Download Integumentary System - Catherine Huff`s Site

Integumentary System :
Skin
skin is the largest organ in the
body. Also included are the
accessory organs: hair, sweat
glands, sebaceous glands, nails
and variations
Skin:
The study of skin is dermatology.
The skin has a variety of functions including:
*barrier against invasion of micro-organisms
*protects underlying structures from injury
*prevents the body from drying
*inhibits excess water intake (from aquatic species)
*regulates temperature
*receptor for sensations of touch, heat, cold, pressure
and pain.
*disposal of waste products
The body produces heat by
metabolizing ingested food and the
amount of heat produced is the
result of the amount of work done
by the muscles.
Most of body heat is lost by:
Radiation: heat energy is
transmitted as rays to the
surrounding areas.
Conduction: heat energy passes by direct
contact through a non-moving medium.
Eg: when an animal lies on a cold surface it
loses heat directly to that surface.
Or
when an animal is lying on a surgery table
the heat is lost directly to the surface of the
table and through the incision made
Convection: heat transfer occurs
in a gas or liquid by the
circulation of currents from one
region to another. This is the heat
loss responsible for the wind chill
factor
Evaporation; heat is lost as
perspiration or other fluids on the
skin. Air currents can increase
evaporative heat loss through
convection.
Most of the remainder of heat loss
occurs through mucous
membranes and lesser amounts
lost through digestive and urinary
tracts
Composition of skin
the skin is composed of two
layers:
the epidermis: outer, thinner layer
the dermis: the thicker inner layer
dermis
epidermis
The Epidermis:
is made up of stratified squamous
epithilial tissue,
the layers from the dermis
outward are
Stratum germinativum:
(basal layer)
The cells in this inner most layer
multiply continuously to
compensate for the constant loss
of cells from the surface of the
epidermis. These cells push
upward into each layer and
eventually die.
Stratum spinosum:
(spinous layer)
The cells begin to shrink and
draw apart. This layer is only
one or two cells thick. It is
thicker on parts of the body that
endure rugged wear (footpads)
Stratum granulosum:
(granular layer)
The cells in this layer contain
granules visible in the cytoplasm.
This layer may not be present in
some areas of thin skin.
Keratinization or cornification
packs the cells with fibrous
protein called keratin
Stratum lucidum:
(clear layer)
This layer is made up of closly
packed clear cells. This layer is
found in tissue that endure
rugged wear.
Stratum corneum:
(horny layer)
This layer is made of flat lifeless
cornified cells. They appear as
overlapping dry scales that make up the
outer skin layer. If unbroken, they will
prevent the entrance of microorganisms.
Keratinization gives the special
epidermal parts (hooves, horns, beaks)
their strength.
Cornified
Skin color is determined by the
amount of melanin in the stratum
germinativum layer. Heredity,
the sun and some hormones
affect the skin color
The absence of normal
pigmentation is called albinism.
True albinism prevents
pigmentation of the skin, hair and
eyes. This condition may be
associated with other lethal traits
as well as a lack of protection
from the sun
Skin color can also be affected
by the blood supply. Eg. Skin
color can take on a blue hue
(cyanosis) when oxygen supply
is compromised
The dermis (corium) is made up
of dense, fibrous connective
tissue containing blood vessels
and nerves. Small involuntary
muscles (arrector pili) are
attached to the hair follicles.
When these muscles contract, the
hairs stiffen. This increases the
animals ability to insulate itself
against cold.
Sebaceous glands, sweat glands,
sensation receptors are found in
the dermis layer.
The subcutaneous layer under the
dermis is the hypodermis or
subcutis. It consists of loose
connective tissue and adipose
tissue.
Skin structure differs throughout
the body. It is tough, stretchable
and varies in thickness.
Hair
Mammals have three types of
hair.
*primary
*secondary
*tactile
Primary hairs are also called
guard hairs and these make up
the top coat. These hairs are stiff
with a smooth appearance. This
arrangement allows rain to run
off the coat preventing chilling
of the animal
Secondary hairs are also called
wool hairs and make up the
undercoat. These hairs are soft,
thin and wavy.
Tactile hair are usually thicker
and longer than primary hair and
is most often found about the
face. These hairs grow deep
from the hypodermis or
superficial muscle layer and act
as a touch receptor.
Hair develops from the hair
papilla, located at the base of the
hair follicle. Cells at the base
increase, push upward and
keratinize forming the visible
hair shaft. Hair follicles are
positioned at 30 – 60 degree
angle to the skin.
The two arrangements for hair
growth:
simple: primary hairs grow from
separate follicular openings
complex: two to five guard hairs
erupt from a single follicle.
Hair color is important for
thermal regulation. In general,
lighter color coats are cooler.
Animal hair grows in cycles.
Factors affecting the shedding
cycle: temperature, nutrition,
hormones, genetics, state of
health.
Sweat glands are excretory organs
of the skin that cool the body.
Apocrine sweat glands are found
throughout the body and secrete a
strong smelling substance in the
hair
Eccrine sweat glands are coiled
tubular structures embedded in
the dermis and produce a watery
sweat. These glands are found in
limited areas usually the footpads
and nostrils
The sebaceous glands secrete a
substance called sebun which
lubricates the skin and hair,
waterproofs the coat, gives the
coat a glossy sheen, increases the
spread of sweat, slows bacterial
growth, and serves as a territorial
marker.
Examples of these glands are:
Circumoral glands:
These glands are found in the
lips of cats. During grooming or
when a cat rubs it’s head against
and object, the secretion is
deposited to mark territory
Horn glands:
These glands produce a musk
odor that attracts females to
males during breeding season.
They are located caudo-medially
to the horn base.
Anal sacs:
These are cutaneous pouches that
express a foul smelling fluid that
is expressed during defication
and is used as a territorial
marker.
Ceruminous glands:
These are classified as modified
sweat glands. They are located in
the external ear canal. It excretes
a yellowish waxy substance called
cerumen (earwax)
Nails, Claws and Hooves.
All three of these structures have
the following parts in common:
*wall
*sole
*pad
In primates the nail is the wall
and it grows from the epidermis.
The sole is located beneath the
nail at the open end. The pad
corresponds with the finger tips
In carnivores the claw is the wall,
which has been compressed
laterally. The sole is the
underside of the wall and is flaky
in texture. The pad corresponds
to the foot pads
Plantigrade animals have well
developed footpads.
Digitigrade animals include cats
and dogs. Only the digital and
metacarpal pads make ground
contact
Ungulates include hoofed animals
The hoof is the wall, the sole is
the underside of the hoof, the
footpad is the bulb or heel.
Dewclaws, chestnuts and ergots
are modified epidermal
structures. In the dog and pig,
the dewclaw has a rudimentary
bone. In ruminants the dewclaws
are like miniature hooves and
they serve no practical purpose