Biology 141 - Virginia Community College System
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Transcript Biology 141 - Virginia Community College System
Biology 141
Integumentary System
Chapter 5
The Integument
Integument: Skin – largest body organ
Integumentary System:
– Skin
– Hair
– Nails
Function:
– Protection
– Maintain body temperature
– Provide sensory input
Dermatology: medical specialty dealing with the
integumentary system
Structure of the Skin
Cutaneous
membrane: skin
– Epidermis – superficial layer
– Dermis – deep layer
Subcutaneous
membrane
– Hypodermis – fat layer; not technically
a part of the skin.
Structure of the Skin
The
2 layers of
skin;
– epidermis
Multilayered
epithelial tissue
thinner
– Dermis
Connective
thicker
tissue
Epidermis
Cell types found in the epidermis:
– Keratinocytes:
multilayered
Produce keratin protein (tough, water repellant)
– Melanocytes
Produces
pigment melanin to protect nuclear DNA in
keratinocytes
– Langerhans cell
Immune
response
– Merkel cells
Contact
Merkle discs to detect sensations
Epidermis
Tissue Layers
Composed
of different strata (layers)
– outermost - dead cells
– Innermost - Cells divide
Cells
Layers
die as they are pushed upward
originate from the deepest
cell layer of columnar cells called the
stratum germinativum.
Sublayers of the Stratum
germinativum
Stratum basale ("base layer")
– Cells of stratum basale are closest to the blood supply in
the dermis and are thus the healthiest
– Only these cells can reproduce
Stratum spinosum ("spiny layer")
– Cells are pushed from below and become "squished" and
look "spiny" on cross sectional view
– Because the cells are farther away from the dermal
blood supply, they are less healthy and thus don't
reproduce
Basal Cell Carcinoma
Low magnification (left) of skin cross-section of shows
different layers (epidermis, dermis and subcutaneous
tissue), and
areas of tumor invasion.
Higher magnification (right): tumor cells resemble those in
the normal basal cell layer of the epidermis.
Tumor cells appear to bud off from the epidermis and grow
downward as islands and cords of basophilic cells with
hyperchromatic nuclei.
Epidermis Tissue Layers
(deep to superficial)
Stratum germinativum ("growth layer")
– stratum basal – germination basement layer
– Stratum spinosum – “thorn-like”
Stratum granulosum "grainy layer"
Stratum lucidum "clear layer"
Stratum corneum “horny layer” (top layer)
Epidermis: Tissue Layers
stratum
basal:
– Single row of cuboidal or columnar
keratinocytes.
– Some are stem cells
– Contains
Melanocytes
Langerhans
cells
Merkle cells and discs
Epidermis: Tissue Layers
stratum
basal –
– Damage to this layer damages stem
cells
Unable
to regenerate skin
Require skin grafts
Grafts can be autologous (same individual)
or transplanted from a donor.
– Skin sheets can also be grown in the lab
Epidermis: Tissue Layers
stratum
spinosum
– multilayered keratinocytes
– Few Langerhans cells and Melanocytes
Epidermis: Tissue Layers
stratum
granulosum
– Multilayered, flattened keratinocytes
– Cells undergoing apoptosis
– Secretes water repellant
– cells loose nuclei, appear grainy
– Keratohyalin (a precursor to keratin)
forms in granules here
Epidermis: Tissue Layers
stratum lucidum:
– Multilayered, dead
keratinocytes
with large amount of
keratin
– Translucent and flattened
– Found only in thick skin
(hairless)
Fingertips
Palms
soles
Epidermis: Tissue Layers
stratum corneum:
–
–
–
–
–
Multilayered
Flat, dead keratinocytes
primarily keratin protein
"horny layer" - cells have processes
Flattened cells filled with keratin form
"keratinized layer" and make this "keratinized
stratified squamous epithelium"
– Constant friction results in callus formation
Dermis
Dermis:
– Connective tissue
– Contains
Blood
vessels
Nerves
Glands
Hair follicles
Dermis
2 main regions:
Papillary:
upper layer
Reticular:
deep layer
Dermis
Papillary:
upper layer
lies
next to the epidermis
contains the derma papillae (projections into
the upper epidermis)
– epidermal ridges creat fingerprints, palm prints
and footprints.
