The Structure and Function of Skin

440 Pages·1974·19.044 MB·English

by  William Montagna (Auth.)

DEDICATION
to
ALL OF OUR TEACHERS
THE STRUCTURE AND
FUNCTION OF SKIN
THIRD EDITION
William Montagna and Paul F. Parakkal
OREGON REGIONAL PRIMATE RESEARCH CENTER
BEAVERTON, OREGON
ACADEMIC PRESS New York and London 1974
A Subsidiary of Harcourt Brace Jovanovich, Publishers
COPYRIGHT © 1974, BY ACADEMIC PRESS, INC.
ALL RIGHTS RESERVED.
NO PART OF THIS PUBLICATION MAY BE REPRODUCED OR
TRANSMITTED IN ANY FORM OR BY ANY MEANS, ELECTRONIC
OR MECHANICAL, INCLUDING PHOTOCOPY, RECORDING, OR ANY
INFORMATION STORAGE AND RETRIEVAL SYSTEM, WITHOUT
PERMISSION IN WRITING FROM THE PUBLISHER.
ACADEMIC PRESS, INC.
Ill Fifth Avenue, New York, New York 10003
United Kingdom Edition published by
ACADEMIC PRESS, INC. (LONDON) LTD.
24/28 Oval Road, London NW1
Library of Congress Cataloging in Publication Data
Montagna, William.
The structure and function of skin.
Previous editions by W. Montagna.
Includes bibliographies.
1. Skin. I. Parakkal, Paul F., joint author.
II. Title. [DNLM: 1. Skin-Anatomy and physiology.
2. Skin-Physiology. WR101 M758s 1974]
QM481.M6 1974 611V77 73-0439
ISBN 0-12-505263-4
PRINTED IN THE UNITED STATES OF AMERICA
Preface
This book was written by two biologists, a teacher and his former
pupil, each of whom is unaccountably but deeply devoted to all matters
pertaining to skin. Written primarily for dermatologists, whether sea-
soned veterans or neophytes, it should be useful to all biologists who
are interested in biomedical disciplines. If it is incomplete, it is because
our knowledge of human skin is still limited and fragmented; if it
contains some errors, it is because most of the available facts, morpho-
logical or biochemical, are not yet fully or exactly known. Finally, if it
reflects our bias, it is because the subject of cutaneous biology has more
than its share of controversial areas on which, like most other authors,
we have taken a stand. We have not limited our treatment exclusively
to human skin, but it is our point of reference. We regard human skin
as a complex and complicated template that shares in unique fashion
the biological principles of other organ systems. Many well-known data
on human skin and much information from comparative cutaneous
biology were deliberately omitted lest this book grow to encyclopedic
proportions.
We must declare at once that there are many more authors than the
two listed on the case. In a very real sense, this book is the product
of a family effort. For example, Drs. Kenji Adachi, Michael Im, Dennis
Knutson, Robert Kellum, Alan Shalita, and, in particular, Mary Bell
have contributed enormously to the chapter on sebaceous glands. The
chapter on the dermis was written almost entirely by our former student
Dr. Jeffrey Pinto and that on eccrine sweat glands by our friend and
ix
Preface
χ
former colleague Dr. Richard Dobson. Dr. Robert Bradfield has written
the remarkably lucid and concise account of the effects of protein
deficiency on hair growth. Dr. Kenji Adachi and our former student
Dr. Michael Im have written most of what we have included on
metabolism, and Dr. Giuseppe Moretti has done yeoman work on the
chapter on hair. Our friend Dr. Vicente Pecoraro has contributed the
results obtained by his group using the trichogram technique.
But our indebtedness does not end here. All of the delineations were
executed by our master artist Joel Ito and much of the photography
by our own "Steichen" Harry Wohlsein. Nearly all of the superb elec-
tron photomicrographs were prepared by Dr. Mary Bell and some of
the scanning electron micrographs by our colleague Dr. Wolf H.
Fahrenbach. Many of the histological materials used reflect the incom-
parable technical skill of Nickolas Roman. Elizabeth Macpherson helped
us with the bibliography and some illustrations. Cathy Taylor was help-
ful with many of the illustrations. Margaret Shininger not only typed,
but organized, supervised, checked for accuracy, and devoted herself
unstintingly to every detail of the book. And finally, running throughout
is the unmistakable evidence of Margaret Barss's perceptive knowledge
of and love for the English language and her keen sense of logic and
clarity. To all of these selfless friends and colleagues and to other con-
tributors too numerous to name, we are forever grateful.
