Integumentary system

• Integumentary system

  This system has two major parts

  - The cutaneous membrane

  - Accessory structures
• Cutaneous Membrane

  - Our skin is the cutaneous membrane.

  - It is composed of 2 main layers

  - The epidermis or superficial layer

  - The dermis deep connective tissue
• Accessory Structures

  - This includes: hair, hair follicles, exocrine glands and nails.

  - These structures are imbedded within the dermis and project to the epidermis.
• Epidermis

  - This layer is composed of 5 smaller layers

  - The cells of the epidermis are stratified squamous epithelium.

  - The cells contain large amounts of a protein keratin

  - The epidermis is avascular, nutrients and oxygen diffuse up from the dermis

  - The outer layers are dead cells and require no nutrients.
• Epidermis

  - Thin skin – 4 layers of keratinocytes (cells with large amounts of protein keratin)

  - Thick skin – 5 layers of keratinocytes

  – thick skin is only found on the palms of your hands and soles of your feet (durability)
• Layers of the epidermis - stratum (come lets go get some beer)

  1. stratum Corneum
  2. stratum Lucidum
  3. stratum Granulosum
  4. stratum Spinosum
  5. stratum Basale
• Stratum Corneum 

  -  Exposed surface

  - Contains many layers (15-30) of keratinized cells packed tightly together.

  - Lipid layer from sebaceous glands coat the surface to protect it and make it waterproof.
• Stratum Lucidum  

  - Clear and glassy

  - Thick skin of palms and soles of feet.
• Stratum Granulosum

  - 3 to 5 layers

  - Cells have stopped dividing here 

  - Cells are accumulating keratin
• Stratum Spinosum  

  - 8-10 layers

  - Cells continue to divide

  - Contain dendritic dells (Langerhans) that fight microorganisms and skin cancers
• Stratum Basale

  - Deepest layer, interlocks with the dermis. 

  - Forms epidermal ridges – fingerprints

  - Contains basal cells that divide and move up through the layers 

  - Tactile discs and melanocytes are located here.
• Dermis 

  - Located between epidermis and subcutaneous layer

  - Anchors epidermal accessory structures (e.g., hair follicles and sweat glands)

  - Two components

  - Outer papillary layer 

  - Deeper reticular layer
• Papillary layer

  - Consists of areolar tissue

  - Contains capillaries, lymphatic vessels, and sensory neurons

  -  Named for dermal papillae that project between epidermal ridges

  - Meissner corpuscles for light touch
• Reticular layer

  - Consists of dense irregular connective tissue

  - Contains collagen and elastic fibers

  - Receptors for deep pressure, vibration

  - The dermis contains all cells of connective tissue proper
• Dermal strength and elasticity

  • Collagen fibers
  • Very strong, resist stretching
  • Easily bent or twisted
  • Limit flexibility to prevent tissue damage
  • Elastic fibers
  • Permit stretching and then recoil to original length
  • Provide flexibility
• Skin turgor

  • Fibers and water provide flexibility and resilience
  • Pull skin, if it stays up = dehydrated, returns = hydrated
• Tension lines (cleavage lines)

  • Produced by parallel bundles of collagen and elastic fibers in the dermis
  • Resist forces applied to skin
  • A cut made parallel to a tension line remains shut, heals well

  - A cut at a right angle pulls open and scars
• Skin damage

  Loss of skin turgor is caused by :

  - Aging

  - Hormones

  - Dehydration (reversible)

  - UV radiation

  Excessive distortion of skin from pregnancy or weight gain may cause stretch marks
• Subcutaneous layer

  • Lies deep to dermis
  • Connected to reticular layer by connective tissue
  • Stabilizes position of the skin
  • Primarily adipose tissue
  • Large arteries and veins are in superficial region
  • Site of subcutaneous injections using hypodermic needles
  • Distribution of subcutaneous fat determined by sex hormones
  • This is NOT part of the skin but rather connects the skin to the body.
• Skin color is influenced by two pigments in the epidermis 