– Contain capillaries
– Contain Meisssner corpuscles (tactile receptors)
– Contain free nerve endings
Senses temperature, pain, itch, tickle
Dermis
Reticular:
deep layer
Attaches
to the subcutaneous layer
Dense irregular connective tissue
contains more collagen fibers
– increasing the strength of the skin.
Contains:
– Few adipose cells
– Hair follicles
– Nerves and Pacinian corpuscles (deep pressure)
– Sebaceous glands (oil)
– Sudoriforous glands (sweat)
Accessory Structures
Receptors:
Meissner’s corpuscles
and Pacinian corpuscles
Meissner’s: located in the papillary
layer of dermis
– project into the papillae.
– touch receptors
Pacinian:
spherical, onion-like
– Lie deep in the reticular layer
– pressure
Sensory receptors in the Dermis
Meissner’s
Corpuscle detects
light touch
Papillary layer
Pacinian Corpuscle
detects deep touch
(pressure)
Reticular layer
Dermis
Tears
in the reticular region of the
dermis result in stretch marks.
Incisions
against the grain of the
collagen fibers = wide scar
Incisions
with the grain = thin scar
Structural Basis of Skin Color
Skin color pigments:
– Melanin
– Hemoglobin
– Carotene
Melanin – number of melanocytes the
same in all people
– Amount of melanin produced varies
– Accumulation results in
Age
spots
Freckles
moles
Melanin
Function:
– Absorbs UV radiation
– Prevents damage to DNA in epidermal
cells
– Neutralizes free radicals
Hemoglobin
Found in RBCs
Skin color depends
on amount of
oxygen in the
blood
– Blue – cyanotic: low
oxygen
– Yellow - jaundice:
high bilirubin
Liver
damage
– Red – erythema:
engorgement of
capillaries
Injury
Heat
Infection
Inflammation
Allergic
reaction
– White – pallor: low
number of RBC
Shock
anemia
Carotene
Yellow-orange
pigment found in egg
yolks and orange vegetables
– Precursor to vitamin A
– Excessive dietary intake results in
accumulation in the subcutaneous layer
Albinism / Vitiligo
Albinism:
Inherited inability to
synthesize melanin
– Melanin is not produced in skin, hair,
and eyes.
Vitiligo:
partial or complete loss of
melanocytes in patches of skin
– Immune system attacks and destroys
melanocytes.
Accessory Structures
Hair: pili
Columns of dead, keratinized cells compactly cemented together.
hair shaft – portion of the hair that
projects above the surface.
root – portion below the surface
extending into the dermis.
Hair
Hair
shaft and root consist of 3
concentric layers of cells:
– Medulla
– Cortex
– Cuticle
Human Hair
Cuticle showing scales
No medulla, brown
pigment granules in cortex
Light medulla
Hair
Hair follicle:
composed of the
root sheath –
encasement with 2
layers:
– Internal root sheath
produced by matrix,
surrounds root
– External root
sheath
extension
epidermis
of
The Dermal root
sheath is part of
the dermis
Hair
bulb
- enlarged
region of the root
containing the
follicular papilla
(involution of
loose connective
tissue).
Hair
arrector
pili
muscle –
smooth muscle
that upon
contraction
forces the skin
into goose
bumps.
Accessory Structures
Glands: sebaceous and sweat glands
Sebaceous glands:
Usually connected to hair follicles
secretes sebum (oil)
Moisturizes hair and skin
– keeps hair pliable.
– Keeps skin soft
– Inhibits bacteria
Acne:
Inflammation of a sebaceous gland.
Normal sebaceous gland
Blocked sebaceous gland
Sudoriferous Glands
(Sweat glands)
2 main types of glands: eccrine and apocrine
eccrine:
– empty directly out through the skin surface
– tubular with a coiled basal portion located deep in the
dermis
– Regulates body temperature
apocrine:
–
–
–
–
larger, empty directly into the hair follicle canal
secretory portion located in the subcutaneous layer
Excretory duct opens into hair follicle
stimuli: psychic factors; emotions, sexual excitement
Sudoriferous Glands
Accessory
structures and location
Ceruminous Glands
Modified
ear.
sweat glands in the external
– Produce ear wax (cerumen)
– Provides a sticky barrier
Nails
Tightly packed, hard, keratinized epithelial
cells.
