Download Integument Introduction: • The integument (or skin) is a composite

Integument
Introduction:
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The integument (or skin) is a composite organ.
On the surface, is the epidermis, below it is the dermis, and between them
lies the basement membrane (basal lamina and reticular lamina).
The epidermis is derived from the ectoderm and produces the basal lamina.
The dermis develops from the mesoderm and mesenchyme and produce sthe
reticular lamina.
Between the integument and the deep body musculature is a transitional
subcutaneous region made up of loss connective and adipose tissues.
In microscopic examination, this region is termed the hypodermis.
In gross anatomical dissection, the hypodermis is referred to as the
superficial fascia.
Makes up 15% of the human body weight, the epidermis produces hair,
feathers, baleen, claws, nails, horns, beaks, and some types of scales.
The dermis gives rise to dermal bones and osteoderms of reptiles.
Collectively, epidermis and dermis form teeth, denticles, and scales of fish. In
fact the absence of one, the other by itself is incapable of or inhibited from
producing these structures.
As the critical border between the organism and its exterior environment, the
integument:
o Forms part of the exoskeleton and thickens to resist mechanical injury.
o Prevents the entrance of pathogens.
o Helps hold the shape of an organism.
o Osmotic regulation and movement of gases and ions to and fom the
circulation.
o Gathers needed heat, or radiates the excess, and house sensory
recptors.
o Holds feathers for locomotion, hair for insulation, and horns for
defense.
o Block UV light and display bright colors during courtship.
Embryonic Origin and Development of Skin:
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By the end of neurulation in the embryo, most skin precursors are delineated.
The single-layered surface ectoderm proliferates to give rise to the
multilayered epidermis.
The deep layer of the epidermis, the strautum basale (Strautum
germinativum), rests upon the basement membrane. Through active cell
division, the stratum germinativum replenishes the single layer of outer cells
called the periderm.
The dermis arises from several sources,principally from the dermatome. The
segmental epimeres (somites) divide, producing the sclerotome medially, the
embryonic source of the vertebrae, and the dermomyotome layerally. Inner
cell of the dermomyotome become rearranged into the myotome, the major
source of skeletal muscle. The outer wall of the dermomyotome spreads out
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under the ectoderm as a more or less distinct dermatome that differentiates
into the connective tissue component of the dermis.
Cells of the nural crest origin migrate into the region between dermis and
epidermis, contributing to bony armor and to skin pigment cells called
chromatophores (literally “color bearing”) which usually reside in the dermis,
though in some species they may send pseudopods into the epidermis to take
up residence there themselves. Often, chromatophores are scattered within
the hypodermis. Nerves and blood vessels invade the integument to round
out its structural composition.
Structurally, the integument is composed of two layers, epidermis and dermis,
separated by the basement membrane. Vascularization and innervation are
added, along with contributions from the neural crest.
Interaction between epidermis and dermis stimulates specilizations such as
teeth, feathers, hair and scales.
Specialization
Glands:
Two types:
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Sebaceous glands: Produce an oily secretion sebum, that is released into
hair follicles in order to condition and help waterproof fur. Sebaceous glands
are absent from the palms of hands and soles of feet, but they are present
without associated hair, at the angle of the mouth, on the penis, near the
vagina, and next to the mammary nipples. At these sites, their secretion
lubricates the skin surface the wax glands of the outer ear canal, which
secrete earwax, and Meibomian glands of the eyelid, which secret an oily
film over the surface of the eyeball, probably are derived from sebaceous
glands.
Sweat glands: Produce a watery product called perspiration, or sweat. Two
types are usually recognized, based on the viscosity of their sweat (viscous or
thin), their associations (with or without hair follicles), and their functional
onset (at puberty or before).
o One type produces thin sweat, is not associated with hair follicles, and
functions before puberty. Its products function in regulation of body
temperature.
o The other produces viscous sweat, is associated with hair follicles, and
begins functioning at puberty. It is responsible for “body odor”.
o Both types of sweat glands are long, coiled invaginations of the
epidermis that reach deep within the dermis but maintain continuity
through the surface of the skin even through the cornified stratum
corneum.
o Surface evaporation of the sweat helps dissipate heat. However, sweat
also contains waste products; therefore, the integument represents
one avenue for elimination of metabolic by-products.
Scent glands: Derived from sweat glands and produce secretions that play a
part in social communication. These glands may be located almost anywhere
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on the body. Secretions of these glands are used to mark territory, identify
the individual, and communicate during courtship.
Mammary glands: Produces milk, a watery mixture of fats, carbohydrates,
and proteins that nourishes the young. Ectodermal mammary ridges, within
which mammary glands form, are located along the ventrolateral side of the
embryo. The number of mammary glands varies among species. Release of
milk to a suckling is lactation.
o Lactation has been reported in males of a species of Malaysian fruit
bat. Outside of this bat, lactation has been reported only in
domesticated male animals, result of abnormal inbreeding and in
pathological conditions. With these exceptions, mammary glands
become functional only in females.
o Mammary glands consist of numerous lobules. Each lobule is a
cluster of secretory alveoli in which milk is produced. The alveoli can
open into a common duct that, in turn, can open directly to the surface
through a raised epidermal papilla, or nipple. A circular pigmented
area of skin called the areola usually surrounds the nipple.
o Alveolar ducts also can open into a common chamber, or cistern,
within a long color of epidermis called the teat. The teat forms a
secondary duct carrying milk from the cistern to the surface. Adipose
tissue can build up beneath the mammary glands to produce breasts.
Horns and Antlers:
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Horned lizards have processes extending from behind the head that look like
horns but are specialized, pointed epidermal scales. Mammals are the only
vertebrates with true horns or antlers.
The skin, together with the underlying bone, contributes to both true horns
and antlers. As these structures take shape, the underlying bone rises up,
carrying the overlying integument with it. In horns, the associated
integument produces a tough, cornified sheath that fits over the bony core.
In antlers, the overlying living skin (called “velvet”) apparently shapes and
provides vascular supply to the growing one. Eventually falling off to
unsheathe the bare bone, the actual material of the finished antlers.
Typically only males have antlers, which are branched and shed annually.
There are notable exceptions. The annual cycle of antler growth and loss in
the whitetail deer is under hormonal control. In spring, the length of daylight
increases thus stimulating the pituitary gland to release hormones that
stimulate antler growth. By late spring, the growing antlers are covered with
velvet. By fall, the hormones produced by the testes inhibit the pituitary, and
the velvet dries. By thrashing and rubbing, the deer wipes the velvet off to
expose the fully formed, but now dead, bone of the antlers. This structure is
used for male-male competition to gain access to reproductively receptive
females. Following this mating season, further hormonal changes leading to a
weakening of the antler at its base of attachment to the living bone of the
skull. The antlers then shed during the winter.
The horn commonly occurs in both males and females, and is retained yearround. It continues to growth throughout the life of an individual. The horn is
unbranched and formed of a bony core and keratinized sheath.
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Horns of the pronghorn are forked in adult males. The old outer cornified
sheath, but not the bony core, is shed annually in the winter. He new sheath
beneath, already in palace becomes grown and forked by summer. The horns
of giraffes are different still. They develop from cartilaginous processes that
ossify, fuse to the top of the skull and remain covered with living noncornified skin. The rhinoceros horn does not include a bony core, so it is
exclusively a product of the integument. It forms from compacted keratinous
fibers.