1
Q
Organs of Integumentary System
A
Skin Hair Oil & Sweat Glands Nails Sensory Receptors
2
Q
Functions of Integumentary System
A
Regulates body temp Stores blood Protects body from external environment Detects cutaneous sensations Extremes and absorbs substances Synthesizes vitamin D
3
Q
Epidermis
A
Superficial, thin layer
Composed of epithelial tissue
Avascular
4
Q
Dermis
A
Deeper, thicker layer
Composed of connective tissue
Contains a blood and nerve supply
5
Q
Epidermal Cells
A
Contains 4 types of cells:
- Keratinocytes
- Melanocytes
- Intraepidermal Macrophrages
- Tactile Epithelial Cells
6
Q
Keratinocytes
A
-Compose about 90% of epidermal cells
-Arranges in 4-5 layers and produce keratin
-Also produce lamellar granules that release a water-repellant sealant that decreases water entry and loss and inhibits passage of foreign molecules
-
7
Q
Melanocytes
A
- 8% of epidermal cells
- develop from neural crest of a developing embryo and produce melanin
- have cuboidal cell body with arm-like projections that go between keratinocytes
- 1 melanocyte : 30 keratinocytes
- arm-like projections transfer melanin to keratinocytes
- inside keratinocytes, melanin cluster to form protective veil over nucleus on the side toward the skin surface
- melanocytes themselves are susceptible to damage by UV light
8
Q
Melanin
A
-pigment that contributes to skin colour and absorbs damaging UV light
9
Q
Intraepidermal Macrophage cells/Langerhan Cells
A
- arise from red bone marrow and migrate to epidermis
- have long projections that go in between keratinocytes
- participate in immune responses mounted against microbes that invade the skin
- easily damaged by UV light
10
Q
Tactile Epithelial Cells / Merkel Cells
A
- least numerous cells
- located in deepest layer of the epidermis where they contact the flattened process of a sensory neuron - a tactile disc
- Tactile epithelial cells and tactile discs detect touch sensations
11
Q
Formation of Epidermis
A
- Several distinct layers of keratinocytes in various stages of development form epidermis
- Epidermis has 4 layers:
- Stratum Basale
- Stratum spinosum
- Stratum granulosum
- Stratum Lucidem (in thick skin only)
- Stratus Corneum (can be thick or thin depending on skin type)
12
Q
Stratum Basale
A
- Deepest layer
- Single row of cuboidal/columnar keratinocytes
- Nuclei of these keratinocytes are large, cytoplasm contains many ribosomes, small Golgi, few mitochondria, and little rough ER.
- Cytoskeleton includes scattered intermediate filaments called keratin intermediate filaments which form keratin.
- Keratin protects deeper level from injury
- Melanocytes and Tactile epithelial cells scattered among keratinocytes
- Sometimes referred to as stratum germinativum due to its role in forming new cells
13
Q
Stratum Spinosum
A
- Superficial to stratum Basale
- Contains numerous keratinocytes produced by stem cells in stratum basale, arranged in 8-10 layers
- few tactile epithelial cells
- Cells in more superficial layers become slightly flattened
- At each spinelike projection, bundles of keratin intermediate filaments insert into desmosomes, which tightly join the cells to one another
- This arrangement provides both strength and flexibility to skin
14
Q
Stratum Granulosum
A
- Middle of epidermis
- 3-5 layers of flattened keratinocytes that are undergoing apoptosis
- Nuclei and other organelles of these cells being to degenerate as they move further from their source of nutrition (dermal blood vessels)
- keratin intermediate filaments no longer being produced, but they become more abundant because the organelles in the cell are regressing
- distinctive darkly staining protein granules called keratohyalin (involved in assembling keratin intermediate filaments into keratin)
- Lamellar granules also present which fuse with plasma membrane and release lipid-rich secretion
- secretion is deposited in the spaces between cells of 3 superficial epidermal layers.
- lipid rich secretion acts as water-repellant sealant
- Stratum granulosum marks transition between metabolically active strata and dead cells.
15
Q
Stratum Lucidum
A
- Present in thick skin of areas such as fingertips, palms, and soles.
- 4-6 layers of clear, flat, dead keratinocytes that contain large amounts of keratin and thickened plasma membrane.
- keratin is more regularly arranged parallel to the skin surface to provide extra toughness.
16
Q
Stratum Corneum
A
- most superficial layer
- average of 25-30 layers of flattened, dead keratinocytes, but can range depending on thickness of skin
- thin, flat, plasma membrane enclosed packages of keratin are called corneocytes or squames.
