Skin

Epidermis and Dermis

Epidermis• The epidermis is the outer layer of

our skin

• It is made of several layers:1. Stratum corneum2. Stratum lucidum3. Stratum granulosum4. Stratum germinativum

Stratum corneum• The stratum corneum is the layer we

touch and care for; it is only dead cells

• This layer contains NO blood vessels (i.e. nutrients can’t be brought to the epidermis)

• When the cells die, they undergo a chemical process that changes them from soft, easily damaged cells into ones that are harder and tougher.

• Keratin is a protein that helps harden these cells and makes them waterproof, thereby helping to prevent water loss by the body

• Although dead, these cells can pass on sensations such as pressure to the nerve endings in the layers below the epidermis

Stratum Germinativum

• The stratum germinativum (jer-min-a-tiv-um) is the bottom layer of cells in the epidermis, which is made up of cells which divide to produce new cells (cell division)

• As new cells are produced, they push older cells above them toward the surface of the skin.

• The outer layer is constantly shedding dead cells

• The SG layer of the epidermis produces the pigment melanin which gives skin color, and allows the skin to tan

• Melanin production is stimulated by exposure to ultraviolet light; doses of sunlight cause the skin to tan

• Prolonged exposure to the sun may destroy several layers of epidermal cells and cause sunburn/blisters

• Freckles are caused by uneven distribution of melanin (small irregular patches)

Dermis• Underneath the epidermis

• Contains living tissues which are specialized to monitor the changes that occur in the environment immediately around the body

• Contain collagen fibres: limits how much the skin can be stretched

• Contains elastic fibres: pulls the skin back after stretching

• Contains blood vessels: for regulating body temperature in response to impulses from special heat/cold receptors

– There are also touch, pressure, and pain receptors; found within different levels of the dermis

• Contains many dermal papillae: blood in these dome-shaped structures nourish the germinative layer above

Between the Dermis and Epidermis

• Where the epidermis and the dermis meet, there is a wavelike layer formed of many tiny cones and ridges

• These patterns show through the surface of the skin on the hands and feet, some of them becoming fingerprints

• The patterns emerge while the baby is developing in the uterus and never change, except with respect to size

• Patterns on the skin of fingers can be classified into 10 basic arrangements of loops and whorls

• Even identical twins will have some differences (even if they are not obvious from facial feature, body size etc)