Lecture 4: Integument Structure and Function

Integument

Largest organ in the body

Cutaneous membrane + Accessory structures

Protects the rest of the body from the environment

Cutaneous membrane

Epidermis and dermis

Functions of integument

Barrier, sense organ, thermal homeostasis, vitamin D and calcium homeostasis

Thick skin characteristics

Thick epidermis

Thin dermis

Hairless

Palmar and plantar surfaces

Thin skin characteristic

Thin epidermis

Thick dermis

Hairy

Everywhere else

Epidermis cell type

Stratified squamous epithelium

Thick skin epidermis layer from superficial to deep

Stratum corneum

Stratum lucidum

Stratum granulosum

Stratum spinosum

Stratum basale

Thin skin epidermis layer from superficial to deep

Stratum corneum

Stratum granulosum

Stratum spinosum

Stratum basale

Where are epidermal cells generated, differentiated, and shed?

Generated: Deepest layers (strata)

Differentiate: Middle layers

Shed: Superficial layers

What cells proliferate in the skin?

Basal cells → Goes through regular cell division → One daughter cell will be another basal cell, the other will be a keratinocyte

Where are keratinocytes found

Stratum spinsosum and up

What do kertainocytes do?

Pack as much kertain as possible into the cell

Limits insensible perspiration

What happens when keratinocytes get to the stratum granulosum

Nuclei and organelles are lost

Keratin vs. collagen

Keratin: Inside of the cell body

Collagen: Extracellular connective tissue fibre

Insensible perspiration

Water loss through cutaneous membrane itself (not through sweat glands)

What does melanin do

Absorb UV photons and turns it into harmless heat

Where are melanoctyes found and what do they do

Stratum basale

Produce melanin pigemtns and transfer them to keratinocytes

Melanosomes

Organelle inside melanocyte

Packed with melanin

Transferred via vesicle transport

Dermis tissue type and layers of dermis

Connective tissue

Stratum papillare

Stratum reticulare

Stratum Papillare

Areolar tissue

Under basement membrane

Stratum Reticular

Dense, irregular, elastic

High collagen fibres per volume of matrix

Gives strength

Phases of integument repairment

Inflammatory phase

Migratory phase

Proliferation phase

Scarring phase

Inflammatory phase

Mast cells trigger inflammatory response

Bleeding occurs at the injury site

Increase blood flow

Attraction of immune phagocytic cells

Migratory phase

Scab forms at the surface

Patrolling macrophages remove debris and pathogens

Rapid cell division and migration along wound edges to replace missing cells

Formulation of granulation tissue (old matrix + blood + blood vessels + mesenchymal cells) → In dermis

Proliferation phase

Deeper portions of the clot dissolves

Fibroblasts produce new collagen fibres and ground substance

Scarring phase

Scar tissue formation

How does the epidermis repair itself?

Proliferation of basal cells → Produces 2 daughter basal cells instead of 1 basal and 1 keratinocyte → Later go back to normal proliferation → Keratinocytes repopulate other layers of epidermis

How does the dermis repair itself?

Recruitment → Mesenchymal cells attracted to the inflammation

Proliferation

Differentiation → Offspring differentiates into fibroblasts → Makes collagen

Keloid scar formation

Very high proliferation and secretion from fibroblasts → Secretes collagen → Pushes the epidermis out

Callus

Thickening of the stratum corneum, caused by keratinocytes being more strongly cross-linked = longer/more force to shed

What is embedded in the dermis

Accessory structures → Sensory neurons, glands, hairs

2 Types of Nociceptive neurons

Free nerve endings

Sensory nerve

Glands

Epithelial structures

Contribute to protection and/or homeostasis

Sebaceous glands

Secretes sebum

Helps with barrier

Associated with hair follicles

Sweat glands

Secrete sweat

Apocrine gland (found in axillary and pubic regions; non-functional until puberty; associated with hair)

Eccrine gland (found everywhere; not associated with hair)

Helps with thermal homeostasis as a sensor and an effector

Evaporative cooling

Sweating → turning liquid to gas by evaporation

Radiant cooling

To stay warm: Blood circulation avoids surface of skin to retain heat

To cool off: Blood circulates to the surface of the skin to dispel heat

How does the epidermis participate in calcium homeostasis?

Synthesizes Vitamin D, which is needed to synthesize calcitriol, which regulates calcium levels

Melanin and vitamin D synthesis tradeoff between dark and light skin

Dark skin → Less UV light reaches basal layers = less vitamin D = less cell damage

Light skin → More UV light reaches basal layers = more vitamin D = more cell damage

What do visible signs of aging tell you about the skin?

The skin and other integumentary structures are changing

Effects of aging on the epidermis

Fewer melanocytes = Less melanin production = weaker defence against UV

Drier epidermis = less resistant to bacteria

Thinning epidermis

Decreased perspiration = Less effective sweat glands

Fewer active follicles

Effects of aging on the dermis

Diminished immune response

Thinning dermis

Loss of elastin

Reduced blood supply

Slower skin repair

Altered hair and fat distribution

Hair and nails

Highly keratinized accessory structures found within the integumentary system

Protective roles

Hair shafts and nail bodies are made up of dead cells