Page 149 - Atlas of Histology with Functional Correlations

The endocrine system can be separated into the following three parts.

Endocrine Cells

Endocrine glands can be also considered as individual cells (unicellular glands)
that are scattered throughout different organs including the digestive organs

(enteroendocrine cells), respiratory tract, pancreatic ducts, and others.
Collectively, these scattered individual endocrine cells constitute the diffuse
neuroendocrine system (DNES). These cells are considered neuroendocrine
because they produce and release hormones similar to those of neurosecretory
cells in the central nervous system (CNS).

Endocrine Tissues

In certain organs, such as the pancreas and the reproductive organs of both sexes,
endocrine cells are seen as clusters mixed together with exocrine glands. The

endocrine tissues are surrounded by capillary networks, whereas the cells of
exocrine glands are attached to excretory ducts.

Major Endocrine Organs

The major endocrine organs in the organism are the separate pituitary gland,
thyroid glands, parathyroid glands, and adrenal glands. The primary
functions of these organs are to synthesize, store, and release the specific

hormones into the systemic circulation as needed.

Supplemental micrographic images are available at
www.thePoint.com/Eroschenko13e under Cell and Cytoplasm.

FIGURE 4.13 | Unbranched Simple Tubular

Exocrine Glands: Intestinal Glands

Unbranched simple tubular glands without excretory ducts are best represented

by the intestinal glands (crypts of Lieberkühn) in the large intestine (A and
B) and rectum. The surface epithelium and the secretory cells of these glands
are lined with numerous goblet cells; these are unicellular exocrine glands.
Similar but shorter intestinal glands with goblet cells are also found in the small

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