Histo Integ

• SKIN

  • Referred to as the cutaneous membrane
  • The subcutaneous membrane is called as hypodermis it anchors the dermis in the underlying tissue;
  • it is not a layer of the skin
  • Two layers of cutaneous membrane: sebaceous and sweat glands
  • Two layers of the skin: epidermis and dermis
  • Epidermis- outer layer
  • Dermis- inner layer
• Main layers – superficial to deep

  • Epidermis
  • Dermis
  • Hypodermis – not always considered

  part of skin
• Functions of the Skin

  1. Protection

  • acts as a barrier

  b. Sensation

  • huge or large sense organs: touch

  c. Excretion

  • excretion of sweat through appendages
  • excretion of unwanted substances and functions in thermoregulation
  • d. Vitamin D production
  • Needed to absorb calcium
  • Exposure to UV light
  • e. Immunity
  • f. Body temperature Homeostasis
• LAYERS OF THE SKIN

  Epidermis

  • Outer layer of the skin
  • Keratinized stratified squamous

  epithelium

  -Avascular (hardened by keratin)

  • Renews itself every 20-30 days
• Cell Types in Epidermis

  • Keratinocytes
  • Melanocytes
  • langherhan cells
  • merkel cells
• Keratinocytes - It is the principal cell type because it is

  the most abundant and comprised 85-95% of the total cell population

  • Function: keratin production –
  • Responsible for the renewal process
  • Serves as stem cells
  • Callus: thickened skin
• Melanocytes - Responsible for the melanin

  production. Produce melanin which accumulates on superficial side of nucleus

  • Prevents DNA mutation from the UV radiation
  • Accumulation of melanin results in freckles and moles
  • Melanin is the pigment responsible for the brown or black color of skin
  • Accounts for 7-10% of cell population
  • Membrane bound granules are called melanosomes wherein melanin production takes place
  • Bound to basal lamina by hemidesmosome
  • Tyrosine - amino acid source
• Langerhans Cells

  • Antigen-presenting cells
  • Present in other stratified squamous-

  epithelia

  • oral cavity, esophagus and vagina

  counterpart of macrophage

  • Comprise 3-8% of the cell population

  present in the epidermis

  • Contain Birbeck or vermiform

  granules

  • rod-shaped granules

  
  

  • Is also hard to identify in H&E
• Merkel Cells

  Most numerous in palms and soles

  (thick type of skin)

  • Bound to keratinocytes by

  desmosomes

  • Disc-shaped cells with short

  cytoplasmic processes
• Merkel disc - The combination of Merkel cells

  and sensory neurons that responds to pressure or touch
• Skin Color in Epidermis

  • Melanin
  • Carotene
  • Hemoglobin
• Melanin

  • Brown and black pigment
• Carotene

  • Orange-yellow pigment from some vegetables
  • Vitamin A precursor – vitamin A forms retinal which is needed for sight
  • Accumulates in adipose and stratum corneum cells
• Hemoglobin

  • Red, oxygen-carrying pigment in erythrocytes
  • More obviously detected in fair skin
• Types of Skin According to Thickness of Epidermis

  • Thick skin
  • Thin skin
• Thick Skin

  • Covers palms and doles
  • Dermal papillae are longer
  • The dermal papillae serve as boundary between dermis and epidermis and are usually found in the dermis
  • Epidermal Ridges is the counterpart of dermal papillae in epidermis
  • Contains numerous sweat glands but no hair follicle & sebaceous glands
• Thin Skin

  • Wider in terms of distribution
  • Covers the whole body except palms and soles
  • Stratum Basale similar to thick skin but thinner corneum layer and stratum spinosum
  • Stratum granulosum and lucidum are not present
  • The absence of stratum granulosum varies, some location covered in thin skin have stratum granulosum but are not well developed
  • Totally absent stratum lucidum
• Five Strata of the Epidermis from deep to superficial:

  • Stratum Basale
  • Stratum Spinosum
  • Stratum Granulosum
  • Stratum Lucidum
  • Stratum Corneum
• Stratum Basale

  • Also called as stratum germinativum
  • Highly mitotic (produces new skin layer)
  • 25% melanocytes
  • Deepest layer of the epidermis (closest

  to the dermis)

  • Found close to the dermal blood supply
  • Consists of a single layer of columnar or cuboidal cells which rest on the basement membrane
  • Basal cells are stem cells of the epidermis
• Stratum Spinosum

  • Slightly mitotic
  • Contains Langerhans’s macrophages
  • Several layers of many-sided

  (polyhedral) cells

  • The desmosomes would look

  spiny therefore called as spinosum
• Stratum Granulosum

  • Also contains Langerhans’s cell
  • Made up of 3-5 layers of flattened keratinocytes
  • Cannot undergo mitosis
  • Contains keratohyaline granules
  • Helps form keratin
  • Non membrane bound granules
  • Contains lamellar granules
  • Lipid containing granules
  • Membrane bound granules
  • Lamellar granules with

  desmosomes would serve as

  barrier against the entry or exit if

  substances in skin
• Stratum Lucidum

  • Also called as clear layer

  They appear clear layer with no cells, anucleated and devoid of

  organelles under the microscope

  • Only found in thicker epidermis palms, soles, callus
  • Completely keratinized
  • Dead cells
  • Contains 4-6 layers of closely packed,

  clear cells that contain gel-like

  substance eleiden
• Stratum Corneum

  • Outermost layer
  • Also completely keratinized
  • 15-20 rows of flat Dead cells
  • Tough, waterproofing protection
• Dermis

