Module 2

• Integument


  composite organ
• Epidermis


  from single layered surface ectoderm
• Dermis comes from several sources:

  Mesoderm and mesenchyme
• Dermis

  Produces the reticular lamina
• Dermis

  is mainly dermatome
• Dermis

  Somites produce sclerotome medially and dermomyotome laterally 

• Dermis

  Dermomyotome outer wall spreads under ectoderm to form connective tissue of dermis
• Dermis

  Somites produce sclerotome medially; dermomyotome laterally
• Integument


  Largest organ (~15% of body weight)
• INTEGUMENT


  Large surface area in humans (1.5-2 m squared)
• 3 Layers of integument

  Epidermis - keratinized stratified squamous epithelium

  Dermis - connective tissue layer

  Hypodermis - below
• Integument


  Variable thickness (1-2 mm)

  Dermis up to 6 mm
• 1.

  A) Mucous gland

  B) Granular gland

  C) Stratum germinativum

  D) Basal lamina

  E) Chromatophores

  F) Stratum laxum

  G) Stratum compactum

  H) Epidermis

  I) Dermis

  
• Integument: Functions

  Protection (trauma, fluid loss, chemical attacks, UV, infection)

  Acidic nature maintains bacterial communities in check

  Sensory (touch, pressure, pain, temperature)

  Thermoregulation (insulation, evaporative cooling)

  Vitamin D3 synthesis

  Excretion of salts, water, organic wastes

  Gas exchange

  Nonverbal communication
• Dermis

  Dermal bones - produced through intramembranous ossification

  Placoderms, some mammals (e.g armadillos)

  Plies - collagen fibers woven into layers

  Cloth fabric-like allows bending but resists distortions in body shape
• Epidermis

  Mucus production prevents desiccation

  Fishes - bacterial infection protection, laminar flow

  Lissamphibia - bacterial infection protection, prevents desiccation
• Skin

  Skin parts

  A) Mucous gland

  B) Granular gland

  C) Basal lamina

  D) Stratum germinativum

  E) Chromatophores

  F) Epidermis

  
• Epidermis

  Stratum corneum - outermost layer; keratinized
• Keratinization

  accumulation of keratin from dying epidermal cells
• Keratinization

  Produced by keratinocytes

  Alpha (soft) - Flexible

  Beta (hard) - Specializations

  Callus - thick protective keratinized layer
• Phylogeny: Agnatha


  No layer of dead cells = no keratinization in almost all cells

  Horny teeth (lampreys)

  Slime glands - row of ducts ventrally along the body

  Copious slime production
• Phylogeny: Fishes

  No layer of dead cells = no keratinization in almost all cells

  Mucus production
• Two cell types in fishes

  Epidermal cells and Unicellular glands
• 4 types of unicellular glands in fishes

  Club cell - excitation (alarm/fear)

  Granular cell

  Goblet cell

  Sacciform cell - deterrent chemicals
• Photophores

  light-emitting organs
• Chromatophores


  pigment-bearing cells
• Chrondrichthyes

  Dermal bone absent

  Placoid scales present

  Dermis with fabric-like arrangement of fibrous connective tissue
• Chondrichthyes

  Placoid scales present

  Develops in dermis; projects through epidermis

  Tip made of enamel; pulp cavity within

  Controls wake formation during swimming
• Bony fishes

  Dermis divided into superficial loose connective tissue & dense fibrous connective tissue

  Dermal scales do not pierce slime-

  coated epidermis
• Bony fishes

  Cosmoid scales (Fossil coelacanths & lungfishes)

  Two basal bone layers

  Isopedine – dense lamellar base

  Spongy vascular bone

  Outer surface – dentin (cosmine) with layer of enamel
• Ganoid scales (Polypteriformes, Gars)


  Thick enamel (ganoine) surface layer

  Modified cosmoid scales

  Cosmine replaced by dentine
• Cycloid and ctenoid scales (Teleostei)


  Cycloid scales with concentric rings (circuli)

  Ctenoid scales with posterior projections (ctenii)
• Amphibians

  metamorphose to terrestrial form

  Dermal scales only present in Apoda (no legs)

  Skin specialized as respiratory surface for gas exchange

  Capillary beds in lower epidermis

  Anura (frogs) rely on cutaneous respiration
• Urodela


  Aquatic larval has Leydig cells for protection against microbes

  Adult has nuptial pads on digits of males which are calluses of cornified epidermis
• Amphibians

  Mucus and poison glands on dermis

  Chromatophores in epidermis but mostly in dermis

  Capillary beds reach to lower epidermis for respiration
• Reptiles

  Extensive keratinization; fewer skin glands

  Scales from folded epidermis
• Reptiles

  Hinge - flexible junction between scales
• Reptiles

  Scutes - large platelike scales
• Reptiles

  Gastralia - dermal bones in abdominal area
• Reptiles

  Osteoderms - epidermis-supporting dermal bones