biology 211 anatomy & physiology i skin the integumentary system
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Biology 211Anatomy & Physiology I
Skin
The Integumentary System
The Integumentary System
• Skin=Integument• Skin + accessory organs (hair, nails, and cutaneous
glands)= Integumentary system• Dermatology=scientific study and medical treatment of
the integumentary system• Skin-the most vulnerable organ—exposed to radiation,
trauma, infections, injurious chemicals• Lgst. organ—15% body wt
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: Stratified squamous epithelium; outer layer is "keratinized" or "cornified"
Dermis:Dense irregular connective tissue
Hypodermis:Adipose connective tissue (technically not part of system
Three Layers of skin:
Epidermis: Avascular. Depends on blood vessels in underlying dermis for its nutrition
Cells formed by mitosis in deepest, or basal, layer, then get pushed into more superficial layers or "stata"
Stratum Basale = Single row of dividing cells
Stratum Spinosum = Three or four layers of cells; Some cell division
Stratum Granulosum = Three or four layers of cells; Actively synthesizing protein keratin
Stratum Lucidum = One or two layers of dying cells
Stratum Corneum = 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:
Melanocytes produce pigment melanin & transfer it to keratinocytes
Langerhans cells (immune cells) protect against pathogens and toxins
Merkel cells detect touch and pressure; transfer this information to sensory receptors in the dermis
Skin Color• Most significant factor is melanin
– 2 forms (1) eumelanin (brownish black) and (2) pheomelanin (reddish yellow)
• Other factors include hemoglobin (red to pink) and carotene (yellow)
• Different races have same # of melanocytes, amount of melanin produced differs
• Melanin accumulates in keratinocytes
Abnormal Color
• Cyanosis—blue, lack of hemoglobin• Erythema—abnormal redness, increased blood flow or
blood pooling• Pallor—pale, ashen, poor blood flow• Albinism—lack of melanin• Jaundice—yellowing, hi levels of bilirubin (hi rate of
erythrocyte destruction• Bronzing—deficiency of glucocorticoids• Hematoma—bruise, blood clot
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:
Papillary layer just below epidermis
Reticular layer 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 = Fibroblasts / Fibrocytes Macrophages Mast cells Lymphocytes etc.
Fibers = Collagen (therefore strong, flexible) Elastic (therefore stretchable)
Weight gain tears collagen fibers producing striae (stretch marks)
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
- Distribuled over all skin except: palms of hands soles of feet nipples glans of penis & clitoris minor labia
- Formed in follicles located deep in dermis
- Consists of layers of dead, highly keratinized keratinocytes
Function of Hair
• Trunk and limb hair considered vestigial• Scalp only place where it is thick enough to retain heat• Eyebrows enhance facial features• Vibrassae (guard hair) are used to filter particulates from
the ear and nose
Shaft
Bulb
Root
Medulla: Loosely arranged keratinocytesCortex: Densely packed keratinocytesCuticle: Keratinocytes loosely arranged like scales
Black or brown color due to eumelanin produced by melanocytes and transferred to keratinocytes in follicle. Red color produced by pigment called pheomelanin
Blonde color produced by intermediate levels of pheomelanin and low levels of eumelanin
Texture of hair due to The rounder the hair shaft, the straighter it will be The flatter the hair shaft, the more curled it will be
Each hair is associated with:
One or more sebacious (oil) glands
An arrector pili muscle
A plexus of nerves aroundthe root
Sweat Glands
- 2 to 3 million
- Two types: Merocrine: Distributed over all skin except nipples (Eccrine) Simple coiled glands in dermis Duct leads to sweat pore on surface Secreted watery sweat for cooling Apocrine: Located only in axillary, pubic, anal regions Larger than eccrine glands Duct opens into opening of hair follicle Secretes thicker sweat, high content of proteins and fats. Contains specific scent molecules: sexual, fear, etc.
Sweat is usually 99% water with a pH between 4 and 6
Sweat glands produce 500ml of insensible perspiration (no noticable wetness)daily
Diaphoresis—sweating with wetness (up to 1 l per hr when exercising or in heat)
Two specially modified sweat glands:
Ceruminous—found in the external ear canal. Secretion combines with sebum and dead epidermal cells to form earwax (keeps eardrum pliable, canal waterproof and has a bactericidal effect)
Mammary --milk producing glands found in the female breast (modified apocrine 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 nail matrix at proximal end, hidden under eponychium or cuticle
Deeper layers of epidermis = nail bed
Average growth:0.5 mm per week
Nails
• Flat nails allow for fleshy, sensitive fingertips• Serve as tools for digging, grooming and manipulation• Useful in medical diagnosis
– Iron deficiency—flat or concave– Long term hypoxia (oxygen deficiency)—clubbed
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, invade dermis Highly malignant
Burns
• Leading cause of accidental death• Classified by depth of tissue involvement• 1st degree—involves epidermis only• 2nd degree—involves epidermis and some dermis• 3rd degree—involves epidermis, dermis and some
deeper tissue are destroyed• 1st and 2nd degree burns are considered partial thickness
burns, and 3rd degree is a full thickness burn