  • Also called as corium
  • Deeper layer of skin
  • Contains hair follicles, glands, nerves, and vessels (appendages)
  • All four tissue types present
  • Mainly strong, flexible CT- two layers

  Two Layers of the Dermis

  • Papillary
  • Reticular
• Papillary Layer - Areolar or loose type of connective

  tissue

  • Contains areolar CT

  Dermal Papillae - Located in the papillary layer.

  • Indent into epidermis
  • Forms fingerprints
  • Important for grip
  • Contains blood vessels
  • Meissner’s Corpuscles – nerve (touch) receptors
  • In epidermis, Merkel’s discs counterpart is the Meissner’s corpuscles
• Reticular Layer

  • Dense irregular CT
  • Contains blood vessels, nerves, glands, adipose
  • Two types of fibers in reticular: collagen and elastic
  • Collagen – prevents overstretching and tearing of skin
  • Elastin – allows skin to stretch
  • stretch marks – dermal tears
• Hypodermis

  • Not usually considered part of the skin
  • Also called subcutaneous layer
  • Site of subcutaneous injections absorbed directly into blood stream
  • Anchors skin to underlying organs, shock absorption, insulation
  • Composed mostly of adipose tissue
  • Very vascular
  • Pacinian Corpuscles – nerve endings responsible for sensitivity to deep pressure touch and high frequency vibration
• Sensory Nerve Endings in Skin

  • Free nerve endings
  • Encapsulated Nerve endings
  • Expanded Tip endings
• Free nerve endings - most abundant

  • most sensitive to touch, pain and temperature
  • superficial and found in epidermis (stratum granulosom)
• Expanded tip endings

  Merkel discs = touch and

  pressure

  • Expanded or broad tip
• Encapsulated nerve endings - Encapsulated are further

  surrounded by capsule

  • Ruffini corpuscles =deep pressure and stretch (found in hypodermis and reticular layer in skin)
  • End bulbs of Krause = touch and pressure (found in dermis papillary layer)
  • Pacinian corpuscles= vibration, stretch, pressure (found in hypodermis)
  • Meissner’s corpuscles = touch
• Important Structures of the Hair

  1. Hair shaft

  • Project from skin

  2. Hair Root

  • Embedded in the skin
  • Lies within the follicle

  3. Hair Follicle

  • Collective term for the combination of hair root plus the internal and external root sheaths
  • Extend into dermis
• Hair Follicle additional structures:

  1. Hair Bulb

  • Contains CT, vessels, and nerves
  • Expanded proximal part of hair follicle

  2. Hair Papilla

  • Distal part made up of blood vessels and nerves

  3. Germinal Matrix

  • Part of hair bulb
  • Cells in here are responsible for hair growth (hair matrix)
• Three Histologic Layer of Hair

  1. Medulla (core)
  2. Cortex ( surround core)
  3. Cuticles (Outermost)
• NAILS

  • Scale-like modifications of the

  epidermis

  • Heavily keratinized
  • Stratum Basale extends beneath the nail bed to form nail matrix
  • Responsible for growth (matrix region)
  • Lack of pigment makes them colorless
  • Lunula “little moon” – area of cell growth (white semicircle at base of nail)
  • Cuticle – area of skin that covers base of nail
  • Nail body rests on the nail bed (underneath body)
  • Nail root is the proximal part of nail
  • Nail matrix are cells responsible for nail growth
• Types of Sweat Glands (Cutaneous Glands)

  • Eccrine Glands
  • Apocrine Glands
  • Ceruminous Glands
  • Sebaceous Glands
• Eccrine Glands

  • Widely distributed in skin: abundant on palms, soles, forehead
  • Sweat composition: mostly water with a slightly acidic 4-6 pH
  • Function: thermoregulation
• Apocrine Glands

  • Ducts empty into hair follicles
  • Found mainly in anogenital & axillary region
  • Begin to function at puberty due to hormones
  • Organic contents: Fatty acids and proteins
  • can have a yellowish color that stains clothes
  • Odor is from associated bacteria
  • Antibacterial properties: secretion for

  protection
• Ceruminous Glands

  • Modified apocrine gland
  • Found in outer 1/3 of ear canal
  • Produce ear wax to trap “invaders”
• Sebaceous Glands

  • All over except palms and soles of feet, produces sebum or oil for waterproofing
  • Lubricant for skin & kills bacteria (antibacterial)
  • Most with ducts that empty into hair follicles
  • Glands are activated at puberty: stimulated by hormones
  • Acne – active infection of sebaceous glands