Skip to Main Content

++

The thyroid gland synthesizes the hormones thyroxine (T4) and triiodothyronine (T3), iodine-containing amino acids that regulate the body’s metabolic rate. Adequate levels of thyroid hormone are necessary in infants for normal development of the CNS, in children for normal skeletal growth and maturation, and in adults for normal function of multiple organ systems. Thyroid dysfunction is one of the most common endocrine disorders encountered in clinical practice. Although abnormally high or low levels of thyroid hormones may be tolerated for long periods of time, usually there are symptoms and signs of overt thyroid dysfunction.

++

Anatomy

++

The normal thyroid gland is a firm, reddish brown, smooth gland consisting of two lateral lobes and a connecting central isthmus (Figure 20–1). A pyramidal lobe of variable size may extend upward from the isthmus. The normal weight of the thyroid ranges from 30–40 g. It is surrounded by an adherent fibrous capsule from which multiple fibrous projections extend deeply into its structure, dividing it into many small lobules. The thyroid is highly vascular and has one of the highest rates of blood flow per gram of tissue of any organ.

++
Figure 20–1
Graphic Jump Location

The human thyroid.

(Redrawn, with permission, from Ganong WF. Review of Medical Physiology, 22nd ed. McGraw-Hill, 2005.)

++

Histology

++

Histologically, the thyroid gland consists of many closely packed acini, called follicles, each surrounded by capillaries and stroma. Each follicle is roughly spherical, lined by a single layer of cuboidal epithelial cells and filled with colloid, a proteinaceous material composed mainly of thyroglobulin and stored thyroid hormones. When the gland is inactive, the follicles are large, the lining cells are flat, and the colloid is abundant. When the gland is active, the follicles are small, the lining cells are cuboidal or columnar, the colloid is scanty, and its edges are scalloped, forming reabsorption lacunae (Figure 20–2). Scattered between follicles are the parafollicular cells (C cells), which secrete calcitonin, a hormone that inhibits bone resorption and lowers the plasma calcium level (see Chapter 17).

++
Figure 20–2
Graphic Jump Location

Normal and abnormal thyroid histology.

(Redrawn, with permission, from Ganong WF. Review of Medical Physiology, 22nd ed. McGraw-Hill, 2005; Chandrasoma P, Taylor CE. Concise Pathology, 3rd ed. Originally published by Appleton & Lange. Copyright © by the McGraw-Hill Companies, Inc.; Greenspan FS, Gardner DG [editors]: Basic and Clinical Endocrinology, 7th ed. McGraw-Hill, 2004.)

++

The ultrastructure of a follicular epithelial cell is diagrammed in Figure 20–3. The cells vary in appearance with the degree of gland activity. The follicular cell rests on a basal lamina. The nucleus is round and centrally located. The cytoplasm contains mitochondria, rough endoplasmic reticulum, and ribosomes. The apex ...

Want remote access to your institution's subscription?

Sign in to your MyAccess profile while you are actively authenticated on this site via your institution (you will be able to verify this by looking at the top right corner of the screen - if you see your institution's name, you are authenticated). Once logged in to your MyAccess profile, you will be able to access your institution's subscription for 90 days from any location. You must be logged in while authenticated at least once every 90 days to maintain this remote access.

Ok

About MyAccess

If your institution subscribes to this resource, and you don't have a MyAccess profile, please contact your library's reference desk for information on how to gain access to this resource from off-campus.

Subscription Options

AccessPharmacy Full Site: One-Year Subscription

Connect to the full suite of AccessPharmacy content and resources including 30+ textbooks such as Pharmacotherapy: A Pathophysiologic Approach and Goodman & Gilman's The Pharmacological Basis of Therapeutics, high-quality videos, images, and animations, interactive board review, drug and herb/supplements databases, and more.

$595 USD
Buy Now

Pay Per View: Timed Access to all of AccessPharmacy

24 Hour Subscription $34.95

Buy Now

48 Hour Subscription $54.95

Buy Now

Pop-up div Successfully Displayed

This div only appears when the trigger link is hovered over. Otherwise it is hidden from view.