- no longer contain nuclei or organelles
- corneocytes within each layer overlap one another like scales
- neighbouring layers form strong connections also
- plasma membrane of adjacent corneocytes are arranged in complex, wavy folds that fit together like a puzzle to hold layer together
- cells are continuously shed and replaced by cells from deeper strata
- constant exposure of skin to friction stimulates increased keratin production resulting in calluses
17
Q
Dermis
A
- Composed of dense, irregular connective tissue
- contains collagen and elastin fibers
- thicker than epidermis
- great tensile strength
- ability to stretch and recoil easily
- cells in dermis are scattered and include fixed cells and wandering cells
- predominant fixed cell = fibroblasts
- wandering cell = macrophages, mast cells, eosinophils, neutrophils and dermal interstitial dendritic cells.
- dermis essential to survival of epidermis
18
Q
Layers of dermis
A
- Thin, superficial, papillary region
- Thick, deeper reticular region
19
Q
Papillary Region
A
- 20% of thickness of dermal layer
- contains thin collagen fibres and fine elastic fibers
- surface area increased by dermal papillae that project into undersurface of epidermis
- dermal papillae increase contact region between dermis and epidermis
- in thick skin they are longer and more abundant than in think skin
- all dermal papillae contain capillary loops
- some contain corpuscles of touch (sensitive nerve endings to detect touch)
- other dermal papillae contain free nerve endings
- different free nerve endings initiate signals like warmth, coolness, tickling and itching,
20
Q
Reticular Region
A
- attached to subcutaneous layer
- contains bundles of thick collagen fibres, scattered fibroblasts and various wandering cells, and some coarse elastic fibres
- presence of some adipose cells in deepest part of layer
- collagen arranged in a netlike manner and more regular that papillary region
- this orientation aligns with the local tensile forces to help skin resist stretching
- blood vessels, nerves, hair follicles, sebaceous glands and sudoriferous glands occupy space between fibres
- in some regions, collagen fibres orient in a certain direction due to natural tension of bony projections, muscles, and joint movements.
- Tension lines indicate predominant directions of underlying collagen
21
Q
Dermis
A
- both layers contain dense horizontal networks of small blood vessels
- Collagen and elastic fibres allow skin ability to stretch, elasticity, and ability to return to normal shape after stretching
22
Q
Epidermal Ridges
A
- series of ridges and grooves
- straight lines or patterns of loops
- produced during 3rd month of fetal development
- increase surface ares to increase grip by increasing friction
- creates stronger bond between epidermis and dermis in regions of high friction
- increase number or corpuscles of touch increasing tactile sensitivity
23
Q
Cutaneous Arterial Plexus
A
-located at junction of dermis and subcutaneous layer and sends branches that supply the sebaceous and sudoriferous glands, deep portion of hair follicles, and adipose tissue
24
Q
Papillary Arterial Plexus
A
- formed at level of papillary region
- sends branches that supply the capillary loops in dermal papillae, sebaceous glands and the superficial portion of hair follicles.
- accompanied by venous plexuses that drain blood from dermis into larger subcutaneous veins.
25
How do nutrients and oxygen reach epidermis
- nutrients and oxygen diffuse to the avascular epidermis from blood vessels in the dermal papillae
- epidermal cells of stratum basale (closest to blood vessels) receive most of the nutrients and oxygen
- these cells are the most active metabolically and continuously undergo cell division to produce new keratinocytes
- as new keratinocytes are pushed further from the blood supply, the epidermal strata above the stratum basale receive fewer nutrients and the cells become less active - eventually dying
26
Summary of Papillary Region
Superficial portion of dermis accounting for about 20% of dermis
Consists of areolar connective tissue with thin collagen fibres and fine elastic fibres
Contains dermal papillae that house blood capillaries, corpuscles of touch, and free nerve endings
27
Summary of Reticular Region
Deeper portion of the dermis accounting for about 80% of the dermis
Consists of dense irregular connective tissue with bundles of thick collagen and some coarse elastic fibres
Spaces between fibres contain some adipose cells, hair follicles, nerves, sebaceous and sudoriferous glands.
