GROWTH INDUCED BY DAMAGE
5
appears later in development than that for cell proliferation. But once
there, damage activates them both by the same stimulus mechanism
(Abercrombie, 1964).
2. The Response
of the Hair
Follicles
The response of the hair follicles to damage has not been reviewed as
thoroughly as the response of the epidermis and connective tissues of the
skin. Therefore we shall discuss it in some detail. To help make our
discussion more intelligible a short introduction to hair growth cycles is
presented.
Hair follicles in mammals undergo cycles of growth and rest (Argyris,
1963; Chase, 1954; Montagna, 1962). The structure of the hair follicles
differs at various stages of the hair growth cycle, therefore a complete
understanding of the nature of the response of hair follicles to damage
requires that we know precisely the stage of the hair growth cycle that
the hair follicles are in at the time of injury. It is possible to know the
precise stage of the hair growth cycle in those mammals in which hair
follicles go through the hair growth cycles synchronously or in which the
stage of the hair growth cycle can be controlled by plucking. This can be
done for example, in the mouse, rat, or hamster (Chase, 1954). However,
in mammals in which the hair follicles undergo cycles of growth and rest
independently of each other, such as in man and guinea pig (Chase,
1954), it is extremely difficult, if not impossible to know the precise stage
of the hair growth cycle for each hair follicle at any one moment. Therefore, from the experimentalist viewpoint it is probably best to study
wound healing in mammals in which the hair growth cycle can be
controlled (Argyris, 1963). Our discussion will concern principally the
effect of wounds on the hair follicles in the skin of mice, since only in
mice has the response of hair follicles to damage been studied in any
detail under conditions in which the hair growth cycles have been
controlled.
a. The Response of Hair Follicles Immediately
Adjacent to the Wound.
Hair follicles within 1 mm of the wound lose their sebaceous glands (Fig.
cord of cells. Arrow points to a few sebaceous cells, all that is left of the sebaceous
gland. Note that from the sebaceous cells to the epidermis, all the hair follicle cells
are enlarged and basophilic. Below the level of the sebaceous cells, not all the hair
follicle cells have undergone this transformation. Bottom right (8) is the adjacent
section of the growing hair follicle showing that the cells of the internal root sheath
which are involved in keratinization are not transformed into enlarged basophilic
cells. Also note that the dermal papilla is unaffected (from Argyris and Bell, 1959).
5
appears later in development than that for cell proliferation. But once
there, damage activates them both by the same stimulus mechanism
(Abercrombie, 1964).
2. The Response
of the Hair
Follicles
The response of the hair follicles to damage has not been reviewed as
thoroughly as the response of the epidermis and connective tissues of the
skin. Therefore we shall discuss it in some detail. To help make our
discussion more intelligible a short introduction to hair growth cycles is
presented.
Hair follicles in mammals undergo cycles of growth and rest (Argyris,
1963; Chase, 1954; Montagna, 1962). The structure of the hair follicles
differs at various stages of the hair growth cycle, therefore a complete
understanding of the nature of the response of hair follicles to damage
requires that we know precisely the stage of the hair growth cycle that
the hair follicles are in at the time of injury. It is possible to know the
precise stage of the hair growth cycle in those mammals in which hair
follicles go through the hair growth cycles synchronously or in which the
stage of the hair growth cycle can be controlled by plucking. This can be
done for example, in the mouse, rat, or hamster (Chase, 1954). However,
in mammals in which the hair follicles undergo cycles of growth and rest
independently of each other, such as in man and guinea pig (Chase,
1954), it is extremely difficult, if not impossible to know the precise stage
of the hair growth cycle for each hair follicle at any one moment. Therefore, from the experimentalist viewpoint it is probably best to study
wound healing in mammals in which the hair growth cycle can be
controlled (Argyris, 1963). Our discussion will concern principally the
effect of wounds on the hair follicles in the skin of mice, since only in
mice has the response of hair follicles to damage been studied in any
detail under conditions in which the hair growth cycles have been
controlled.
a. The Response of Hair Follicles Immediately
Adjacent to the Wound.
Hair follicles within 1 mm of the wound lose their sebaceous glands (Fig.
cord of cells. Arrow points to a few sebaceous cells, all that is left of the sebaceous
gland. Note that from the sebaceous cells to the epidermis, all the hair follicle cells
are enlarged and basophilic. Below the level of the sebaceous cells, not all the hair
follicle cells have undergone this transformation. Bottom right (8) is the adjacent
section of the growing hair follicle showing that the cells of the internal root sheath
which are involved in keratinization are not transformed into enlarged basophilic
cells. Also note that the dermal papilla is unaffected (from Argyris and Bell, 1959).