Skip to Main Content

We have a new app!

Take the Access library with you wherever you go—easy access to books, videos, images, podcasts, personalized features, and more.

Download the Access App here: iOS and Android

20: Thyroid Disease

Douglas C. Bauer, MD, &; Stephen J. McPhee, MD

Introduction

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.

Normal Structure & Function

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

The human thyroid. (Redrawn, with permission, from Barrett KE et al, eds. Ganong’s Review of Medical Physiology, 24th ed. McGraw-Hill, 2012.)

image
View Full Size||Download Slide (.ppt)

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

Normal and abnormal thyroid histology. (Redrawn, with permission, from Barrett KE et al, eds. Ganong’s Review of Medical Physiology, 24th ed. McGraw-Hill, 2012; Chandrasoma P et al, eds. Concise Pathology, 3rd ed. Originally published by Appleton & Lange. Copyright © by The McGraw-Hill Companies, Inc.; Gardner DG et al, eds. Greenspan’s Basic and Clinical Endocrinology, 9th ed. McGraw-Hill, 2011.)

image
View Full Size||Download Slide (.ppt)

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 ...

Pop-up div Successfully Displayed

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

This site uses cookies to provide, maintain and improve your experience. MH Privacy Center Close