Transcript studentnotes2010

Integumentary System
Chapter 6
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 Introduction
A.Organs are body structures composed of two or more
different tissues.
B.The skin and its accessory organs make up the integumentary
system.
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 Skin and Its Tissues
A. The skin is a largest organ responsible for:
*maintaining homeostasis through temperature
regulation
*protection of underlying tissues
*retardation of water loss
*housing sensory receptors
* synthesizing certain chemicals
*excreting wastes
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B. The skin consists of an outer epidermis and a dermis,
connected to underlying tissue by the subcutaneous layer
(hypodermis).
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Epidermis
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1. The epidermis is made up of stratified squamous epithelium
and lacks blood vessels.
2. The layer of reproducing cells (the stratum basale), which lies
at the base of the epidermis, is well-nourished by dermal blood
vessels.
3. Cells are pushed outward as new cells are formed, and become
keratinized as they die. 4 or 5 layers (STRATA) may be seen.
4.The epidermis is important because it protects
against water loss, mechanical injury, chemicals, and
microorganisms.
5.Melanocytes,which lie deep in the epidermis and
underlying dermis, produce a pigment called melanin
that protects deeper cells from the sun's ultraviolet
rays.
6.Melanocytes pass melanin to nearby cells through
cytocrine secretion.
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4 or 5 Layers (STRATA) of the Epidermis
stratum basale
always present
DEEP
stratum spinosum
always present
stratum granulosum always present
stratum lucidum
found in the thicker palms and soles
stratum corneum always present
Superficial
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Stratum Basale
• Deepest single layer of
cells
• Combination of
melanocytes, keratinocytes
& stem cells that undergo
mitosis
• Cells attached to each
other & to basement
membrane
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Stratum Spinosum
• 8 to 10 cell layers held
together
• During slide
preparation, cells
shrink and look spiny
• Melanin taken in by
nearby melanocytes
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Stratum Granulosum
• 3 - 5 layers of flat dying
cells
• Show nuclear
degeneration
• Contain dark-staining
granules
• Contain granules that
release lipid that repels
water
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Stratum Lucidum
• Seen in thick skin on
palms & soles of
feet
• Three to five layers
of clear, flat, dead
cells
• Contains precursor
of keratin
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Stratum Corneum
• 25 to 30 layers of flat
dead cells filled with
keratin and surrounded
by lipids
• Continuously shed
• Barrier to light, heat,
water, chemicals &
bacteria
• Friction stimulates
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Figure 06.02
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Dermis
1.
The dermis binds the epidermis to underlying tissues.
Epidermal ridges and dermal papillae cause the border
to be uneven.
2. The dermis consists of connective tissue with collagen
and elastic fibers within a gel-like ground substance.
3. Dermal blood vessels carry nutrients to upper layers of
skin and help to regulate temperature.
4. The dermis also contains nerve fibers, sensory fibers,
hair follicles, sebaceous glands, and sweat glands.
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Dermal Growth & Repair
• Dermis does not shed like epidermis
• Can regenerate when injured
• Starts to produce new tissue: will
become a scar
• Cut or incision can make a lesser scar if
made in the same direction as cleavage
lines
• Stretch marks (striae)- caused by rapid
growth & tearing of elastic tissue;
causes scarring
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Cleavage or Tension Lines
• Elastin and
collagen fibers
oriented in some
directions more
than others
• Important in
surgery
– If incision
parallel to lines
there is less
gapping, faster
healing, less scar
tissue
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Skin Color
–
Skin color results from a combination of genetic,
environmental, and physiological factors.
•
•
•
•
Melanin produced in epidermis by melanocytes
– same number of melanocytes in everyone, but differing amounts of
pigment produced
– results vary from yellow to tan to black color
– melanocytes make melanin
» UV in sunlight increases melanin production
Clinical observations
– freckles or liver spots = melanocytes in a patch
– albinism = inherited lack of pigment
– vitiligo = autoimmune loss of melanocytes in areas of the skin produces
white patches
Carotene in dermis
–
yellow-orange pigment (precursor of vitamin A)
–
found in stratum corneum & dermis
Hemoglobin
–
red, oxygen-carrying pigment in blood cells
–
if other pigments are not present, epidermis is translucent so pinkness will be evident
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Subcutaneous Layer
1. The subcutaneous layer (hypodermis) is composed of
loose connective tissue and insulating adipose tissue.