WILLIAM MONTAGNA
PAUL F. PARAKKAL*
* Present address: Division of Research Grants, National Institutes of Health,
Bethesda, Maryland.
Introduction
The first edition of this book, published in 1956, was a modest effort
that reflected mainly the limited results of the author's own morphologi-
cal studies of skin. Six years later a more ambitious second edition was
published. Now, after more than ten years, the third edition represents
both individual and team work, claiming two authors—a teacher and
his former student—and notable contributions from many former stu-
dents, colleagues, and friends. For example, the chapter on sebaceous
glands is a digest of the knowledge of nearly all modern authorities on
that subject. This collaboration is as it should be, for in the short span
of seventeen years studies in cutaneous biology have advanced at such
speed and in such volume that it is impossible for any one person to
keep pace with them.
The extension and deepening of our knowledge of skin is evident at
all levels, from the purely morphological to the biochemical. Aided by
the vast advances in technology, skin research has surged forward and
publications have mushroomed. However, such rapid progress has some-
times created new problems. As new instrumentation and techniques
became available, investigative dermatologists were able to look at old
details in many different ways; however, less able investigators began
to dabble into research that was quasi foreign to them and to inundate
the literature with floods of studies, many of them sadly uncritical. For
example, in the early days of the evolution of the electron microscope,
that redoubtable instrument was sometimes used with more exuberance
than skill. Fortunately, however, standards have risen, and with minor
xi
xii Introduction
exceptions the results obtained today in the electron microscopy of skin
compare well with those obtained in any other organ.
Our intention is far from deliberately discouraging the young explorer
from venturing into new territory, whether for the sheer love of learn-
ing or for more practical reasons. But the scientific adventurer should
proceed only if he is equipped, first with an idea and then with basic
knowledge, an absence of bias, keen senses, and a readiness to accept
facts. Those who have ignored these cardinal principles in studying
skin have spewed out an enormous amount of worthless conjecture, too
often dangerously disguised as fact.
In the hierarchy of the biological sciences, none are more exalted
than those which use numbers because somehow numerical results con-
vey the impression of being "exact." Theoretically, such exactitude is
the goal of every scientist, but sometimes these mathematical disciplines
are manipulated by scientists who are hopelessly inept in them. Never-
theless, such triflings in physiology, pharmacology, and biochemistry
have sometimes been published as fact. Numbers, to be magic, must
carry authority.
Another pitfall in skin research has been the danger of losing sight
of the whole in a sincere, if somewhat misguided, search for the parts.
With the advent of electron microscopy, the cutting of skin into as thin
sections as possible has become a fetish. This procedure certainly is
indispensable for achieving cytological details, but for studying the
general architecture and pathways of such structures as nerves, vessels,
and fibers, it is the worst possible one to follow. Indeed, for such pur-
poses the thinner the sections, the more worthless they are. Years ago
the most important lesson taught by the esteemed Professor Howard B.
Adelmann at Cornell University was his insistence that beginning stu-
dents in histology collect areolar connective tissue from a freshly killed
animal, tease it out on slides, just as Bichat had done in the eighteenth
century, study it and then, and only then, study the details by fixation
and staining. We would do well to follow his lead.
Yet another common disaster is the comparative approach and use
of animal models as substitutes for the human integument. Many derma-
tologists fail to appreciate the fact that the resemblance of human skin
to that of various breeds of hairless mice and dogs and sparsely haired
pigs is only superficial and does not constitute a real similarity. Still
implicit in the reports of many workers is the mistaken conviction that
human skin is largely glabrous, that is, without hair. No wonder it
Introduction xiii
comes as a shock to some to learn that man has more hair than the
gorilla! If we knew all there is to know about the skin of most extant
animals, we would be in the enviable position of knowing exactly which
species to select for specific experimental purposes pertinent to human
medicine. Unfortunately, most studies in comparative cutaneous biology
are poorly documented and we know next to nothing about the skin of
some animals. This is a serious problem since no skin, not even that of
the great apes, is quite like that of man.
