THE INTEGUMENTARY SYSTEM

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THE INTEGUMENTARY SYSTEM
Prepared by Hugh PotterBiology DepartmentUnion
County College
Source of Images ADAM, Inc
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(No Transcript)
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INTRODUCTION TO THE SKIN
The integumentary system consists of the
skin and the derivatives of the epidermis such as
hair, glands and nails. The skin is also
classified as a cutaneous epithelial membrane.

A. Stratum corneum is a dead upper portion of
the epidermis B. Living epidermis consists of
several layers of cells which manufacture
keratin. C. Dermis is the layer of skin
containing blood vessels, glands and nerve endings
A
B
C
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EPIDERMIS - THIN SKIN
The epidermis of skin is a stratified squamous
epithelium consisting of several layers of cells.
These cells are called keratinocytes because of
their ability to produce the tough, fibrous
protein keratin. The surface of the epidermis is
covered with a layer of dead tissue called the
stratum corneum. On some of the surfaces of the
body, the epidermis is thin and delicate, e.g.,
the under surfaces of the upper arms.
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KERATIN FORMATION
Keratin fiber is formed from keratohyaline.
Keratohyaline is formed in the stratum granulosum
(black asterisk). It is in this region that the
keratinocytes die. Immediately above this layer
is a clear translucent layer, the stratum lucidum
(red asterisk). The stratum corneum (sc) is the
uppermost layer
sc


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Keratinocytes Most abundant cell type. Cells
are held together by desmosomes and are organized
into layers. 1. Stratum germinativum Cells
found just above the basement membrane which
undergo rapid cell divisions. 2. Stratum
spinosum is a middle portion of the epidermis
several cells thick.. The cells have a "spiny
appearance". 3. Stratum granulosum is a layer
just above the spinosum in which large amounts of
keratohyalin is being synthesized. 4. Stratum
lucidum - The keratinocytes in this layer are
filled with keratohyalin and a fibrous protein,
keratin. Keratin is tough, durable and water
resistant. Keratin is also the chief component in
hair and nails. 5. Stratum corneum is the
outermost layer of the epidermis composed of
flattened, dead, keratin-filled cells. This dead
layer provides protection from abrasion, strong
chemicals, microbial invasion and dehydration.
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Other cell types in the epidermis include 1.
Langerhans cells are T lymphocytes (cells that
mount an immune response) located within the
stratum spinosum. These cells will initiate an
immune response against microbes and epidermal
skin cancers. 2. Merkel cells are located among
the cells of the germinativium. They are
sensitive to touch. 3. Melanocytes are also
located in the germinativium often under the
basal cells just above the basement membrane.
They manufacture a brown pigment called melanin.
Melanin is packaged within vesicles called
melanosomes in the cytoplasm of the melanocytes.
These vesicles are transferred into the overlying
keratinocytes, darkening the skin. Melanin is a
helpful material in the skin. It tends to
surround the nucleus of the keratinocyte
protecting the DNA of that cell from damage due
to ultraviolet light from the sun. It also seems
to neutralize damaging chemicals called free
radicals that accumulate in traumatized tissues.
Cancer of the melanocytes, melanoma, is an
extremely dangerous and malignant neoplasm.
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Changes in Skin Color 1. Tanning Effect Due
to the activity of melanocytes.2. Reddening of
skin occurs due to an increased blood flow in the
underlying dermis. For example, an increase in
body temperature which leads to a vasodilation of
blood vessels in the dermis. 3. Strong
emotional states will lead to an increase in
blood flow in the dermis. 4.  Blanching of Skin
("turning pale") occurs due to decreased blood
flow to the skin. This decreased blood flow may
be caused by a sudden drop in blood pressure,
hypothermia and emotional states. 5.  Cyanosis
bluish color in skin due to sustained reduction
in blood supply to the skin6.  Jaundice When
liver function is interrupted due to cirrhosis,
liver cancer or blockage of bile flow, yellow
bile pigments and bilirubin accumulate in the
skin and whites of the eyes.
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The Dermis 1. Located below the epidermis it
contains all of the accessory organs of epidermal
origin, such as, hair follicles and glands. 2.
It also has extensive networks of blood vessels,
lymphatic vessels nerve endings and nerve fibers.
3. The dermis consists of two major layers
a. The Papillary layer contains loose (areolar)
connective tissue with a rich supply of blood
capillaries. It also contains the nerve endings
for touch and pain. b. The Reticular layer
contains dense irregular bundles of collagen,
elastic and reticular fibers. These fibrous
bundles blend into the papillary layer above and
into the underlying subcutaneous layer.
