Chapter Summary

Endocrine glands are characterized by the absence of ducts and the presence of a rich vascular network. The parenchymal cells of endocrine glands are usually arranged in short cords, follicles, or clusters, although other arrangements are also common.

II. THYROID GLAND

A. Capsule

The capsule of the thyroid gland consists of a thin collagenous connective tissue from which septa extend into the substance of the gland, subdividing it into lobules.

I. PITUITARY GLAND

The pituitary gland is invested by a connective tissue capsule. The gland is subdivided into four component parts.

A. Pars Anterior

1. Cell Types

a. Chromophils

1. Acidophils

Stain pink with hematoxylin and eosin. They are found mostly in the center of the pars anterior.

2. Basophils

Stain darker than acidophils with hematoxylin and eosin. They are more frequently found at the periphery of the pars anterior.

b. Chromophobes

Chromophobes are smaller cells whose cytoplasm is not granular and has very little affinity for stain. They may be recognized as clusters of nuclei throughout the pars anterior.

B. Pars Intermedia

The pars intermedia is rudimentary in man. Small basophils are present as well as colloid-filled follicles.

C. Pars Nervosa and Infundibular Stalk

These have the appearance of nervous tissue. The cells of the pars nervosa are pituicytes, resembling neuroglial cells. They probably support the unmyelinated nerve fibers, whose terminal portions are expanded, since they store neurosecretions within the pars nervosa. These expanded terminal regions are known as Herring bodies.

D. Pars Tuberalis

The pars tuberalis is composed of cuboidal cells arranged in cords. They may form small colloid-filled follicles.

B. Parenchymal Cells

The parenchymal cells of the thyroid gland form colloidfilled follicles composed of

1.Follicular Cells (simple cuboidal epithelium)

2.Parafollicular Cells (clear cells) located at the periphery of the follicles

C. Connective Tissue

Slender connective tissue elements support a rich vascular supply.

III. PARATHYROID GLAND

A. Capsule

The gland is invested by a slender collagenous connective tissue capsule from which septa arise to penetrate the substance of the gland.

B. Parenchymal Cells

1. Chief Cells

Chief cells are numerous, small cells with large nuclei that form cords.

2. Oxyphils

Oxyphils are larger, acidophilic, and much fewer in number than chief cells.

C. Connective Tissue

Collagenous connective tissue septa as well as slender reticular fibers support a rich vascular supply. Fatty infiltration is common in older individuals.

IV. SUPRARENAL GLAND

The suprarenal gland is invested by a collagenous connective tissue capsule. The gland is subdivided into a cortex and a medulla.

A. Cortex

The cortex is divided into three concentric zones: zona glomerulosa, zona fasciculata, and zona reticularis.

1. Zona Glomerulosa

The zona glomerulosa is immediately deep to the capsule. It consists of columnar cells arranged in arches and spherical clusters.

2. Zona Fasciculata

The thickest zone of the cortex is the zona fasciculata.The more or less cuboidal cells (spongiocytes) are arranged in long, parallel cords. Spongiocytes appear highly vacuolated except for those of the deepest region, which are smaller and much less vacuolated.

3. Zona Reticularis

The innermost zone of the cortex is the zona reticularis. It is composed of small, dark cells arranged in irregularly anastomosing cords. The intervening capillaries are enlarged.

B. Medulla

The medulla is small in humans and is composed of large, granule-containing chromaffin cells arranged in short

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cords. Additionally, large autonomic ganglion cells are also present. A characteristic of the medulla is the presence of large veins.

V. PINEAL BODY

A. Capsule

The capsule, derived from pia mater, is thin collagenous connective tissue. Septa derived from the capsule divide the pineal body into incomplete lobules.

B. Parenchymal Cells

1. Pinealocytes

Pinealocytes are recognized by the large size of their nuclei.

2. Neuroglial Cells

Neuroglial cells possess smaller, denser nuclei than the pinealocytes.

C. Brain Sand

Characteristic of the pineal body are the calcified accretions in the extracellular spaces, known as brain sand or corpora arenacea.

CHAPTER OUTLINE

Graphics

Graphic 11-1 Skin and Its Derivatives p. 262

Graphic 11-2 Hair, Sweat Glands, and Sebaceous

Glands p. 263

Tables

Table 11-1 Characteristics of Thick and Thin Skin Table 11-2 Nonepithelial Cells of the Epidermis

Plates