid and thyroglobulin.

Thyroglobulin

A large glycoprotein produced in the thyroid gland that serves as a storage form of thyroid hormones.

T4

Thyroxine, a major hormone secreted by the thyroid gland that plays a key role in regulating metabolism; 90% of thyroid hormone secreted.

T3

Triiodothyronine, a more potent thyroid hormone secreted in small amounts, responsible for many metabolic processes.

rT3

Reverse Triiodothyronine- 1 % of the hormones secreted by the thyroid gland, it is an inactive form of T3 that can inhibit the effects of T3 on metabolism.

Which is the most abundant thyroid hormone?

T4

Iodine

An essential element required for the synthesis of thyroid hormones

True or False: Table Salt is iodized to prevent iodine deficiency

True

Iodide Pump

A transporter that actively transports iodide into follicular cells of the thyroid gland against its concentration gradient.

True or False: In the Iodine pump, Iodine is 30 times higher in the lumen compared to ECF

True

What is Thyroglobulin made of? What does the formation entail?

A large glycoprotein containing 140 tyrosine aa thyroid hormone are formed within TG

What is the process of the oxidation of Iodide?

1. Iodide enters the follicular cell

2. Iodide oxidized by thyroid peroxidase (TPO)

3. TPO enzyme on the apical (lumen) surface oxidized (active) iodide is formed

What is Iodide oxidized by?

Thyroid peroxidase (TPO)

What is the process of the organification of iodide?

1. The binding of iodine with the thyroglobulin active iodide added to tyrosine residues of TG iodination is catalyzed by specific enzyme (iodinase)

2. Tyrosine first iodized to

   1. Monoiodotyrosine (MIT)

   2. Diiodotyrosine (DIT)

What is MIT?

Monoiodotyrosine

What is DIT

Diiodotyrosine

Two DIT (Diiodotyrosine) are coupled to form….?

T4

One DIT and one MIT are coupled to form….?

T3

Where is thyroid hormone stored?

As part of TG in the lumen of the follicle (colloid)

True or False: The total amount stored is sufficient to supply the body with the required thyroid hormone for 2 to 3 months

True

What is the process that removes iodine from thyroxine (T4) to convert it into triiodothyronine (T3)

Deiodination

TSH (Thyroid-Stimulating Hormone) is produced by what?

Anterior pituitary

What Digests TG and releases T4 and T3?

Proteinases

What 3 things transport thyroid hormone

Thyroid-binding globulin, Thyroxine Binding Prealbumin, and albumin.

What is TBG?

Thyroxine Binding Globulin

What is TSH controlled by?

Hypothalamus

What does TRH (Thyrotropin-Releasing Hormone) do?

Stimulates the release of TSH from the anterior pituitary.

What are the 3 domains on the receptor?

Transactivation domain, DNA-binding domain, Ligand- binding domain

What is TSH (Thyroid Stimulating Hormone) produced by?

Anterior Pituitary

What 3 factors effect TSH secretion Regulation

Electrical Stimulation (Increase secretion of TSH) , Cold Temperatures (Increase secretion of TSH), Emotional Reactions can affect is (increase or decrease), Increased thyroid hormone in the body (decreases the secretion of TSH)

How to thyroid hormones act?

Act by binding to thyroid hormone receptors (nuclear receptors)

What are the three thyroid hormone receptors?

Transactivation domain, DNA-binding domain, Ligand binding domain

What sequences of promoter DNA do DNA-binding domain binds to?

Hormone response elements

Hyperthyroidism

Excessive thyroid hormone production

Hypothyroidism

Insufficient thyroid hormone production

What are the three effects of the thyroid hormone?

Calorogenic, Sympathomimetic, Cardiovascular

What is Calorogenic?

Increased heat production

What is Sympathomimetic?

Fight or Flight

What are the 3 types of thyroid?

Hypothyroid, Euthyroid, Hyperthyroid

What is Exophthalmos?

Protrusion of the eyeball

Grave's Disease

An autoimmune disorder that leads to overproduction of thyroid hormones, often associated with symptoms of hyperthyroidism.

What is Cretinism?

A condition resulting from extreme hypothyroidism during infancy and childhood, characterized by severe growth and developmental retardation.

Thyroidectomy

A surgical procedure to remove part or all of the thyroid gland, often performed to treat thyroid cancer or hyperthyroidism.

What is Goiter?

An enlargement of the thyroid gland

Thyroid Nodules

Lumps in the thyroid gland, which can be benign or malignant; often detected via ultrasound.

Calcitonin

A hormone produced by the parafollicular cells of the thyroid that helps regulate calcium levels in the blood.

Thyroid Scan

A nuclear medicine test that evaluates the structure and function of the thyroid gland using radioactive iodine.

Radioactive Iodine Therapy

A treatment for hyperthyroidism or thyroid cancer that uses radioactive iodine to destroy overactive thyroid cells.

Myxedema Coma

A life-threatening condition resulting from severe hypothyroidism, characterized by unconsciousness, hypothermia, and respiratory failure.