First half of Chapter 6 Flashcards
What is the integumentary system
(Fancy name for skin) consists of skin and accesory organs; hair, nails and cutaneous glands.
Inspection
Inspection of the skin, hair and nails is significant part of a physical exam. Skin is the most vulnerable organ. Relieves more medical treatment than any other organ. Largest organ in our body.
Skin Thickness : Thick and Thin
Thick skin covers front of hands, bottoms of feet, has sweat glands but no hair follicles or sebaceous (oil) glands. Thin skin covers the rest possesses hair follicles, sebaceous glands and sweat glands.
Functions of the skin: resistance to trauma and infection
Keratin(predominant in skin), Dermacidin and defensins. Acid mantle.
Functions of the skin: Other barrier functions(keep out)
Water, UV radiation and harmful chemicals.
Functions of the skin: Vitamin D synthesis
Skin carries out of first step, liver and kidneys complete process.
Functions of the skin: sensation
Sensation: skin is an extensive sense organ. Receptors for temperature, touch, pain and more.
Functions of the skin: Thermoregulation
Thermoregulation:
Thermoreceptors(cool and conserve heat), Vasoconstriction/vasodilation. Perspiration.
Functions of the skin: Nonverbal communication
Nonverbal communication:
Facial expression
Importance in social acceptance and self image.
The Epidermis
Epidermis—keratinized stratified squamous epithelium
(inside cells but dead cells)
Includes dead cells at skin surface packed with tough keratin protein
Lacks blood vessels
Depends on the diffusion of nutrients from underlying connective tissue
Contains sparse nerve endings for touch and pain
Cells of the Epidermis: Stem cells
Undifferentiated cells that give rise to keratinocytes
In deepest layer of epidermis (stratum basale)
Cells of the Epidermis: Keratinocytes
Great majority of epidermal cells
Synthesize keratin
Cells of the Epidermis: Melanocytes
Melanocytes
Synthesize pigment melanin that shields DNA from ultraviolet radiation
Occur only in stratum basale but have branched processes that spread among keratinocytes and distribute melanin
Cells of the Epidermis: Tactile cells
Tactile cells: Touch receptor cells associated with dermal nerve fibers
In basal layer of epidermis
Cells of the Epidermis: Dendritic cells
Dendritic cells
Macrophages originating in bone marrow that guard against pathogens
Found in stratum spinosum and granulosum. Special type of immune cells.
Stratum basale (deepest epidermal layer)Layers of the Epidermis
Thin skin contains four strata; thick skin contains five strata
Stratum basale (deepest epidermal layer):A single layer of stem cells and keratinocytes resting on the basement membrane
Stem cells divide and give rise to keratinocytes that migrate toward skin surface to replace lost cells
Also contains a few melanocytes and tactile cells
Stratum spinosum (Layers of the Epidermis)
Several layers of keratinocytes joined together by desmosomes and tight junctions
Named for appearance of cells after histological preparation (spiny)
Also contains some dendritic cells.(resist pulling apart)
Layers of the Epidermis,Stratum granulosum
Stratum granulosum
Three to five layers of flat keratinocytes
Cells contain dark-staining keratohyalin granules(related to keratin)
Layers of Epidermis, Stratum lucidum
Thin, pale layer found only in thick skin
Keratinocytes packed with clear protein eleidin(only in thick skin)
Layers of epidermis:Stratum corneum
Stratum corneum (surface layer) Several layers (up to 30) of dead, scaly, keratinized cells Resists abrasion, penetration, water loss
The Life History of a Keratinocyte:Keratinocytes
are produced by mitosis of stem cells in stratum basale or mitosis of keratinocytes in deepest part of stratum spinosum
Mitosis requires abundant oxygen and nutrients, so once cells migrate away from blood vessels of the dermis, mitosis cannot occur
The Life History of a Keratinocyte:New keratinocytes
push older ones toward the surface
Over time, keratinocytes flatten, produce more keratin and membrane-coating vesicles
In 30 to 40 days a keratinocyte makes its way to the skin surface and flakes off (exfoliates) as dander
Slower in old age
Faster in injured or stressed skin
Calluses or corns—thick accumulations of dead keratinocytes on hands or feet.
The Life History of a Keratinocyte:Four important events occur in stratum granulosum:
Keratohyalin granules release filaggrin—a protein that binds keratin into tough bundles
Cells produce tough envelope proteins beneath their membranes
Membrane-coating vesicles release lipid mixture that spreads out over cell surface and waterproofs it
Keratinocytes’ organelles degenerate and the cells die
The Life History of a Keratinocyte: Epidermal water barrier
Epidermal water barrier:
Water retention is fostered by tight junctions between skin cells and the waterproofing that occurs in the stratum granulosum
Helps prevent dehydration
Does not prevent the absorption of water by the stratum corneum when we soak in a bath (“prune fingers”)
Dermis
Dermis—connective tissue layer beneath epidermis.