28
Structural basis of skin colour
- Melanin, hemoglobin, and carotene are the 3 main pigments
- 2 forms of melanin: PHEOMELANIN (yellow-red) and EUMELANIN (brown-black) are most apparent in hair
- 2 types of freckles: EPHELIDES (light freckles) and LENTIGINES (dark/sunburn freckles)
- Nevus: a round flat/raised area that usually develops in childhood and represents a benign localized overgrowth of melanocytes (aka a mole)
29
Synthesis of melanin
- melanocytes synthesize melanin from the amino acid TYROSINE in the presence of TYROSINASE
- synthesis occurs in organelle called melanosome
- UV light increases enzymatic activity in melanosomes
- DNA damage by UV light stimulates melanin production to protect against further damage
30
Carotene
- yellow/orange pigments
- precursor to vitamin A (used to synthesize pigments for vision) is stored in the stratum Corneum and fatty areas of the dermis and subcutaneous level in response to dietary intake
- large intakes of carotene will cause skin to turn orange
31
Tattooing and Body Piercing
- ink deposited into collagen and cells of dermis
- becomes trapped in fibrocytes of upper layer
-insertion of jewelry through an artificial opening
32
Subcutaneous Layer / Hypodermis
- layer deep to the dermis
- connective tissue layer - not part of skin
- in some regions may be a loose connective tissue called areolar tissue
- some regions may have a thick layer of fibrous bands of collagen accompanied by adipose tissue
- fibres that extend from dermis, attach skin to hypodermis, which attaches to underlying fascia (connective tissue surrounding muscle/bone)
- serves as storage depot for fat.
- contain large blood vessels to supply and drain capillaries of skin
- contains encapsulated nerve endings called lamellated corpuscles (sensitive to pressure)
33
Functions of Subcutaneous
- loose binding tissue that unites skin to deeper structures, while still allowing skin to move freely.
- forms tough fat pads composed of fibrous bands of collagen in adipose tissues which absorb shock and protect underlying muscle/bone
- principle site of energy storage
- adipose tissue is active metabolic tissue with numerous nerve endings and rich vascular networks that help regulate and mobilize the energy stores
- serves as layer of insulation that helps retard heat loss from body
34
Hair
- sense covering of pili
- absent from palms, palmar surfaces of fingers, soles, and plantar surfaces of toes
- genetic/hormone influences hair thickness and distribution
- hair on head can protect skin from UV rays and injury
- hair in nose/ear can protect those structures
- touch receptors associated with hair follicles are activated by even slightest movement
35
Anatomy of Hair
-composed of columns of dead, keritanized epidermal cells bonded together by extra cellular proteins
36
Hair shaft
-superficial portion of hair
-projects from surface of skin
-shape of shaft varies with different ethnic groups
-straight hair has round shafts
Wavy hair has oval shafts
-curly hair has kidney shaped shafts
37
Hair root
- portion of hair deep to the shaft that penetrates the dermis and sometime subcutaneous layer
- root and shaft consist of:
1. Inner medulla (2-3 rows of cells containing pigment granules)
2. middle cortex (major part of shaft made of elongated cells)
3. Cuticle (single layer of thin flat cells that are keratinized)
38
Hair follicle
- surrounds root of hair
- made up of external root sheath and internal root sheath
- external: downward continuation of epidermis containing all epidermal layers near surface, and at the base contains only stratum basale
- internal: produced by hair matrix and forms cellular tubular sheath of epithelium between external root sheath and hair
- together referred to as epithelial root sheath
- dense dermis surrounding the hair follicle is called dermal root sheath
39
Hair bulb
- onion shaped structure at the base of the follicle surrounding dermal root sheath
- houses a nipple-shaped indentation called the papilla of the hair (contains areolar connective tissue and many blood vessels)
- also contains germinal layer called hair matrix
- hair matrix cells arise from stratum basale
- hair matrix cells responsible for growth of hair
- hair matrix cells give rise to cells of internal tooth sheath
40
Arrector Pili
- extends from superficial dermis of skin to connective tissue sheath around hair follicle
- when stimulated the arrector pili muscles contract pulling the hair shafts perpendicular to skin surface
41
Hair root plexus
- formed by dendrites of neuron surrounding each hair follicle
- sensitive to touch
- initiates nerve impulses if hair shaft is moved
42
Hair growth
- each hair follicle goes through growth cycle
- growth stage: cells of hair matrix divide and are pushed upward
- regression stage: cells stop dividing, hair follicle shrinks, hair stops growing
- resting stage: after resting a new cycle beings
43
Types of Hairs
Vellus hairs: short fine hairs aka peach fuzz
Terminal hairs: pubic hair, hair on head, eyebrows, lashes etc
44
Skin Glands
-single/groups of epithelial cells that secrete a substance
45
Sabaceous Glands
- oil glands
- simple, branches rounded glands
- connected to hair follicles
- secreting portion lies in dermis, opens into neck of hair follicle
- in some areas open directly to surface of skin (lips)
- found everywhere except palms and soles
- most numerous where there is most hair
- base of gland has a lining of cuboidal cells which divide to produce more cells
- lumen eventually fills with cells which then develop lipid-filled vesicles in their cytoplasm and rupture to fill the duct with an oil secretion called sebum.