In retrospect, when the first edition of this book was published,
scarcely any other book on skin could be found in the English language
except Rothman's pioneer work "The Physiology and Biochemistry of
Skin." In the interval between that first edition and this one, many sym-
posia and books dealing with one or another aspect of skin have been
published. But the danger remains that in pursuing minutiae and
grubbing away at the particular, the investigator can easily lose sight
of its relation to the whole. To remedy this myopia in regard to skin,
we have drawn upon the accumulated data derived from embryology,
histology, anatomy, physiology, biochemistry, and pharmacology. This
volume then is an attempt to integrate and synthesize and provide
as total a view of this organ as can be found in a small book. This
view is so important to the survival of the species that to neglect it is
to court disaster. Our emphasis has been on human skin because despite
the similarities between it and other mammalian skin which are clearly
delineated in the comparative studies reported here, man's skin is in
the last analysis unique.
WILLIAM MONTAGNA
PAUL F. PARAKKAL
1
An Introduction to Skin
Comers (1953) description of human skin as the "monumental facade
of the human body" though somewhat poetic captures most of its essen-
tial aspects. Certainly, skin envelops the entire body, is the chief means
of identifying individual human beings, and is the major organ of sexual
attraction. Its relatively hairless condition and its flawless conformity
to the contours of the body, especially in youth, add an esthetic quality
that is uniquely human. It is customary to speak of it as the largest
organ of the body, but this must be accepted with some reservation.
Even when we acknowledge that skin is the heaviest single organ, we
cannot assert that it is the "largest" organ of the body, at least not in
surface area. Despite its wide extent, it is only slightly plicated and,
depending on the size of the individual, is only some two yards square.
Compare this with the entire surface of the gastrointestinal tract or the
404 million alveoli in the lungs with a total surface of about five square
yards when collapsed during expiration and 19 or more square yards
when distended during deep inspiration ( Testut, 1945 ).
Functionally, skin is a most extraordinary organ. Among its numerous
functions, none are more important than preventing the organism from
desiccating and protecting it from its environment even while maintain-
ing it in uninterrupted communication with the environment. The
1
2 1. An Introduction to Skin
remarkable ability of skin to adapt to its surroundings accounts not
only for the seemingly endless structural and functional differences
between the various species but for certain basic patterns common to all.
In mammals, the most striking structural differences exist between
the glabrous and the hairy skin. For example, with some singular excep-
tions (burrowing animals are a case in point), heavily haired skin has
considerably less tactile sensibility than skin with few or sparse hairs
because hair buffers the epidermis from contact with stimuli. Animals
with extremely sensitive skin receive continuous external stimuli to
which they must respond. Thus cutaneous sensitivity is intimately linked
with reaction, which in turn depends on a brain that is adequate to
receive and respond to messages. Thus, superlative cutaneous sensibility
places the responsibility for action on the brain, which in most large
animals is probably too small to assume it. The exceptions to this
general pattern are equally important.
If, for example, the vast surface area of such bulky animals as whales,
elephants, hippopotami, and rhinoceroses were equipped with nerve
receptors numerically comparable to those in man, these animals would
probably require a larger brain than they have to respond to the volleys
of stimuli transmitted to it. On the other hand, exquisite cutaneous
sensibility would be both useless and detrimental to such mammoth
creatures; their bodies are so large and rigid that they would be helpless
to rid themselves of annoyances signaled by the skin. The very tough
skin of feral rhinoceroses, for example, is generally "pock marked" with
open raw wounds mostly suffered in combat; still, neither the wounds
nor the tick birds that keep them from healing by their constant picking
seem to bother the animals. When the skin of these animals is com-
pared with the heavily furred skin of horses, which are phylogenetically
close relatives, the differences in adaptation to and protection against
the environment become apparent. Despite his size, the horse is nimble
and mobile, with a long free-moving neck and head that enable the
recumbent animal to reach any part of his body. The switching of his
long tail serves to shoo off annoying vermin from his posterior. On the
other hand, the stocky rhino, relatively short-legged and short-necked,
lacks such defenses against his rugged environment and relies instead
on his nearly impenetrable skin, no doubt endowed with high thresholds
of sensibility. To be sure, lacking experimental data, no one knows
exactly how sensitive the skin of these animals is.
Two distinct patterns emerge from the study of hairy and glabrous
skin. First, the epidermis is always thicker in glabrous than in hairy