| Question | Answer |
| Largest organ
Accounts for 7% of body weight
Varies in thickness from 1.5–4.4mm
Divided into two distinct layers
Epidermis
Dermis | The Skin |
| lies deep to the dermis | Hypodermis |
| What are the functions of the Skin and Hypodermis? | Protection— from bumps, chemicals, water loss, UV radiation
Regulation of body temperature
Excretion— urea, salts, and water lost through sweat
Production of vitamin D
Sensory reception—keeps us aware of conditions at the body’s surface |
| 4 main cell types of Epidermis | Keratinocytes -tratum spinosum; produce keratin a fibrous protein
Melanocytes-basal layer; secrete pigment
Tactile epithelial cells-basal layer; attached to sensory nerve endings
Dendritic cells-stratum spinosum; part of immune system; macrophage-like |
| most abundant cell type in epidermis
Arise from deepest layer of epidermis
Produce keratin, a tough fibrous protein
Produce antibodies and enzymes
Dead at skin's surface | Keratinocytes |
| 5 Layers of the Epidermis | A) Stratum basale (stratum geminativum)
B) Stratum spinosum
C) Stratum granulosum
D) Stratum lucidum (only in thick skin)
E) Stratum corneum |
| Deepest layer of epidermis
Attached to underlying dermis
Cells actively divide
Stratum basale contains
Merkel cells—associated with sensory nerve ending
Melanocytes—secrete the pigment melanin | A) Stratum basale |
| “Spiny” appearance caused by artifacts of histological preparation
Contains thick bundles of intermediate filaments (tonofilaments)
Resist tension
Contain protein prekeratin and star-shaped dendritic cells
Function in immune system (as macrophages) | B) Stratum spinosum (spiny layer) |
| Consists of keratinocytes and tonofilaments
Tonofilaments contain:
Keratohyaline granules—help form keratin
Lamellated granules—contain a waterproofing glycolipid | C) Stratum granulosum |
| Occurs only in thick skin
Locations of thick skin—palms and soles
Composed of a few rows of flat, dead keratinocytes | D) Stratum lucidum (clear layer) |
| Thick layer of dead keratinocytes and thickened plasma membranes
Protects skin against abrasion and penetration | E) Stratum corneum (horny layer) |
| Second major layer of the skin
Strong, flexible connective tissue
Richly supplied with blood vessels and nerves | Dermis |
| 2 layers of the dermis | Papillary layer—includes dermal papillae
Reticular layer
Deeper layer—80% of thickness of dermis |
| Creases on palms are called: | Flexure lines |
| Deep to the skin—also called superficial fascia
Contains areolar and adipose CT
Anchors skin to underlying structures
Helps insulate the body | Hypodermis |
| 3 pigments that contribute to skin color: | i) Melanin
Most important pigment—made from tyrosine
ii) Carotene
Yellowish pigment from carrots and tomatoes
iii) Hemoglobin
Caucasian skin contains little melanin
Allows crimson color of blood to show through |
| scalelike modification of epidermis
Made of hard keratin | Nails |
| Parts of The Nail | Free edge
Body
Root
Nail folds
Eponychium—cuticle |
| Flexible strand of dead, keratinized cells
Hard keratin—tough and durable | Hair |
| 2 Parts of Hair | Root—imbedded in the skin
Shaft—projects above skin's surface |
| 3 layers of Hair | i) Medulla—central core
ii) Cortex—surrounds medulla
iii) Cuticle—outermost layer |
| Extend from epidermis into dermis | Hair follicles |
| Deep, expanded end of the hair follicle | Hair bulb |
| Knot of sensory nerves around hair bulb | Root plexus |
| Bundle of smooth muscle
Hair stands erect when this contracts | Arrector pili muscle |
| Body hairs of women and children | Vellus hairs |
| Hair of scalp
Axillary and pubic area (at puberty) | Terminal hairs |
| Occur over entire body
Except palms and soles
Secrete sebum—an oily substance | Sebaceous Glands |
| entire cell breaks up to form secretion
Most are associated with a hair follicle | Holocrine secretion |
| Functions of sebum | Collects dirt; softens and lubricates hair and skin |
| glands (sudoriferous glands) widely distributed on body | Sweat glands |
| a blood filtrate
99% water with some salts
Contains traces of metabolic wastes
About 2% urea | Sweat |
| 2 types of sweat glands | Eccrine gland (merocrine)
Most numerous—produce true sweat
Apocrine gland
Confined to axillary, anal, and genital areas
Musky odor-attracts mate
Signal about immune system, MHC
(Ceruminous glands and mammary glands are modified apocrine glands) |
| only upper epidermis is damaged from burns | First-degree burn |
| upper epidermis and upper part of dermis is also damaged from burns | Second-degree burn
(Blisters appear
Skin heals with little scarring) |
| Consumes thickness of skin
Burned area appears white, red, or blackened | Third-degree burn |
| Least malignant and most common skin cancer | Basal cell carcinoma |
| Skin cancer that arises from keratinocytes of stratum spinosum | Squamous cell carcinoma |
| A cancer of melanocytes
The most dangerous type of skin cancer | Melanoma |
| Develops from embryonic ectoderm | Epidermis |
| Develop from mesoderm | Dermis and hypodermis |
| Develop from neural crest cells | Melanocytes |
| vernix caseosa | produced by Fetal sebaceous glands |
| Fetal skin is well formed after the fourth month. At 5–6 months, the fetus is covered with lanugo (downy hairs) | Fetal skin is well formed after the fourth month. At 5–6 months, the fetus is covered with lanugo (downy hairs) |
