BIOL 1103 Week 7: Integumentary System

Accessory structures in the skin

Hair, glands, nails

Skin

Largest organ in the body, spread out over layers over the surface of the body

Layers of the skin (outermost to innermost)

• Epidermis

• Dermis

• Hypodermis

Layers of the epidermis (outermost to innermost)

• Stratum corneum

• Stratum lucidum

• Stratum granulosum

• Stratum spinosum

• Stratum basale

Keratinocytes (~90% of skin cells)

Produces keratin, which protects and keeps the skin waterproof

Melanocytes (~8% of skin cells)

Produces melanin, one of the major pigments responsible for skin color, also protects the skin
from UV rays

Stratum basale

Single row of cuboidal or columnar cells, made of rapidly dividing keratinocytes and melanocytes to replenish the cells above

Stratum spinosum

8-10 rows of live keratinocytes and melanocytes packed tightly together containing pre-keratin. Surfaces of cells appear “spiny”

Stratum granulosum

3-5 rows of flattened, dying keratinocytes, losing nuclei and organelles. Contains granules of keratohyalin

Stratum lucidum

Clear, flat, dead keratinocytes. Only in areas where the skin is thick (palm, soles), contains eleidin (eventually transformed into keratin)

Stratum corneum

• 20-30 layers of flat, dead keratinocytes. Shed during abrasion

• Keratin instead of cytoplasm

• Glycolipids in extracellular space

Hair

Strand of dead, keratinized cells that aid with sensation, protection, & temperature regulation

Two types of sudoriferous (sweat) glands

Apocrine sweat glands & eccrine sweat glands

Apocrine sweat glands

Produces sweat, associated with hair follicle, located in armpits and groin area

Eccrine sweat glands

Produces sweat and are throughout the skin in most regions of the body

Sebaceous (oil) glands

Secretes sebum (oily substance), coating the surface of hairs preventing drying out and hair becoming brittle

Sebum

Oily substance that aids in keeping skin hydrated and has some anti-microbial properties

Ceruminous (wax) glands

Secretes cerumen (wax) located in the ear canal

Ear wax functions

• Protects ear against dust, insects, etc

• Anti-microbial properties

Nails

Made of compacted, keratin filled, dead epithelial cells. Protects fingers & toes, helps to scratch, grasp, and manipulate objects

In which ways does the skin protect?

• Mechanical protection

• Prevents dehydration

• UV radiation protection

• Antimicrobial properties

What is the function of lipid secretions in the skin?

They help to prevent cells in the skin from dehydrating, and has anti-microbial properties

What in the skin protects against UV radiation?

Melanin in melanocytes and keratinocytes absorb UV radiation

Function of lagerhans cells and macrophages in the skin

Activates the immune response after encountering a pathogen in the skin

What substance does the skin excrete to reduce body heat?

Sweat is excreted to reduce body heat, produced by sudoriferous glands

Receptors in the skin and their function

• Mechanoreceptors (touch, pressure)

• Thermoreceptors (temperature)

• Nociceptors (pain)

How does the skin play a role in removing waste products?

Sweating can carry waste products (salt, urea, ammonia, CO2) from the body

How does UV radiation help the skin synthesize vitamin D?

UV radiation from the sun stimulates the skin to convert an inactive form of vitamin D to an active form

Epidermis

Outermost layer of the skin

Dermis

Middle layer of the skin, between the epidermis and hypodermic

Hypodermis

The deepest layer of the skin that attaches the dermis to underlying muscles and bones

Eleidin

Protein-rich substance found in the stratum lucidum, eventually becoming keratin as it moves through the layers of the epidermis

Instead of cytoplasm, what do the keratinocytes in the stratum corneum have?

They have keratin instead of cytoplasm

What are hair and nails made of, and how are they different?

Hair and nails are both made of keratin-filled dead cells. Hair is made of softer, more flexible keratinized cells while nails are made of harder, more rigid keratinized cells