Essentials of Human Anatomy & Physiology, 7th ed.by Elaine N. Marieb

Chapter 4Skin and Body Membranes

Anatomy

· Skin = cutaneous membrane = integument = epidermis + dermis

· Integumentary System = Skin + skin derivativesSkin derivatives· Sweat glands· Oil glands· Hairs· Nails

Skin and Body Membranes: Integumentary System, Anatomy

Skin = Integument• Covers 15-20 ft.2

• Weighs ~ 9 lbs.• Every square inch contains ~

15 feet of blood vessels, 12 feet of nerves, 650 sweat glands, 100 oil glands, 1500 sensory receptors, over 3 million cells.

• Entire epidermis regenerates every 25-45 days!

Skin and Body Membranes: Integument

· Epidermis – outer layer· Stratified squamous epithelium· Avascular· Often keratinized (hardened

by keratin)

• Dermis· Dense irregular connective

tissue

Deep to dermis is the hypodermisNot part of the skin

Anchors skin to underlying organsComposed mostly of adipose tissue

Skin and Body Membranes: Integument

Figure 4.4

Skin and Body Membranes: Integumentary System, Anatomy

Layers of Epidermis

Stratum basale (deepest layer)• Cells undergoing mitosis• Lies next to dermis• Contains two cell types:

keratinocytes & melanocytes

Stratum spinosum (spiny layer)• Keratinocytes mature, filling cells with

keratin protein• Phagocytic white blood cells – Langerhans cells

Stratum granulosum (granular layer)• 3-5 rows of flattened keratinocytes (produce keratin)

Skin and Body Membranes: Layers of Epidermis

Stratum lucidum (clear layer)• Occurs only in thick, glaborous (hairless) skin

Stratum corneum (outermost layer)• Shingle-like dead cells filled with keratin• 5-50 cell layers thick, depending upon location

Skin and Body Membranes: Layers of Epidermis

The stratum corneum is thickest in the soles

of the feet. It’s thinnest

in the eyelids.

MelaninSkin and Body Membranes: Epidermis

• The pigment, melanin, is produced by melanocytes in the stratum basale.

• Color is yellow to brown to black• Melanocytes have cellular extensions,

called dendrites that weave between the cells of the stratum basale and spinsoum. The keratinocytes absorb melanin from the dendrites, and skin is evenly colored…usually.

• Amount of melanin produced depends upon genetics and exposure to sunlight

Figure 4.4

Skin and Body Membranes: Integumentary System, Anatomy

Dermis• Dense, irregular

connective tissue

• Thickness varies• Two layers:

papillary &reticular

Papillary layer• Most superficial dermal layer

• Capillaries which provide nutrients to the avascular epidermis through diffusion

• Sense receptors: pain receptors (free nerve endings) & touch receptors (Meissner’s corpuscles)

• Projections called dermal papillae

Skin and Body Membranes: Dermis

As the epidermis layers superficially to the dermis, the pattern of dermal

papillae is amplified. Your fingerprints, handprints, and footprints are the pattern of your dermal papillae!

Skin and Body Membranes: Dermis, papillary layer

Reticular layer• Thicker than papillary layer

• Blood vessels (arterioles, venules) help maintain body temperature homeostasis

• Sweat and oil glands• Deep pressure receptors – Pacinian corpuscles• Connective tissue fibers: Collagen & Elastin

Skin and Body Membranes: Dermis

Skin and Body Membranes: Integumentary System, Anatomy

Separation of bundles of

collagen fibers form lines of

cleavage in the skin. (Langer’s cleavage lines)

Why do surgeons make incisions

along these lines?

Skin and Body Membranes: Dermis, reticular layer

Figure 4.4

Skin and Body Membranes: Integumentary System, Anatomy

Appendages of the Skin:

Hair & Nails

Skin and Body Membranes: Integumentary System, Anatomy

Hair• Produced by

hair bulb matrix• Consists of hard

keratinized epithelial cells

• Melanocytes provide pigment for hair color

• Composed of a root & shaft

Figure 4.7c

Skin and Body Membranes: Skin appendages, hair

Root the part of hair enclosed in the follicle.

Shaft the part of hair projecting from the surface of the scalp or skin

Skin and Body Membranes: Skin appendages, hair

Shaft· Central medulla· Cortex surrounds

medulla· Cuticle on outside of

cortex (heavily keratinized)

Figure 4.7b

Skin and Body Membranes: Skin appendages, hair

The shape of the hair shaft determines the macroscopic

appearance of the hair.Flat shaft = curly/kinky hair

Oval shaft = wavy hairRound shaft = straight hair

Skin and Body Membranes: Skin appendages, hair

Associated Hair Structures· Hair follicle

• Dermal and epidermal sheath surround hair root

· Arrector pili muscle• Smooth muscle that

surrounds hair follicles and contracts when cold or frightened

· Sebaceous gland· Sweat gland

Skin and Body Membranes: Skin appendages, hair

Figure 4.4

Skin and Body Membranes: Integumentary System, Anatomy

Nails· Heavily keratinized, scale-like modifications of

the epidermis.· Only two layers of epidermis extend beneath

the nail bed: stratum basale & stratum

spinosum

Skin and Body Membranes: Skin appendages, nails

• Lack of pigment makes them colorless

Nail Structures· Free edge· Body· Root of nail· Nail folds -skin

folds that border nail

· Cuticle -thick proximal nail fold

· Lunula –white crescent

Skin and Body Membranes: Skin appendages, nailsSlide 4.22

Figure 4.9