2. It binds the skin to underlying organs and contains
the blood vessels that supply the skin.
3. No sharp boundary exists between the dermis and
subcutaneous layer.
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 Accessory Organs of the Skin
A. Nails
1. Nails are protective coverings over the ends of fingers and
toes.
2. Nails consist of stratified squamous epithelial cells
overlying the nail bed, with the lunula as the most actively
growing region of the nail root.
3. As new cells are produced, older ones are pushed outward
and become keratinized.
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B. Hair Follicles
1. Hair can be found in nearly all regions of the skin.
2. Individual hairs develop from cells at the base of the hair
follicle, an invagination of the lower epidermis that dips down into
the dermis.
3. As new cells are formed, old cells are pushed outward and
become keratinized, and die forming the hair shaft.
4. A bundle of smooth muscle cells, called the arrector pili muscle,
attaches to each hair follicle. These muscles cause goose bumps
when cold or frightened.
5. Hair color is determined by genetics; melanin from melanocytes is
responsible for most hair colors. Dark hair has eumelanin while
blonde and red hair have pheomelanin.
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Did you know…
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Dark hair contains true melanin
Blond and red hair contain melanin with iron and sulfur added
Graying hair is result of decline in melanin production
White hair has air bubbles in the medullary shaft
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C. Sebaceous Glands
1. Sebaceous glands
(holocrine glands) are
associated with hair follicles
and secrete sebum that
waterproofs and moisturizes
the hair shafts.
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D.
Sweat Glands
1. Sweat glands (sudoriferous glands) are either
eccrine, which respond to body temperature, or
apocrine, which respond to body temperature, stress,
and sexual arousal.
2. Modified sweat glands, called ceruminous glands,
secrete wax in the ear canal.
3. Mammary glands, another modified type of sweat
glands, secrete milk.
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 Regulation of Body
Temperature
A. Proper temperature regulation is vital to maintaining
metabolic reactions.
B. The skin plays a major role in temperature regulation with
the hypothalamus controlling it.
C. Active cells, such as those of the heart and skeletal muscle,
produce heat.
D. Heat may be lost to the surroundings from the skin through
radiation.
E. The body responds to excessive heat by dilation of dermal
blood vessels and sweating.
F. The body responds to excessive cooling by constricting
dermal blood vessels, inactivating sweat glands, and shivering.
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 Skin as a Sense Organ
Sensation is the conscious or subconscious awareness of external or internal stimuli.
For a sensation to arise, four events typically occur:
i. a stimulus capable of activating specific sensory neurons must occur
ii. a sensory receptor or sense organ must respond to the stimulus and transduce
(convert) it into a nerve impulse
iii. nerve impulses are conducted to the brain
iv. a region of the brain must receive and integrate the nerve impulses, producing a
sensation
Somatic Sensations: Somatic sensations arise from stimulation of sensory
receptors embedded in: skin or subcutaneous layer
i. Some parts of the body are densely populated with receptors (e.g., tip of tongue,
lips, fingertips) and other parts of the body have few receptors (e.g., back of
neck).
ii. Somatic sensations that arise from stimulation of the skin surface are called
cutaneous sensations
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 Skin as a Sense Organ
Touch receptors- can feel many stimuli
Touch / pressure / position (mechanoreceptors): They are sensitive to stimuli
that distort their cell membranes. They contain mechanically regulated ion
channels, which open and close in response to movement. There are three
classes: tactile, baroreceptors, and proprioceptors.
Tactile receptors provide the sensations of touch, pressure, and vibration.
Distinctions between them are not well defined. Fine touch and pressure
receptors provide detailed information about a source of stimulation,
including the exact location, shape, size, texture, and movement. These
receptors are extremely sensitive and have relatively narrow receptive
fields. Crude touch and pressure receptors provide poor localization and
information. Tactile receptors range in complexity from free nerve endings
to specialized sensory complexes complete with accessory cells and
supporting structures. There are at least six tactile receptors on the skin
and called by various names according to the source:
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 Skin as a Sense Organ
Free nerve endings are sensitive to touch and pressure. They are situated
between epidermal cells and have no apparent differences in structure with
those of the free nerve endings that provide temperature or pain
sensations.