  - Melanin

  - Carotene
• Melanin

  - Red-yellow or brown-black pigment

  - Produced by melanocytes

  - Stored in intracellular vesicles (melanosomes)

  - Transferred to keratinocytes

  - Dark-skinned people have large, numerous melanosomes

  - Protects skin from ultraviolet (UV) radiation 

  - Small amounts of UV radiation are beneficial

  - Too much can damage DNA and cause cancer
• Carotene

  • Orange-yellow pigment
  • Found in orange vegetables
  • Accumulates in epidermal cells, deep dermis, and subcutaneous layer
  • Can be converted to vitamin A, required for
  • Maintenance of epithelia
  • Synthesis of photoreceptor pigments in eye
• Blood flow and oxygenation influence skin color 

  •  Hemoglobin is bright red when bound to oxygen
  • When blood vessels dilate from heat, skin reddens
  • When blood flow to skin decreases, skin pales
  • Hemoglobin turns dark red when oxygen is release
  • Can result in cyanosis (bluish skin)
  • May be caused by extreme cold, heart failure, severe asthma, etc
• Illness and skin colour

  • Jaundice: Buildup of bile produced by liver, skin and whites of eyes may turn yellow
  • Pituitary tumor: Excess melanocyte stimulating hormones increases production of melanin
  • Addison’s disease: Causes pituitary gland to release excess ACTH, which has an effect similar to MSH 
  • Vitiligo: Loss of melanocytes causing loss of color
• Hairs cover almost all of the body, except 

  •  Palms of hands, sides of fingers
  • Sides and soles of feet, sides of toes
  • Lips
  • Portions of external genitalia
• Functions of hair

  - Protect and insulate

  - Guard openings from particles and insects 

  - Serve as sensory receptors
• Hair follicles

  - Extend deep into dermis

  - Produce nonliving hairs

  - Wrapped in a dense connective tissue sheath

  - Base is surrounded by sensory nerves (root hair plexus)

  - Arrector pili muscle

  - Involuntary smooth muscle

  - Contraction causes hairs to stand up 

  - Produces “goose bumps”
• Types of hairs

  - Vellus hairs

  - Soft, fine hairs that cover most of body surface

  - Terminal hairs

  - Heavy, pigmented hairs

  - On head, eyebrows, and eyelashes 

  - Other parts of body after puberty
• Hair color

  - Produced by melanocytes at hair matrix 

  - Determined by genes
• Exocrine glands in skin

  • Sebaceous glands (oil glands)
  • Sweat glands: apocrine and eccrine sweat glands
  • Sebaceous follicles
• Sebaceous glands (oil glands)

  - Holocrine glands

  - Discharge lipid secretion (sebum) into hair follicles

  • Lubricates and protects hair shaft
  • Inhibits growth of bacteria
• Sebaceous follicles

  - Large sebaceous glands not associated with hair

  - Discharge sebum directly onto skin surface

  - Located on face, back, chest, nipples, external genitalia
• Apocrine sweat glands

  - Found in armpits, around nipples, and in pubic region

  - Secrete products into hair follicles via merocrine secretion 

  - Produce sticky, cloudy secretions

  - Nutrient source for bacteria, which cause odors 

  - Surrounded by myoepithelial cells

  - Squeeze secretions out of glands in response to hormonal or nervous signals
• Eccrine (merocrine) sweat glands

  • Coiled, tubular glands that discharge directly onto skin surface(sensible perspiration)
  • Widely distributed on body surface
  • Especially on palms and soles
  • Secretions are 99% water plus salt, etc.
  • Functions include
  • Providing protection from environmental hazards
  • Cooling surface of skin to reduce body temperature 
  • Excreting water and electrolytes
• Nails

  Protect tips of fingers and toes

  - Made of dead cells packed with keratin

  - Metabolic disorders can change nail structure, e.g. pitted nails may result from psoriasis