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Dermal Blood Supply 1. The Cutaneous Plexus
When arteries supplying the skin reach the
subcutaneous layer, they form a network of
branches called the cutaneous plexus. Branches
from this plexus supply the subcutaneous fat and
various structures in the dermis such as hair
follicles and sweat glands. 2. The Papillary
plexus capillary beds that follow the contours
of the epidermal-dermal boundary. Interruptions
in this circulatory flow can result in epidermal
and dermal deterioration and necrosis, e.g.,
decubitis ulcers and diabetic foot.
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B. Innervation of the skin The skin is richly
innervated. The functions of these nerves
include 1. Control of blood flow through the
skin. 2. Adjusting the rate of glandular
secretions. 3. Sensory reception The
sensory receptors of the skin respond to two
basic types of stimulation, mechanical change and
pain.
Pacinian Corpuscle
Meissners Corpuscle
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Mechanoreceptors of the skin 1. Meissners
corpuscles located within the dermal papillae,
they respond to light touch. Meissners
corpuscles are located immediately under the
epidermis within the dermal papillae. These
nerve endings respond to light touch. 2.
Pacinian corpuscles located deep within the
reticular layer, Pacinian corpuscles are
sensitive to deep pressure and vibrations. They
are located in the deep dermis or subcutaneous
layer. They are also common in the glans penis
of the male and in the pancreas. The role they
may play in the latter organ has never been
determined. 3. Merkels disks are
specialized nerve endings found at the ends of
nerve fibers. These disks are closely associated
with the epidermal Merkels cells and respond to
fine touch.
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Nociceptors Pain receptors are especially
abundant in the upper skin, joint capsules, the
periosteum of bone and the walls of  blood
vessels. Very few pain receptors are located in
visceral organs or deep tissues. There are three
types of pain receptors 1.  Those sensitive to
temperature extremes.2.  Those sensitive to
mechanical damage.3.  Those sensitive to
chemicals, e.g., metabolites from traumatized
tissues such as aracidonic acid and
prostaglandins.      Very strong pain stimuli
will excite all three types of receptors. For
example, severe trauma of any kind (burns, cuts,
corrosive chemicals) will often be described as
"burning" or acute pain.
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Hair Follicle Hair follicles project deep into
the dermis and subcutaneous fat from the surface
of the skin. Each hair follicle consists of the
following 1.  Hair Papilla a small clump of
connective tissue, capillaries and nerves which
supports the growth of the hair. 2.  Hair Bulb
consists of the epithelium that surrounds the
papilla. This structure is an invagination of the
epidermis. Cells from the basal layer of the bulb
divide and are pushed up into the root of the
hair. 3.  Hair shaft begins at a point about
midway between the papilla and the skin
surface. 4. The arrector pili are small bands
of smooth muscle which extend from the connective
tissue sheath of the follicle and anchor in the
papillary layer of the dermis. This muscle is
stimulated to  contract by strong emotional
states or cold temperatures. These stimuli
operate through the nervous system to cause the
hairs to become erect.
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SUBCUTANEOUS LAYER
The subcutaneous layer of skin contains abundant
adipose tissue. In addition, many blood
vessels, nerve endings and hair follicles can
usually be seen.
Adipose tissue
Hair Follicle
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HISTOLOGY OF THE HAIR FOLLICLE
The hair follicle is an epidermal sheath
that surrounds the hair. Sebaceous glands are
usually attached to the side of a follicle.
Their oily secretion enters the follicle and
follows it to the surface. The hair grows from
the bulb, the swollen lower end of the follicle.
The bulb is invested with blood vessels and
nerves which are essential for the continued
growth of the hair.
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Glands in the Skin The skin contains a number
of exocrine glands Sebaceous glands Holocrine
glands which discharge an oily secretion called
sebum. The gland cells originate in the
periphery of the gland. As they mature, the cells
manufacture sebum, a mixture of triglycerides,
cholesterol, proteins and electrolytes. As the
cells reach the opening or lumen of the gland,
they rupture releasing their product (holocrine
secretion). There are two types of sebaceous
glands1.  Simple branched alveolar glands
empty their secretion into the follicle of a
hair.2.  Sebaceous follicles large sebaceous
glands that are connected directly to the
epidermis and are not associated with a hair.
They are found in the skin of the face, back,
chest and nipples. Sebum functions by
lubricating the skin and retarding the growth of
bacteria.
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ACNE
Acne is a condition of the skin which is shared
by individuals of all ages. Each pimple is in
fact an inflammed sebaceous gland. The causes of
the inflammation include inadequate cleansing of
the skin to remove superficial oils, endocrine
changes during puberty and pregnancy, dietary
effects and emotional stress. It is easy to
understand why teenagers so often exhibit this
problem.
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SEBACEOUS AND SWEAT GLANDS
Sebaceous glands (Sb) are usually associated with
a hair and release their holocrine secretion
(sebum) into the hair shaft which carries it to
the surface. Sweat glands come in two varieties.