Structure:
– Nail body: visible portion
Pink
due to capillary bed
– Free edge: part that extends past the digit
White
due to lack of capillaries
– Nail root: portion buried in a fold of skin
Nails
Types of Skin
2
types of skin based on structure:
– Thin (hairy) skin
– Thick (hairless skin)
Functions of the Skin
Thermoregulation:
– by sweat and blood flow
– Excrete salts, water, and
small amounts of CO2 and
urea
– Absorbs lipid molecules
(vitamins A,D,E and K,
drugs, lotions, poisons,
heavy metals, steroids)
Blood reservoir
– 8-10% of blood flow
Protection
– Against external assault
Cutaneous sensations
– Tactile, pressure, pain,
temperature, tickle
Excretion and absorption
Synthesis of vitamin D
– UV light activates
precursor molecules that
can be modified by the
liver. Vit. D produces
calcitrol which aids in the
absorption of calcium in
the GI tract.
Maintaining Homeostasis: Skin
Wound Healing
Wound
routes:
healing can occur via 2
– Epidermal Wound Healing – affects only
the epidermis.
– Deep Wound Healing – wound extends
to dermis and subcutaneous layers
Epidermal Wound Healing
Injury
response:
– Basal cells detach from the basement
membrane.
– Hormone (epidermal growth factor)
stimulates basal stem cells to divide to
replace migrating cells.
– Migrating cells move across wound
– Cells stop migrating upon touching
other cells (contact inhibition)
Deep Wound Healing
4 phases:
– Inflammatory:
clot
formation closes the wound, WBC kill invaders
– Migratory:
scab
formation, epithelial cells migrate, fibroblasts
produce fibrin for scar tissue
– Proliferative:
Extensive
growth of epithelial cells, depositing
collagen fibers
– Maturation:
Scab
sloughs off, collagen fibers organize
Development of the Integumentary
System
Epidermis
is derived from the
ectoderm
Dermis is derived from the
mesoderm
Aging and the Integumentary
System
Most
changes occur in the dermis
– Collagen fibers decrease in number
– Elastic fibers loose elasticity
– Fibroblast (produce collagen and
elastin) decrease in number
– Decrease number of melanocytes – gray
hair
– Subcutaneous adipose tissue is lost
– Healing is longer
Sun Damage
UV A rays:
– Not absorbed by the ozone layer
– Penetrate deep into skin and absorbed by
melanocytes
– Depress the immune system
– Darken the skin
UV B rays:
– Some absorbed by ozone
– Penetration of skin not as deep
– Cause sunburn
Sun Damage
Sunscreen
– Absorb UV B, but allow UV A rays to
reach the skin
Sunblock
– Block both UV A and UV B rays
Skin Cancer
Basal cell carcinoma
– 78% of all skin cancers
– Tumors arise from the stratum basale
– Rarely metastasize
Squamous cell carcinoma
– 20% of all skin cancers
– Arise from squamous cell of epidermis
– metastasize
Malignant melanoma
– 2% of all skin cancers
– Arise from melanocytes
– Metastasize rapidly (can kill within months)
Skin Cancer
Basal cell
carcinoma
squamous
cell
carcinoma
melanoma
Burns
Burns
are graded by severity:
– First degree: only epidermis, red
– Second degree: all epidermis and part
of dermis, blisters
– Third degree: all epidermis, dermis and
subcutaneous layers, black
– Fourth degree: muscle layers are
burned
Burns
Half
of all patients with over 70% of
the body burned, dies.
Estimating
surface area for burns
uses the rule of nines.
Burns
Head and neck (front and back)
– 9%
Each upper limb (front and back)
– 9%
Trunk (front and back)
– 4 x 9% (or 36%)
Each lower limb
– 9% front
– 9% back
Perineum (anal and urogenital region)
– 1%
Pressure Ulcers
Decubitus
ulcers caused by constant
deficiency of blood flow from
prolonged pressure against an
object.
Occur
most often in bedridden
patients.