Chapter 5: The Integumentary System

https://www.youtube.com/watch?v=d-IJhAWrsm0&list=PLF2F5D171DA2715B7

Size of the Integument

The integument is the largest system of the body:

16% of body weight

1.5 to 2 m2 in area

Connections to other systems

Circulatory system:

blood vessels in the dermis

Nervous system:

sensory receptors for pain, touch, and temperature

Functions of Skin

Protects underlying tissues and organs

Excretes salts, water, and organic wastes (glands)

Maintains body temperature (insulation and evaporation)

Functions of Skin

Synthesizes vitamin D3

Stores lipids

Detects touch, pressure, pain, and temperature

Parts of the Integument

The integument is made up of

2 parts:

1. cutaneous membrane (skin)

2. accessory structures

hair, nails and glands

Parts of the Cutaneous Membrane

Outer epidermis:

superficial epithelium (epithelial tissues)

Inner dermis:

connective tissues

Skin Structure

Epidermis—outer layer

Stratified squamous epithelium

Outer layers keratinized (hardened by keratin)

Dermis

Dense connective tissue (beneath thin layer of loose CT)

Layers of the Epidermis

Stratum corneum – outer 20-30 layers of dead, heavily keratinized cells

Stratum lucidum - thick, hairless, “clear layer” skin of palms and feet only

Stratum granulosum – “grainy layer” produces keratin

Stratum spinosum – “spiny layer” has an immune response

Stratum basale – a.k.a. stratum germinativum; stem cells here give rise to all other epidermal cells. Melanocytes located here.

Thin Skin Covers most of the body

Has 4 layers of keratinocytes

Thick Skin

Covers the palms of the hands and soles of the feet

Has 5 layers of keratinocytes

Keratin, Melanin, and an Amazing Factoid!

Keratin – tough, pliable protein; water resistant; gives skin, hair, and nails protective properties

Stratum corneum is ‘cornified’ = filled with keratin

Cells are shed everyday; stratum basale totally replaces epidermis every 25 – 45 days!!

Melanin – pigment of skin color Produced by melanocytes (usually in stratum basale)

Color is yellow to brown to black

Amount depends upon genetics and exposure to sunlight

Protects skin from sun damage

Dermis – deep to epidermis: 2 layers (has capillaries and sensory neurons)

1. Papillary layer (upper dermal region)

Projections called dermal papillae

Capillary loops, pressure and pain receptors, fingerprints, made of areolar tissue

2. Reticular layer (deepest skin layer). Made of collagen & elastic fibers.

Blood vessels

Sweat and oil glands

Hair follicles

Deep pressure receptors

Damage to the Dermis:Skin Damage

Sagging and wrinkles (reduced skin elasticity) are caused by:

dehydration

age

hormonal changes

UV exposure

Stretch Marks

Thickened tissue resulting from:

excessive stretching of skin due to:

pregnancy

weight gain

Lines of Cleavage

Clinically significant: A cut parallel to a cleavage line will usually remain closed and heals with little scarring.

A cut at a right angle to a cleavage line will be pulled open as severed elastic fibers recoil and will result in greater scarring.

The skin contains two types of exocrine glands:

1. Sebaceous glands (oil glands):

secrete sebum -- inhibits bacteria growth, lubricates and protects hair and skin.

2. Sweat glands: (2 types)

I. apocrine – located in armpits and pubic region, produce a sticky, cloudy, and potentially odorous secretion. Begin secreting at puberty.

I. Mammary glands of the breast are modified apocrine sweat glands, a complex interaction between sex and pituitary hormones controls their development and secretion.

II. merocrine – secrete “sweat” onto the skin, composed of 99% H2O. Found all over the skin, the palms and soles have the highest number per cm2. Cools the skin surface, flushes the surface of the skin.

Hair

Produced by hair follicles

Consists of keratinized epithelial cells

Melanocytes provide pigment

Arrector pili – smooth muscle attached to follicle and papillary layer cause ‘goosebumps’

Nails – heavily keratinized modifications of epidermis

Stratum basale in nail matrix responsible for growth, nail itself is mostly dead cells (like hair)

The Subcutaneous Layer Subcutaneous layer (hypodermis):

Not part of the skin

Composed of loose connective tissue: areolar & adipose tissue.

½ of your fat is stored here

Lots of blood vessels, location of hypodermic injections.

Review

Burns – damage from heat, electricity, UV, chemicals

Severity of Burns First-degree burns

Epidermis only

Red and swollen (typical sunburn)

Second-degree burns

Epidermis and upper dermis damaged

Red with blisters

Third-degree burns

Entire skin layer destroyed

Burn is gray-white or black

Burns – damage from heat, electricity, UV, chemicals

Rule of 9’s to estimate burn area.

Skin Cancer

Figure 5–6

Skin Cancer – uncontrolled cell division in skin

Skin cancer = #1 cancer

Basal cell carcinoma – least malignant, most common, (stratum basale)

Squamous cell carcinoma – easy cure early, but does metastasize to lymph nodes, (stratum spinosum)

Malignant melanoma – most deadly, rapid metastasis to lymph and blood, (melanocytes)

ABCD Rule: detecting malignant melanoma

A = Asymmetry – opposite sides don’t match

B = Border irregularity – borders not smooth

C = Color – one mole, several colors

D = Diameter - >6mm (pencil eraser)

Hair and Hair Follicles

Figure 4.7c