The

Integumentary

System

The Integumentary System

1. The Skin and the hypodermis

2. Appendages of the skin

The Skin and the Hypodermis

Functions:

– Cushions and insulates deeper organs

– Protects from injury, chemicals, heat, and cold

– Excretes urea, salt & water through sweat

– Prevents water loss

– Regulates Body Temperature

– Regulates calcium and phosphate Levels

– Screens out UV rays from the sun

– Contains sensory receptors associated with nerve

endings

– Excretes sweat, sebum, and milk

The Skin and the Hypodermis

• Skin – the largest organ

– Varies in thickness form 1.5 to 4mm

– Divided into two distinct layers

i. Epidermis

ii. Dermis

– Hypodermis – fatty layer, lies deep to the

dermis

Skin Structure

Skin Structure

Epidermis

• Composed of keratinized

stratified squamous epithelial

cells

• Contains four main cell types

– Keratinocytes

– Melanocytes

– Merkel cells

– Langerhans cells (Epidermal

DENDRITIC cells)

Keratinocytes and Melanocytes

Epidermis

• Keratinocytes – most abundant cell type

– Arise from deepest layer of epidermis

– Produce keratin – a tough fibrous protein

– Keratinocytes at skin's surface are dead

Layers of the Epidermis

1. Stratum basale

2. Stratum spinosum

3. Stratum granulosum

4. Stratum lucidum

5. Stratum corneum

5 Layers: from inside outwards

Epidermal Cells and Layers

Layers of Epidermis 1. Stratum basale or Stratum

germinativum

Lies next to dermis

Most cells are kertatinocytes

Cells undergo mitosis

Merkel cells (Tactile cells)- associated with sensory nerve ending

Melanocytes- secrete the pigment melanin; long cytoplasmic processes branch out into layers above

Melanin pigment surrounds keratinocyte nuclei

Layers of Epidermis

1. Stratum basale or Stratum germinativum

2. Stratum spinosum – intermediate filaments, Langerhans cells (dendritic cells)

Receptor-mediated endocytosis;

communicate to lymph nodes

3. Stratum granulosum

4. Stratum lucidum –

5. Stratum corneum

Layers of Epidermis

1. Stratum basale or Stratum germinativum

2. Stratum spinosum

3. Stratum granulosum- Consists of flattened keratinocytes (dead cells), granules

Keratin & glycolipid

4. Stratum lucidum

5. Stratum corneum

Layers of Epidermis

1. Stratum basale or Stratum germinativum

2. Stratum spinosum

3. Stratum granulosum

4. Stratum lucidum – cells flatter, dead keratinocytes

Occurs only in hairless, thick skin (palm & sole)

Accumulate keratin

Farther away from blood supply dead

5. Stratum corneum

Thin vs Thick Skin

Layers of Epidermis

1. Stratum basale or Stratum germinativum

2. Stratum spinosum

3. Stratum granulosum

4. Stratum lucidum

5. Stratum corneum

Cornified dead cells

Filled with keratin

Protects against injury & desiccation

Melanin

Pigment produced by melanocytes

Color: yellow to brown to black

Melanocytes - stratum basale

Amount of melanin produced

• genetic control

• exposure to sunlight

Dermis

• Second layer of the skin

• Richly supplied with

nerves and blood

vessels (plexus)

• Has two layers

1. Papillary layer –

superficial 20%

2. Reticular layer – deeper

80%

Skin Structure

Skin Structure

1. Papillary layer

– Superficial layer, areolar connective tissue

– Dermal papillae project into epidermis

– Epidermal ridges formed

2. Reticular layer

– Dense irregular CT

– reticulum: network of collagen & elastic fibers

Skin Structure

Flexion Creases & Dermis

Continual folding of skin

over joints

Dermis is attached

tightly to underlying

structures

Fingerprints

Dermal ridges elevate the epidermis Epidermal Ridges

Reticular Layer of Dermis

Wrinkles

Lines of cleavage / Tension Lines: Less

dense regions

Represent the separations between

bundles of collagen fibers in reticular

dermis

Structures in the Dermis

Blood vessels

Tactile (Meissner’s) Corpuscles Sense of light touch

Lamellated (Pacinian) Corpuscles Pressure sensors

Structures in the Dermis

Tactile (Meissner’s) Corpuscles

Lamellated (Pacinian) Corpuscles

Free Nerve Endings

Sense of temperature and pain

Root Hair Plexus

Sensory nerves

around hair bulb

Sense movement of

hair and skin

Hypodermis

• Not part of skin

• Contains areolar and adipose connective

tissues

• Anchors skin to underlying structures

• Helps insulate the body

Hypodermis (Superficial Fascia or

Subcutaneous Fat)

Abnormal Skin Colors

• Cyanosis - blueness from deficiency of oxygen in the

circulating blood (cold weather)

• Erythema – abnormal redness due to dilated cutaneous

vessels (anger, sunburn, embarrassment)

• Jaundice - yellowing of skin and sclera due to excess of

bilirubin in blood (liver disease)

• Albinism - a genetic lack of melanin

• Hematoma - a bruise (visible clotted blood) showing

through skin

• Pallor – pale color under stress, shock, cold, severe

anemia

Skin Markings • Hemangiomas (birthmarks)

