Biomedical Engineering Reference
In-Depth Information
2.2.4
The Stroma of Several Organs Is Nonregenerative
In organs other than skin or peripheral nerves a clear distinction between regenera-
tive and nonregenerative tissues can be made only tentatively due to the paucity of
data from well-defined models of defect healing. In the large majority of studies
reviewed in Chap. 1, the experimental injury inflicted was not designed to differen-
tiate between regenerative and non-regenerative tissues in an organ. A few studies
have, however, been conducted in a manner that provides useful preliminary infor-
mation on this important property of tissues.
Among the organs that have been studied with emphasis on the regenerative
activity of individual tissues are blood vessels and certain internal organs. In the
preceding chapter reference was made to the observation that traumatic removal
of the endothelial lining of blood vessels (intima) led to spontaneous reendotheli-
alization provided that the injury did not extend through the basement membrane
deeply into the adjacent layer (media); if the injury was deep, the blood vessel wall
suffered irreversible fibrotic changes (Stemerman and Ross 1972; Schwartz et al.
1975; Stemerman et al. 1977). Similarly, it was observed that the gastric epithelium
responded to superficial injury (erosion) by reepithelialization; however, a deeper
injury that extended to the submucosa and muscularis propria led to formation of
ulcers (Graham et al. 1992). Likewise, injury of the epithelia in the urinary bladder
and the gall bladder was followed by reepithelialization but injury to the underlying
stroma was not regenerated (Goss 1964).
Extensive data on the healing response of several organs have been reviewed
(Vracko 1974). The data were derived from studies on skeletal muscle fibers (All-
brook 1962; Vracko and Benditt 1972), the lung (Vracko 1972), the kidney (Oliver
1953), and the pancreas (Tiscornia et al. 1965; Fitzgerald et al. 1968; Lehv and
Fitzgerald 1968). In some of these studies, the injuries inflicted were relatively
slight and caused the epithelia in each of these organs to die without disrupting the
basement membrane; these methods included freezing, ischemia, and use of phar-
macological agents that caused cell necrosis. In other studies, however, the injury
protocols were quite more severe, occasionally involving severe crushing, cauter-
ization with heat or treatment with strong acids, or large-scale surgical excision of
organ tissues. These severe injuries usually ruptured the basement membrane in the
various organs.
Provided that the injury was slight and limited to the epithelia of these internal
organs, the response invariably was regeneration of the epithelia. Deeper injuries,
that is., those in which the basement membrane was penetrated, resulted in irre-
versible damage, consisting of scar formation and loss of function. The conclusion
that emerged was that an injury that is limited to epithelia leads to healing with
spontaneous regeneration whereas extension of the injury through the basement
membrane leads to irreversible healing (repair; Vracko 1974).
In this useful review, the emphasis throughout was on the effect of the injury on
the approximately 100-nm thin basement membrane; the integrity of the underlying
stroma following injury was typically not explicitly discussed (Vracko 1974). Con-
sidering that the basement membrane is closely attached to the underlying stroma,
