BIOLOGY: Integumentary System

INTEGUMENTaRY SYTEM

Skin
- serves as covering of our body
- consists of skin, nails, hair, glands
- surface area: 1.4 – 1.9 m2
- weighs more than 2x the brain
- weighs about 3kg

Physiological Functions

1.    Protection

2.    Chemical Synthesis
- everyone has same number of melanocyte
- skin makes Vit. D & lipid cholesterol

3.    Sensory Perception

4.    Store Water & Fats

Structure of Skin

Epidermis (90% of cells are found)
- outermost layer of skin, 10 – 30 cells thick
- made up of keratin
- scaly layer (dead skin cells)

Layers:
    a. Stratum Corneum (horny layer)
    b. Stratum Lucidum
    c. Stratum Granulosum
    d. Stratum Spinosum
    e. Stratum Germinativum (basale layer)

Specialized Epidermal Cells

1.    Melanocyte

2.    Keratinocyte

3.    Langerhans cells
- produced in the bone marrow
- help cells of immune system recognize dangerous cells

4.    Merkel cells
- found in sensitive hairless areas
- found in the deepest layer of epidermis (germinativum)
- contact nerve endings
- touch receptor

Dermis
- inner layer (15 – 40 cells)
- richly supplied with blood cells
- contains relatively fewer cells than epidermis
- made up of fibrous protein & other large molecules
- contains diff. types of sensory receptors

Structural Component

1.    Collagen
- accounts to ¾ of skin weight
- skin strength

2.    Elastin
- composed of elastic fiber
- elasticity

3.    Reticular Layer
- lower layer of dermis
- composed of course collagen & elastic fibers
- anchorage of glands & hair follicles

Skin appendages

Hair
- composed primarily of keratin
- protein is packed into dead keratinocytes
- dead keratinocytes fused together to form hair

Structure

1.    Shaft – portion of hair above skin

2.    Root – portion of hair below skin

3.    Hair Follicle – indentation of the epidermis where hair grows

4.    Bulb – (keratinocytes). Contains blood vessels that nourish the hair

5.    Arrector Pili – contained within hair follicle muscle that contracts in response to cold, etc

Hair Color is due to melanin in bulb

1.    Dark – true melanin

2.    Blond & Red – melanin has sulfur & iron

3.    Gray – aged melanocytes

4.    White – air bubbles incorporated in growing hair

Type of hair is due to shape of shaft

1.    Straight – round shaft

2.    Wavy – oval-shaped shaft

3.    Curly – elliptical shaft

Nails
- made of hard keratin filled epidermal cells
- rate of nail growth 1mm / week

Functions

1.    Protects the ends of the digits from injury

2.    Helps us grasp small objects & enables us to scratch

Parts

1.    Nail body – visible part of nail

2.    Free edge – portion of nail body that extends part of the end of digits

3.    Lunula – pale, semi circular area on base of nail body

4.    Root – buried part of nail

Sweat Glands
- adult human has 1.6 million to 4 million sweat glands
- can secrete up to 10L of fluids everyday

1.    Eccrine Glands
- found almost all over the body
- most numerous in palms and soles
- lift opens into surface of body
- cools the body

Apoccrine Glands
- found in the armpit, genital areas, surrounding the mammary gland
- opens into hair follicles to surface of skin
- no known functions