– discolored skin caused by benign tumors of dermal blood

capillaries

• Freckles and moles = aggregations of melanocytes

– freckles are flat; moles are elevated

• Friction ridges leave oily fingerprints on touched surfaces

– unique pattern formed during fetal development

• Flexion creases mark lines where skin folds during flexion of

joints

Appendages of the Skin

1. Hair & hair follicles

2. Sebaceous glands

3. Sweat glands

4. Nails

Accessory Structures of the Skin • Hair

• Muscles (Arrector pili)

• Sebaceous Glands

• Sudoriferous Glands

• Mammary Glands

• Ceruminous Glands

• Nails

Hair = Pilus

Hair & Hair Follicles

• Hair- long flexible strand of

keratinized cells

• Hair follicle – tubular

invagination of the epidermis

• Hair produced by hair follicle

• Daughter cells pushed up,

keratinized & die

Structure of Hair

• Three zones along the length of a

hair:

1. Hair bulb: a swelling at

the dermal base

2. Hair root: embedded in

the skin

3. Hair shaft: projects

above the skin surface

Hair Shaft and Hair Root have 3 layers

Cuticle

Cortex

Medulla

C.S. of a Hair

600X

• Three concentric layers of keratinized

cells

1. Cuticle – single layer of scale-like

cells that overlap

2. Cortex – several layers of flattened

cells

3. Medulla – large cells

Scanning EM of hair shaft

Scale-like cells of the cuticle

L.S. of Base of Follicle

Hair Shaft (Cuticle, cortex, Medulla)

Structure of Hair Follicle

Blood capillaries

• Extends into the dermis

• Deep end of follicle is

expanded: Hair Bulb

• Hair Papilla: Connective tissue

projecting into the bulb.

• Hair Matrix: epithelial cells

above the papilla in the bulb;

form the growth zone

• Cells of matrix divide

• Root hair plexus: Knot of

sensory nerves around hair bulb

Hair Bulb

Hair Papilla

Hair matrix

L.S. of Base of Follicle

1

2a

2b

Wall of hair follicle is composed of 2 sheaths:

1. Connective tissue root sheath: Outer (from Dermis)

2. Epithelial root sheath: Inner (Epidermis) surround hair root

L.S. of Base of Follicle

Melanocytes provide pigment for hair color

Hair Associated Structures

Arrector pili

Smooth muscle

Extend from dermal papillae

Contract- hair pulled upright

(PILOERECTION)

Arrector Pili

Functions of Hair

• Senses

• Guards

• Shields

• Protects

Hair Color

Eumelanin pigment in

black & brown hair Blond hair contain pheomelanin

pigment, but little eumelanin.

Hair color: different

melanin pigments

in cells of cortex

Red hair contains little

eumelanin but lots of

pheomelanin.

Hair Color

White hair - air bubbles in medulla

and lack of pigment in cortex.

Gray hair - mix of white & pigmented

hairs; lack tyrosinase

Hair Texture

Straight hair:

Round in C.S.

Wavy hair: Oval

in C.S.

Curly hair: Flat in

C.S.

Oil glands

Present all over, except palms & soles

Simple alveolar glands;

Holocrine secretion

Ducts empty into a hair follicle

Secretion~ SEBUM Lubricant for skin

Kills bacteria

Slows water loss

Sebaceous Glands

Sebaceous

Gland

Hair

Follicle

Sebaceous Glands

Acne

Excess sebum is produced. Duct is blocked.

Bacterial infection leads to inflammation.

May burst into the dermis.

Blackheads

Blocked sebum oxidizes & dries

Darkens to form blackhead

Produce sweat

Widely distributed in skin

Temperature regulation

Excretory product: is a blood filtrate, passes

through secretory cells of sweat glands, released

by exocytosis

Composition- 99% water, salts, ‘acidic’ excretory

products

Sweat Glands or Sudoriferous glands

Two types

Eccrine (or merocrine) glands – more numerous

Apocrine glands

Sweat Glands or Sudoriferous glands

Sweat Glands

Coiled simple tubular gland

Open via duct to a pore on skin

surface

Usually do not extend as far

into dermis

Produce acidic sweat (pH 4-6)

Involved in heat-regulating

system

Eccrine / Merocrine Glands

Dense in palms and

soles (~3000 per sq inch)

• Ducts empty into hair follicles

• Scalp, neck, axillary & genital areas

• Sweat also contains lipids, proteins

• Body odor

Apocrine Sweat Glands

Apocrine Sweat

Glands

(wide lumen)

Merocrine Sweat

Glands

(narrow lumen)

Modified Sweat Glands

• Ceruminous glands – external ear canal

• Mammary glands

Ceruminous Glands

Location

Secretion combines with sebum

earwax

Waterproof, keeps eardrum

flexible

Block foreign particles, kills

bacteria

• Milk-producing glands

• Modified apocrine sweat

gland

• Ducts open on the nipple

Mammary Glands

Mammary Glands

Nails

Scale-like modifications of the epidermis

Heavily keratinized

Each nail has

A free edge

A body- visible attached part

A root- embedded

Nail overlapped by folds of skin- Nail Folds

Thick proximal nail fold- Cuticle / Eponychium

Nails

Stratum basale of epidermis extends beneath

the nail as the nail bed Proximal thickened area of nail bed - nail matrix Responsible for growth

Cells produced become keratinized and die No pigment – colorless (pink?)

Nails

Region over thickened

nail matrix: White Crescent

Toe Nail