powerpoint lecture

advertisement
Anatomy & Physiology I
Lecture 4
Chapter 5: The Integumentary
System
The Integumentary System
• The skin and its derivatives that function in
protection for the rest of the body
The Skin
• Consists of two distinct regions:
• Epidermis—superficial region
• Epithelial tissue
• Dermis—underlies epidermis
– Mostly fibrous connective tissue
– vascularized
Let’s go deeper
• Hypodermis (superficial fascia)
– Subcutaneous layer deep to skin
– Not part of skin but is also protective
• Mostly adipose tissue that absorbs shock &
insulates
• Anchors skin to underlying structures – mostly
muscles
Figure 5.1 Skin structure.
Hair shaft
Dermal papillae
Epidermis
Subpapillary
plexus
Papillary
layer
Sweat pore
Appendages of
skin
Eccrine sweat gland
Arrector pili muscle
Sebaceous (oil)
gland
Hair follicle
Hair root
Dermis Reticular
layer
Hypodermis
(subcutaneous
tissue; not part
of skin)
Nervous structures
Sensory nerve fiber
with free nerve endings
Lamellar corpuscle
Hair follicle receptor
(root hair plexus)
© 2013 Pearson Education, Inc.
Cutaneous plexus
Adipose tissue
The Epidermis
• Keratinized stratified squamous epithelium
• Four or five distinct layers
– Stratum basale
– Stratum spinosum
– Stratum granulosum
– Stratum lucidum (only in thick skin)
– Stratum corneum
Cells of Epidermis
• Four cell types
– Keratinocytes
– Melanocytes
– Dendritic (Langerhans) cells
– Tactile (Merkel) cells
Cells of Epidermis
• Keratinocytes
– Produce fibrous protein keratin
– Most cells of epidermis
– Tightly connected by desmosomes
• Melanocytes
– 10–25% of cells in deepest epidermis
– Produce pigment melanin
– Protect apical surface of keratinocyte nucleus from UV
damage
Cells of the Epidermis
• Dendritic (Langerhans) cells
– Macrophages – key activators of immune system
• Tactile (Merkel) cells
– Sensory touch receptors
Figure 5.2a The main structural features of the skin epidermis.
Stratum corneum
Most superficial layer; 20–30 layers of dead cells
Flat membranous sacs filled with keratin.
Stratum granulosum
Typically five layers of flattened cells, organelles deteriorating;
Stratum spinosum
Several layers of keratinocytes unified by desmosomes.
Stratum basale
Deepest epidermal layer; one row of actively mitotic stem
cells
Dermis
© 2013 Pearson Education, Inc.
Layers of Epidermis
• From deep to superficial:
•
•
•
•
•
Stratum basale
Stratum spinosum
Stratum granulosum
Stratum lucidum (only in thick skin)
Stratum corneum
Stratum Basal (Germinativum)
• Deepest epidermal layer
– Attached to dermis
• Single row of stem cells, actively mitotic
– Produces two daughter cells
• One cell journeys from basal layer to surface
• One cell remains in stratum basale as stem cell
• 10-25% of layer is Melanocytes
Stratum Spinosum
• Several layers thick
• Cells contain web-like system of intermediate
prekeratin filaments attached to desmosomes
• Abundant melanosomes and dendritic cells
Stratum Granulosum
• Thin - four to six cell layers
• Cells flatten
– Nuclei and organelles disintegrate
• Keratinization begins
– Help form keratin in upper layers
• Cell accumulate keratohyaline and lamellar granules
• Their water-resistant glycolipid slows water loss
Stratum Lucidum
• Only in thick skin
• Thin, translucent band superficial to the
stratum granulosum
• A few rows of flat, dead keratinocytes
Stratum Corneum
• 20–30 rows of dead, flat, anucleate keratinized
membranous sacs
• Three-quarters of epidermal thickness
• Though dead, its cells have functions
– Protect deeper cells from environment and water loss
– Protect from abrasion and penetration
– Barrier against biological, chemical, and physical
assaults
Figure 5.2b The main structural features of the skin epidermis.
Keratinocytes
Stratum corneum
Most superficial layer; 20–30 layers of dead cells,
essentially flat membranous sacs filled with keratin.
Glycolipids in extracellular space.
Stratum granulosum
Typically five layers of flattened cells, organelles
deteriorating; cytoplasm full of lamellar granules
(release lipids) and keratohyaline granules.
Stratum spinosum
Dendritic
Several layers of keratinocytes unified by desmosomes.
cell
Cells contain thick bundles of intermediate filaments
made of pre-keratin.
Sensory
Stratum basale
nerve
Dermis
Deepest epidermal layer; one row of actively
ending
mitotic stem cells; some newly formed cells
Melanin
Tactile
become part of the more superficial layers.
granule
(Merkel) cell
See occasional melanocytes and dendritic
Melanocyte
Desmosomes
cells.
© 2013 Pearson Education, Inc.
