152
UNIT ONE
PRACTICE
8
Distinguish between exocrine and endocrine glands.
9
Explain how exocrine glands are classif
ed.
10
Distinguish between a serous cell and a mucous cell.
5.3
CONNECTIVE TISSUES
General Characteristics
Connective
(ko
˘-nek
tiv)
tissues
comprise much of the body
and are the most abundant type of tissue by weight. They
Most exocrine secretory cells are merocrine, and they
can be further subclassiF
ed based on their secretion of serous
fl uid or mucus.
Serous fl
uid
is typically watery and has a high
concentration of enzymes. Serous cells secreting this fl uid,
which lubricates, are commonly associated with the visceral
and parietal membranes of the thoracic and abdominopelvic
cavities. The thicker fl uid,
mucus,
is rich in the glycoprotein
mucin.
Cells in the inner linings of the digestive, respiratory,
and reproductive systems secrete abundant mucus, which is
protective. Mucous cells and goblet cells secrete mucus, but in
different parts of the body.
Table 5.5
summarizes the charac-
teristics of the different types of epithelial tissues.
TABLE
5.3
|
Types of Exocrine Glands
Type
Characteristics
Example
Unicellular glands
A single secretory cell
Mucous-secreting goblet cell (see f
g. 5.4)
Multicellular glands
Glands that consist oF many cells
Simple glands
Glands that communicate with the surFace by means oF ducts
that do not branch beFore reaching the secretory portion
1.
Simple tubular gland
Straight tubelike gland that opens directly onto surFace
Intestinal glands oF small intestine (see f
g. 17.3)
2.
Simple coiled tubular gland
Long, coiled, tubelike gland; long duct
Eccrine (sweat) glands oF skin (see f
g. 6.11)
3.
Simple branched tubular gland
Branched, tubelike gland; duct short or absent
Gastric glands (see f
g. 17.19)
4.
Simple branched alveolar
gland
Secretory portions oF gland expand into saclike compartments
along duct
Sebaceous gland oF skin (see f
g. 5.13)
Compound glands
Glands that communicate with surFace by means oF ducts that
branch repeatedly beFore reaching the secretory portion
1.
Compound tubular gland
Secretory portions are coiled tubules, usually branched
Bulbourethral glands oF male (see f
g. 22.4)
2.
Compound alveolar gland
Secretory portions are irregularly branched tubules with
numerous saclike outgrowths
Mammary glands (see f
g. 23.30)
(a)
Merocrine gland
(b)
Apocrine gland
(c)
Holocrine gland
Secretion
Pinched off
portion of cell
(secretion)
Intact
cell
Disintegrating cell
and its contents
(secretion)
New cell
forming by
mitosis and
cytokinesis
FIGURE 5.12
Glandular secretions. (
a
) Merocrine glands release secretions without losing cytoplasm. (
b
) Apocrine glands lose small portions oF
their cell bodies during secretion. (
c
) Holocrine glands release entire cells f
lled with secretory products.
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