Summary
Summary H77 - SV Guyton and Hall
- Course
- Institution
- Book
Samenvatting van H77 uit Guyton and Hall's Textbook of Medical Physiology.
[Show more]
Connected book
Book Title:
Author(s):
- Edition:
- ISBN:
- Edition:
More summaries for
-
Test Bank for Guyton and Hall Textbook of Medical Physiology (Guyton Physiology) 13th Edition by John E. Hall Chapter 1-85
-
Test Bank in Conjunction with Guyton and Hall Textbook of Medical Physiology,Hall,13e
-
Summary of reabsorption in renal tubules
Seller
Follow
CarmenHorenberg
Reviews received
Content preview
Guyton and HallCHAPTER 77 – Thyroid Metabolic Hormones
The thyroid secretes 2 major hormones:
Thyroxine (T4) 93%
Triiodothyronine (T3) 7%
The thyroid gland also secretes calcitonin, a hormone involved in calcium metabolism.
Thyroid secretion is controlled primarily by thyroid-stimulating hormone (TSH) secreted by
the anterior pituitary gland.
All the thyroxine is eventually converted to triiodothyronine in the tissues, so both are
functionally important. Triiodothyronine is about 4x more potent as thyroxine, but it is
present in the blood in much smaller quantities and has a shorter lifespan.
The thyroid gland is composed of follicles that are filled with colloid and lined with cuboidal
epithelial cells that secrete into the interior of the follicles. The major constituent of colloid
is the large glycoprotein thyroglobulin, which contains the thyroid hormones. The gland also
contains C cells that secrete calcitonin, a hormone that contributes to regulation of plasma
calcium ion concentration.
Iodine is required for the formation of thyroxine. The first step in this formation is the
transport of iodides from the blood into the thyroid glandular cells and follicles. This
pumping of the iodide to the interior of the cell is achieved by the action of a sodium-iodide
symporter (NIS). This process of concentrating the iodide in the cell is called iodide trapping.
The rate of iodide trapping is influenced by several factors, the most important being the
concentration of TSH; TSH stimulates the activity of the iodide pump. Iodide is transported
out of the thyroid cells across the apical membrane into the follicle by a chloride-iodide ion
counter-transporter called pendrin.
Thyroid hormones form within the thyroglobulin molecule. Thyroglobulin contains tyrosine
amino acids that combine with iodine to form the thyroid hormones. The thyroxine and
triiodothyronine hormones formed from the tyrosine amino acids remain part of the
thyroglobulin molecule during synthesis of the thyroid hormones and even afterward as
stored hormones in the follicular colloid.
Most of the thyroglobulin is not released into the circulating blood; instead, thyroxine and
triiodothyronine are cleaved from the thyroglobulin molecule, and then these free
hormones are released. 3 quarters of the iodinated tyrosine in the thyroglobulin never
become thyroid hormones but remain MIT and DIT. These are also freed from the
thyroglobulin molecules. However, they are not secreted into the blood, but their iodine is
cleaved from them to be used again for recycling.
The hormone finally delivered to and used by the tissues is mainly triiodothyronine.
The benefits of buying summaries with Stuvia:
Guaranteed quality through customer reviews
Stuvia customers have reviewed more than 700,000 summaries. This how you know that you are buying the best documents.
Quick and easy check-out
You can quickly pay through credit card or Stuvia-credit for the summaries. There is no membership needed.
Focus on what matters
Your fellow students write the study notes themselves, which is why the documents are always reliable and up-to-date. This ensures you quickly get to the core!
Frequently asked questions
What do I get when I buy this document?
You get a PDF, available immediately after your purchase. The purchased document is accessible anytime, anywhere and indefinitely through your profile.
Satisfaction guarantee: how does it work?
Our satisfaction guarantee ensures that you always find a study document that suits you well. You fill out a form, and our customer service team takes care of the rest.
Who am I buying these notes from?
Stuvia is a marketplace, so you are not buying this document from us, but from seller CarmenHorenberg. Stuvia facilitates payment to the seller.
Will I be stuck with a subscription?
No, you only buy these notes for $3.35. You're not tied to anything after your purchase.
Can Stuvia be trusted?
4.6 stars on Google & Trustpilot (+1000 reviews)
85443 documents were sold in the last 30 days
Founded in 2010, the go-to place to buy study notes for 14 years now