Keratinocytes and Melanocyte
Network
The Walking Dead!
• Average person shed 50,000 dead cells every
minute
– 40 lbs of skin in a lifetime
Dermis
• Strong, flexible connective tissue (proper)
– Fibroblasts, macrophages, mast cells and white
blood cells
• Contains:
– nerve fibers; blood and lymphatic vessels, hair
follicles, and oil and sweat glands
• Contains two layers
Figure 5.1 Skin structure.
Hair shaft
Dermal papillae
Epidermis
Subpapillary
plexus
Papillary
layer
Sweat pore
Appendages of
skin
Eccrine sweat gland
Arrector pili muscle
Sebaceous (oil)
gland
Hair follicle
Hair root
Dermis Reticular
layer
Hypodermis
(subcutaneous
tissue; not part
of skin)
Nervous structures
Sensory nerve fiber
with free nerve endings
Lamellar corpuscle
Hair follicle receptor
(root hair plexus)
© 2013 Pearson Education, Inc.
Cutaneous plexus
Adipose tissue
Papillary Layer of the Dermis
• Papillary
– Areolar connective tissue with collagen and elastic
fibers and blood vessels
– Phagocytes can patrol for microorganisms
• Home to dermal papillae
– Superficial peglike projections
Papillary Layer of the Dermis
• Dermal Papillae
– indent the superior epidermis
– conatin capillary loops, pain and touch receptors
• Friction ridges
– the collection of skin ridges created by dermal
papillae
– enhance gripping and touching ability
– give us our fingerprint
Figure 5.4a Dermal modifications result in characteristic skin markings.
Openings of
sweat gland ducts
© 2013 Pearson Education, Inc.
Friction
ridges
Friction ridges of
fingertip (SEM 12x)
Reticular Layer of Dermis
• Majority of dermal thickness
• Dense fibrous connective tissue
– Elastic fibers provide stretch-recoil properties
• Collagen fibers
– Provide strength and resiliency
– Bind water
Reticular Layers form Cleavage Lines
• Cleavage lines
– formed from the separation between thick
bundles of interlacing collagen fibers
• Externally invisible
• Important to surgeons
– Incisions parallel to cleavage lines gap less and
heal more readily
Figure 5.4b Dermal modifications result in characteristic skin markings.
© 2013 Pearson Education, Inc.
Cleavage lines in the
reticular dermis
Reticular Layer of the Dermis
• Cleavage lines
– Collagen gives skin strength
– Collagen binds water to keep skin hydrated
• Flexure lines
– dermal folds that occur at or new joints, where
dermis is tightly secured to deeper structures
Figure 5.4c Dermal modifications result in characteristic skin markings.
Flexure lines
on digit
Flexure lines
on the palm
© 2013 Pearson Education, Inc.
Flexure lines of the
hand
Skin Color
• Three pigments contribute to skin color:
– Melanin
– Carotene
– Hemoglobin
Melanin
• Two forms
– Reddish-yellow to brownish-black
• Color differences due to amount and form
– Produced in melanocytes
– Same relative number in all people
• Migrates to keratinocytes to form "pigment
shields" for nuclei
Carotene
• Yellow to orange pigment
– Most obvious in palms and soles (St. corneum
thick)
• Accumulates in stratum corneum and
hypodermis
• Yellowish-tinge of some asians – carotene and
melanin variations
Hemoglobin
• Pinkish hue of fair skin
• Red blood cells circulating through the dermal
capillaries
• Hemoglobin seen easier in lighter melanin
Caucasians
Appendages of the Skin
• Derivatives of the epidermis
– Hairs and hair follicles
– Nails
– Sweat glands
– Sebaceous (oil) glands
• Function: Maintain body homeostasis
Hairs and Hair Follicles
• Functions are protective;
–
–
–
–
Warn of insects on skin
Physical trauma
Heat loss
Sunlight
• Hair pigments
– Melanins (yellow, rust, brown, black); trichosiderin in
red hair
– Gray/white hair: decreased melanin production,
increased air bubbles in shaft
Structure of a Hair
• Flexible strands produced by hair follicles and
consist of dead, keratinized cells
• Hair shaft dictates properties of hair
– flat = hair is kinky
– oval = hair is silky, wavy
– round = hair is straight, course
Hair Follicle
• Supports the hair
• Extends down the epidermal surface into the
dermis
• At base (hair bulb) knot of sensory nerves
– hair follicle receptors
– papilla contains capillary bed
Figure 5.5a Skin appendages: Structure of a hair and hair follicle.
Follicle wall
• Peripheral
connective tissue
(fibrous) sheath
• Glassy membrane
• Epithelial root sheath
• External root sheath
• Internal root sheath
Hair shaft
Hair
•Cuticle
• Cortex
•Medulla
Diagram of a cross section of a hair within its follicle
Arrector
pili
Sebaceous
gland
Hair root
Hair bulb
© 2013 Pearson Education, Inc.