Root hair plexus is made up of free nerve endings to detect hair movement.
Merkel's discs are fine touch and pressure neurons located in the lower
epidermal layer of the skin.
Meissner's corpuscles are fine touch and pressure receptors located in the
eyelids, lips, fingertips, nipples, and external genitalia.
Pacinian corpuscles are large receptors sensitive to deep pressure and to
pulsing or high-frequency vibrations. They are found in the skin, fingers,
breasts, and external genitalia, as well as in joint capsules, mesenteries, the
pancreas, and walls of the urinary bladder.
Ruffini corpusles are located in the dermis of the skin and are sensitive to
pressure and distortions of the skin.
Basically:
Superficial layer of dermis (fine touch & 2 pt discrimination)
Deeper in the dermis (crude touch)
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 Skin as a Sense Organ
Pain receptors- can feel a change from touch to something
different, it hurts. More nerves are involved in the sensation =
free nerve endings
Superficial portions of the skin, in joint capsules, within the periostea of
bones, around the walls of blood vessels, plus a few in deep tissues or
most visceral organs. These can produce fast pain (prickling) or slow pain
(burning or aching).
Temperature receptors- can detect both hot or cold
They are free nerve endings scattered immediately beneath the skin
surface and located in skeletal muscles, the liver, and hypothalamus. Cold
receptors are three to four times more numerous than warm receptors,
but there are no known structural differences between the two.
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 Healing of Wounds and Burns
A. Inflammation, in which blood vessels dilate and
become more permeable, causing tissues to become red
and swollen, is the body's normal response to injury.
B. Superficial cuts are filled in by reproducing epithelial
cells.
C. Deeper cuts are closed off by clots, covered by
scabs, and eventually filled in by fibroblasts, making
connective tissue. Blood vessels extend into the area,
injured tissues are replaced, and the scab falls off.
D. Large wounds leave scars and healing may be
accompanied by the formation of granulations.
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 Skin Disorders
• Burns
– Partial thickness burns: 1st & 2nd degree
– 1st degree- only epidermis; red, painful, slight swelling
– 2nd degree- epidermis and dermis; red, pain, swelling,
blistering
– Full thickness burn: 3rd degree
– 3rd degree- epidermis & dermis are completely destroyed; no
pain due to destruction of sense receptors
Skin Grafts may be needed:
•
•
New
Skin
–
–
–
skin can not regenerate if stratum basale and its stem cells are destroyed
graft is covering of wound with piece of healthy skin
autograft from self
isograft from twin
autologous skin
» transplantation of patients skin grown in culture
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• Photodamage
– Ultraviolet light (UVA and UVB) both
damage the skin
– Acute overexposure causes sunburn
– DNA damage in epidermal cells can lead to
skin cancer
– UVA damages collagen and elastic fibers
and lead to wrinkling of the skin
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• Pressure Sores
– Decubitus ulcers
– Caused by constant deficiency of blood
flow to tissue
– Areas affected is skin over bony
prominence in bedridden patients
– Preventable with proper care
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• Skin Cancer
– 1 million cases diagnosed per year
– 3 common forms of skin cancer
• basal cell carcinoma (rarely metastasize)
• squamous cell carcinoma (may metastasize)
• malignant melanomas (metastasize rapidly)
– most common cancer in young women
– arise from melanocytes ----life threatening
– key to treatment is early detection watch for changes in
symmetry, border, color and size
– risks factors include-- skin color, sun exposure, family
history, age and immunological status
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Do you know your ABCDE’s of Skin Cancer?
A- Asymmetry:
Normal moles or freckles are completely symmetrical. If you were to draw
a line through a normal spot, you would have two symmetrical halves. In
cases of skin cancer, spots will not look the same on both sides.
B- Border:
A mole or spot with blurry and/or jagged edges.
C- Color:
A mole that is more than one hue is suspicious and needs to be evaluated
by a doctor. Normal spots are usually one color. This can include
lightening or darkening of the mole.
D- Diameter:
If it is larger than a pencil eraser (about 1/4 inch or 6mm), it needs to be
examined by a doctor. This is includes areas that do not have any other
abnormalities (color, border, asymmetry).
E- Elevation:
Elevation means the mole is raised above the surface and has an uneven
surface
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