Integumentary system

Epidermis

protective shield, avascular, made of epithelial tissue

Dermis

underneath the epidermis, vascularized, made up of mainly dense connective tissue

Hypodermis (subcutaneous tissue/ superficial fascia)

not part of the skin but part of the integumentary system, mostly adipose tissue that absorbs shock & insulates, anchors skin to underlying structures, mainly muscles 

Epidermis tissue type

Keratinized stratified squamous epithelium 

Keratinocytes 

Make fibrous protein keratin (fibrous protein gives protective properties)

Keratinocytes cells

make up most of the epidermis, arise in stratum basale: dead, scale-like, keratin-filled sacs by time reach skin surface, new epidermis 25-45 days.

Dendritic cells

Macrophages - patriol and ingest foreign substances - activate the immune system

Tactile(Merkel) cells

Sensory touch receptors

Layers of epidermis

Stratum basale, Stratum spinosum, Stratum granulosum, Stratum lucidum( absent in thinner skin), Stratum corneum

Stratum basale (basal layer)

deepest epidermal layer, firmly attached to dermis, single row of stem cells: mitosis happens here, melanocytes make up 10-25% of the layer

Stratum spinosum (prickly)

various layers thick, Keratinocytes with many melanosomes and dendritic cells, desmosomes and tight junctions keep cells tightly together

Stratum Granulosum (Granular layer)

thin layer: 4-6 flat cells thick, Keratinization begins - keratinocytes begin to flatten and fill with keratin,

cells above stratum granulosum die due to

being too far from dermal capillaries, and the glycolipid coating cuts off from nutrients 

Stratum lucidum

only found in thick skin, made up of two rows of flat, dead keratinocytes

Stratum corneum (horny layer)

outer layer - ¾ of epidermis, protects against biological, chemical, and physical assaults, is almost waterproof, and sheds regularly 

Stratum corneum cells

20-30 rows of dead, flat, anucleate cells filled w/ keratin and protein and a glycolipid coating

Dermis

Strong, flexible connective tissue, semi-fluid matrix with fibers, nerves, blood, and lymphatic vessels, and appendages. made of two layers: papillary and reticular

Papillary dermis

superficial layer, Areolar connective tissue: loose collagen and elastic fibers, and blood vessels, lets phagocytes patrol for microorganisms

Dermal papillae

superficial peg-like projections, contain papillary loops, pain receptors, and touch receptors, create dermal ridges( cause epidermal ridges > friction ridges - help with/ grip and sense of touch ), sweat glands along ridges > fingerprints 

Reticular layer (reticular dermis)

deepest layer, 80% of dermal thickness, dense irregular connective tissue

Collagen fibers

give strength and resiliency and bind water

cleavage lines

formed by areas with less dense collagen

flexure lines 

deep skin crease at joint 

3 main factors that determine skin color

melanin, carotene, hemoglobin

Melanin

polymer made of AA tyrosine, produced in melanocytes and transported in melanosomes

Caroten

yellow-orange pigment, exists in the stratum corneum and fat of hypodermis, may be made into vitamin A for vision and epidermal health

Erythema (redness)

fever, hypertension, inflammation, allergy, embarrassment

derivatives the of epidermis

hairs and hair follicles, nails, sweat glands, and sebaceous(oil) glands

Hair (pili)

dead, keratinized cells (hard keratin), tougher and more durable than those in epidermal cells

Hair bulb 

expanded deep end, hair follicle receptor (root hair plexus) forms around hair bulb (sensory nerve endings- touch receptors) 

Hair papilla

dermal papilla that protrudes into the hair bulb - capillaries (blood supply, nutrients, tells where to grow)

Arrector pili

smooth muscle attached to the follicle, makes “goosebumps”

Vallus hair

pale, fine body hair of children and adult females

Terminal hair

coarse, long hair of brows, and scalp, at puberty, appears in the axillary and pubic regions and beard area of males

hair growth

2 mm per week on average, the lifespan of follicles varies, head is 4 years, and brows are few months

hair thinning

occurs in both sexes after 40, terminal hair gets replaced with vellus hair

fingernails

scale-like modifications of epidermis, protective cover for the distal, dorsal surfaces of fingers and toes. made of hard keratin.

Sweat Glands

AKA: Sudoriferous glands. All skin surfaces except nipples and parts of the external genitalia. 3 million per person. 2 types: Eccrine(merocrine) glands and apocrine glands.

Myoepithelial cells

contract upon nervous system stimulation to force sweat into ducts

Eccrine glands 

Most numerous compared to apocrine, Abundant on palms, soles, and forehead, Ducts connect to pores on skin surface, Function in thermoregulation

sweat

99% water with salts, dermcidin(microbe-killing peptide), and metabolic wastes

Apocrine glands

Primarily in axillary and anogenital areas, Larger than eccrine sweat glands, Ducts empty into hair follicles, Made up of true sweat plus fatty substances and proteins

Ceruminous glands

lining of the external ear canal; secrete cerumen(earwax)

protection: chemical barriers 

skin secretions (dermcidin, bacterial substances, defensins, wounded skin releases cathelicidin) defend against bacteria

Physicla barriers Physical

keratin blocks most water and water-soluble substances, allowing for limited skin penetration

biological barriers

dendritic cells in epidermis (capture and migrate and lymph node —> immune response),  macrophages in dermis (2nd line of defense; dispose of viruses and bacteria)

insensible perspiration 

.5 L/day of routine unnoticeable sweat (when body temp is normal)

sensible perspiration

dilation of dermal vessels and increased sweat gland activity cool the body

Cutaneous sensation

many cutaneous sensory receptors: part of the nervous system, detect temp, touch, and pain

Metabolic functions

synthesis of vitamin D precursor, synthesis of collagenase, supports liver, keratinocyte enzymes aid may disarm cancer-causing chems and activate anti-inflammatory drugs