Chapter 4: Skin & Body Membranes

Functions of the Skin  Thermoregulation  Protects body from mechanical damage (bumps/cuts), chemical damage, UV radiation, bacteria  Mini-excretory system to urea, salt and water  Sensory receptors  Manufactures protein and vitamin D

Structure of the Skin  1. Epidermis: stratified squamous epithelium that can keratinize. Cells are called keratinocytes. –Outermost layer: avascular –Keratin: fibrous protein component of nails, hair, calluses, and skin surface

5 layers of epidermis  1. Stratum Basale or germinativum –Deepest layer –Gets nutrients –Cells divide here –New melanocytes and keratinocytes push up to become part of S.spinosum and S.granulosum

 2. Stratum spinosum –Keratinocytes provide a waterproof layer  3. Stratum granulosum –3-5 rows of flat cells –Cells fill with keratin granules –(cells die as they leave this row)

5 layers (cont)  4. Stratum lucidum –Only found in palms and soles of feet –Clear flat, dead cells

5 layers (cont)  5. Stratum corneum –Outermost layer 20-30cell layers thick. –Full of keratin –Shed and replaced every days.

Skin color  Melanin: produced as body’s natural sunscreen –Protects against UV rays by shielding the DNA in the pigment –Colors range from yellow to black and are formed in the S. basale. (Freckles and moles)

Skin color  Carotene- orange yellow pigment deposited in the S. corneum.  Other colors –Cyanosis: poorly oxygenated blood causes blue skin

–Erythema: redness if embarrassed, fever, hypertension, allergy –Pallor or blanching: from fear, anger, anemia or low blood pressure

Skin color (cont)  Other colors –Jaundice: yellow from liver disorder, excess bilirubin in the blood. –Bruises- site where blood has escaped

Dermis (your “hide”) Dense connective tissue. Dense connective tissue.  Collagen: toughness & skin hydration  elastic fibers: elasticity/ stretching  Your leather shoes!

Regions of the Dermis  1. Papillary layer: fingerlike projections called dermal papillae.

–Form fingerprints, genetically determined –Contain capillary loops which provide nutrients to epidermis above.

Papillary layer  Contains pain receptors (free nerve endings) and touch receptors (Meissner’s corpuscles)

Regions of dermis (cont)  2. Reticular layer –Deepest skin layer –Contains blood vessels and capillaries (Maintains body temperature) –Sweat and oil glands –Deep pressure receptors called Pacinian corpuscles

Subcutaneous Layer  Aka: Hypodermis (below dermis)  Absorbs shock and insulates deeper tissue  Mostly adipose

Did you get it?  Create a simple diagram showing all the 3 major layers of the skin. Within each layer, label the sublayers as well.

Accessory Organs 1. Sebaceous Glands  Exocrine gland  Sebum (oil) lubricates skin and kills bacteria  arrector pili squeezes gland and forces oil out

Acne  Sensitive to male hormones –Acne at puberty  Ducts become blocked and secretions accumulate  Inflammation (pimple)  bacterial infection

2. Sweat Glands  sudoriferous –2.5 million/person A. Eccrine Glands  Discharge onto skin through tube  All over body  Water, salt, urea, uric acid, vitamin C, lactic acid (mosquitoes), ammonia are produced  Heat regulation

B. Apocrine  Secretes into hair follicle –Axilllary and genital areas  Fun Fact: Odor caused by bacteria!

Accessory Structures  Hair –Produced in hair follicles –Hair papilla –Formed by stratum basale cells –Root/shaft

 Hair Shaft –Dead, keratinized cells –3 layers  Cuticle- surface  Cortex- provides stiffness  Medulla- core, soft

 Hair (cont) –Hormones account for hair development in scalp, pubic regions –arrector pilli muscles (smooth muscle): connect each side of hair to dermal tissue

 Hair color –Produced by melanocytes  Type of hair depends on shaft  flat: curly/kinky  Round: straight

Nails  Protect tips of fingers/ grasp objects  Structure –Scale-like modification of the epidermis –Dead cells filled with keratin –Colorless (except for lunula) pink from blood vessels underneath

Homeostasis  Injury/repair –Scab: blood clot (temporary fix) –Keloid: thickened area of scar tissue, covered by a shiny smooth epidermal surface (harmless)

Development of skin  Lanugo: hairy covering of fetus, shed by birth  Vernix caseosa: white, cheesy covering of fetus produced by oil glands to protect skin  Optimal appearance of skin

Old Age  Amount of subcutaneous fat decreases (cold intolerance)  Less oil production and fewer collagen fibers (dryness/bruises)  By 50, # hair follicles dropped by 30%.  Melanin decreases/absent (gray or white)

Skin Cancer  1. Basal cell carcinoma: from S. basale –Least malignant, most common –Slow growing, 99% curable if surgically removed

Skin Cancer  2. Squamous cell carcinoma: from S. spinosum. Forms an ulcer often on the head –Will spread to lymph nodes –Prognosis is good if radiation or surgery

Skin cancer (cont)  3. Melanoma: cancer of the melanocytes –Often deadly –Forms where pigment is present (moles) –Spreads to surrouding lymph and blood vessels –Wide surgical excision and chemotherapy