Biology 211Anatomy & Physiology I

Dr. Thompson

The Integumentary System

Skin =

Largest organ in body

Skin + accessory organs (hair, nails, glands)

= scientific study and medical treatment of the integumentary system

Exposed to radiation, trauma, infections, chemicals, etc.

=

Functions of Integumentary System (skin & its products)

Barrier to keep water and solutes in

Barrier to keep bacterial, dirt, etc. out

Protection against abrasion

Contains sensory receptors for touch, temperature, pressure, pain, etc.

Temperature regulation via hair, sweat, & amount of blood flow

Blood reservoir

Synthesis of vitamin D

Excretion

Epidermis: .epithelium; outer layer is "keratinized" or "cornified"

Dermis:.

Hypodermis:

Three Layers of skin:

Epidermis:

Cells formed by mitosis in deepest, or basal, layer, then get pushed into more superficial layers or "stata"

= Single row of dividing cells

= Three or four layers of cells; Some cell division

= Three or four layers of cells; Actively synthesizing protein keratin

= One or two layers of dying cells

= Many layers of flat, dead, scale-like cells full of keratin

(Epidermis)

Primary cell type in epidermis = keratinocytes which produce large amounts of protein keratin

Other cell types:

produce pigment melanin & transfer it to keratinocytes

(really macrophages) clean up debris

detect touch and pressure; transfer this information to sensory receptors in the dermis

Most significant factor is melanin 2 forms (brownish black) (reddish yellow)

Additional pigment: = yellowHemoglobin in blood = red/pink

Different races: similar numbers of melanocytes, amount of melanin produced differs

Melanin accumulates in keratinocytes

Skin Color

= lack of melanin

= red; increased blood flow, inflammation

= blue; lack of oxyhemoglobin

= pale; decreased blood flow

= yellow; erythrocyte destruction, liver failure

Abnormal Skin Color

Keratinocytes move from stratum basale to stratum corneum, dying as they do so. Average = 6 - 8 wks

- Keratinocytes in stratum basale (& stratum spinosum) lie along basement membrane; divide by mitosis

- Older cells die but remain attached to each other

- Older ones pushed toward surface by newer cells

- Cells eventually shed from stratum corneum

- Keratinocytes synthesize large amounts of keratin and flatten out as they move toward surface

- Melanocytes transfer melanin to keratinocytes

(Epidermis)

Dermis:

Dense irregular connective tissue

Separated from epidermis (stratified squamous epithelium) by basement membrane

Highly vascular

Highly innervated

Two Layers:

just below epidermis

forms deep 80%

Dermis:

Contains many types of sensory receptors for touch, pressure, vibration, pain, temperature, etc.

Some = simple nerve endings

Others = complex structures with multiple cell types

Dermis = Dense irregular connective tissue. Thus:

Cells =

Fibers =

Appendages of the skin

Hair follicles and hairSweat glandsSebaceous (oil) glandsNails on fingers and toes

All begin as epidermis of embryo; grow down into dermis

Hair

Distributed over all skin except: palms of hands soles of feet nipples glans of penis & clitoris minor labia

Minimal trunk & limb hairThicker on scalp to retain heatEyebrows enhance facial features, shade eyesNostril hair filters dust & other particulatesPubic hair, axillary hair, anal hair retain pheromones

Hair

Formed in

Consists of layers of dead, highly keratinized keratinocytes

Loosely arranged keratinocytes

Densely packed keratinocytes

Keratinocytes loosely arranged like

scales

Black or brown color due to produced by melanocytes and transferred to keratinocytes in follicle. Red color produced by pigments called

Blonde color produced by intermediate levels of pheomelanin and low levels of eumelanin

Texture of hair due to shape of the hair shaft.

The rounder the hair shaft, the

The flatter the hair shaft, the

Black or brown color due to eumelanin produced by melanocytes and transferred to keratinocytes in follicle.

Red color produced by pigments called pheomelanin

Blonde color produced by intermediate levels of pheomelanin and low levels of eumelanin

Each hair is associated with:

Sweat Glands

- 2 to 3 million

Two types: : Distributed over all skin except nipples Simple coiled glands in dermis Duct leads to sweat pore on surface Secrete watery sweat for cooling

: Located only in axillary, pubic, anal regions Larger than eccrine glands Duct opens into opening of hair follicle Thicker sweat, high content of protein and fats Contains scent molecules: sexual, fear, etc.

Sweat is usually

Contains significant amounts of sodium, potassium, calcium, chloride, and trace amounts of other minerals

at rest, more at warmer temperatures

during moderate to intense exercise

in external ear canal. Secretion combines with sebum to form earwax

in breast

Modified Sweat Glands

Sebaceous (oil) glands:

- Branched tubular glands

- Duct opens into opening of hair follicle

- Secretes sebum, consisting of lipids, proteins, ions, carbohydrates,

Nails:

- Tips of fingers and toes - Thick layer of densely packed keratinocytes - Produced by at proximal end, hidden under or cuticle

Deeper layers of epidermis =

Average growth:0.5 mm per week

Major cause of accidental death

Classified by depth of tissue involvement Superficial: involves epidermis only Partial thickness: involves epidermis and some dermis Full thickness: epidermis, dermis, and deeper tissue destroyed

Burns:

Carcinomas (cancers) of the skin:

Basal Cell Carcinoma: Keratinocytes of stratum basale proliferate, invade dermis Relatively low malignancy

Squamous Cell Carcinoma: Keratinocytes of epidermis proliferate May or may not invade dermis Moderate malignancy

Malignant Melanoma: Melanocytes of epidermis proliferate and invade dermis Highly malignant