Anatomy: Integumentary System

BIOL-N 261 Chapter 4

Integumentary system

Comprised of the integument (skin) and its accessory structures (hair, nails. sweat, and oil glands)

Skin

Largest organ of the body

Functions of the integument

• Physical protection

• Regulation of body temperature

• Excretion (and secretion)

• Nutrition (synthesis)

• Sensation

• Immune defense

Subcutaneous layer

Deep to the dermis

Epidermis

Stratified squamous epithelium layer of the skin

Dermis

Underlying loose connective tissue layer of the skin

Keratinocytes

The most abundant cell type in the epidermis that produce keratin (tough fibrous proteins) that gives epidermis its protective properties

Keratinocyte properties

• Arise from the deepest layer of epidermis from cells undergoing almost continuous mitosis

• Cells are dead, flat sacs which are completely filled with keratin by the time they reach the surface

Melanocytes

Produce melanin, a dark skin pigment

Merkel cells

Sensory cells that serve as receptors for touch

Langerhans cells

Fixed macrophages that police our outer body surface, using receptor-mediated endocytosis to take up foreign proteins

Thick skin

5 strata

Thin skin

4 strata

Stratum basale or stratum germinativum

• Innermost/deepest basal layer

• Single row of cells consists of basal cells (stem cell keratinocytes)

• Contains Merkel cells and melanocytes

Stratum spinosum

• Comprised of keratinocytes, which contain thick bundles of pre-keratin

• Also contains Langerhans cells

• Keratinocytes in this layer take on a spiky appearance due to the production of tonofibrils

Tonofibrils

Interconnecting proteins located in the stratum spinosum, which increase stability in this layer

Stratum granulosum

• Keratinocytes produce keratohyalin (helps form keratin) and keratin

• Keratin fibers develop as cells become thinner and flatter

• Gradually the cell membranes thicken, the organelles disintegrate, and the cells die

Stratum lucidum

Appears as a “glassy” layer in thick skin only

Stratum corneum

• Multiple layers of flattened, dead, interlocking keratinocytes

• Typically relatively dry

• Water resistant, but not waterproof

Properties of the dermis

• Divided into two layers: papillary and reticular layers

• Richly supplied with nerve fibers and blood vessels

• Functions in nourishment and temperature regulations

Papillary layer

Superficial portion (20%) of the dermis that is comprised of loose areolar connective tissue proper

Dermal papillae

Finger-like pegs which project into the epidermis (Ionizing radiation can make these retract)

Reticular layer

Deeper 80% layer of the dermis, comprised of dense irregular connective tissue

Reticular layer properties

• Provides strength and resilience to skin

• Blood vessels, glands, muscles, hair follicles and nerves are all found in this layer

Fingerprints

Identical twins have the same DNA, but different ______

Cutaneous plexus

Network of blood vessel at the border of the reticular layer and the subcutaneous layer

Papillary plexus

Highly-branched network of blood vessels just deep to the epidermis

Tactile discs

Formed from the union of a Merkel cell and a sensory nerve ending

Free dendrites

Sensitive to pain and temperature

Factors that determine skin color

• Thickness of the stratum corneum

• Amount of pigments in the epidermis

• Carotene (yellow-orange pigment found in carrots and in green and orange leafy vegetables)

Hypodermis (subcutaneous layer, fatty layer, or superficial fascia)

Layer deep to the skin; not part of the integumentary system but shares some of the skin’s functions

Functions of the hypodermis

• Stores fat

• Anchors the skin to underlying structures

• Acts as an insulator

Arrector pili muscle

Allows movement of hairs, as in “goose bumps’

Sebaceous (oil) glands

• Secrete oily lipid (sebum) that coats hair shaft and epidermis

• Provide lubrication and antibacterial action

Sweat (sudoriferous) glands

Distributed over entire skin surface, except on the nipples and parts of the external genetalia

Myoepithelial cells

Small contractile cells that squeeze the secretion, or sweat, out of a sweat gland

Eccrine (or Merocrine) sweat glands

Most numerous type, especially on the palms and soles

Properties of eccrine (or merocine) sweat glands

• Produce thin secretions, mostly water

• Important in thermoregulation and excretion (some antibacterial action)

• Controlled primarily by nervous system

Apocrine sweat glands

• Mostly confined to axillary, anal and genital areas

• Produce a special kind of sweat consisting of fatty substances and proteins, via merocrine secretion

Calluses

Mechanical stress can trigger stem cell divisions, resulting in these

Scar tissue

The inability to completely heal after severe damage may result in this

a. Papillary layer

b. Reticular layer

c. Cutaneous plexus

d. Papillary plexus

Identify structures a-d in the following image of skin

a. Subcutaneous layer

b. Sebaceous gland

Identify structures a & b in following image of skin