- sebum is mixture of fats, cholesterol, proteins and inorganic salts
- sebum coats surface of hairs to prevent from dying
- sebum prevents excessive evaporation of water from skin, keeps skin soft, and inhibits growth of certain bacteria
46
Sudoriferous Glands
- cells of sweat glands release their secretion by exocytosis and empty them onto the skin surface through pores or into hair follicles
- eccrine or apocrine
47
Eccrine Sweat glands/merocrine
- simple, cuboidal tubular glands
- most common
- creates pore in epidermis
- open along apex of epidermal ridges
- help regulate body temp through evaporation (thermoregulation)
- sweat that evaporate from skin before it is perceived as moisture is termed insensible perspiration
- sweat excreted in large amounts and is seen as moisture is called sensible perspiration
- also elimates urea, uric acids, and ammonia
48
Appocrine Sweat glands
- simple, cuboidal tubular glands but have larger ducts and lumens than eccrine glands
- found mainly in skin of axilla, groin, bearded areas
- release secretions by pinching off a portion of the cells
- Secretion released by exocytosis
49
Ceruminous Glands
- modified sweat glands in external ear
- produce waxy lubricating secretion
- secretary portion of glands lie in subcutaneous layer deep to sebaceous glands
- ducts open either to surface of external auditory canal or into ducts of sebaceous glands
- combined secretion of ceruminous and sebaceous glands is called cerumen (earwax)
- provides sticky barrier that prevents entry of foreign substance
50
Nails
- tightly packed, hard, keratinized epidermal cells
| - consists of nail body, free edge, and a nail root
51
Nail Body
- visible portion of the nail
- flattened, keratinized cells
- cells do not shed
- below body is a layer of epithelium and deeper layer of dermis'-appears pink because of underlying capillaries
52
Free edge
- nail body that extends past distal end of digit
| - white because there are no underlying capillaries
53
Nail Root
- buried in fold of skin
- lunula: crescent-shaped area at proximal end. Appears white because of thickened stratum basale and doesn't allow vascular tissue to show through
- hyponychium: thickened stratum Corneum that attaches free edge to fingertip
54
Nail Bed
- skin below nail plate that extends from lunula to hyponychium
- epidermis of Nail bed lacks stratum granulosum
- eponychium: aka cuticle is the narrow band of epidermis that extends from and adheres to the margin of the nail wall (consists of stratum Corneum)
55
Nail Matrix
- portion of epithelium proximal to the nail root
- superficial nail matrix cells divide mitotically to produce new nail cells
- harder, outer layer pushed forwards over stratum basale
- growth rate of nail is determined by rate at which nail matrix cells divide... influence by age, health, nutrition
56
Functions of Nails
- protect distal end of digits
- provide support and counter pressure to palmar surface of fingers to enhance touch perception and manipulation
- allow us to grasp and manipulate small objects and can be used to scratch and groom the body
57
Thin Skin
- found in all parts of body except palmar areas and soles
- lacks stratum lucidum
- thin strata spinosum and Corneum
- lack epidermal ridges due to poorly developed and fewer dermal papillae
- hair follicles present
- sebaceous glands present
- few sudoriferous glands
- few sensory receptors
58
Thick Skin
- found in palmar areas and soles
- thicker strata Corneum and spinosum
- presence of strata lucidum
- epidermal ridges present due to well-developed and more numerous dermal papillae
- absence of hair follicles
- absence of sebaceous glands
- numerous sudoriferous glands
- more sensory receptors
59
Functions of skin
- thermoregulation
- blood reservoir
- protection
- cutaneous sensations
- excretion and absorption
- synthesis of vitamin d
60
Development of integumentary system
- epidermis derived from ectoderm, which covers the surface of the embryo
- at week 4 epidermis consists of 1 layer of skin
- at week 7 basal layer divides to form superficial protective layer of flattened cells called periderm
- by month 5 the sloughed off periderm and secretions from sebaceous glands mix to form vernix caseosa
- vernix caseosa covers and protects skin of fetus from amniotic fluid and facilitates birth