Composed mainly of collagen
Well supplied with blood vessels, sweat glands, sebaceous glands, and nerve endings
Houses hair follicles and nail roots
Is the tissue of the facial skin to which skeletal muscles attach and cause facial expressions of emotion
Has a wavy, conspicuous boundary with the superficial epidermis
Dermal papillae
are upward, finger-like extensions of dermis
Epidermal ridges
are downward waves of epidermis
Prominent waves on fingers produce friction ridges of fingerprints.
Hypodermis
Subcutaneous tissue
Has more areolar and adipose than dermis has
Pads body and binds skin to underlying tissues
Common site of drug injection since it has many blood vessels.
Subcutaneous fat
Energy reservoir
Thermal insulation
Thicker in women
Thinner in infants, elderly
Skin Color:Melanin
Melanin—most significant factor in skin color
Produced by melanocytes, accumulates in keratinocytes
Two forms of the pigment:
Eumelanin—brownish black
Pheomelanin—reddish yellow (sulfur-containing)
People of different skin colors have the same number of melanocytes
Darker skinned people
Produce greater quantities of melanin
Melanin breaks down more slowly
Melanin granules more spread out in keratinocytes
Melanized cells seen throughout the epidermis
Lighter skinned people
Melanin clumped near keratinocyte nucleus
Little melanin seen beyond stratum basale
Skin Color
This color fades as melanin is degraded and old cells are exfoliated. Exposure to UV light stimulates melanin secretion and darkens skin.
Other pigments can influence skin color
Hemoglobin—pigment in red blood cells
Adds reddish to pinkish hue to skin
Carotene—yellow pigment acquired from egg yolks and yellow/orange vegetables
Concentrates in stratum corneum and subcutaneous fat.
The Evolution of Skin Color
Variations in skin color result from multiple evolutionary selection pressures, especially differences in exposure to UV light (UV accounts for up to 77% of skin tone variation)
UV light has both harmful and beneficial effects
Adversely: it causes skin cancer, breaks down folic acid
Beneficially: it stimulates vitamin D synthesis
Populations that evolved in the tropics have well-melanized skin to protect against excessive UV
The Evolution of Skin Color, continued
Populations that evolved in far northern and southern latitudes (weak sun) have light skin to allow adequate UV
Populations that evolved at high altitudes or dry climates (less UV filtering) also are darker skinned
Importance of vitamin D for calcium (crucial for pregnancy, lactation) might explain why women are lighter skinned than men
Hair and Nails
Hair, nails, and cutaneous glands are accessory organs (appendages) of the skin. Hair and nails are composed of mostly dead, keratinized cells
Pliable soft keratin makes up stratum corneum of skin
Compact hard keratin makes up hair and nails
Tougher and more compact due to numerous cross-linkages between keratin molecules
Pilus
Pilus—another name for a hair; pili—plural of pilus
Hair
Hair—a slender filament of keratinized cells growing from a tube in the skin called a hair follicle
Hair covers most of the body
Hair does not cover: palms, soles; palmar, plantar, and lateral surfaces and distal segments of fingers and toes; lips, nipples, and parts of genitals
Limbs and trunk have 55 to 70 hairs per cm2
Face has about 10 times as many
100,000 hairs on an average person’s scalp
Differences in hairiness across individuals is mainly due to differences in texture and pigment of hair
Three types of hair-Lanugo
Lanugo: fine, downy, unpigmented hair that appears on the fetus in the last 3 months of development
Three types of hair-Vellus
Vellus: fine, pale hair that replaces lanugo by time of birth
Two-thirds of the hair of women
One-tenth of the hair of men
All of hair of children except eyebrows, eyelashes, and hair of the scalp
Three types of hair-Terminal
Terminal: longer, coarser, and more heavily pigmented
Forms eyebrows, eyelashes, and the hair of the scalp
After puberty, forms the axillary and pubic hair
Male facial hair and some of the hair on the trunk and limbs
Structure of the Hair and Follicle:
Hair is divisible into three zones along its length
Bulb:
Bulb: a swelling at the base where hair originates in dermis or hypodermis
Only living hair cells are in or near bulb
Structure of the Hair and Follicle:
Hair is divisible into three zones along its length:Root
Root-the remainder of the hair in the follicle
Structure of the Hair and Follicle:
Hair is divisible into three zones along its length:Shaft
the portion above the skin surface