Figure 5.5c Skin appendages: Structure of a hair and hair follicle.
Hair shaft
Arrector
pili
Sebaceous
gland
Hair root
Hair bulb
Follicle wall
•Peripheral connective
tissue (fibrous) sheath
•Glassy membrane
•Epithelial root sheath
• External root sheath
• Internal root sheath
Hair root
• Cuticle
• Cortex
• Medulla
Hair matrix
Hair papilla
Melanocyte
Subcutaneous
adipose tissue
Diagram of a longitudinal view of the expanded hair
© 2013 Pearson Education, Inc. bulb of the follicle, which encloses the matrix
Arrector pili
• Bundle of smooth muscle
• Associated with each hair follicle
• Contraction pulls hair follicle upright and
dimples the skin surface
– goose bumps
Nails
• Scale-like modifications of epidermis
– Protective cover for distal, dorsal surface of fingers
and toes
• Contain hard keratin
• Nail matrix at base of nail responsible for its
growth
Sweat Glands
• ~3 million per person
• Two main types
– Eccrine (merocrine) sweat glands
– Apocrine sweat glands
Eccrin Sweat Glands
• Majority of sweat glands
– Abundant on palms, soles and forehead
• Simple, coiled, tubular glands that function in
thermoregulation
– Regulated by sympathetic nervous system
• Their secretion is sweat (filtrate of the blood)
– 99% water, salts, vitamin c, antibodies, dermcidin
(microbe-killing peptide), metabolic wastes
Figure 5.7a Photomicrograph of a sectioned sebaceous gland (90x).
Sebaceous
gland
Dermal
connective
Hair in
hair follicle
tissue
Sebaceous
gland duct
Sweat
pore
Eccrine
gland
Secretory cells
Photomicrograph of a
sectioned sebaceous
gland (90x)
© 2013 Pearson Education, Inc.
Apocrine Sweat Glands
• Roughly 2000 confined to axillary and
anogenital areas of body
• Empty into hair follicles, rather than on the
skin (eccrine)
• Contain sweat, fatty substances and protein
– with bacterial decomposition = body odor
Apocrine Sweat Glands
• Begin functioning at puberty
– possibly the human equivalent to animals’ sexual
scent glands
– sexual foreplay increase their activity
– do not participate in body cooling (sweat)
– precise function not known
– activated by nerve fibers during pain and stress
Modified Apocrine Glands
• Ceruminous glands
– lining of external ear canal; secrete cerumen
(earwax)
• Mammary glands
– secrete milk
Sebaceous Glands
• Widely distributed
– Not in thick skin of palms and soles
• Most develop from hair follicles and secrete into
hair follicles
• Softens hair and skin
• Stimulated by hormones, especially androgens
– Secrete sebum consisting of lipids and cell fragments
– Acts as a bactericidal
Figure 5.7a Photomicrograph of a sectioned sebaceous gland (90x).
Sebaceous
gland
Dermal
connective
Hair in
hair follicle
tissue
Sebaceous
gland duct
Sweat
pore
Eccrine
gland
Secretory cells
Photomicrograph of a
sectioned sebaceous
gland (90x)
© 2013 Pearson Education, Inc.
Functions of the Skin
•
•
•
•
•
•
Protection
Body temperature regulation
Cutaneous sensation
Metabolic functions
Blood reservoir
Excretion
Protection
• Three types of barriers
• Chemical barriers
– secretions and melanin
– acid mantle: the low pH of secretion
– antibiotic properties of secretion
• Physical barriers
– only lipid solvents can dissolve through skin
• Biological barriers
– innate immunity (macrophages
Body Temperature Regulation
• Body temperature normal:
– ~500 ml/day of perspiration
• Body temperature rises:
– dilation of dermal vessels and increased sweat gland
activity
• Cold external environment
– Dermal blood vessels constrict causing warm blood to
bypass skin
– Skin temperature drops to slow passive heat loss
Cutaneous Sensatioin
• Cutaneous sensory receptors
– exteroceptors
• Part of nervous system
– detect temperature, touch, and pain
Metabolic Functions
• Fueled by sunlight
• Synthesis of:
– Vitamin D precursor
– Collagenase for collagen turnover
• Keratinocyte enzymes:
– Chemical conversion of carcinogens
– Activate some steroid hormones (cortisone to
hydrocortison)
Blood Reservoir
• Dermal vascular supply can hold up to 5% of
body’s blood volume
• Constriction of dermal blood vessels force
blood to where its needed
– vascular shunts
Excretion
• Body eliminates some of the nitrogen wastes
– ammonia, urea, etc.
• Sweating also increases loss of water and salts
that must be constantly added back
• Major function for liquid secretion is kidneys
Lab Exercise for Today
• Exercise 7
Download
Related flashcards

Neuroscience

42 cards

Brain disorders

34 cards

Brain disorders

35 cards

Sleep disorders

43 cards

Sleep disorders

45 cards

Create Flashcards