The most numerous are the eccrine glands (Sw).
The watery merocrine product of these glands
travels through a duct to the surface of the
skin. Here it evaporates and cools the body.
Apocrine sweat glands are found around the areola
of the nipple, in the labia majora and axilla.
Their secretion is thicker and more odiferous
than the eccrine secretion.
Sb
Sb
Sw
Sw
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Merocrine (eccrine) sweat glands1. Very
numerous. In the adult, the skin may contain 2 to
5 million merocrine glands per square inch. Palms
and the soles of the feet have the highest
concentration. 2. Merocrine glands are smaller
than the apocrine glands.They produce a watery
sweat containing electrolytes, lysozymes,
antibodies and other ingredients.3. The
functions of these glands includea.  Removing
heat from bodys surface to lower body
temperature. b.  Excretion of water, electrolytes
and nitrogenous wastes.c.  Protection from
chemical and microbial Apocrine glands Located
in the armpits, groin and around the nipples.
They produce a sticky, cloudy, odorous secretion
into a hair follicle. These secretions become
intensified at the time of puberty under the
influence of the nervous and endocrine systems.
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SWEAT GLANDS
Sweat glands are located in the deep dermis.
They are usually associated with small blood
vessels and nerves. In response to hyperthermia,
the eccrine sweat glands release a serous liquid
to the surface of the skin via a duct. The
evaporation of this liquid from the surface of
the skin cools the body. In the arm pits and
groin, apocrine sweat glands secrete an oily
material. Sweat glands (sg) are unbranched,
coiled, tubular glands distributed throughout the
skin. They are not found in the nail beds,
margins of the lips, glans penis or ear drum.
They are most numerous in the palms of the hands
and soles of the feet.
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Functions of the Skin A.  Regulation of body
temperature 1. During hyperthermia blood
vessels (arteries) in the skin dilate due to
nerve stimulation from the brain. Blood flow to
the skin increases. 2. Warm water moves from
the blood to the merocrine sweat glands by
filtration. This warm sweat now moves to the
skins surface by the duct from the gland. 3.
The warm sweat evaporates from the skins surface
taking excess body heat with it. 4. Body
temperature comes down and sweating is reduced
(negative feedback).
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During hypothermia 1. Blood vessels in the
skin constrict due to nerve stimulation from the
brain. This reduces blood flow to the skin. 2.
Radiant heat loss is reduced from the skin.
Sweat production decreases. 3. Body heat is
retained in the trunk and head or "core" of the
body. 4. Shivering, an involuntary contraction
of skeletal muscles due to nerve stimulation,
helps to generate body heat. This is the result
of the breakdown or "burning" of glucose in the
skeletal muscles.
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B. Protection from ultraviolet light 1.
Ultraviolet light penetrates the epidermis and
stimulates the melanocytes to increase their
production of melanin.2. Melanocytes inject
packages of melanin called melanosomes into cells
of the lower epidermis. As these darkened cells
divide, they are pushed to the top of the
epidermis. 3. Eventually, the entire epidermis
becomes a "sunscreen" blocking out much of the
harmful ultraviolet light.
The arrow indicates the layer of melanocytes in
the lowest level of the epidermis.
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MELANOMA
Cancer of the Melanocytes
Melanoma is a neoplasm of the melanin producing
cells. The cancer usually begins when a mole
(actually a benign tumor) becomes malignant.
Overexposure to sunlight is thought to be a cause
of melanoma. However, some forms may have a
hereditary basis. Melanoma is one of the most
metastatic and invasive cancers. The prognosis
for an individual with advanced melanoma is not
good. Any change in a mole or nevus should be
followed up with a visit to the dermatologist.
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C. Protection from infection by microbes 1.
The tough impervious epidermis forms a barrier to
microbes, as long as it is intact. 2. The
formation of sweat and sebum flushes away
microbes on the surface of the skin, as well as
those in sweat gland pores and hair follicles.
The pH of sweat and sebum tends to retard the
growth of bacteria. Sweat also contains lysozymes
and antibodies which attack microbes. 3. The
blood-rich dermis reacts quickly to microbial
invasion through the activities of various cells.
Tissue basophils release chemicals which increase
the blood supply to an infected region of skin.
Phagocytic cells such as the macrophages and
neutrophils physically attack microbes. The
combined reaction of these cells is referred to
as inflammation.
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D. Protection from excessive water loss or
dehydration. The tough, keratinized epidermis
forms a watertight cover on the body keeping body
water in. E. Production of Vitamin D - Some of
the ultraviolet light striking the skin passes
through the melanin sunscreen and causes a
chemical change in the blood leading to the
formation of vitamin D. This vitamin is required
for the body to absorb calcium from the
intestine. Calcium is essential for the
development of teeth and bones.