Thyroid Physiology 1

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

Which of the following best describes the primary function of the thyroid gland in vertebrates?

Regulation of metabolic rate (correct)

Regulation of calcium homeostasis

Regulation of reproductive hormones

Regulation of blood glucose levels

Where are the parathyroid glands typically located in relation to the thyroid gland?

Cranial to both thyroid lobes

Within the thyroid tissue itself (correct)

Caudal to both thyroid lobes

Dorsal to the left thyroid lobe, ventral to the right thyroid lobe

What is the role of thyroglobulin (TG) in thyroid hormone synthesis?

To provide tyrosine for thyroid hormone synthesis (correct)

To transport iodide into the follicular cells

To convert T4 into T3

To stimulate TSH production

Which of the following is the primary messenger system utilized by TSH on thyroid follicular cells?

Cyclic adenosine monophosphate (cAMP) (C) Signup and view all the answers

What is the role of the enzyme thyroid peroxidase during synthesis of thyroid hormone?

Iodinates tyrosine residues within thyroglobulin (C) Signup and view all the answers

Which of the following best describes the location of the thyroid gland?

In the upper neck, on either side of the trachea (D) Signup and view all the answers

What is the primary component of colloid within the thyroid follicle?

Thyroglobulin (B) Signup and view all the answers

How does cold ambient temperature affect the secretion of TRH?

Increases the secretion of TRH (C) Signup and view all the answers

What are the immediate precursors to T3 and T4 inside the colloid?

Monoiodotyrosine (MIT) and Diiodotyrosine (DIT) (B) Signup and view all the answers

Which of the following is the major secretory product of the thyroid gland?

Thyroxine (T4) (D) Signup and view all the answers

Which of the following is the primary function of the sodium-iodide symporter (NIS)?

To facilitate the transport of iodide into the follicular cell. (A) Signup and view all the answers

What is the role of thyroid peroxidase (TPO) in thyroid hormone synthesis?

To convert iodide to iodine, and add it to thyroglobulin. (C) Signup and view all the answers

Which of the following best describes the location where thyroglobulin (TG) is synthesized and stored?

Synthesized in the follicular cells and stored in the colloid. (A) Signup and view all the answers

What are the products of the coupling reaction catalyzed by Thyroid Peroxidase (TPO)?

Triiodothyronine (T3) and thyroxine (T4). (D) Signup and view all the answers

Methimazole is a medication for treating hyperthyroidism. What is its primary mechanism of action?

It blocks the action of TPO. (D) Signup and view all the answers

Which step of thyroid hormone synthesis directly involves the protein pendrin?

Oxidation of iodide and transport into the colloid. (A) Signup and view all the answers

What is the immediate precursor to T3?

One molecule of MIT and one of DIT. (A) Signup and view all the answers

What ion is transported into the cell by NIS along with iodide?

Na+ (D) Signup and view all the answers

In which location does the iodination of tyrosine on thyroglobulin occur?

In the colloid. (C) Signup and view all the answers

What is the role of H2O2 in thyroid hormone synthesis?

It serves as a cofactor for the enzyme TPO. (D) Signup and view all the answers

Study Notes

Thyroid Physiology Overview

All vertebrates possess a thyroid gland, a crucial endocrine gland regulating metabolism and affecting various body systems
Thyroid gland disorders are commonly managed by general practitioners

Thyroid Gland Anatomy

Two lobes (left and right) positioned in the upper neck, on either side of the trachea
Parathyroid glands are embedded within the thyroid tissue

Anatomy Detail

External parathyroid glands are located craniodorsolateral to the thyroid
Internal parathyroid glands are located near the caudal pole of the thyroid, embedded within the gland

Learning Objectives

Describe the thyroid follicle's composition
Explain the thyroid axis and negative feedback loop
List the four steps of hormone synthesis
Explain the roles of iodine/iodide, NIS, thyroglobulin, thyroid peroxidase, MIT, DIT, TSH, and colloid in T4/T3 synthesis

Thyroid Axis

Hypothalamus releases thyrotropin-releasing hormone (TRH)
TRH stimulates the anterior pituitary gland
Anterior pituitary releases thyroid-stimulating hormone (TSH)
Thyroid gland produces thyroid hormones (T3 and T4)
Increased thyroid hormones lead to higher metabolic rates in cells

Negative Feedback Loop

Increased T3 and T4 levels inhibit TRH and TSH release
This maintains a stable level of thyroid hormones

Thyroid Hormone Synthesis

Two major components in the process: Tyrosine, and Iodide
Tyrosine is a component of thyroglobulin, stored in the colloid
Iodide is derived from dietary iodide

Thyroid Hormone Synthesis Steps

Step 1: Iodide trapping -Iodine from the diet is converted to iodide.
-Iodide travels though bloodstream to the thyroid gland, and is taken up by the Na-Iodine Symporter (NIS)
Step 2: Oxidation -lodine is oxidized then transported into the colloid.
Step 3: Organification -TPO adds iodine to tyrosines within the thyroglobulin and forms MIT and DIT
Step 4: Coupling
- MIT and DIT couple together to form T3 and T4

Thyroid Follicle

Follicular cells: a single layer of cuboidal epithelium
Colloid: stores thyroglobulin (TG)
Parafollicular cells (C cells): are also present

Thyroid Hormone Release

TSH stimulates the release of T3 and T4 from thyroglobulin
T3 and T4 enter the bloodstream

Thyroid Peroxidase (TPO)

Catalyzes essential reactions in thyroid hormone synthesis e.g. oxidation of iodide, coupling of MIT/DIT etc
A target of drug therapy (e.g., methimazole) for hyperthyroidism

Studying That Suits You

Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

Description

Explore the essential functions and anatomy of the thyroid gland in this comprehensive quiz. Understand its role in metabolism, hormone synthesis, and the negative feedback system. Test your knowledge on thyroid disorders and their management by practitioners.